4.3: The College Essay Assignment- Analysis, Rubrics, and Critical Thinking
The Prompt: What Does “Analyze” Mean Anyway?
Often, the handout or other written text explaining the assignment—what professors call the assignment prompt —will explain the purpose of the assignment, the required parameters (length, number and type of sources, referencing style, etc.), and the criteria for evaluation. Sometimes, though—especially when you are new to a field—you will encounter the baffling situation in which you comprehend every single sentence in the prompt but still have absolutely no idea how to approach the assignment. No one is doing anything wrong in a situation like that. It just means that further discussion of the assignment is in order. Here are some tips:
- Focus on the verbs . Look for verbs like “compare,” “explain,” “justify,” “reflect” or the all-purpose “analyze.” You’re not just producing a paper as an artifact; you’re conveying, in written communication, some intellectual work you have done. So the question is, what kind of thinking are you supposed to do to deepen your learning?
- Put the assignment in context . Many professors think in terms of assignment sequences . For example, a social science professor may ask you to write about a controversial issue three times: first, arguing for one side of the debate; second, arguing for another; and finally, from a more comprehensive and nuanced perspective, incorporating text produced in the first two assignments. A sequence like that is designed to help you think through a complex issue. Another common one is a scaffolded research paper sequence: you first propose a topic, then prepare an annotated bibliography, then a first draft, then a final draft, and, perhaps, a reflective paper. The preparatory assignments help ensure that you’re on the right track, beginning the research process long before the final due date, and taking the time to consider recasting your thesis, finding additional sources, or reorganizing your discussion. 5 If the assignment isn’t part of a sequence, think about where it falls in the semester, and how it relates to readings and other assignments. Are there headings on the syllabus that indicate larger units of material? For example, if you see that a paper comes at the end of a three-week unit on the role of the Internet in organizational behavior, then your professor likely wants you to synthesize that material in your own way. You should also check your notes and online course resources for any other guidelines about the workflow. Maybe you got a rubric a couple weeks ago and forgot about it. Maybe your instructor posted a link about “how to make an annotated bibliography” but then forgot to mention it in class.
- Try a free-write . When handing out an assignment, teachers often ask students to do a five-minute or ten-minute free-write. A free-write is when you just write, without stopping, for a set period of time. That doesn’t sound very “free;” it actually sounds kind of coerced. The “free” part is what you write—it can be whatever comes to mind. Professional writers use free-writing to get started on a challenging (or distasteful) writing task or to overcome writers block or a powerful urge to procrastinate. The idea is that if you just make yourself write, you can’t help but produce some kind of useful nugget. Thus, even if the first eight sentences of your free write are all variations on “I don’t understand this” or “I’d really rather be doing something else,” eventually you’ll write something like “I guess the main point of this is …” and then you’re off and running. As instructors, we’ve found that asking students to do a brief free-write right after I hand out an assignment generates useful clarification questions. If your instructor doesn’t make time for that in class, a quick free-write on your own will quickly reveal whether you need clarification about the assignment and, often, what questions to ask.
- Ask for clarification the right way . Even the most skillfully crafted assignments may need some verbal clarification, especially because students’ familiarity with the field can vary enormously. Asking for clarification is a good thing. Be aware, though, that instructors get frustrated when they perceive that students want to skip doing their own thinking and instead receive an exact recipe for an 'A' paper.  You’re an adult. You chose college. You chose this class. You’re free to exercise your right to fail.” Similarly, avoid asking the professor about what he or she “wants.” You’re not performing some service for the professor when you write a paper. What they “want” is for you to really think about the material.
- So what does analyze mean? Analyze means breaking down a topic into component parts and exploring and examining those various parts to come to some sort of new understanding.
Table 4.3.1 -- Clarifying Questions for Essay Assignments
| Questions that may not get you a useful answer | Preferable alternatives |
|---|---|
| I don’t get it. Can you explain this more? or What do you want us to do? | I see that we are comparing and contrasting these two cases. What should be our focus? Their causes? Their impacts? Their implications? All of those things? or I’m unfamiliar with how art historians analyze a painting. Could you say more about what questions I should have in mind to do this kind of analysis? (Note: be specific with your questions.) |
| How many sources do we have to cite? | Is there a typical range for the number of sources a well written paper would cite for this assignment? or Could you say more about what the sources are for? Is it more that we’re analyzing these texts in this paper, or are we using these texts to analyze some other case? |
| What do I have to do to get an 'A' on this paper? | Could I meet with you to get feedback on my (pre-prepared) plans/outline/thesis/draft? or I’m not sure how to approach this assignment. Are there any good examples or resources you could point me to? |
Three Common Types of College Writing Assignments
From our experience, you are likely to get three kinds of writing assignments based upon the instructor’s degree of direction for the assignment. We’ll take a brief look at each kind of academic writing task.
The Closed Writing Assignment
- Does your advertisement employ techniques of propaganda, and if so what kind?
- Was the South justified in seceding from the Union?

These kinds of writing assignments present you with two counter claims and ask you to determine from your own analysis the more valid claim. They resemble yes-no questions. These topics define the claim for you, so the major task of the writing assignment then is working out the support for the claim. They resemble a math problem in which the teacher has given you the answer and now wants you to “show your work” in arriving at that answer. Be careful with these writing assignments, however, because often these topics don’t have a simple yes/no, either/or answer (despite the nature of the essay question). A close analysis of the subject matter often reveals nuances and ambiguities within the question that your eventual claim should reflect. Perhaps a claim such as, “In my opinion, Hitler was mad” might work, but I urge you to avoid such a simplistic thesis. This thesis would be better: “I believe Hitler's unhinged mind borders on insanity but doesn’t quite reach it.”
The Semi-Open Writing Assignment
- Discuss the role of law in Antigone.
- Show how the Fugitive Slave Act influenced the Abolitionist Movement.
Although these topics chart out a subject matter for you to write about, they don’t offer up claims you can easily use in your paper. It would be a misstep to offer up claims such as, “Law plays a role in Antigone." Such statements express the obvious and what the topic takes for granted. The question, for example, is not whether law plays a role in Antigone, but rather what sort of role law plays. What is the nature of this role? What influences does it have on the characters or actions or theme? This kind of writing assignment resembles a kind of archeological dig. The teacher cordons off an area, hands you a shovel, and says dig here and see what you find. Be sure to avoid summary and mere explanation in this kind of assignment. Despite using key words in the assignment such as “explain,” “illustrate,” analyze,” “discuss,” or “show how,” these topics still ask you to make an argument. Implicit in the topic is the expectation that you will analyze the reading and arrive at some insights into patterns and relationships about the subject. Your eventual paper, then, needs to present what you found from this analysis—the treasure you found from your digging. Determining your own claim represents the biggest challenge for this type of writing assignment.
The Open Writing Assignment
- What does it mean to be an “American” in the 21st Century?
- Analyze the influence of slavery upon one cause of the Civil War.
These kinds of writing assignments require you to decide both your writing topic and your claim (or thesis). Which character in the Inferno will I pick to analyze? What two themes in Pride and Prejudice will I choose to write about? Many students struggle with these types of assignments because they have to understand their subject matter well before they can intelligently choose a topic. For instance, you need a good familiarity with the characters in The Inferno before you can pick one. You have to have a solid understanding defining elements of American identity as well as 21st century culture before you can begin to connect them. This kind of writing assignment resembles riding a bike without the training wheels on. It says, “You decide what to write about.” The biggest decision, then, becomes selecting your topic and limiting it to a manageable size.
Rubrics as Road Maps
If a professor provides a grading rubric with an assignment prompt, thank your lucky stars (and your professor). If the professor took the trouble to prepare and distribute it, you can be sure that he or she will use it to grade your paper. He or she may not go over it in class, but it’s the clearest possible statement of what the professor is looking for in the paper. If it’s wordy, it may seem like those online “terms and conditions” that we routinely accept without reading. But you really should read it over carefully before you begin and again as your work progresses. A lot of rubrics do have some useful specifics. Ours, for example, often contain phrases like “makes at least six error-free connections to concepts or ideas from the course,” or “gives thorough consideration to at least one plausible counter-argument.” Even less specific criteria (such as “incorporates course concepts” and “considers counter-arguments”) will tell you how you should be spending your writing time.
Even the best rubrics aren’t completely transparent. They simply can’t be. Take, for example, this AAC&U rubric . It has been drafted and repeatedly revised by a multidisciplinary expert panel and tested multiple times on sample student work to ensure reliability. But it is still seems kind of vague. What is the real difference between “demonstrating a thorough understanding of context, audience, and purpose” and “demonstrating adequate consideration” of the same? It depends on the specific context. So how can you know whether you’ve done that? A big part of what you’re learning, through feedback from your professors, is to judge the quality of your writing for yourself. Your future managers are counting on that. At this point, it is better to think of rubrics as roadmaps, displaying your destination, rather than a GPS system directing every move you make.
Behind any rubric is the essential goal of higher education: helping you take charge of your own learning, which means writing like an independently motivated scholar. Are you tasked with proposing a research paper topic? Don’t just tell the professor what you want to do, convince him or her of the salience of your topic, as if you were a scholar seeking grant money. Is it a reflection paper? Then outline both the insights you’ve gained and the intriguing questions that remain, as a scholar would. Are you writing a thesis-driven analytical paper? Then apply the concepts you’ve learned to a new problem or situation. Write as if your scholarly peers around the country are eagerly awaiting your unique insights. Descriptors like “thoroughness” or “mastery” or “detailed attention” convey the vision of student writers making the time and rigorous mental effort to offer something new to the ongoing, multi-stranded academic conversation. What your professor wants, in short, is critical thinking.
Critical Thinking in the College Essay Assignments
What’s critical about cr itical thinkin g? Why do college professors gravitate towards essay assignments that encourage critical thinking?
Critical thinking is one of those terms that has been used so often and in so many different ways that if often seems meaningless. It also makes one wonder, is there such a thing as uncritical thinking? If you aren’t thinking critically, then are you even thinking?
Despite the prevalent ambiguities, critical thinking actually does mean something. The Association of American Colleges and Universities usefully defines it as “a habit of mind characterized by the comprehensive exploration of issues, ideas, artifacts, and events before accepting or formulating an opinion or conclusion.” 6
That definition aligns with the best description of critical thinking I ever heard; it came from junior high art teacher, Joe Bolger. 7 He once asked, “What color is the ceiling?” In that withering 'tween tone, we reluctantly replied, “Whiiiite.” He then asked, “What color is it really?” We deigned to aim our pre-adolescent eyes upwards, and eventually began to offer more accurate answers: “Ivory?” “Yellow-ish tan.” “It’s grey in that corner.” After finally getting a few thoughtful responses, Mr. Bolger said something like, “Making good art is about drawing what you see, not what you think you’re supposed to see.” The AAC&U definition, above, essentially amounts to the same thing: taking a good look and deciding what you really think rather than relying on the first idea or assumption that comes to mind.
The critical thinking rubric produced by the AAC&U describes the relevant activities of critical thinking in more detail. To think critically, one must …
- “clearly state and comprehensively describe the issue or problem,”
- “independently interpret and evaluate sources,”
- “thoroughly analyze assumptions behind and context of your own or others’ ideas,”
- “argue a complex position and one that takes counter-arguments into account,” and
- “arrive at logical and well informed conclusions”. 8
While you are probably used to providing some evidence for your claims, you can see that college-level expectations go quite a bit further. When professors assign an analytical paper, they don’t just want you to formulate a plausible-sounding argument. They want you to dig into the evidence, think hard about unspoken assumptions and the influence of context, and then explain what you really think and why.
Interestingly, the AAC&U defines critical thinking as a “habit of mind” rather than a discrete achievement. And there are at least two reasons to see critical thinking as a craft or art to pursue rather than a task to check off. First, the more you think critically, the better you get at it . As you get more and more practice in closely examining claims, their underlying logic, and alternative perspectives on the issue, it’ll begin to feel automatic. You’ll no longer make or accept claims that begin with “Everyone knows that …” or end with “That’s just human nature.” Second, just as artists and crafts persons hone their skills over a lifetime, learners continually expand their critical thinking capacities, both through the feedback they receive from others and from their own reflections . Artists of all kinds find satisfaction in continually seeking greater challenges. Continual reflection and improvement is part of the craft.
This comment about critical thinking was provided by student, Aly Button: "As soon as I see the phrase 'critical thinking,' the first thing I think is more work. It always sounds as if you’re going to have to think harder and longer. But I think the AAC&U’s definition is on point; critical thinking is a habit. Seeing that phrase shouldn’t be a scary thing because by this point in many people’s college career this is an automatic response. I never expect an answer to a question to be in the text; by now I realize that my professors want to know what I have to say about something or what I have learned. In a paper or essay, the three-step thesis process is a tool that will help you get this information across. While you’re doing the hard work (the thinking part), this formula offers you a way to clearly state your position on a subject. It’s as simple as: make a general statement, make an arguable statement, and finally, say why it is important. This is my rule of thumb, and I would not want to start a thesis-driven paper any other way!
Critical thinking is hard work. Even those who actively choose to do it experience it as tedious, difficult, and sometimes surprisingly emotional. Nobel-prize winning psychologist Daniel Kahneman explains that our brains aren’t designed to think; rather, they’re designed to save us from having to think. 9 Our brains are great at developing routines and repertoires that enable us to accomplish fairly complex tasks like driving cars, choosing groceries, and having a conversation without thinking consciously and thoroughly about every move we make. Kahneman calls this “fast thinking.” “Slow thinking,” which is deliberate and painstaking, is something our brains seek to avoid. That built-in tendency can lead us astray. Kahneman and his colleagues often used problems like this one in experiments to gauge how people used fast and slow thinking in different contexts:
A bat and ball cost $1.10.
The bat costs one dollar more than the ball.
How much does the ball cost?
Most people automatically say the ball costs $0.10. However, if the bat costs $1 more, than the bat would cost $1.10 leading to the incorrect total of $1.20. The ball costs $0.05. Kahneman notes, “Many thousands of university students have answered the bat-and-ball puzzle, and the results are shocking. More than 50% of students at Harvard, MIT, and Princeton gave the intuitive—incorrect—answer.” These and other results confirm that “many people are overconfident, prone to place too much faith in their intuitions.” Thinking critically—thoroughly questioning your immediate intuitive responses—is difficult work, but every organization and business in the world needs people who can do that effectively. Some students assume that an unpleasant critical thinking experience means that they’re either doing something wrong or that it’s an inherently uninteresting (and oppressive) activity. While we all relish those times when we’re pleasantly absorbed in a complex activity (what psychologist Mihaly Czikszentmihalyi calls “flow” 12 ), the more tedious experiences can also bring satisfaction, sort of like a good work-out.
Critical thinking can also be emotionally challenging, researchers have found. Facing a new realm of uncertainty and contradiction without relying on familiar assumptions is inherently anxiety-provoking because when you’re doing it, you are, by definition, incompetent. Recent research has highlighted that both children and adults need to be able to regulate their own emotions in order to cope with the challenges of building competence in a new area. 13 The kind of critical thinking your professors are looking for—that is, pursuing a comprehensive, multi-faceted exploration in order to arrive at an arguable, nuanced argument—is inevitably a struggle and it may be an emotional one. Your best bet is to find ways to make those processes as efficient, pleasant, and effective as you can .
Kaethe Leonard, another student, says: "The thing no one tells you when you get to college is that critical thinking papers are professors’ favorites. College is all about learning how to think individual thoughts so you’ll have to do quite a few of them. Have no fear though; they do get easier with time. The first step? Think about what you want to focus on in the paper (aka your thesis) and go with it.
The demands students face are not at all unique to their academic pursuits. Professional working roles demand critical thinking, as 81% of major employers reported in an AAC&U-commissioned survey 14 , and it’s pretty easy to imagine how critical thinking helps one make much better decisions in all aspects of life. Embrace it. And just as athletes, artists, and writers sustain their energy and inspiration for hard work by interacting with others who share these passions, look to others in the scholarly community—your professors and fellow students—to keep yourself engaged in these ongoing intellectual challenges. While writing time is often solitary, it’s meant to plug you into a vibrant academic community. What your professors want, overall, is for you to join them in asking and pursuing important questions about the natural, social, and creative worlds.
Other Resources
- This website from the Capital Community College Foundation has some good advice about overcoming writer’s block. And student contributor Aly Button recommends this funny clip from SpongeBob Squarepants .
- The Foundation for Critical Thinking maintains a website with many useful articles and tools.
- The Online Writing Laboratory (OWL) at Purdue University is a wonderful set of resources for every aspect of college writing. Especially germane to this chapter is this summary of the most common types of writing assignments.
- This website , BrainBashers.com, offers logic puzzles and other brain-teasers for your entertainment.
Exercise 1
- Free-write on an assignment prompt. If you have one, do that one. If not, here’s one to practice with: A. “Please write a five-page paper analyzing the controversy surrounding genetically modified organisms (GMOs) in the food supply.” B. What clarification questions would you like to ask your professor? What additional background knowledge do you need to deeply understand the topic? What are some starter ideas that could lead to a good thesis and intriguing argument?
- Find a couple of sample student papers from online paper mills such as this one (Google “free college papers”) and journals featuring excellent undergraduate writing (such as this one from Cornell University ), and use the AAC&U rubric on critical thinking to evaluate them. Which descriptor in each row most closely fits the paper?


3.1: The idea of a relation
A relation between a set \(X\) and \(Y\) is a subset of the Cartesian product . That one sentence packs in a whole heck of a lot, so spend a moment thinking deeply about it. Recall that \(X \times Y\) yields a set of ordered pairs, one for each combination of an element from \(X\) and an element from \(Y\) . If \(X\) has 5 elements and \(Y\) has 4, then \(X \times Y\) is a set of 20 ordered pairs. To make it concrete, if \(X\) is the set { Harry, Ron, Hermione }, and \(Y\) is the set { Dr. Pepper, Mt. Dew }, then \(X \times Y\) is { (Harry, Dr. Pepper), (Harry, Mt. Dew), (Ron, Dr. Pepper), (Ron, Mt. Dew), (Hermione, Dr. Pepper), (Hermione, Mt. Dew) }. Convince yourself that every possible combination is in there. I listed them out methodically to make sure I didn’t miss any (all the Harry’s first, with each drink in order, then all the Ron’s, etc. ) but of course there’s no order to the members of a set, so I could have listed them in any order.
Now if I define a relation between \(X\) and \(Y\) , I’m simply specifying that certain of these ordered pairs are in the relation, and certain ones are not. For example, I could define a relation \(R\) that contains only { (Harry, Mt. Dew), (Ron, Mt. Dew) }. I could define another relation \(S\) that contains { (Hermione, Mt. Dew), (Hermione, Dr. Pepper), (Harry, Dr. Pepper) }. I could define another relation \(T\) that has none of the ordered pairs; in other words, \(T = \varnothing\) .
A question that should occur to you is: how many different relations are there between two sets \(X\) and \(Y\) ? Think it out: every one of the ordered pairs in \(X \times Y\) either is, or is not, in a particular relation between \(X\) and \(Y\) . Very well. Since there are a total of \(|X|\cdot|Y|\) ordered pairs, and each one of them can be either present or absent from each relation, there must be a total of
\[2^{|X|\cdot|Y|}\]
different relations between them. Put another way, the set of all relations between \(X\) and \(Y\) is the power set of \(X \times Y\) . I told you that would come up a lot.
In the example above, then, there are a whopping \(2^6\) , or 64 different relations between those two teensey little sets. One of those relations is the empty set. Another one has all six ordered pairs in it. The rest fall somewhere in the middle. (Food for thought: how many of these relations have exactly one ordered pair? How many have exactly five?)
Notation
I find the notation for expressing relations somewhat awkward. But here it is. When we defined the relation \(S\) , above, we had the ordered pair (Harry, Dr. Pepper) in it. To explicitly state this fact, we could simply say \[\text{(Harry, Dr.~Pepper)} \in S\] and in fact we can do so. More often, though, mathematicians write:
Harry \(S\) Dr. Pepper.
which is pronounced “Harry is \(S\) -related-to Dr. Pepper." Told you it was awkward.
If we want to draw attention to the fact that (Harry, Mt. Dew) is not in the relation \(S\) , we could strike it through to write
Harry --\(S\)-- Mt. Dew


3.4: Analogical Arguments
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When I strike a match it will produce a flame. It is natural to take the striking of the match as the cause that produces the effect of a flame. But what if the matchbook is wet? Or what if I happen to be in a vacuum in which there is no oxygen (such as in outer space)? If either of those things is the case, then the striking of the match will not produce a flame. So it isn’t simply the striking of the match that produces the flame, but a combination of the striking of the match together with a number of other conditions that must be in place in order for the striking of the match to create a flame. Which of those conditions we call the “cause” depends in part on the context. Suppose that I’m in outer space striking a match (suppose I’m wearing a space suit that supplies me with oxygen but that I’m striking the match in space, where there is no oxygen). I continuously strike it but no flame appears (of course). But then someone (also in a space suit) brings out a can of compressed oxygen that they spray on the match while I strike it. All of a sudden a flame is produced. In this context, it looks like it is the spraying of oxygen that causes flame, not the striking of the match. Just as in the case of the striking of the match, any cause is more complex than just a simple event that produces some other event. Rather, there are always multiple conditions that must be in place for any cause to occur. These conditions are called background conditions . That said, we often take for granted the background conditions in normal contexts and just refer to one particular event as the cause. Thus, we call the striking of the match the cause of the flame. We don’t go on to specify all the other conditions that conspired to create the flame (such as the presence of oxygen and the absence of water). But this is more for convenience than correctness. For just about any cause, there are a number of conditions that must be in place in order for the effect to occur. These are called necessary conditions (recall the discussion of necessary and sufficient conditions from chapter 2, section 2.7). For example, a necessary condition of the match lighting is that there is oxygen present. A necessary condition of a car running is that there is gas in the tank. We can use necessary conditions to diagnose what has gone wrong in cases of malfunction. That is, we can consider each condition in turn in order to determine what caused the malfunction. For example, if the match doesn’t light, we can check to see whether the matches are wet. If we find that the matches are wet then we can explain the lack of the flame by saying something like, “dropping the matches in the water caused the matches not to light.” In contrast, a sufficient condition is one which if present will always bring about the effect. For example, a person being fed through an operating wood chipper is sufficient for causing that person’s death (as was the fate of Steve Buscemi’s character in the movie Fargo). Because the natural world functions in accordance with natural laws (such as the laws of physics), causes can be generalized. For example, any object near the surface of the earth will fall towards the earth at 9.8 m/s2 unless impeded by some contrary force (such as the propulsion of a rocket). This generalization applies to apples, rocks, people, wood chippers and every other object. Such causal generalizations are often parts of explanations. For example, we can explain why the airplane crashed to the ground by citing the causal generalization that all unsupported objects fall to the ground and by noting that the airplane had lost any method of propelling itself because the engines had died. So we invoke the causal generalization in explaining why the airplane crashed. Causal generalizations have a particular form:
For any x, if x has the feature(s) F , then x has the feature G
For example:
For any human, if that human has been fed through an operating wood chipper , then that human is dead .
For any engine, if that engine has no fuel , then that engine will not operate .
For any object near the surface of the earth, if that object is unsupported and not impeded by some contrary force , then that object will fall towards the earth at 9.8 m/s 2 .
Being able to determine when causal generalizations are true is an important part of becoming a critical thinker. Since in both scientific and every day contexts we rely on causal generalizations in explaining and understanding our world, the ability to assess when a causal generalization is true is an important skill. For example, suppose that we are trying to figure out what causes our dog, Charlie, to have seizures. To simplify, let’s suppose that we have a set of potential candidates for what causes his seizures. It could be either:
- eating human food,
- the shampoo we use to wash him,
- his flea treatment,
- not eating at regular intervals,
or some combination of these things. Suppose we keep a log of when these things occur each day and when his seizures (S) occur. In the table below, I will represent the absence of the feature by a negation. So in the table below, “~A” represents that Charlie did not eat human food on that day; “~B” represents that he did not get a bath and shampoo that day; “~S” represents that he did not have a seizure that day. In contrast, “B” represents that he did have a bath and shampoo, whereas “C” represents that he was given a flea treatment that day. Here is how the log looks:
| Day 1 | ~A | B | C | D | S |
|---|---|---|---|---|---|
| Day 2 | A | ~B | C | D | ~S |
| Day 3 | A | B | ~C | D | ~S |
| Day 4 | A | B | C | ~D | S |
| Day 5 | A | B | ~C | D | ~S |
| Day 6 | A | ~B | C | D | ~S |
How can we use this information to determine what might be causing Charlie to have seizures? The first thing we’d want to know is what feature is present every time he has a seizure. This would be a necessary (but not sufficient) condition. And that can tell us something important about the cause. The necessary condition test says that any candidate feature (here A, B, C, or D) that is absent when the target feature (S) is present is eliminated as a possible necessary condition of S. 3 In the table above, A is absent when S is present, so A can’t be a necessary condition (i.e., day 1). D is also absent when S is present (day 4) so D can’t be a necessary condition either. In contrast, B is never absent when S is present—that is every time S is present, B is also present. That means B is a necessary condition, based on the data that we have gathered so far. The same applies to C since it is never absent when S is present. Notice that there are times when both B and C are absent, but on those days the target feature (S) is absent as well, so it doesn’t matter.
The next thing we’d want to know is which feature is such that every time it is present, Charlie has a seizure. The test that is relevant to determining this is called the sufficient condition test. The sufficient condition test says that any candidate that is present when the target feature (S) is absent is eliminated as a possible sufficient condition of S. In the table above, we can see that no one candidate feature is a sufficient condition for causing the seizures since for each candidate (A, B, C, D) there is a case (i.e. day) where it is present but that no seizure occurred. Although no one feature is sufficient for causing the seizures (according to the data we have gathered so far), it is still possible that certain features are jointly sufficient. Two candidate features are jointly sufficient for a target feature if and only if there is no case in which both candidates are present and yet the target is absent. Applying this test, we can see that B and C are jointly sufficient for the target feature since any time both are present, the target feature is always present. Thus, from the data we have gathered so far, we can say that the likely cause of Charlie’s seizures are when we both give him a bath and then follow that bath up with a flea treatment. Every time those two things occur, he has a seizure (sufficient condition); and every time he has a seizure, those two things occur (necessary condition). Thus, the data gathered so far supports the following causal conditional:
Any time Charlie is given a shampoo bath and a flea treatment, he has a seizure.
Although in the above case, the necessary and sufficient conditions were the same, this needn’t always be the case. Sometimes sufficient conditions are not necessary conditions. For example, being fed through a wood chipper is a sufficient condition for death, but it certainly isn’t necessary! (Lot’s of people die without being fed through a wood chipper, so it can’t be a necessary condition of dying.) In any case, determining necessary and sufficient conditions is a key part of determining a cause.
When analyzing data to find a cause it is important that we rigorously test each candidate. Here is an example to illustrate rigorous testing. Suppose that on every day we collected data about Charlie he ate human food but that on none of the days was he given a bath and shampoo, as the table below indicates.
| Day 1 | A | ~B | C | D | ~S |
|---|---|---|---|---|---|
| Day 2 | A | ~B | C | D | ~S |
| Day 3 | A | ~B | ~C | D | ~S |
| Day 4 | A | ~B | C | ~D | S |
| Day 5 | A | ~B | ~C | D | ~S |
| Day 6 | A | ~B | C | D | S |
Given this data, A trivially passes the necessary condition test since it is always present (thus, there can never be a case where A is absent when S is present). However, in order to rigorously test A as a necessary condition, we have to look for cases in which A is not present and then see if our target condition S is present. We have rigorously tested A as a necessary condition only if we have collected data in which A was not present. Otherwise, we don’t really know whether A is a necessary condition. Similarly, B trivially passes the sufficient condition test since it is never present (thus, there can never be a case where B is present but S is absent). However, in order to rigorously test B as a sufficient condition, we have to look for cases in which B is present and then see if our target condition S is absent. We have rigorously tested B as a sufficient condition only if we have collected data in which B is present. Otherwise, we don’t really know whether B is a sufficient condition or not.
In rigorous testing , we are actively looking for (or trying to create) situations in which a candidate feature fails one of the tests. That is why when rigorously testing a candidate for the necessary condition test, we must seek out cases in which the candidate is not present, whereas when rigorously testing a candidate for the sufficient condition test, we must seek out cases in which the candidate is present. In the example above, A is not rigorously tested as a necessary condition and B is not rigorously tested as a sufficient condition. If we are interested in finding a cause, we should always rigorously test each candidate. This means that we should always have a mix of different situations where the candidates and targets are sometimes present and sometimes absent.
The necessary and sufficient conditions tests can be applied when features of the environment are wholly present or wholly absent. However, in situations where features of the environment are always present in some degree, these tests will not work (since there will never be cases where the features are absent and so rigorous testing cannot be applied). For example, suppose we are trying to figure out whether CO2 is a contributing cause to higher global temperatures. In this case, we can’t very well look for cases in which CO2 is present but high global temperatures aren’t (sufficient condition test), since CO2 and high temperatures are always present to some degree. Nor can we look for cases in which CO2 is absent when high global temperatures are present (necessary condition test), since, again, CO2 and high global temperatures are always present to some degree. Rather, we must use a different method, the method that J.S. Mill called the method of concomitant variation . In concomitant variation we look for how things vary vis-à-vis each other. For example, if we see that as CO2 levels rise, global temperatures also rise, then this is evidence that CO2 and higher temperatures are positively correlated. When two things are positively correlated , as one increases, the other also increases at a similar rate (or as one decreases, the other decreases at a similar rate). In contrast, when two things are negatively correlated , as one increases, the other decreases at similar rate (or vice versa). For example, if as a police department increased the number of police officers on the street, the number of crimes reported decreases, then number of police on the street and number of crimes reported would be negative correlated. In each of these examples, we may think we can directly infer the cause from the correlation—the rising CO2 levels are causing the rising global temperatures and the increasing number of police on the street is causing the crime rate to drop. However, we cannot directly infer causation from correlation. Correlation is not causation. If A and B are positively correlated, then there are four distinct possibilities regarding what the cause is:
- A is the cause of B
- B is the cause of A
- Some third thing, C, is the cause of both A and B increasing
- The correlation is accidental
In order to infer what causes what in a correlation, we must rely on our general background knowledge (i.e., things we know to be true about the world), our scientific knowledge, and possibly further scientific testing. For example, in the global warming case, there is no scientific theory that explains how rising global temperatures could cause rising levels of CO2 but there is a scientific theory that enables us to understand how rising levels of CO2 could increase average global temperatures. This knowledge makes it plausible to infer that the rising CO2 levels are causing the rising average global temperatures. In the police/crime case, drawing on our background knowledge we can easily come up with an inference to the best explanation argument for why increased police presence on the streets would lower the crime rate—the more police on the street, the harder it is for criminals to get away with crimes because there are fewer places where those crimes could take place without the criminal being caught. Since criminals don’t want to risk getting caught when they commit a crime, seeing more police around will make them less likely to commit a crime. In contrast, there is no good explanation for why decreased crime would cause there to be more police on the street. In fact, it would seem to be just the opposite: if the crime rate is low, the city should cut back, or at least remain stable, on the number of police officers and put those resources somewhere else. This makes it plausible to infer that it is the increased police officers on the street that is causing the decrease in crime.
Sometimes two things can be correlated without either one causing the other. Rather, some third thing is causing them both. For example, suppose that Bob discovers a correlation between waking up with all his clothes on and waking up with a headache. Bob might try to infer that sleeping with all his clothes on causes headaches, but there is probably a better explanation than that. It is more likely that Bob’s drinking too much the night before caused him to pass out in his bed with all his clothes on, as well as his headache. In this scenario, Bob’s inebriation is the common cause of both his headache and his clothes being on in bed.
Sometimes correlations are merely accidental, meaning that there is no causal relationship between them at all. For example, Tyler Vigen 4 reports that the per capita consumption of cheese in the U.S. correlates with the number of people who die by becoming entangled in their bedsheets:
And the number of Mexican lemons imported to the U.S. correlates with the number of traffic fatalities 5 :
Clearly neither of these correlations are causally related at all—they are accidental correlations . What makes them accidental is that we have no theory that would make sense of how they could be causally related. This just goes to show that it isn’t simply the correlation that allows us to infer a cause, but, rather, some additional background theory, scientific theory, or other evidence that establishes one thing as causing another. We can explain the relationship between correlation and causation using the concepts of necessary and sufficient conditions (first introduced in chapter 2): correlation is a necessary condition for causation, but it is not a sufficient condition for causation.
Our discussion of causes has shown that we cannot say that just because A precedes B or is correlated with B, that A caused B. To claim that since A precedes or correlates with B, A must therefore be the cause of B is to commit what is called the false cause fallacy . The false cause fallacy is sometimes called the “post hoc” fallacy. “Post hoc” is short for the Latin phrase, “post hoc ergo propter hoc,” which means “before this therefore because of this.” As we’ve seen, false cause fallacies occur any time someone assumes that two events that are correlated must be in a causal relationship, or that since one event precedes another, it must cause the other. To avoid the false cause fallacy, one must look more carefully into the relationship between A and B to determine whether there is a true cause or just a common cause or accidental correlation. Common causes and accidental correlations are more common than one might think.
Exercise
Determine which of the candidates (A, B, C, D) in the following examples pass the necessary condition test or the sufficient condition test relative to the target (G). In addition, note whether there are any candidates that aren’t rigorously tested as either necessary or sufficient conditions.
1.
| Case 1 | A | B | ~C | D | ~G |
| Case 2 | ~A | B | C | D | G |
| Case 3 | A | ~B | C | D | G |
2.
| Case 1 | A | B | C | D | G |
| Case 2 | ~A | B | ~C | D | ~G |
| Case 3 | A | ~B | C | ~D | G |
3.
| Case 1 | A | B | C | D | G |
| Case 2 | ~A | B | C | D | G |
| Case 3 | A | ~B | C | D | G |
4.
| Case 1 | A | B | C | D | ~G |
| Case 2 | ~A | B | C | D | G |
| Case 3 | A | ~B | C | ~G | ~G |
5.
| Case 1 | A | B | C | D | ~G |
| Case 2 | ~A | B | C | D | G |
| Case 3 | A | ~B | C | ~D | ~G |
6.
| Case 1 | A | B | ~C | D | ~G |
| Case 2 | ~A | B | C | D | ~G |
| Case 3 | A | ~B | ~C | ~D | G |
7.
| Case 1 | A | B | ~C | D | G |
| Case 2 | ~A | ~B | C | D | ~G |
| Case 3 | A | ~B | C | ~D | ~G |
8.
| Case 1 | A | B | ~C | D | ~G |
| Case 2 | ~A | ~B | ~C | D | ~G |
| Case 3 | A | ~B | ~C | ~D | ~G |
9.
| Case 1 | A | B | ~C | D | G |
| Case 2 | ~A | ~B | C | D | G |
| Case 3 | A | ~B | ~C | D | ~G |
10.
| Case 1 | ~A | B | ~C | D | ~G |
| Case 2 | ~A | B | C | D | G |
| Case 3 | ~A | ~B | ~C | D | G |
For each of the following correlations, use your background knowledge to determine whether A causes B, B causes A, a common cause C is the cause of both A and B, or the correlations is accidental.
1. There is a positive correlation between U.S. spending on science, space, and technology (A) and suicides by hanging, strangulation, and suffocation (B).
2. There is a positive correlation between our dog Charlie’s weight (A) and the amount of time we spend away from home (B). That is, the more time we spend away from home, the heavier Charlie gets (and the more we are at home, the lighter Charlie is.
3. The height of the tree in our front yard (A) positively correlates with the height of the shrub in our backyard (B).
4. There is a negative correlation between the number of suicide bombings in the U.S. (A) and the number of hairs on a particular U.S President’s head (B).
5. There is a high positive correlation between the number of fire engines in a particular borough of New York Cite (A) and the number of fires that occur there (B).
6. At one point in history, there was a negative correlation between the number of mules in the state (A) and the salaries paid to professors at the state university (B). That is, the more mules, the lower the professors’ salaries.
7. There is a strong positive correlation between the number of traffic accidents on a particular highway (A) and the number of billboards featuring scantily-clad models (B).
8. The girth of an adult’s waist (A) is negatively correlated with the height of their vertical leap (B).
9. Olympic marathon times (A) are positively correlated with the temperature during the marathon (B). That is, the more time it takes an Olympic marathoner to complete the race, the higher the temperature.
10.The number gray hairs on an individual’s head (A) is positively correlated with the number of children or grandchildren they have (B).
3
This discussion draws heavily on chapter 10, pp. 220-224 of Sinnott-Armstrong and Fogelin’s
Understanding Arguments, 9th edition (Cengage Learning).
4
http://tylervigen.com/spurious-correlations
5
Stephen R. Johnson, The Trouble with QSAR (or How I Learned To Stop Worrying and Embrace
Fallacy). J. Chem. Inf. Model., 2008, 48 (1), pp. 25–26.


31.7: Jazz Chord Voicings
In this section we will define guide tones and learn about two types of jazz chord voicings.
31.7.1 Guide Tones
Guide Tones are the 3rd and 7th of a chord. In any circle of fifths progressions (including ii–V–I and iii–vi–ii–V) the guide tones move by step.
Play through the entire circle of fifths with dominant 7th chords (C7–F7–B♭7, etc.) with the bass note in the left hand and the guide tones (3rd and 7th) in the right hand and observe how the 3rd and 7th are the same for bass notes a tritone from each other.
Also, you can play through the circle of fifths alternating between 7(13) chords and 7(♯9) chords—C7(13)–F7(♯9)–B♭7(13)–E♭7(♯9)—with the right hand descending chromatically. This can be repeated with all of the bass notes a tritone away (starting on F♯ in the left hand) and the qualities are exchanged for all the chords.
31.7.2 Jazz Chord Voicings
In this section we will examine two categories of voicings.
- The first category (“spread” voicings) has 5-note chords with the root, 3rd, and 7th as the lowest notes with other chord members voiced above, often in the interval of a fourth or fifth. (The root will always be the lowest note, while the 3rd can be voiced above or below the 7th).
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The second category (“close” voicings) has 5-note chords with the bass note in the left hand and the other four notes in “close position” in the right hand, usually with the 7th or 3rd of the chord as the lowest note in the right hand.
Some chords (like sus chords) do not have a 3rd, and some do not have or a 7th (like C6 or C69). In those cases, voice the sus4 like you would the 3rd, and likewise voice the 6th as you would the 7th.
Sometimes you will need to omit the fifth to maintain five parts.


8.7: Trace Minerals
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Trace minerals are classified as minerals required in the diet each day in smaller amounts, specifically 100 milligrams or less. These include copper, zinc, selenium, iodine, chromium, fluoride, manganese, molybdenum, and others
-
- 8.7A: Prelude to Trace Minerals
- Although trace minerals are needed in smaller amounts it is important to remember that a deficiency in a trace mineral can be just as detrimental to your health as a major mineral deficiency.
-
- 8.7B: Iron
- Iron is needed for the production of other iron-containing proteins such as myoglobin. Myoglobin is a protein found in the muscle tissues that enhances the amount of available oxygen for muscle contraction. Iron is also a key component of hundreds of metabolic enzymes. Many of the proteins of the electron-transport chain contain iron–sulfur clusters involved in the transfer of high-energy electrons and ultimately ATP synthesis.
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- 8.7C: Copper
- Copper, like iron, assists in electron transfer in the electron-transport chain. Furthermore, copper is a cofactor of enzymes essential for iron absorption and transport. The other important function of copper is as an antioxidant. Symptoms of mild to moderate copper deficiency are rare. More severe copper deficiency can cause anemia from the lack of iron mobilization in the body for red blood cell synthesis.
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- 8.7D: Zinc
- Zinc is a cofactor for over two hundred enzymes in the human body and plays a direct role in RNA, DNA, and protein synthesis. Zinc also is a cofactor for enzymes involved in energy metabolism. As the result of its prominent roles in anabolic and energy metabolism, a zinc deficiency in infants and children blunts growth.
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- 8.7E: Iodine
- Iodine is essential for the synthesis of thyroid hormone, which regulates basal metabolism, growth, and development. Low iodine levels and consequently hypothyroidism has many signs and symptoms including fatigue, sensitivity to cold, constipation, weight gain, depression, and dry, itchy skin and paleness.
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- 8.7F: Chromium
- The functioning of chromium in the body is less understood than that of most other minerals. It enhances the actions of insulin so plays a role in carbohydrate, fat, and protein metabolism. Currently, the results of scientific studies evaluating the usefulness of chromium supplementation in preventing and treating Type 2 diabetes are largely inconclusive. More research is needed to better determine if chromium is helpful in treating certain chronic diseases and, if so, at what doses.
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- 8.7G: Manganese
- Manganese is a cofactor for enzymes that are required for carbohydrate and cholesterol metabolism, bone formation, and the synthesis of urea. The recommended intake for manganese is 2.3 mg per day for adult males and 1.8 mg per day for adult females. Manganese deficiency is uncommon. The best food sources for manganese are whole grains, nuts, legumes, and green vegetables.
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- 8.7H: Molybdenum
- Molybdenum also acts as a cofactor that is required for the metabolism of sulfur-containing amino acids, nitrogen-containing compounds found in DNA and RNA, and various other functions. The recommended intake for molybdenum is 46 mcg per day for both adult males and females. The food sources of molybdenum is varies depending on the content in the soil in the specific region.
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- 8.7I: Fluoride
- Fluoride is known mostly as the mineral that combats tooth decay. It assists in tooth and bone development and maintenance.
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- 8.7J: Selenium
- Selenium is a cofactor of enzymes that release active thyroid hormone in cells and therefore low levels can cause similar signs and symptoms as iodine deficiency. The other important function of selenium is as an antioxidant.
Thumbnail: A pile of iodized salt. (CC BY-SA 3.0; Drtony999 )


4.13: Nicotine Receptor Agonists
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- Ernstmeyer & Christman (Eds.)
- Chippewa Valley Technical College via OpenRN
Nicotine binds to and activates nicotinic acetylcholine receptors, mimicking the effect of acetylcholine at these receptors.
Indications: Nicotine patches are used as an aid to smoking cessation and for the relief of nicotine withdrawal signs and symptoms as part of a comprehensive behavioral smoking cessation program.
Nursing Considerations: Nicotine is a hazardous drug; use safe handling and disposal precautions. Apply one new patch every 24 hours on skin that is dry, clean, and hairless. Remove backing from patch and immediately press onto skin. Hold for 10 seconds. Wash hands after applying or removing the patch. Save pouch to use for patch disposal. Dispose of the used patches by folding sticky ends together and putting in pouch. The used patch should be removed and a new one applied to a different skin site at the same time each day. Do not wear more than one patch at a time. Discontinue use and call provider if an allergic reaction occurs, such as difficulty breathing or rash, or symptoms of nicotine overdose occur, such as nausea, vomiting, dizziness, weakness, and rapid heartbeat. It may also cause vivid dreams or sleep disturbances. If these occurrences occur, patients should be counseled to remove the patch at bedtime and apply a new one in the morning.
Patient Teaching & Education: Emphasize that the patient should stop smoking completely while on nicotine replacement therapy to avoid additive nicotine levels higher than smoking alone. Advise patients that participating in a comprehensive smoking cessation program improves success. If using a nicotine patch, patients should be aware that skin sensitivity at the site of patch placement typically resolves within one hour. [1]
Alert: Advise patient to keep all nicotine products, including used inhaler cartridges, nasal spray bottles, and patches out of the reach of children and pets.
Now let’s take a closer look at the medication grid on nicotine patch in Table 4.5. [2] Medication grids assist students to learn key points about each medication class. Basic information related to a common generic medication in this class is outlined, including administration considerations, therapeutic effects, and side effects/adverse effects. Prototype/generic medication listed in the medication grid is also hyperlinked directly to a free resource from the U.S. National Library of Medicine called Daily Med. Because information about medication is constantly changing, nurses should always consult evidence-based resources to review current recommendations before administering specific medication.
|
Class/Subclass |
Prototype/Generic |
Administration Considerations |
Therapeutic Effects |
Side/Adverse Effects |
|---|---|---|---|---|
| Nicotinic Agonist | nicotine patch |
Hazardous drug; use safe handling and disposal precautions
Check for allergy to adhesives See administration guidelines in packaging Use cautiously in patients with recent myocardial infarction, serious arrhythmias, coronary artery disease, severe or worsening angina, hypertension, vasospastic diseases, or peripheral vascular disease Patients taking monoamine oxidase inhibitors (MAOIs) require lower dosage Can cause fetal harm |
Used for nicotine addiction by slowly reducing dose and avoiding withdrawal effects |
Discontinue use and call provider if:
-Allergic reaction such as difficulty breathing or rash -Irregular heartbeat or palpitations -Symptoms of nicotine overdose such as nausea, vomiting, dizziness, weakness, and rapid heartbeat |
- uCentral from Unbound Medicine. https://www.unboundmedicine.com/ucentral ↵
- This work is a derivative of Daily Med by U.S. National Library of Medicine in the public domain . ↵


43.5A: Fertilization
- Describe the process of fertilization
Fertilization
Fertilization is the process in which gametes (an egg and sperm) fuse to form a zygote. The egg and sperm are haploid, which means they each contain one set of chromosomes; upon fertilization, they will combine their genetic material to form a zygote that is diploid, having two sets of chromosomes. A zygote that has more than two sets of chromosomes will not be viable; therefore, to ensure that the offspring has only two sets of chromosomes, only one sperm must fuse with one egg.
In mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy.
Process of fertilization : (a) Fertilization is the process in which sperm and egg fuse to form a zygote. (b) Acrosomal reactions help the sperm degrade the glycoprotein matrix protecting the egg and allow the sperm to transfer its nucleus.
To ensure that no more than one sperm fertilizes the egg, once the acrosomal reactions take place at one location of the egg membrane, the egg releases proteins in other locations to prevent other sperm from fusing with the egg. If this mechanism fails, multiple sperm can fuse with the egg, resulting in polyspermy. The resulting embryo is not genetically viable and dies within a few days.
Key Points
- A mammalian egg is covered by a layer of glycoproteins called the zona pellucida, which the sperm must penetrate in order to fertilize the egg.
- Upon binding with the egg, the sperm initiates the acrosome reaction, in which it releases digestive enzymes that degrade the zona pellucida, allowing the plasma membrane of the sperm to fuse with that of the egg.
- Upon fusion of the two plasma membranes, the sperm’s nucleus enters the egg and fuses with the nucleus of the egg.
- Both the sperm and the egg each contain one half the normal number of chromosomes, so when they fuse the resulting zygote is a diploid organism with a complete set of chromosomes.
- When the egg is successfully fertilized, it releases proteins that prevent it from being fertilized by another sperm, a condition known as polyspermy.
Key Terms
- fertilization : the act of fecundating or impregnating animal or vegetable gametes
- zona pellucida : a glycoprotein membrane surrounding the plasma membrane of an oocyte
- acrosome : a structure forming the end of the head of a spermatozoon
- polyspermy : the penetration of an ovum by more than one sperm


15.5: Camming
Camming is “the internet streaming of adult content” (Dictionary, 2022). This could include nudity and/or masturbation. Often, the person camming is available to chat with online viewers, in exchange for money. Someone may be requested to perform certain activities, often sexual, in front of a webcam for paying clients. People who do camming are referred to as cam girls/boys, or cam or webcam models. There are various online sites that host camming. Most camming is done by women.
According to Dr. Angela Jones, author of Camming: Money, Power, and Pleasure in the Sex Work Industry , through camming, people can earn money, feel powerful and experience pleasure, while doing sex work that is safe and legal. She also explores the racism and xenophobia present within the industry. Nonwhite and non-native English speaking cam models have fewer opportunities and make less money than white native English-speaking workers.
During the Covid-19 pandemic, camming became more popular as a way for people to earn income working from home. Some people who had never done sex work entered during the pandemic, frequently through cam work. Others who had been seeing clients in person switched to online as a way to maintain physical and social distancing (Drolet, 2020).


2.2: The Functions of the Skeletal System
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Learning Objectives
- Define bone, cartilage, and the skeletal system
- List and describe the functions of the skeletal system
Bone , or osseous tissue , is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body. In the areas of the skeleton where bones move (for example, the ribcage and joints), cartilage , a semi-rigid form of connective tissue, provides flexibility and smooth surfaces for movement. The skeletal system is the body system composed of bones and cartilage and performs the following critical functions for the human body:
- supports the body
- facilitates movement
- protects internal organs
- produces blood cells
- stores and releases minerals and fat
Support, Movement, and Protection
The most apparent functions of the skeletal system are the gross functions—those visible by observation. Simply by looking at a person, you can see how the bones support, facilitate movement, and protect the human body.
Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body. Without the skeletal system, you would be a limp mass of organs, muscle, and skin.
Bones also facilitate movement by serving as points of attachment for your muscles. While some bones only serve as a support for the muscles, others also transmit the forces produced when your muscles contract. From a mechanical point of view, bones act as levers and joints serve as fulcrums (Figure \(\PageIndex{1}\)). Unless a muscle spans a joint and contracts, a bone is not going to move. For information on the interaction of the skeletal and muscular systems, that is, the musculoskeletal system, seek additional content.
Bones also protect internal organs from injury by covering or surrounding them.
CAREER CONNECTION: Orthopedist
An orthopedist is a doctor who specializes in diagnosing and treating disorders and injuries related to the musculoskeletal system. Some orthopedic problems can be treated with medications, exercises, braces, and other devices, but others may be best treated with surgery (Figure \(\PageIndex{3}\)).
While the origin of the word “orthopedics” (ortho- = “straight”; paed- = “child”), literally means “straightening of the child,” orthopedists can have patients who range from pediatric to geriatric. In recent years, orthopedists have even performed prenatal surgery to correct spina bifida, a congenital defect in which the neural canal in the spine of the fetus fails to close completely during embryologic development.
Orthopedists commonly treat bone and joint injuries but they also treat other bone conditions including curvature of the spine. Lateral curvatures (scoliosis) can be severe enough to slip under the shoulder blade (scapula) forcing it up as a hump. Spinal curvatures can also be excessive dorsoventrally (kyphosis) causing a hunch back and thoracic compression. These curvatures often appear in preteens as the result of poor posture, abnormal growth, or indeterminate causes. Mostly, they are readily treated by orthopedists. As people age, accumulated spinal column injuries and diseases like osteoporosis can also lead to curvatures of the spine, hence the stooping you sometimes see in the elderly.
Some orthopedists sub-specialize in sports medicine, which addresses both simple injuries, such as a sprained ankle, and complex injuries, such as a torn rotator cuff in the shoulder. Treatment can range from exercise to surgery.
Mineral Storage, Energy Storage, and Hematopoiesis
On a metabolic level, bone tissue performs several critical functions. For one, the bone matrix acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium, and potassium. These minerals, incorporated into bone tissue, can be released back into the bloodstream to maintain levels needed to support physiological processes. Calcium ions, for example, are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses.
 The softer connective tissue that fills the interior of most bone is referred to as bone marrow (Figure \(\PageIndex{4}\)). There are two types of bone marrow: yellow marrow and red marrow. Yellow marrow contains adipose tissue; the triglycerides stored in the adipocytes of the tissue can serve as a source of energy. Red marrow is where hematopoiesis —the production of blood cells—takes place. Red blood cells, white blood cells, and platelets are all produced in the red marrow.
Chapter Review
The major functions of the bones are body support, facilitation of movement, protection of internal organs, storage of minerals and fat, and hematopoiesis. Together, the muscular system and skeletal system are known as the musculoskeletal system.
Review Questions
Q. Which function of the skeletal system would be especially important if you were in a car accident?
A. storage of minerals
B. protection of internal organs
C. facilitation of movement
D. fat storage
Answer: B
Q. Bone tissue can be described as ________.
A. dead calcified tissue
B. cartilage
C. the skeletal system
D. dense, hard connective tissue
Answer: D
Q. Without red marrow, bones would not be able to ________.
A. store phosphate
B. store calcium
C. make blood cells
D. move like levers
Answer: C
Q. Yellow marrow has been identified as ________.
A. an area of fat storage
B. a point of attachment for muscles
C. the hard portion of bone
D. the cause of kyphosis
Answer: A
Q. Which of the following can be found in areas of movement?
A. hematopoiesis
B. cartilage
C. yellow marrow
D. red marrow
Answer: B
Q. The skeletal system is made of ________.
A. muscles and tendons
B. bones and cartilage
C. vitreous humor
D. minerals and fat
Answer: B
Critical Thinking Questions
The skeletal system is composed of bone and cartilage and has many functions. Choose three of these functions and discuss what features of the skeletal system allow it to accomplish these functions.
Answer:
It supports the body. The rigid, yet flexible skeleton acts as a framework to support the other organs of the body.
It facilitates movement. The movable joints allow the skeleton to change shape and positions; that is, move.
It protects internal organs. Parts of the skeleton enclose or partly enclose various organs of the body including our brain, ears, heart, and lungs. Any trauma to these organs has to be mediated through the skeletal system.
It produces blood cells. The central cavity of long bones is filled with marrow. The red marrow is responsible for forming red and white blood cells.
It stores and releases minerals and fat. The mineral component of bone, in addition to providing hardness to bone, provides a mineral reservoir that can be tapped as needed. Additionally, the yellow marrow, which is found in the central cavity of long bones along with red marrow, serves as a storage site for fat.
Glossary
- bone
- hard, dense connective tissue that forms the structural elements of the skeleton
- cartilage
- semi-rigid connective tissue found on the skeleton in areas where flexibility and smooth surfaces support movement
- hematopoiesis
- production of blood cells, which occurs in the red marrow of the bones
- orthopedist
- doctor who specializes in diagnosing and treating musculoskeletal disorders and injuries
- osseous tissue
- bone tissue; a hard, dense connective tissue that forms the structural elements of the skeleton
- red marrow
- connective tissue in the interior cavity of a bone where hematopoiesis takes place
- skeletal system
- organ system composed of bones and cartilage that provides for movement, support, and protection
- yellow marrow
- connective tissue in the interior cavity of a bone where fat is stored


8.2: Balancing Calories
Finding a Balance
More than one third of U.S. adults are obese . Weight gain occurs when you consume more calories than your body uses. Reaching and maintaining a healthy weight will help you prevent and control many diseases and conditions. The key is “Finding a Balance” in your lifestyle that includes healthy eating and regular physical activity.
The Caloric Balance Equation
When it comes to maintaining a healthy weight for a lifetime, the bottom line is – calories count! Weight management is all about balance—balancing the number of calories you consume with the number of calories your body uses or “burns off.”
- A calorie is defined as a unit of energy supplied by food. A calorie is a calorie regardless of its source. Whether you’re eating carbohydrates, fats, sugars, or proteins, all of them contain calories.
- Caloric balance is like a scale. To remain in balance and maintain your body weight, the calories consumed (from foods) must be balanced by the calories used (in normal body functions, daily activities, and exercise).
| If you are… | Your caloric balance status is… |
|---|---|
| Maintaining your weight | “ in balance .” You are eating roughly the same number of calories that your body is using. Your weight will remain stable . |
| Gaining weight | “ in caloric excess .” You are eating more calories than your body is using. You will store these extra calories as fat and you’ll gain weight. |
| Losing weight | “ in caloric deficit .” You are eating fewer calories than you are using. Your body is pulling from its fat storage cells for energy, so your weight is decreasing . |
Home Am I in Caloric Balance?
If you are maintaining your current body weight, you are in caloric balance. If you need to gain weight or to lose weight, you’ll need to tip the balance scale in one direction or another to achieve your goal.
If you need to tip the balance scale in the direction of losing weight, keep in mind that it takes approximately 3,500 calories below your calorie needs to lose a pound of body fat . To lose about 1 to 2 pounds per week, you’ll need to reduce your caloric intake by 500—1000 calories per day.
To learn how many calories you are currently eating, begin writing down the foods you eat and the beverages you drink each day.  Also, begin writing down the physical activity you do each day and the length of time you do it. Here are simple paper and pencil tools to assist you:
Want to try an interactive approach evaluate your food intake and physical activity? Go to the SuperTracker . The site will give you a detailed assessment and analysis of your current eating and physical activity habits.
Physical activities (both daily activities and exercise) help tip the balance scale by increasing the calories you expend each day. For examples, go to How Many Calories Does Physical Activity Burn?
Find out how many calories your body needs to maintain, lose, or gain weight by clicking here.
The bottom line is… each person’s body is unique and may have different caloric needs. A healthy lifestyle requires balance, in the foods you eat, in the beverages you consume, in the way you carry out your daily activities, and in the amount of physical activity or exercise you include in your daily routine. While counting calories is not necessary, it may help you in the beginning to gain an awareness of your eating habits as you strive to achieve energy balance. The ultimate test of balance is whether or not you are gaining, maintaining, or losing weight.
To review these key concepts, watch the video below:
- Finding a Balance. Authored by : Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion. Provided by : Centers for Disease Control and Prevention. Located at : https://www.cdc.gov/healthyweight/calories/ . License : Public Domain: No Known Copyright
- Finding a Balance video. Authored by : Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion. Provided by : Centers for Disease Control and Prevention. Located at : https://www.cdc.gov/cdctv/healthyliving/healthyeating/finding-balance-obesity.html . License : Public Domain: No Known Copyright


3.6: Motion with Constant Acceleration (Part 2)
Putting Equations Together
In the following examples, we continue to explore one-dimensional motion, but in situations requiring slightly more algebraic manipulation. The examples also give insight into problem-solving techniques. The note that follows is provided for easy reference to the equations needed. Be aware that these equations are not independent. In many situations we have two unknowns and need two equations from the set to solve for the unknowns. We need as many equations as there are unknowns to solve a given situation.
\[x = x_{0} + \bar{v}t\]
\[\bar{v} = \frac{v_{0} + v}{2}\]
\[v = v_{0} + at\]
\[x = x_{0} + v_{0}t + \frac{1}{2} at^{2}\]
\[v^{2} = v_{0}^{2} + 2a(x - x_{0})\]
Before we get into the examples, let’s look at some of the equations more closely to see the behavior of acceleration at extreme values. Rearranging \(v = v_0 + at\), we have
\[a = \frac{v - v_{0}}{t} \ldotp\]
From this we see that, for a finite time, if the difference between the initial and final velocities is small, the acceleration is small, approaching zero in the limit that the initial and final velocities are equal. On the contrary, in the limit t → 0 for a finite difference between the initial and final velocities, acceleration becomes infinite.
Similarly, rearranging \(v^2 = v^2_0 + 2a(x-x_0) \), we can express acceleration in terms of velocities and displacement:
\[a = \frac{v^{2} - v_{0}^{2}}{2(x - x_{0})} \ldotp\]
Thus, for a finite difference between the initial and final velocities acceleration becomes infinite in the limit the displacement approaches zero. Acceleration approaches zero in the limit the difference in initial and final velocities approaches zero for a finite displacement.
On dry concrete, a car can decelerate at a rate of 7.00 m/s 2 , whereas on wet concrete it can decelerate at only 5.00 m/s 2 . Find the distances necessary to stop a car moving at 30.0 m/s (about 110 km/h) on (a) dry concrete and (b) wet concrete. (c) Repeat both calculations and find the displacement from the point where the driver sees a traffic light turn red, taking into account his reaction time of 0.500 s to get his foot on the brake.
Strategy
First, we need to draw a sketch Figure \(\PageIndex{1}\). To determine which equations are best to use, we need to list all the known values and identify exactly what we need to solve for.
Solution
- First, we need to identify the knowns and what we want to solve for. We know that v 0 = 30.0 m/s, v = 0, and a = −7.00 m/s 2 (a is negative because it is in a direction opposite to velocity). We take x0 to be zero. We are looking for displacement \(\Delta\)x, or x − x 0 . Second, we identify the equation that will help us solve the problem. The best equation to use is $$v^{2} = v_{0}^{2} + 2a(x - x_{0}) \ldotp$$This equation is best because it includes only one unknown, x. We know the values of all the other variables in this equation. (Other equations would allow us to solve for x, but they require us to know the stopping time, t, which we do not know. We could use them, but it would entail additional calculations.) Third, we rearrange the equation to solve for x: $$x - x_{0} = \frac{v^{2} - v_{0}^{2}}{2a}$$and substitute the known values: $$x - 0 = \frac{0^{2} - (30.0\; m/s)^{2}}{2(-7.00\; m/s^{2})} \ldotp$$Thus, $$x = 64.3\; m\; on\; dry\; concrete \ldotp$$
- This part can be solved in exactly the same manner as (a). The only difference is that the acceleration is −5.00 m/s 2 . The result is $$x_{wet} = 90.0\; m\; on\; wet\; concrete \ldotp$$
- When the driver reacts, the stopping distance is the same as it is in (a) and (b) for dry and wet concrete. So, to answer this question, we need to calculate how far the car travels during the reaction time, and then add that to the stopping time. It is reasonable to assume the velocity remains constant during the driver’s reaction time. To do this, we, again, identify the knowns and what we want to solve for. We know that \(\bar{v}\) = 30.0 m/s, t reaction = 0.500 s, and a reaction = 0. We take x 0-reaction to be zero. We are looking for x reaction . Second, as before, we identify the best equation to use. In this case, x = x 0 + \(\bar{v}\)t works well because the only unknown value is x, which is what we want to solve for. Third, we substitute the knowns to solve the equation: $$x = 0 + (30.0\; m/s)(0.500\; s) = 15.0\; m \ldotp$$This means the car travels 15.0 m while the driver reacts, making the total displacements in the two cases of dry and wet concrete 15.0 m greater than if he reacted instantly. Last, we then add the displacement during the reaction time to the displacement when braking (Figure \(\PageIndex{2}\)), $$x_{braking} + x_{reaction} = x_{total},$$and find (a) to be 64.3 m + 15.0 m = 79.3 m when dry and (b) to be 90.0 m + 15.0 m = 105 m when wet.
Significance
The displacements found in this example seem reasonable for stopping a fast-moving car. It should take longer to stop a car on wet pavement than dry. It is interesting that reaction time adds significantly to the displacements, but more important is the general approach to solving problems. We identify the knowns and the quantities to be determined, then find an appropriate equation. If there is more than one unknown, we need as many independent equations as there are unknowns to solve. There is often more than one way to solve a problem. The various parts of this example can, in fact, be solved by other methods, but the solutions presented here are the shortest.
Suppose a car merges into freeway traffic on a 200-m-long ramp. If its initial velocity is 10.0 m/s and it accelerates at 2.00 m/s 2 , how long does it take the car to travel the 200 m up the ramp? (Such information might be useful to a traffic engineer.)
Strategy
First, we draw a sketch Figure \(\PageIndex{3}\). We are asked to solve for time t. As before, we identify the known quantities to choose a convenient physical relationship (that is, an equation with one unknown, t.)
Solution
Again, we identify the knowns and what we want to solve for. We know that x 0 = 0, v 0 = 10 m/s, a = 2.00 m/s 2 , and x = 200 m.
We need to solve for t. The equation x = x 0 + v 0 t + \(\frac{1}{2}\)at 2 works best because the only unknown in the equation is the variable t, for which we need to solve. From this insight we see that when we input the knowns into the equation, we end up with a quadratic equation.
We need to rearrange the equation to solve for t, then substituting the knowns into the equation:
\[200\; m = 0\; m + (10.0\; m/s)t + \frac{1}{2}(2.00\; m/s^{2})t^{2} \ldotp\]
We then simplify the equation. The units of meters cancel because they are in each term. We can get the units of seconds to cancel by taking t = t s, where t is the magnitude of time and s is the unit. Doing so leaves
\[200 = 10t + t^{2} \ldotp\]
We then use the quadratic formula to solve for t,
\[t^{2} + 10t - 200 = 0\]
\[t = \frac{-b \pm \sqrt{b^{2} - 4ac}}{2a},\]
which yields two solutions: t = 10.0 and t = −20.0. A negative value for time is unreasonable, since it would mean the event happened 20 s before the motion began. We can discard that solution. Thus,
\[ t = 10.0\; s \ldotp\]
Significance
Whenever an equation contains an unknown squared, there are two solutions. In some problems both solutions are meaningful; in others, only one solution is reasonable. The 10.0-s answer seems reasonable for a typical freeway on-ramp.
A manned rocket accelerates at a rate of 20 m/s 2 during launch. How long does it take the rocket to reach a velocity of 400 m/s?
A spaceship has left Earth’s orbit and is on its way to the Moon. It accelerates at 20 m/s 2 for 2 min and covers a distance of 1000 km. What are the initial and final velocities of the spaceship?
Strategy
We are asked to find the initial and final velocities of the spaceship. Looking at the kinematic equations, we see that one equation will not give the answer. We must use one kinematic equation to solve for one of the velocities and substitute it into another kinematic equation to get the second velocity. Thus, we solve two of the kinematic equations simultaneously.
Solution
First we solve for v 0 using \(x = x_{0} + v_{0}t + \frac{1}{2} at^{2} = \frac{1}{2}t^{2}\):
\[x - x_{0} = v_{0}t + \frac{1}{2} at^{2} = \frac{1}{2}t^{2}\]
\[1.0 \times 10^{6}\; m = v_{0} (120.0\; s) + \frac{1}{2} (20.0\; m/s^{2})(120.0\; s)^{2}\]
\[v_{0} = 7133.3\; m/s \ldotp\]
Then we substitute v 0 into v = v 0 + at to solve for the final velocity:
\[v = v_{0} + at = 7133.3\; m/s + (20.0\; m/s^{2})(120.0\; s) = 9533.3\; m/s \ldotp\]
Significance
There are six variables in displacement, time, velocity, and acceleration that describe motion in one dimension. The initial conditions of a given problem can be many combinations of these variables. Because of this diversity, solutions may not be easy as simple substitutions into one of the equations. This example illustrates that solutions to kinematics may require solving two simultaneous kinematic equations.
With the basics of kinematics established, we can go on to many other interesting examples and applications. In the process of developing kinematics, we have also glimpsed a general approach to problem solving that produces both correct answers and insights into physical relationships. The next level of complexity in our kinematics problems involves the motion of two interrelated bodies, called two-body pursuit problems .
Two-Body Pursuit Problems
Up until this point we have looked at examples of motion involving a single body. Even for the problem with two cars and the stopping distances on wet and dry roads, we divided this problem into two separate problems to find the answers. In a two-body pursuit problem , the motions of the objects are coupled—meaning, the unknown we seek depends on the motion of both objects. To solve these problems we write the equations of motion for each object and then solve them simultaneously to find the unknown. This is illustrated in Figure \(\PageIndex{4}\).
The time and distance required for car 1 to catch car 2 depends on the initial distance car 1 is from car 2 as well as the velocities of both cars and the acceleration of car 1. The kinematic equations describing the motion of both cars must be solved to find these unknowns.
Consider the following example.
A cheetah waits in hiding behind a bush. The cheetah spots a gazelle running past at 10 m/s. At the instant the gazelle passes the cheetah, the cheetah accelerates from rest at 4 m/s 2 to catch the gazelle. (a) How long does it take the cheetah to catch the gazelle? (b) What is the displacement of the gazelle and cheetah?
Strategy
We use the set of equations for constant acceleration to solve this problem. Since there are two objects in motion, we have separate equations of motion describing each animal. But what links the equations is a common parameter that has the same value for each animal. If we look at the problem closely, it is clear the common parameter to each animal is their position x at a later time t. Since they both start at x 0 = 0, their displacements are the same at a later time t, when the cheetah catches up with the gazelle. If we pick the equation of motion that solves for the displacement for each animal, we can then set the equations equal to each other and solve for the unknown, which is time.
Solution
- Equation for the gazelle: The gazelle has a constant velocity, which is its average velocity, since it is not accelerating. Therefore, we use Equation 3.5.7 with x 0 = 0: $$x = x_{0} + \bar{v} t = \bar{v} t \ldotp$$Equation for the cheetah: The cheetah is accelerating from rest, so we use Equation 3.5.17 with x 0 = 0 and v 0 = 0: $$x = x_{0} + v_{0} t + \frac{1}{2} at^{2} = \frac{1}{2} at^{2} \ldotp$$Now we have an equation of motion for each animal with a common parameter, which can be eliminated to find the solution. In this case, we solve for t: $$x = \bar{v} t = \frac{1}{2} at^{2}$$ $$t = \frac{2 \bar{v}}{a} \ldotp$$The gazelle has a constant velocity of 10 m/s, which is its average velocity. The acceleration of the cheetah is 4 m/s 2 . Evaluating t, the time for the cheetah to reach the gazelle, we have $$t = \frac{2 \bar{v}}{a} = \frac{2(10)}{4} = 5\; s \ldotp$$
- To get the displacement, we use either the equation of motion for the cheetah or the gazelle, since they should both give the same answer. Displacement of the cheetah: $$x = \frac{1}{2} at^{2} = \frac{1}{2} (4)(5)^{2} - 50\; m \ldotp$$Displacement of the gazelle: $$x = \bar{v} t = 10(5) = 50\; m \ldotp$$We see that both displacements are equal, as expected.
Significance
It is important to analyze the motion of each object and to use the appropriate kinematic equations to describe the individual motion. It is also important to have a good visual perspective of the two-body pursuit problem to see the common parameter that links the motion of both objects.
A bicycle has a constant velocity of 10 m/s. A person starts from rest and begins to run to catch up to the bicycle in 30 s when the bicycle is at the same position as the person. What is the acceleration of the person?


10.11: Works Consulted and Further Reading
Adams, Richard E.W. Ancient Civilizations of the New World . Boulder: Westview Press, 1997.
Bourget, Steve and Kimberly L. Jones, eds. The Art and Archaeology of The Moche: An Ancient Society of the Peruvian Coast . Austin: University of Texas Press, 2008.
Bradley, Bruce and Dennis Stanford. “The North Atlantic Ice-Edge Corridor: A Possible Palaeolithic Route to the New World.” World Archaeology 36:4 (December 2004) 459-478.
Clendinnen, Inga. Aztecs: An Interpretation . Cambridge: Cambridge University Press, 1995.
Fagan, Brian M. Ancient North America: The Archaeology of a Continent, 3rd ed. New York: Thames and Hudson, 2000.
Haas, Jonathan and Winifred Creamer. “Crucible of Andean Civilization: The Peruvian Coast from 3000 to 1800 BC.” Current Anthropology 47:5 (October 2006).
Malpass, Michael A. Daily Life in the Inca Empire, 2nd ed. Westport, CT: Greenwood Press, 2009.
Mithen, Steven. After the Ice: A Global Human History, 20,000 – 5000 BC . London: Weidenfeld & Nicolson, 2003.
Pool, Christopher. Olme c Archaeology and Early Mesoamerica. Cambridge: Cambridge University Press, 2007.
Reilly III, F. Kent. “Art, Ritual and Rulership in the Olmec World.” In Smith and Masson, eds.
Read, Kay Almere and Jason J. Gonzalez. Handbook of Mesoamerican Mythology . Santa Barbara: ABCCLIO, 2000.
Restall, Matthew and Amara Solari. 2012 and the End of the World: The Western Roots of the Maya Apocalypse. Lanham, MD: Rowman and Littlefield, 2011.
Silverblatt, Irene Marsha. Moon Sun and Witches : Gender Ideologies and Class in Inca and Colonial Peru. Princeton: Princeton University Press, 1987.
Smith, Michael E. and Marilyn A. Masson, eds. The Ancient Civilizations of Mesoamerica: A Reader. Malden, MA: Blackwell Publishing, 2000.
Stone, Rebecca R. Art of the Andes: From Chavin to Inca : 3rd ed. New York: Thames & Hudson, 2012.
Trubitt, Mary Beth D. “Mound Building and Prestige Goods Exchange: Changing Strategies in the Cahokia Chiefdom.” American Antiquity 65:4, Oct., 2000, pp. 669-690.
Tung, Tiffany. Violence, Ritual, and the Wari Empire: Bioarchaeological Interpretations of the Human Past: Local, Regional, and Global Perspectives. Gainesville: University of Florida Press, 2012.


10.7: Medical Specialists, Diagnostic Testing, and Procedures Related to Blood
Medical Specialists
Hematologist
A hematologist (hē-mā-TŌL-ō-jist) is a physician who specializes in diagnosing and treating blood disorders.
To learn more about a career as a hematologist, visit the American Medical Association’s specialty profile on hematology.
Phlebotomist
A phlebotomist (flĕ-BOT-ŏ-mist) is medical professional trained to withdraw blood or perform blood transfusions. After the blood is collected, it is analyzed by a medical laboratory technician.
Read more about a career as a phlebotomist at Cleveland Clinic’s web page titled Phlebotomist.
Medical Laboratory Technologist/Scientist/Assistant
Medical laboratories employ a variety of individuals in technical positions. Specialized positions are as follows:
- Medical technologist (Mĕd-ĭ-căl Tĕk-nŏl-ŏ-jist) (MT): A medical professional who tests and analyzes blood, other body fluids, and tissue samples.
- Medical laboratory scientists (Mĕd-ĭ-căl LĂB-ŏr-ă-tŏr-ē Sĭ-ĔN-tĭsts) (MLS): A medical professional who performs complex analyses of tissue, blood, and other body fluids.
- Medical laboratory assistants (Mĕd-ĭ-căl LĂB-ŏr-ă-tŏr-ē ă-Sĭs-tănts) (MLA): A medical professional who assists in receiving, preparing, testing, and processing specimen samples.
Read more information about these careers at the American Society for Medical Laboratory Science’s web page called What is a Medical Laboratory Professional?
Diagnostic Testing and Procedures
Apheresis
In traditional blood donation, a unit of whole blood is taken from a donor and sent to a laboratory, where it is separated into its four components: red blood cells, white blood cells, platelets, and plasma. The components are stored and administered to patients who need blood products transfused after surgery, after a severe injury/trauma, or to treat a severe disease or hematological condition. In contrast, during apheresis (ăf-ĕ-RĒ-sĭs), a specific component is removed from a donor’s blood, and the remaining components are returned to the donor while they are still connected to the machine. [1]
Donor apheresis takes longer than a whole blood donation but is easy and painless and has many benefits. For example, an apheresis double red-cell donation (called erythropheresis) separates red blood cells and returns the remaining “non-targeted” plasma and platelets to the volunteer donor. This allows for the collection of twice as many red blood cells from one donation as they would in a whole-blood donation. As another example, a platelet apheresis donation can provide as many platelets as those obtained in four to six whole-blood donations. [2] See Figure 10.12 [3] for an image of an erythropheresis machine.
Blood Product Transfusion
A blood product (blŭd prah-DUHKT) is any therapeutic substance derived from human blood. Types of blood products include whole blood, packed red blood cells (PRBCs), individual factor concentrates, fresh frozen plasma (FFP), platelet concentrates, and cryoprecipitate (i.e., plasma rich in proteins). Transfusion of blood products is a common procedure with nearly 16 million blood components transfused each year in the United States. [4] Nurses typically provide blood transfusions after they are prescribed by a health care provider.
In severe cases of symptomatic, severe anemia (i.e., dyspnea or chest pain) or hemoglobin levels less than 7 g/dL, transfusions of red blood cells are prescribed to rapidly increase hemoglobin levels. See Figure 10.13 [5] for an illustration of a bag of red blood cells. Note the blood type (i.e., A, B, AB, or O) and the Rh factor positive or negative) are indicated on the label to compare with the patient’s lab results. Health care agencies have strict safety procedures that nurses and other health care personnel follow when providing a blood transfusion to prevent the administration of incompatible blood to a patient.
Bone Marrow Aspiration and Biopsy
Bone marrow aspiration (BŌn MĂR-rōw ă-spĭ-RĀ-shŏn) involves the extraction of a small sample of liquid bone marrow from the center of a patient’s bone. Common sites for bone marrow aspiration include the pelvic bone and sternum. The procedure is typically performed after local anesthesia is administered, and then the provider inserts a needle into the bone marrow space and draws out a liquid sample. The aspiration allows for laboratory analysis of the cellular components of the bone marrow (i.e., red blood cells, white blood cells, and platelets). Bone marrow aspiration is helpful for determining the presence of severe blood disorders, such as leukemia, and is also used to monitor disease progression or treatment effectiveness. [6]
Bone marrow biopsy (BŌn MĂR-rōw BĪ-ŏp-sē) involves obtaining a small core of bone and marrow tissue from the bone marrow space. The procedure is often performed in conjunction with bone marrow aspiration.
See Figure 10.14 [7] for an illustration of a bone marrow biopsy.
In contrast to the bone marrow aspiration procedure, the provider uses a larger needle during bone marrow biopsy to remove a cylindrical section of both the bone and marrow. See Figure 10.15 [8] for an image of a bone marrow biopsy needle. Bone marrow biopsy provides a comprehensive evaluation of the bone marrow, allowing for a closer assessment of the bone marrow’s cellular density, structure, and the presence of any abnormal or diseased cells. It helps diagnose a wider range of conditions, including non-hematological disorders like metastatic cancers and immune diseases that may infiltrate the bone marrow. [9]
Bone Marrow Transplant/Stem Cell Transplant
Bone marrow transplant (BŌn MĂR-rōw TRĂNS-plănt), also called stem cell transplant (STĔM Sĕl TRĂNS-plănt), is a potentially curative treatment for severe hematological diseases like sickle cell disease, as well as cancer like leukemia. It typically involves the administration of chemotherapy to destroy the patient’s existing bone marrow and then replacing the bone marrow with healthy stem cells donated from a compatible donor. If successful, transplantation can be curative and result in the patient’s bone marrow taking over the production of healthy red blood cells, white blood cells, and platelets. However, patients undergoing this procedure with donated stem cells must take immunosuppressive medication for the remainder of their lives. [10]
 These parameters help evaluate the overall health of the hematological system and can indicate anemia, infection, or other blood disorders. A CBC with differential (CBC wĭth Dĭf-ĕ-REN-shăl) includes an additional measurement of the different types of white blood cells (i.e., neutrophils, lymphocytes, monocytes, eosinophils, and basophils). See Figure 10.16 [11] for an illustration of CBC with differential test results indicated behind a tube of drawn blood.
- Yale Medicine. (n.d.). Apheresis . https://www.yalemedicine.org/conditions/apheresis ↵
- Yale Medicine. (n.d.). Apheresis . https://www.yalemedicine.org/conditions/apheresis ↵
- “ Fenwal_Erythropheresis_machine_for_plasmapheresis.jpg ” by Elwood P. Dowd is licensed under CC BY-SA 4.0 ↵
- American Red Cross. (n.d.). Importance of the blood supply. https://www.redcrossblood.org/donate-blood/how-to-donate/how-blood-donations-help/blood-needs-blood-supply.html#:~:text=Facts%20About%20Blood%20Needs&text=Approximately%2029%2C000%20units%20of%20red,each%20year%20in%20the%20U.S ↵
- “ Blausen_0086_Blood_Bag.png ” by Blausen.com staff (2014) at “Medical gallery of Blausen Medical 2014.” WikiJournal of Medicine is licensed under CC BY 3.0 ↵
- A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M., Inc.; c1997-2023. Bone marrow aspiration; [reviewed 2022, Apr 9; cited 2023, Nov 5]. https://medlineplus.gov/ency/article/003658.htm ↵
- “Blausen_0097_BoneMarrowBiopsy.png” by Blausen Medical Communications, Inc. is licensed under CC BY 3.0 ↵
- “Multi_Purpose_Bone_Marrow_Biopsy_Needle.jpg” by Thirteen Of Clubs from Minneapolis is licensed under CC BY-SA 2.0 ↵
- A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M., Inc.; c1997-2023. Bone marrow biopsy; [reviewed 2022, Apr 9; cited 2023, Nov 5]. https://medlineplus.gov/ency/article/003934.htm ↵
- National Cancer Institute. (2023, October 5). Stem cell transplants in cancer treatment. National Institutes of Health. https://www.cancer.gov/about-cancer/treatment/types/stem-cell-transplant ↵
- “Complete_blood_count_and_differential.jpg” by SpicyMilkBoy is licensed under CC BY-SA 4.0 ↵