3.12: Summary
Every book that tries to introduce basic programming ideas to novices has to cover roughly the same topics, and in roughly the same order. Mine is no exception, and so in the grand tradition of doing it just the same way everyone else did it, this chapter covered the following topics:
- Getting started . We downloaded and installed R and RStudio
-
Basic commands
. We talked a bit about the logic of how R works and in particular how to type commands into the R console (Section@ref(#firstcommand), and in doing so learned how to perform basic calculations using the arithmetic operators
+
,-
,*
,/
and^
. -
Introduction to functions.
We saw several different functions, three that are used to perform numeric calculations (
sqrt()
,abs()
,round()
, one that applies to text (nchar()
; Section@ref(#simpletext), and one that works on any variable (length()
; Section@ref(#veclength). In doing so, we talked a bit about how argument names work, and learned about default values for arguments. (Section@ref(#functionarguments) -
Introduction to variables. We learned the basic idea behind variables, and how to assign values to variables using the assignment operator
<-
(Section@ref(#assign). We also learned how to create vectors using the combine functionc()
. (Section@ref(#vectors) - Data types. Learned the distinction between numeric, character and logical data; including the basics of how to enter and use each of them. (Sections@ref(#assign) to Sections 3.9
-
Logical operations
.(#logicals) Learned how to use the logical operators
==
,!=
,<
,>
,<=
,=>
,!
,&
and|
. And learned how to use logical indexing. (Section 3.10)
We still haven’t arrived at anything that resembles a “data set”, of course. Maybe the next Chapter will get us a bit closer…
References
R Core Team. 2013. R: A Language and Environment for Statistical Computing . Vienna, Austria: R Foundation for Statistical Computing.
- Source: Dismal Light (1968).
- Although R is updated frequently, it doesn’t usually make much of a difference for the sort of work we’ll do in this book. In fact, during the writing of the book I upgraded several times, and didn’t have to change much except these sections describing the downloading.
- If you’re running an older version of the Mac OS, then you need to follow the link to the “old” page ( http://cran.r-project.org/bin/macosx/old/ ). You should be able to find the installer file that you need at the bottom of the page.
- Tip for advanced Mac users. You can run R from the terminal if you want to. The command is just “R”. It behaves like the normal desktop version, except that help documentation behaves like a “man” page instead of opening in a new window.
- This is probably no coincidence: the people who design and distribute the core R language itself are focused on technical stuff. And sometimes they almost seem to forget that there’s an actual human user at the end. The people who design and distribute RStudio are focused on user interface. They want to make R as usable as possible. The two websites reflect that difference.
- Seriously. If you’re in a position to do so, open up R and start typing. The simple act of typing it rather than “just reading” makes a big difference. It makes the concepts more concrete, and it ties the abstract ideas (programming and statistics) to the actual context in which you need to use them. Statistics is something you do , not just something you read about in a textbook.
- If you’re running R from the terminal rather than from RStudio, escape doesn’t work: use CTRL-C instead.
- For advanced users: yes, as you’ve probably guessed, R is printing out the source code for the function.
- If you’re reading this with R open, a good learning trick is to try typing in a few different variations on what I’ve done here. If you experiment with your commands, you’ll quickly learn what works and what doesn’t
-
For advanced users: if you want a table showing the complete order of operator precedence in R, type
?Syntax
. I haven’t included it in this book since there are quite a few different operators, and we don’t need that much detail. Besides, in practice most people seem to figure it out from seeing examples: until writing this book I never looked at the formal statement of operator precedence for any language I ever coded in, and never ran into any difficulties. - If you are using RStudio, and the “environment” panel (formerly known as the “workspace” panel) is visible when you typed the command, then you probably saw something happening there. That’s to be expected, and is quite helpful. However, there’s two things to note here (1) I haven’t yet explained what that panel does, so for now just ignore it, and (2) this is one of the helpful things RStudio does, not a part of R itself.
-
As we’ll discuss later, by doing this we are implicitly using the
print()
function -
Actually, in keeping with the R tradition of providing you with a billion different screwdrivers (even when you’re actually looking for a hammer) these aren’t the only options. There’s also the
assign
()
function, and the<<-
and->>
operators. However, we won’t be using these at all in this book. -
A quick reminder: when using operators like
<-
and->
that span multiple characters, you can’t insert spaces in the middle. That is, if you type- >
or< -
, R will interpret your command the wrong way. And I will cry. -
Actually, you can override any of these rules if you want to, and quite easily. All you have to do is add quote marks or backticks around your non-standard variable name. For instance
`my sales ` <- 350
would work just fine, but it’s almost never a good idea to do this. -
For very advanced users: there is one exception to this. If you’re naming a function, don’t use
.
in the name unless you are intending to make use of the S3 object oriented programming system in R. If you don’t know what S3 is, then you definitely don’t want to be using it! For function naming, there’s been a trend among R users to prefermyFunctionName
. -
A side note for students with a programming background. Technically speaking, operators
are
functions in R: the addition operator
+
is actually a convenient way of calling the addition function+()
-
A note for the mathematically inclined: R does support complex numbers, but unless you explicitly specify that you want them it assumes all calculations must be real valued. By default, the square root of a negative number is treated as undefined:
sqrt(-9)
will produceNaN
(not a number) as its output. To get complex numbers, you would typesqrt(-9+0i)
and R would now return0+3i
. However, since we won’t have any need for complex numbers in this book, I won’t refer to them again. -
The two functions discussed previously,
sqrt()
andabs()
, both only have a single argument,x
. So I could have typed something likesqrt(x = 225)
orabs(x = -13)
earlier. The fact that all these functions usex
as the name of the argument that corresponds the “main” variable that you’re working with is no coincidence. That’s a fairly widely used convention. Quite often, the writers of R functions will try to use conventional names like this to make your life easier. Or at least that’s the theory. In practice it doesn’t always work as well as you’d hope. - For advanced users: obviously, this isn’t just an RStudio thing. If you’re running R in a terminal window, tab autocomplete still works, and does so in exactly the way you’d expect. It’s not as visually pretty as the RStudio version, of course, and lacks some of the cooler features that RStudio provides. I don’t bother to document that here: my assumption is that if you are running R in the terminal then you’re already familiar with using tab autocomplete.
- Incidentally, that always works: if you’ve started typing a command and you want to clear it and start again, hit escape.
- Another method is to start typing some text and then hit the Control key and the up arrow together (on Windows or Linux) or the Command key and the up arrow together (on a Mac). This will bring up a window showing all your recent commands that started with the same text as what you’ve currently typed. That can come in quite handy sometimes.
-
Notice that I didn’t specify any argument names here. The
c()
function is one of those cases where we don’t use names. We just type all the numbers, and R just dumps them all in a single variable. - I offer up my teenage attempts to be “cool” as evidence that some things just can’t be done.
-
Note that this is a very different operator to the assignment operator
=
that I talked about in Section 3.4. A common typo that people make when trying to write logical commands in R (or other languages, since the “=
versus==
” distinction is important in most programming languages) is to accidentally type=
when you really mean==
. Be especially cautious with this – I’ve been programming in various languages since I was a teenager, and I still screw this up a lot. Hm. I think I see why I wasn’t cool as a teenager. And why I’m still not cool. -
A note for those of you who have taken a computer science class: yes, R does have a function for exclusive-or, namely
xor()
. Also worth noting is the fact that R makes the distinction between element-wise operators&
and|
and operators that look only at the first element of the vector, namely&&
and||
. To see the distinction, compare the behaviour of a command likec(FALSE,TRUE) & c(TRUE,TRUE)
to the behaviour of something likec(FALSE,TRUE) && c(TRUE,TRUE)
. If this doesn’t mean anything to you, ignore this footnote entirely. It’s not important for the content of this book. -
Warning!
TRUE
andFALSE
are reserved keywords in R, so you can trust that they always mean what they say they do. Unfortunately, the shortcut versionsT
andF
do not have this property. It’s even possible to create variables that set up the reverse meanings, by typing commands likeT <- FALSE
andF <- TRUE
. This is kind of insane, and something that is generally thought to be a design flaw in R. Anyway, the long and short of it is that it’s safer to useTRUE
andFALSE
. - Well, I say that… but in my personal experience it wasn’t until I started learning “regular expressions” that my loathing of computers reached its peak.


2.6: Viscosity
Introduction
All liquids have a natural internal resistance to flow termed viscosity. Viscosity is the result of frictional interactions within a given liquid and is commonly expressed in two different ways.
Dynamic Viscosity
The first is dynamic viscosity, also known as absolute viscosity, which measures a fluid’s resistance to flow. In precise terms, dynamic viscosity is the tangential force per unit area necessary to move one plane past another at unit velocity at unit distance apart. As one plane moves past another in a fluid, a velocity gradient is established between the two layers (Figure \(\PageIndex{1}\) ). Viscosity can be thought of as a drag coefficient proportional to this gradient.
The force necessary to move a plane of area A past another in a fluid is given by Equation \ref{1} where \(V\) is the velocity of the liquid, Y is the separation between planes, and η is the dynamic viscosity.
\[ F = \eta A \frac{V}{Y} \label{1} \]
V/Y also represents the velocity gradient (sometimes referred to as shear rate). Force over area is equal to τ, the shear stress, so the equation simplifies to Equation \ref{2} .
\[ \tau = \eta \frac{V}{Y} \label{2} \]
For situations where V does not vary linearly with the separation between plates, the differential formula based on Newton’s equations is given in Equation \ref{3}.
\[ \tau = \eta \frac{\delta V}{\delta Y} \label{3} \]
Kinematic Viscosity
Kinematic viscosity, the other type of viscosity, requires knowledge of the density, ρ, and is given by Equation \ref{4} , where v is the kinematic viscosity and the \(\eta \) is the dynamic viscosity.
\[ \nu = \frac{\eta }{\rho } \label{4} \]
Units of Viscosity
Viscosity is commonly expressed in Stokes, Poise, Saybolt Universal Seconds, degree Engler, and SI units.
Dynamic Viscosity
The SI units for dynamic (absolute) viscosity is given in units of N·S/m 2 , Pa·S, or kg/(m·s), where N stands for Newton and Pa for Pascal. Poise are metric units expressed as dyne·s/cm 2 or g/(m·s). They are related to the SI unit by g/(m·s) = 1/10 Pa·S. 100 centipoise, the centipoise (cP) being the most used unit of viscosity, is equal to one Poise. Table \(\PageIndex{1}\) shows the interconversion factors for dynamic viscosity.
| Unit | Pa*S | Dyne·s/cm 2 or g/(m·s) (Poise) | Centipoise (cP) |
|---|---|---|---|
| Pa*S | 1 | 10 | 1000 |
| Dyne·s/cm 2 or g/(m·s) (Poise) | 0.1 | 1 | 100 |
| Centipoise (cP) | 0.001 | 0.01 | 1 |
| Liquid | \(\eta \) (cP) | Temperature (°C) |
|---|---|---|
| Water | 0.89 | 25 |
| Water | 0.47 | 60 |
| Milk | 2.0 | 18 |
| Olive Oil | 107.5 | 20 |
| Toothpaste | 70,000 - 100,000 | 18 |
| Ketchup | 1000 | 30 |
| Custard | 1,500 | 85-90 |
| Crude Oil (WTI)* | 7 | 15 |
Kinematic Viscosity
The CGS unit for kinematic viscosity is the Stoke which is equal to 10 -4 m 2 /s. Dividing by 100 yields the more commonly used centistoke. The SI unit for viscosity is m 2 /s. The Saybolt Universal second is commonly used in the oilfield for petroleum products represents the time required to efflux 60 milliliters from a Saybolt Universal viscometer at a fixed temperature according to ASTM D-88. The Engler scale is often used in Britain and quantifies the viscosity of a given liquid in comparison to water in an Engler viscometer for 200cm 3 of each liquid at a set temperature.
Newtonian versus Non-Newtonian Fluids
One of the invaluable applications of the determination of viscosity is identifying a given liquid as Newtonian or non-Newtonian in nature.
- Newtonian liquids are those whose viscosities remain constant for all values of applied shear stress.
- Non-Newtonian liquids are those liquids whose viscosities vary with applied shear stress and/or time.
Moreover, non-Newtonian liquids can be further subdivided into classes by their viscous behavior with shear stress:
- Pseudoplastic fluids whose viscosity decreases with increasing shear rate
- Dilatants in which the viscosity increases with shear rate.
- Bingham plastic fluids, which require some force threshold be surpassed to begin to flow and which thereafter flow proportionally to increasing shear stress.
Measuring Viscosity
Viscometers are used to measure viscosity. There are seven different classes of viscometer:
- Capillary viscometers.
- Orifice viscometers.
- High temperature high shear rate viscometers.
- Rotational viscometers.
- Falling ball viscometers.
- Vibrational viscometers.
- Ultrasonic Viscometers.
Capillary Viscometers
Capillary viscometers are the most widely used viscometers when working with Newtonian fluids and measure the flow rate through a narrow, usually glass tube. In some capillary viscometers, an external force is required to move the liquid through the capillary; in this case, the pressure difference across the length of the capillary is used to obtain the viscosity coefficient.
Capillary viscometers require a liquid reservoir, a capillary of known dimensions, a pressure controller, a flow meter, and a thermostat be present. These viscometers include, Modified Ostwald viscometers, Suspended-level viscometers, and Reverse-flow viscometers and measure kinematic viscosity.
The equation governing this type of viscometry is the Pouisille law (Equation \ref{5} ), where Q is the overall flowrate, ΔP, the pressure difference, a , the internal radius of the tube, η, the dynamic viscosity, and l the path length of the fluid.
\[ Q\ =\frac{\pi \Delta Pa^{4}}{8\eta l} \label{5} \]
Here, Q is equal to V/t; the volume of the liquid measured over the course of the experiment divided by the time required for it to move through the capillary where V is volume and t is time.
For gravity-type capillary viscometers, those relying on gravity to move the liquid through the tube rather than an applied force, Equation \ref{6} is used to find viscosity, obtained by substituting the relation Equation \ref{5} with the experimental values, where P is pressure, ρ is density, g is the gravitational constant, and h is the height of the column.
\[ \eta \ =\frac{\pi gha^{4}}{8lV} \rho t \label{6} \]
An example of a capillary viscometer (Ostwald viscometer) is shown in Figure \(\PageIndex{2}\).
Orifice Viscometers
Commonly found in the oil industry, orifice viscometers consist of a reservoir, an orifice, and a receiver. These viscometers report viscosity in units of efflux time as the measurement consists of measuring the time it takes for a given liquid to travel from the orifice to the receiver. These instruments are not accurate as the set-up does not ensure that the pressure on the liquid remains constant and there is energy lost to friction at the orifice. The most common types of these viscometer include Redwood, Engler, Saybolt, and Ford cup viscometers. A Saybolt viscometer is represented in Figure \(\PageIndex{3}\).
High Temperature, High Shear Rate Viscometers
These viscometers, also known as cylinder-piston type viscometers are employed when viscosities above 1000 poise, need to be determined, especially of non-Newtonian fluids. In a typical set-up, fluid in a cylindrical reservoir is displaced by a piston. As the pressure varies, this type of viscometry is well-suited for determining the viscosities over varying shear rates, ideal for characterizing fluids whose primary environment is a high temperature, high shear rate environment, e.g., motor oil. A typical cylinder-piston type viscometer is shown in Figure \(\PageIndex{4}\).
Rotational Viscometers
Well-suited for non-Newtonian fluids, rotational viscometers measure the rate at which a solid rotates in a viscous medium. Since the rate of rotation is controlled, the amount of force necessary to spin the solid can be used to calculate the viscosity. They are advantageous in that a wide range of shear stresses and temperatures and be sampled across. Common rotational viscometers include: the coaxial-cylinder viscometer, cone and plate viscometer, and coni-cylinder viscometer. A cone and plate viscometer is shown in Figure \(\PageIndex{5}\).
Falling Ball Viscometer
This type of viscometer relies on the terminal velocity achieved by a balling falling through the viscous liquid whose viscosity is being measured. A sphere is the simplest object to be used because its velocity can be determined by rearranging Stokes’ law Equation \ref{7} to Equation \ref{8} , where r is the sphere’s radius, η the dynamic viscosity, v the terminal velocity of the sphere, σ the density of the sphere, ρ the density of the liquid, and g the gravitational constant
\[ 6\pi r\eta v\ =\ \frac{4}{3} \pi r^{3} (\sigma - \rho)g \label{7} \]
\[ \eta\ =\frac{\frac{4}{3} \pi r^{2}(\sigma - \rho)g}{6\pi v} \label{8} \]
A typical falling ball viscometric apparatus is shown in Figure \(\PageIndex{6}\).
Vibrational Viscometers
ften used in industry, these viscometers are attached to fluid production processes where a constant viscosity quality of the product is desired. Viscosity is measured by the damping of an electrochemical resonator immersed in the liquid to be tested. The resonator is either a cantilever, oscillating beam, or a tuning fork. The power needed to keep the oscillator oscillating at a given frequency, the decay time after stopping the oscillation, or by observing the difference when waveforms are varied are respective ways in which this type of viscometer works. A typical vibrational viscometer is shown in Figure \(\PageIndex{7}\).
Ultrasonic Viscometers
This type of viscometer is most like vibrational viscometers in that it is obtaining viscosity information by exposing a liquid to an oscillating system. These measurements are continuous and instantaneous. Both ultrasonic and vibrational viscometers are commonly found on liquid production lines and constantly monitor the viscosity.


Skip to main content
-
There is a standard piece of terminology which is that the “focal point” is the point lying on the optical axis at a distance from the mirror equal to the focal length. This term isn't particularly helpful, because it names a location where nothing normally happens. In particular, it is
not
normally the place where the rays come to a focus! --- that would be the
image
point. In other words, we don't normally have \(d_i=f\), unless perhaps \(d_o=\infty\). A recent online discussion among some physics teachers (carnot.physics.buffalo.edu/archives, Feb. 2006) showed that many disliked the terminology, felt it was misleading, or didn't know it and would have misinterpreted it if they had come across it. That is, it appears to be what grammarians call a “skunked term” --- a word that bothers half the population when it's used incorrectly, and the other half when it's used correctly.
-
I would like to thank Fouad Ajami for pointing out the pedagogical advantages of using both equations side by side.


7.8: Learning Activities
Learning Activities
(Answers to “Learning Activities'” can be found in the “Answer Key” at the end of the book. Answers to interactive activity elements will be provided within the element as immediate feedback.)
1. You are working as a triage nurse in a primary care clinic. You just received a phone call from a young woman who is complaining of significant discomfort related to newly diagnosed strep throat.
What instructions can you provide to her to aid in symptom management in order to alleviate discomfort?
2. You are assessing a patient’s head and neck and note the following findings.
Which should be reported to the health care provider?
- Tongue is midline
- White patches noted on both tonsils
- Uvula raises when patient says “Ahhh”
- Speech is slurred
- Thyroid enlarged
Query \(\PageIndex{1}\)
Query \(\PageIndex{2}\)


2.1: Electrons and electronic structure
5
Harper College Chemistry Department
Electron Shells and the Bohr Model
Note that there is a connection between the number of protons in an element, the atomic number that distinguishes one element from another and the number of electrons it has. In all electrically neutral atoms, the number of electrons is the same as the number of protons. Thus, each element, at least when electrically neutral, has a characteristic number of electrons equal to its atomic number.
In 1913, Danish scientist Niels Bohr (1885–1962) developed an early model of the atom. The Bohr model shows the atom has a central nucleus containing protons and neutrons, with the electrons in circular orbits at specific distances from the nucleus, Figure 1 . These orbits form electron shells or energy levels, which are a way of visualizing the number of electrons in the outermost shell. These energy levels are designated by a number and the symbol “n.” For example, 1n represents the first energy level located closest to the nucleus.
Electrons fill shells in a consistent order: they first fill the shells closest to the nucleus, then they continue to fill shells of increasing energy further from the nucleus.The electrons of the outermost energy level determine the atom’s energetic stability and its tendency to form chemical bonds with other atoms to form molecules.
Under standard conditions, atoms fill the inner shells first, often resulting in a variable number of electrons in the outermost shell. The innermost shell has a maximum of two electrons but the next two electron shells can each have a maximum of eight electrons. This is known as the octet rule , which states, with the exception of the innermost shell, that atoms are more stable energetically when they have eight electrons in their valence shell , the outermost electron shell. Figure 2 sho ws examples of some neutral atoms and their electron configurations. Notice that h elium has a complete outer electron shell, with two electrons filling its first and only shell. Similarly, neon has a complete outer 2n shell containing eight electrons. In contrast, chlorine and sodium have seven and one , respectively, in their outer shells, however, by following the octet rule they would be more energetically stable having eight.
VISUAL CONNECTION
An atom may give, take or share electrons with another atom to achieve a full valence shell, the most stable electron configuration. Looking at this figure, how many electrons do elements in group 1 need to lose in order to achieve a stable electron configuration? 1 electron. How many electrons do elements in groups 14 and 17 need to gain to achieve a stable configuration? 4 and 1 electron respectively.
Understanding that the periodic table’s organization is based on the total number of protons (and electrons) helps us know how electrons distribute themselves among the energy levels. The periodic table is arranged in columns and rows based on the number of electrons and their location. Examine more closely some of the elements in the table’s far right column in Figure 3 . The group 18 atoms helium (He), neon (Ne) and argon (Ar) all have filled outer electron shells, making it unnecessary for them to share electrons with other atoms to attain stability. They are highly stable as single atoms because they are non reactive; scientists coin them inert (or noble gases ). Compare this to the group 1 elements in the left-hand column. These elements, including hydrogen (H), lithium (Li) and sodium (Na), all have one electron in their outermost shells. That means that they can achieve a stable configuration and a filled outer shell by donating or sharing one electron with another atom. Hydrogen will donate or share its electron to achieve this configuration, while lithium and sodium will donate their electron to become stable. As a result of losing a negatively charged electron, they become positively charged ions . Group 17 elements, including fluorine and chlorine, have seven electrons in their outermost shells, so they tend to fill this shell with an electron from other atoms or molecules, making them negatively charged ions. Group 14 elements, of which carbon is the most important to living systems, have four electrons in their outer shell allowing them to make several covalent bonds (discussed below) with other atoms. Thus, the periodic table’s columns represent the potential shared state of these elements’ outer electron shells that is responsible for their similar chemical characteristics.
octet rule
atoms are more stable energetically when they have eight electrons in their valence shell, the outermost electron shell, with the exception of the innermost shell
valence electrons


5.6: Additional Measures
-
- Last updated
- Save as PDF
Learning Objectives
- Compute the trimean
- Compute the geometric mean directly
- Compute the geometric mean using logs
- Use the geometric to compute annual portfolio returns
- Compute a trimmed mean
Although the mean, median, and mode are by far the most commonly used measures of central tendency, they are by no means the only measures. This section defines three additional measures of central tendency: the trimean, the geometric mean, and the trimmed mean. These measures will be discussed again in the section "Comparing Measures of Central Tendency."
Trimean
The trimean is a weighted average of the \(25^{th}\) percentile, the \(50^{th}\) percentile, and the \(75^{th}\) percentile. Letting \(P25\) be the \(25^{th}\) percentile, \(P50\) be the \(50^{th}\)and \(P75\) be the \(75^{th}\) percentile, the formula for the trimean is:
\[Trimean = \dfrac{P25 + 2P50 + P75}{4}\]
As you can see from the formula, the median is weighted twice as much as the \(25^{th}\) and \(75^{th}\) percentiles. Table \(\PageIndex{1}\) shows the number of touchdown (TD) passes thrown by each of the \(31\) teams in the National Football League in the \(2000\) season. The relevant percentiles are shown in Table \(\PageIndex{2}\).
Table \(\PageIndex{1}\): Number of touchdown passes
\[\begin{matrix} 37 & 33 & 33 & 32 & 29 & 28 & 28 & 23\\ 22 & 22 & 22 & 21 & 21 & 21 & 20 & 20\\ 19 & 19 & 18 & 18 & 18 & 18 & 16 & 15\\ 14 & 14 & 14 & 12 & 12 & 9 & 6 & \end{matrix}\]
| Percentile | Value |
|---|---|
| 25 | 15 |
| 50 | 20 |
| 75 | 23 |
The trimean is therefore
\[\dfrac{15 + 2 \times 20 + 23}{4} = \dfrac{78}{4} = 19.5.\]
Geometric Mean
The geometric mean is computed by multiplying all the numbers together and then taking the \(n^{th}\) root of the product. For example, for the numbers \(1, 10\) and \(100\), the product of all the numbers is:
\[1 \times 10 \times 100 = 1,000.\]
Since there are three numbers, we take the cubed root of the product (\(1,000\)) which is equal to \(10\). The formula for the geometric mean is therefore
\[ \large\left(\Pi \, X \right)^{1/N}\]
where the symbol \(Π\) means to multiply. Therefore, the equation says to multiply all the values of \(X\) and then raise the result to the \(1/N\)th power. Raising a value to the \(\dfrac{1}{N}^{th}\) power is, of course, the same as taking the \(N^{th}\) root of the value. In this case, \(1000^{1/3}\) is the cube root of \(1,000\).
The geometric mean has a close relationship with logarithms. Table \(\PageIndex{3}\) shows the logs (base \(10\)) of these three numbers. The arithmetic mean of the three logs is \(1\). The anti-log of this arithmetic mean of \(1\) is the geometric mean . The anti-log of \(1\) is \(10^1 = 10\). Note that the geometric mean only makes sense if all the numbers are positive.
| X | \(\log _{10}(X)\) |
|---|---|
| 1 | 0 |
| 10 | 1 |
| 100 | 2 |
The geometric mean is an appropriate measure to use for averaging rates. For example, consider a stock portfolio that began with a value of \(\$1,000\) and had annual returns of \({13\%, 22\%, 12\%, -5\%, and -13\%}\). Table \(\PageIndex{4}\) shows the value after each of the five years.
| Year | Return | Value |
|---|---|---|
| 1 | 13% | 1,130 |
| 2 | 22% | 1,379 |
| 3 | 12% | 1,544 |
| 4 | -5% | 1,467 |
| 5 | -13% | 1,276 |
The question is how to compute average annual rate of return. The answer is to compute the geometric mean of the returns. Instead of using the percents, each return is represented as a multiplier indicating how much higher the value is after the year. This multiplier is \(1.13\) for a \(13\%\) return and \(0.95\) for a \(5\%\) loss. The multipliers for this example are \({1.13, 1.22, 1.12, 0.95,\: and\; 0.87}\). The geometric mean of these multipliers is \(1.05\). Therefore, the average annual rate of return is \(5\%\). Table \(\PageIndex{5}\) shows how a portfolio gaining \(5\%\) a year would end up with the same value (\(\$1,276\)) as shown in Table \(\PageIndex{4}\).
| Year | Return | Value |
|---|---|---|
| 1 | 5% | 1,050 |
| 2 | 5% | 1,103 |
| 3 | 5% | 1,158 |
| 4 | 5% | 1,216 |
| 5 | 5% | 1,276 |
Trimmed Mean
To compute a trimmed mean, you remove some of the higher and lower scores and compute the mean of the remaining scores. A mean trimmed \(10\%\) is a mean computed with \(10\%\) of the scores trimmed off: \(5\%\) from the bottom and \(5\%\) from the top. A mean trimmed \(50\%\) is computed by trimming the upper \(25\%\) of the scores and the lower \(25\%\) of the scores and computing the mean of the remaining scores. The trimmed mean is similar to the median which, in essence, trims the upper \(49\%\) and the lower \(49\%\) of the scores. Therefore the trimmed mean is a hybrid of the mean and the median. To compute the mean trimmed \(20\%\) for the touchdown pass data shown in Table \(\PageIndex{1}\), you remove the lower \(10\%\) of the scores (\({6, 9,\: and\; 12}\)) as well as the upper \(10\%\) of the scores (\({33, 33,\: and\; 37}\)) and compute the mean of the remaining \(25\) scores. This mean is \(20.16\).


1.7: New Page
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- Last updated
- Save as PDF
- Stephen Skripak et al.
- Virginia Tech via Virginia Tech Libraries' Open Education Initiative
Key Takeaways
- The main participants in a business are its owners , employees , and customers .
- Every business must consider its stakeholders , and their sometimes conflicting interests, when making decisions.
- The activities needed to run a business can be divided into functional The business functions correspond fairly closely to many majors found within a typical college of business.
- Businesses are influenced by such external factors as the economy , government , and other forces external to the business. The PESTEL model is a useful tool for analyzing these forces.
References
1 This vignette is based on an honors thesis written by Danielle M. Testa, “Apple, Inc.: An Analysis of the Firm’s Tumultuous History, in Conjunction with the Abounding Future” (Lehigh University), November 18, 2007.
2 Lee Angelelli (1994). “Steve Paul Jobs.” Retrieved from: http://ei.cs.vt.edu/~history/Jobs.html
3 Ibid.
4 Cyrus Farivar (2006). “Apple’s first 30 years; three decades of contributions to the computerIndustry.” Macworld, June 2006, p. 2.
5 Dan Barkin (2006). “He made the iPod: How Steve Jobs of Apple created the new millennium’s signature invention.” Knight Ridder Tribune Business News, December 3, 2006, p. 1.
6 Jon Hilsenrath, Serena Ng, and Damian Paletta (2008). “Worst Crisis Since ’30s, With No End Yet in Sight,” Wall Street Journal, Markets, September 18, 2008. Retrieved from: http://www.wsj.com/articles/SB122169431617549947
7 Steve Hargreaves (2008). “How the Economy Stole the Election,” CNN.com. Retrieved from: http://money.cnn.com/galleries/2008/news/0810/gallery.economy_election/index.html
8 Dan Gallagher (2008). “Analyst says Apple is cutting back production as economy weakens.” MarketWatch. Retrieved from: http://www.marketwatch.com/story/apple-cutting-back-iphone-production-analyst-says?amp%3Bdist=msr_1
9 David Baron (2003). “Facing-Off in Public.” Stanford Business. August 2003, pp. 20-24. Retrieved from: https://www.gsb.stanford.edu/sites/gsb/files/2003August.pdf
10 Transparency Market Research (2014). “Electric Vehicles Market (on-road) (hybrid, plug-in, and battery) – Global Industry Analysis, Size, Share, Growth, Trends and Forecast, 2013 – 2019.” Retrieved from: http://www.transparencymarketresearch.com/electric-vehicles-market.html


19.1: Descriptive Epidemiology
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Learning Objectives
- Describe the role of a descriptive epidemiology
The goal of epidemiology is to establish causal factors for health issues in order to improve the health and safety of entire populations. A population can refer to a town, country, age group, or race. Health issues refer to anything that might impact health in the present or future. For epidemiologists, data on who is most likely to be injured in car crashes can be just as valuable as a topic of inquiry as data on what part of the population is most at risk for developing complications from the flu. In order to accomplish this, epidemiology has two main branches: descriptive and analytical.
Descriptive epidemiology evaluates and catalogs all the circumstances surrounding a person affected by a health event of interest. Analytical epidemiologists use data gathered by descriptive epidemiology experts to look for patterns suggesting causation. The end goal of both branches is to reduce the incidence of health events or diseases by understanding the risk factors for the health events or diseases. Both descriptive and analytical epidemiology often serve public health organizations by providing information that may reduce disease or reduce other kinds of events that impact people’s health.
The primary considerations for descriptive epidemiology are frequency and pattern. Frequency evaluates the rate of occurrence, and pattern helps analytical epidemiologists suggest risk factors. Descriptive epidemiology evaluates frequency and pattern by examining the person, place, and time in relationship to health events.
Descriptive epidemiology examines factors like age, education, socioeconomic status, availability of health services, race, and gender. Evaluations of specific individuals may also include gathering information on behaviors like drug abuse, shift work, eating, and exercise patterns.
Key Points
- Epidemiology is the science concerned with the study of the factors that influence and determine the frequency and distribution of disease, injury, and other health -related events and their causes in a defined human population.
- The more fully a descriptive epidemiologist can describe people, places and times, and any correlations between the three, the more likely it is that patterns will emerge which can be considered as risk factors for certain kinds of health issues.
- Epidemiologists use data as an information source for communicating information to people and to influence public policy.
Key Terms
- socioeconomic : Of or pertaining to social and economic factors.
- epidemiology : The branch of a science dealing with the spread and control of diseases, computer viruses, concepts, etc., throughout populations or systems.
- risk factor : A variable associated with an increased risk of disease or infection.


12.2: Basic Concepts
What Causes Sleep?
There are two internal biological mechanisms that work together to regulate wakefulness and sleep referred to as circadian rhythms and sleep-wake homeostasis.
Circadian rhythms direct a wide variety of body functions including wakefulness, core temperature, metabolism, and the release of hormones. They control the timing of sleep, causing a person to feel sleepy at night and creating a tendency to wake in the morning without an alarm. See Figure 12.1 [1] for an illustration of circadian rhythms. Circadian rhythms are based roughly on a 24-hour clock and use environmental cues, such as light and temperature to determine the time of day. [2]
Sleep-wake homeostasis keeps track of a person’s need for sleep. A pressure to sleep builds with every hour that a person is awake, reaching a peak in the evening when most people fall asleep. The homeostatic sleep drive also regulates sleep intensity, causing a person to sleep longer and more deeply after a period of sleep deprivation. [3] Adenosine is linked to this drive for sleep. While awake, the level of adenosine in the brain continues to rise, with increased levels signaling a shift toward sleep. While sleeping, the body breaks down adenosine. When it gets dark, the body also releases a hormone called melatonin. Melatonin signals the body that it’s time to prepare for sleep and creates a feeling of drowsiness. The amount of melatonin in the bloodstream peaks as the evening wears on. A third hormone, cortisol, is released in the early morning hours and naturally prepares the body to wake up. [4]
Factors that influence a person’s sleep and wakefulness include medical conditions, medications, stress, sleep environment, and foods and fluids consumed, but the greatest influence is exposure to light. Specialized cells in the retina process light and provide messages to the brain to align the body clock with periods of day or night. Exposure to bright artificial light in the late evening can disrupt this process, making it hard to fall asleep. Examples of bright artificial light include the light from a TV screen, computer, or smartphone. Exposure to light can also make it difficult to return to sleep after being awakened. [5]
Night shift workers often have trouble falling asleep when they go to bed and may have trouble staying awake at work because their natural circadian rhythm and sleep-wake cycle are disrupted. Jet lag also disrupts circadian rhythms. When flying to a different time zone, a mismatch is created between a person’s internal clock and the actual time of day. [6]
The rhythm and timing of the body clock change with age. For example, teenagers fall asleep later at night than younger children and adults because melatonin is released and peaks later in the 24-hour cycle for teens. As a result, it’s natural for many teens to prefer later bedtimes at night and sleep later in the morning than adults. [7]
Individuals also need more sleep early in life, when they’re growing and developing. For example, newborns may sleep more than 16 hours a day, and preschool-aged children need to take naps. Young children tend to sleep more in the early evening whereas older adults tend to go to bed earlier and wake up earlier. [8]
Sleep Phases and Stages
When sleeping, individuals cycle through two phases of sleep: rapid eye movement (REM) and non-REM sleep. A full sleep cycle takes 80 to 100 minutes to complete, and most people typically cycle through four to six cycles per night. It is common to wake up briefly between cycles. [9]
Restoration takes place mostly during slow-wave non-REM sleep, during which the body’s temperature, heart rate, and brain oxygen consumption decrease. Brain activity decreases, so this stage is also referred to as slow-wave sleep and is observed during sleep studies. Non-REM sleep has these three stages:
- Stage 1: The transition between wakefulness and sleep.
- Stage 2: The initiation of the sleep phase.
- Stage 3: The deep sleep or slow-wave sleep stage based on a pattern that appears during measurements of brain activity. Individuals spend the most amount of sleep time in this stage during the early part of the night. (Note that the previously considered 4th stage of non-REM sleep is now included within Stage 3). [10]
During REM sleep, a person’s heart rate and respiratory rate increase. Eyes twitch as they rapidly move back and forth and the brain is active. Brain activity measured during REM sleep is similar to activity during waking hours. Dreaming occurs during REM sleep, and muscles normally become limp to prevent acting out one’s dreams. People typically experience more REM sleep as the night progresses. However, hot and cold environments can affect a person’s REM sleep because the body does not regulate temperature well during REM sleep. [11] See Figure 12.2 [12] for an image illustrating stages of sleep with increased REM sleep through the night indicated in solid red lines.
The patterns and types of sleep change as people mature. For example, newborns spend more time in REM sleep. The amount of slow-wave sleep peaks in early childhood and then drops sharply in the teenage years. Slow-wave sleep continues to decrease through adulthood, and older people may not have any slow-wave sleep at all. [13]
Why Is Sleep Important?
Sleep plays a vital role in good health and well-being. Getting enough quality sleep at the right times protects mental health and physical health. Lack of sleep affects daytime performance, quality of life, and safety. The way a person feels while awake depends on what happens while they are sleeping. During sleep, the body is working to support healthy brain function and maintain physical health. In children and teens, sleep also helps support growth and development. [14]
Healthy Brain Function and Emotional Well-Being
Sleep helps the brain work properly. While sleeping, the brain is forming new pathways to help a person learn and remember information. Studies show that a good night’s sleep improves learning and problem-solving skills. Sleep also helps a person pay attention, make decisions, and be creative. Conversely, sleep deficiency alters activity in some parts of the brain, causing difficulty in making decisions, solving problems, controlling emotions and behavior, and coping with change. Sleep deficiency has also been linked to depression, suicide, and risk-taking behavior. [15]
Physical Health
Sleep also plays an important role in physical health. For example, sleep is involved in healing and repairing the heart and blood vessels. Ongoing sleep deficiency is linked to an increased risk of heart disease, kidney disease, high blood pressure, diabetes, and stroke. Sleep helps maintain a healthy balance of the hormones that cause hunger (ghrelin) or a feeling of fullness (leptin). When a person doesn’t get enough sleep, the level of ghrelin increases and the level of leptin decreases, causing a person to feel hungry when sleep deprived. The way the body responds to insulin is also affected, causing increased blood sugar. [16]
Sleep supports healthy growth and development. Deep sleep triggers the body to release hormones that promote normal growth in children and teens. See Figure 12.3. [17] of a sleeping child. These hormones also boost muscle mass and help repair cells and tissues. [18]
Daytime Performance
Getting enough quality sleep at the right times also enhances functioning throughout the day. People who are sleep deficient are less productive at work and school. They take longer to finish tasks, have a slower reaction time, and make more mistakes. After several nights of losing sleep, even a loss of just 1 or 2 hours per night, the ability to function declines. [19] See Figure 12.4 [20] for an image of a student demonstrating sleep deficiency while studying.
Lack of sleep can lead to microsleep. Microsleep refers to brief moments of sleep that occur when one is normally awake. You can’t control microsleep, and you might not be aware of it. For example, have you ever driven somewhere and then not remembered part of the trip? If so, you may have experienced microsleep. Even if you’re not driving, microsleep can affect how you function. If you’re listening to a lecture, for example, you might miss some of the information or feel as if you don’t understand the point. In reality, you may have slept through part of the lecture and not been aware of experiencing microsleep. [21]
Effects of Sleep Deficiency
The damage from sleep deficiency can occur in an instant. For example, drowsy drivers may feel capable of driving. Yet, studies show that sleep deficiency harms one’s driving ability as much as, or more than, being drunk. It is estimated that driver sleepiness is a factor in about 100,000 car accidents each year, resulting in about 1,500 deaths. [22]
Drivers aren’t the only ones affected by sleep deficiency. It can affect people in all lines of work, including health care workers, pilots, students, mechanics, and assembly line workers. As a result, sleep deficiency is harmful not only on a personal level, but also can cause large-scale damage. For example, sleep deficiency has played a role in human errors linked to tragic accidents, such as nuclear reactor meltdowns, grounding of large ships, and aviation accidents. [23]
Sleep deficiency can also cause long-term harm. It increases the risk of obesity. For example, one study of teenagers showed that with each hour of sleep lost, the odds of becoming obese went up. Sleep deficiency increases the risk of obesity in other age groups as well. Sleep also affects how your body reacts to insulin, the hormone that controls your blood glucose (sugar) level. Sleep deficiency results in a higher than normal blood sugar level, which may increase your risk for diabetes. [24] Ongoing sleep deficiency can also change the way in which your immune system responds. For example, if you’re sleep deficient, you may have trouble fighting common infections. [25] In addition, children and teens who are sleep deficient may have problems getting along with others. They may feel angry and impulsive, have mood swings, feel sad or depressed, or lack motivation. They also may have problems paying attention, and they may get lower grades and feel stressed. [26]
 The total sleep lost is called sleep debt. For example, if you lose 2 hours of sleep each night, you’ll have a sleep debt of 14 hours after a week. [27] See Figure 12.5 [28] of an individual feeling the effects of sleep debt on awakening.
Some people nap as a way to deal with sleepiness. Naps can provide a short-term boost in alertness and performance. However, napping doesn’t provide restorative sleep. Some people sleep more on their days off than on work days. They also may go to bed later and get up later on days off. Although extra sleep on days off might help a person feel better, it can upset the body’s sleep–wake rhythm. [29] See Figure 12.6 [30] of an adult napping during the day.
Sleep deficiency can affect people even when they sleep the total number of hours recommended for their age group. For example, people whose sleep is out of sync with their body clocks (such as shift workers) or whose sleep is routinely interrupted (such as caregivers or emergency responders) often need to pay special attention to their sleep needs. [31] Individuals should also talk to a health care provider if they sleep more than eight hours a night, but don’t feel well-rested. This can indicate a sleep disorder or other health problem. [32]
Sleep Disorders
There are several sleep disorders that can cause sleep deficiency, such as insomnia, sleep apnea, and narcolepsy.
Insomnia
Insomnia is a common sleep disorder that causes trouble falling asleep, staying asleep, or getting good quality sleep. Insomnia interferes with daily activities and causes the person to feel unrested or sleepy during the day. [33] Short-term insomnia may be caused by stress or changes in one’s schedule or environment. It can last for a few days or weeks. Chronic insomnia occurs three or more nights a week, lasts more than three months, and cannot be fully explained by another health problem or a medication. Chronic insomnia raises the risk of high blood pressure, coronary heart disease, diabetes, and cancer. [34]
Symptoms of insomnia include the following:
- Lying awake for a long time before falling asleep. This is more common in younger adults.
- Sleeping for only short periods due to waking up often during the night or being awake for most of the night. This is the most common symptom and typically affects older adults.
- Waking up too early in the morning and not being able to get back to sleep.
- Having poor-quality of sleep that causes one to wake up feeling unrested. The person often feels sleepy during the day and has difficulty focusing on tasks. Insomnia can also cause irritability, anxiousness, and depression. [35]
See Figure 12.7 [36] for an illustration of insomnia.
To diagnose insomnia, the health care provider asks about a person’s sleep habits and may request the person to keep a sleep diary for 1-2 weeks. A sleep diary records the time a person goes to sleep, wakes up, and takes naps each day. Timing of activities such as exercising and drinking caffeine or alcohol are also recorded, as well as feelings of sleepiness throughout the day. [37] A sleep study may be ordered to look for other sleep problems, such as circadian rhythm disorders, sleep apnea, and narcolepsy.
Treatment
Lifestyle changes often help improve short-term insomnia. The patient should be educated about healthy sleep habits, such as the following:
- Make your bedroom sleep-friendly. Sleep in a cool, quiet place. Avoid artificial light from the TV or electronic devices, as this can disrupt your sleep-wake cycle.
- Go to sleep and wake up around the same times each day, even on the weekends. If you can, avoid night shifts, irregular schedules, or other things that may disrupt your sleep schedule.
- Avoid caffeine, nicotine, and alcohol before bedtime. Although alcohol can make it easier to fall asleep, it triggers sleep that tends to be lighter than normal. This makes it more likely that you will wake up during the night. The effect of caffeine can last as long as eight hours.
- Get regular physical activity during the daytime (at least 5 to 6 hours before going to bed). Exercising close to bedtime can make it harder to fall asleep.
- Avoid daytime naps, especially in the afternoon. This may help you sleep longer at night.
- Eat meals on a regular schedule and avoid late-night dinners to maintain a regular sleep-wake cycle.
- Limit how much fluid you drink close to bedtime. This may help you sleep longer without having to use the bathroom.
- Learn new ways to manage stress. Follow a routine that helps you wind down and relax before bed. For example, read a book, listen to soothing music, or take a hot bath. Your doctor may also recommend massage therapy, meditation, or yoga to help you relax. Acupuncture may also help improve insomnia, especially in older adults.
- Avoid certain over-the-counter and prescription medicines that can disrupt sleep (for example, some cold and allergy medicines). [38]
A type of counseling called cognitive behavioral therapy for insomnia is usually the first treatment recommended for chronic insomnia. Several prescription medications may also be prescribed to treat insomnia. Some are meant for short-term use while others are meant for long-term use. Some insomnia medications can be habit-forming, and they all can cause dizziness, drowsiness, or worsening of depression or suicidal thoughts. [39] Common medications prescribed to treat insomnia are as follows:
- Benzodiazepines, such as lorazepam (Ativan). Benzodiazepines can be habit-forming and should be taken for only a few weeks. They can interfere with REM sleep.
- Benzodiazepine-receptor agonists, such as zolpidem (Ambien). Side effects may include anxiety. Rare side effects may include a severe allergic reaction or unintentionally doing activities while asleep such as walking, eating, or driving.
- Melatonin-receptor agonists, such as ramelteon (Rozerem). Rare side effects may include doing activities while asleep, such as walking, eating, or driving, or a severe allergic reaction.
- Orexin-receptor antagonists, such as suvorexant (Belsomra). This medicine is not recommended for people who have narcolepsy. Rare side effects may include doing activities while asleep, such as walking, eating, or driving, or not being able to move or speak for several minutes while going to sleep or waking up. [40]
Some patients use over-the-counter (OTC) products as sleep aids. Many contain antihistamines that cause sleepiness. However, they can be unsafe for some people and may not be the best treatment for insomnia. Melatonin supplements are lab-made versions of the sleep hormone melatonin. Many people take melatonin supplements to improve their sleep. However, research has not proven that melatonin is an effective treatment for insomnia. Side effects of melatonin may include daytime sleepiness, headaches, upset stomach, and worsening depression. It can also affect the body’s control of blood pressure, causing high or low blood pressure. [41]
Sleep Apnea
Sleep apnea is a common sleep condition that occurs when the upper airway becomes repeatedly blocked during sleep, reducing or completely stopping airflow. If the brain does not send the signals needed to breathe, the condition may be called central sleep apnea. [42]
Sleep apnea can be caused by a person’s physical structure or other medical conditions. Risk factors include obesity (causing fat deposits in the neck), large tonsils (that narrow the airway), thyroid disorders, neuromuscular disorders, heart or kidney failure (causing fluid buildup in the neck that narrows the airway), genetic syndromes (such as cleft lip or Down’s syndrome), and premature birth (before 37 weeks gestation). [43]
Common signs and symptoms of sleep apnea include the following:
- Reduced or absent breathing, known as apnea events
- Frequent loud snoring
- Gasping for air during sleep
- Excessive daytime sleepiness and fatigue
- Decreases in attention, vigilance, concentration, motor skills, and verbal and visuospatial memory
- Dry mouth or headaches when waking
- Sexual dysfunction or decreased libido
- Waking up often during the night to urinate [44]
Sleep apnea is diagnosed by a health care provider based on the person’s medical history, a physical exam, and results from a sleep study. During sleep studies, the number of episodes of slowed or stopped breathing events are recorded, along with documentation of oxygen levels in the blood during these events. [45]
Treatment
A breathing device, such as a CPAP machine, is the most commonly recommended treatment for patients with sleep apnea. CPAP stands for continuous positive airway pressure therapy. It uses mild air pressure to keep the airways open. See Figure 12.8 [46] for an illustration of a CPAP.
A mouthpiece may be prescribed for patients with mild sleep apnea or if the apnea occurs only when lying on their back. Mouthpieces, or oral appliances, are custom-fit devices that are worn while sleeping. See Figure 12.9 [47] for examples of mouthpieces used to treat sleep apnea. Mouthpieces are custom-fit by a dentist or an orthodontist to the patient’s mouth and jaw. There are two types of mouthpieces that work differently to open the upper airway. Mandibular repositioning mouthpieces are devices that cover the upper and lower teeth and hold the jaw in a position that prevents it from blocking the upper airway. Tongue-retaining devices are mouthpieces that hold the tongue in a forward position to prevent it from blocking the upper airway. [48]
Narcolepsy
Narcolepsy is an uncommon sleep disorder that causes periods of extreme daytime sleepiness and sudden, brief episodes of deep sleep during the day. Signs and symptoms of narcolepsy include extreme daytime sleepiness; falling asleep without warning, called sleep attacks; difficulty focusing or staying awake; and waking frequently at night. Individuals may experience hallucinations while falling asleep or waking up or sleep paralysis, a feeling of being awake but being unable to move for several minutes. Narcolepsy is diagnosed based on medical history, family history, a physical exam, and a sleep study. The sleep study looks at daytime naps to identify disturbed sleep or a quick onset of rapid eye movement (REM) sleep. Treatment for narcolepsy combines medications and behavior changes. Medications used to treat narcolepsy include stimulants, modafinil, and sodium oxybate to treat daytime sleepiness, and sedatives to improve nighttime sleep. Daytime sleepiness is often improved by promoting good quality sleep at night with scheduled naps during the day. [49]
- “ The_master_circadian_clock_in_the_human_brain.jpg ” by Ian B. Hickie, Sharon L. Naismith, Rébecca Robillard, Elizabeth M. Scott, and Daniel F. Hermens is licensed under CC BY 3.0 ↵
- National Institute of Neurological Disorders and Stroke. (2019, August 13). Understanding sleep . U.S. Department of Health & Human Services. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep ↵
- National Institute of Neurological Disorders and Stroke. (2019, August 13). Understanding sleep . U.S. Department of Health & Human Services. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Institute of Neurological Disorders and Stroke. (2019, August 13). Understanding sleep . U.S. Department of Health & Human Services. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). How sleep works. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/how-sleep-works ↵
- National Heart, Lung, and Blood Institute. (n.d). How sleep works. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/how-sleep-works ↵
- National Heart, Lung, and Blood Institute. (n.d). How sleep works. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/how-sleep-works ↵
- “ The_master_circadian_clock_in_the_human_brain.jpg ” by Ian B. Hickie, Sharon L. Naismith, Rébecca Robillard, Elizabeth M. Scott, and Daniel F. Hermens is licensed under CC BY 3.0 ↵
- National Heart, Lung, and Blood Institute. (n.d). How sleep works. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/how-sleep-works ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- “<PHONE_NUMBER>_f2c9e4d164_k.jpg ” by rachel CALAMUSA is licensed under CC BY-SA 2.0 ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- “Study_sleep.jpg” by Nic Ashman, Chippewa Valley Technical College is licensed under CC BY 4.0 ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- “<PHONE_NUMBER>_ff923d2934_k.jpg ” by Navy_NADAP is licensed under CC BY-NC-ND 2.0 ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- “ Sleeping_man_J2.jpg ” by Jamain is licensed under CC BY-SA 3.0 ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep deprivation and deficiency . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency ↵
- National Heart, Lung, and Blood Institute. (n.d). Insomnia. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/insomnia ↵
- National Heart, Lung, and Blood Institute. (n.d). Insomnia. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/insomnia ↵
- National Heart, Lung, and Blood Institute. (n.d). Insomnia. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/insomnia ↵
- “ Depiction_of_a_person_suffering_from_Insomnia_(sleeplessness).png ” by https://www.myupchar.com/en is licensed under CC BY-SA 4.0 ↵
- National Heart, Lung, and Blood Institute. (n.d). Insomnia . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/insomnia ↵
- National Heart, Lung, and Blood Institute. (n.d). Insomnia. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/insomnia ↵
- National Heart, Lung, and Blood Institute. (n.d). Insomnia . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/insomnia ↵
- National Heart, Lung, and Blood Institute. (n.d). Insomnia. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/insomnia ↵
- National Heart, Lung, and Blood Institute. (n.d). Insomnia. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/insomnia ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep apnea. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-apnea ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep apnea. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-apnea ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep apnea. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-apnea ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep apnea. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-apnea ↵
- “ Depiction_of_a_Sleep_Apnea_patient_using_a_CPAP_machine.png ” by https://www.myupchar.com/en is licensed under CC BY-SA 4. 0 ↵
- “ Orthoapnea_,_oral_appliance.jp g” by Orthoapnea is licensed under CC BY-SA 3.0 and “ 3D_printed_mouthpeace.jpg ” by unknown author is licensed under CC BY 3.0 ↵
- National Heart, Lung, and Blood Institute. (n.d). Sleep apnea. U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/sleep-apnea ↵
- National Heart, Lung, and Blood Institute. (n.d). Narcolepsy . U.S. Department of Health & Human Services. https://www.nhlbi.nih.gov/health-topics/narcolepsy ↵


24.1: Anatomy and Normal Microbiota of the Digestive System
- Describe the major anatomical features of the human digestive system
- Describe the normal microbiota of various regions in the human digestive system
- Explain how microorganisms overcome the defenses of the digestive tract to cause infection or intoxication
- Describe general signs and symptoms associated with infections of the digestive system
After a morning of playing outside, four-year-old Carli ran inside for lunch. After taking a bite of her fried egg, she pushed it away and whined, “It’s too slimy, Mommy. I don’t want any more.” But her mother, in no mood for games, curtly replied that if she wanted to go back outside she had better finish her lunch. Reluctantly, Carli complied, trying hard not to gag as she choked down the runny egg.
That night, Carli woke up feeling nauseated. She cried for her parents and then began to vomit. Her parents tried to comfort her, but she continued to vomit all night and began to have diarrhea and run a fever. By the morning, her parents were very worried. They rushed her to the emergency room.
What could have caused Carli’s signs and symptoms?
 The parts of the mouth include the teeth, the gums, the tongue, the oral vestibule (the space between the gums, lips, and teeth), and the oral cavity proper (the space behind the teeth and gums).  Accessory digestive organs include the salivary glands, liver, gallbladder, spleen, and pancreas.
The digestive system contains normal microbiota, including archaea, bacteria, fungi, protists, and even viruses. Because this microbiota is important for normal functioning of the digestive system, alterations to the microbiota by antibiotics or diet can be harmful. Additionally, the introduction of pathogens to the GI tract can cause infections and diseases. In this section, we will review the microbiota found in a healthy digestive tract and the general signs and symptoms associated with oral and GI infections.
Anatomy and Normal Microbiota of the Oral Cavity
Food enters the digestive tract through the mouth, where mechanical digestion (by chewing) and chemical digestion (by enzymes in saliva) begin. Within the mouth are the tongue, teeth, and salivary glands, including the parotid, sublingual, and submandibular glands (Figure \(\PageIndex{2}\)). The salivary glands produce saliva, which lubricates food and contains digestive enzymes.
The structure of a tooth (Figure \(\PageIndex{3}\)) begins with the visible outer surface, called the crown, which has to be extremely hard to withstand the force of biting and chewing. The crown is covered with enamel, which is the hardest material in the body. Underneath the crown, a layer of relatively hard dentin extends into the root of the tooth around the innermost pulp cavity, which includes the pulp chamber at the top of the tooth and pulp canal, or root canal, located in the root. The pulp that fills the pulp cavity is rich in blood vessels, lymphatic vessels, connective tissue, and nerves. The root of the tooth and some of the crown are covered with cementum, which works with the periodontal ligament to anchor the tooth in place in the jaw bone. The soft tissues surrounding the teeth and bones are called gums, or gingiva. The gingival space or gingival crevice is located between the gums and teeth.
Microbes such as bacteria and archaea are abundant in the mouth and coat all of the surfaces of the oral cavity. However, different structures, such as the teeth or cheeks, host unique communities of both aerobic and anaerobic microbes. Some factors appear to work against making the mouth hospitable to certain microbes. For example, chewing allows microbes to mix better with saliva so they can be swallowed or spit out more easily. Saliva also contains enzymes, including lysozyme, which can damage microbial cells. Recall that lysozyme is part of the first line of defense in the innate immune system and cleaves the β-(1,4) glycosidic linkages between N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) in bacterial peptidoglycan (see Chemical Defenses ). Additionally, fluids containing immunoglobulins and phagocytic cells are produced in the gingival spaces. Despite all of these chemical and mechanical activities, the mouth supports a large microbial community.
What factors make the mouth inhospitable for certain microbes?
Anatomy and Normal Microbiota of the GI Tract
As food leaves the oral cavity, it travels through the pharynx, or the back of the throat, and moves into the esophagus, which carries the food from the pharynx to the stomach without adding any additional digestive enzymes. The stomach produces mucus to protect its lining, as well as digestive enzymes and acid to break down food. Partially digested food then leaves the stomach through the pyloric sphincter, reaching the first part of the small intestine called the duodenum. Pancreatic juice, which includes enzymes and bicarbonate ions, is released into the small intestine to neutralize the acidic material from the stomach and to assist in digestion. Bile, produced by the liver but stored in the gallbladder, is also released into the small intestine to emulsify fats so that they can travel in the watery environment of the small intestine. Digestion continues in the small intestine, where the majority of nutrients contained in the food are absorbed. Simple columnar epithelial cells called enterocytes line the lumen surface of the small intestinal folds called villi. Each enterocyte has smaller microvilli (cytoplasmic membrane extensions) on the cellular apical surface that increase the surface area to allow more absorption of nutrients to occur (Figure \(\PageIndex{4}\)).
Digested food leaves the small intestine and moves into the large intestine, or colon, where there is a more diverse microbiota. Near this junction, there is a small pouch in the large intestine called the cecum, which attaches to the appendix. Further digestion occurs throughout the colon and water is reabsorbed, then waste is excreted through the rectum, the last section of the colon, and out of the body through the anus (Figure \(\PageIndex{1}\)).
The environment of most of the GI tract is harsh, which serves two purposes: digestion and immunity. The stomach is an extremely acidic environment (pH 1.5–3.5) due to the gastric juices that break down food and kill many ingested microbes; this helps prevent infection from pathogens. The environment in the small intestine is less harsh and is able to support microbial communities. Microorganisms present in the small intestine can include lactobacilli, diptherioids and the fungus Candida . On the other hand, the large intestine (colon) contains a diverse and abundant microbiota that is important for normal function. These microbes include Bacteriodetes (especially the genera Bacteroides and Prevotella ) and Firmicutes (especially members of the genus Clostridium ). Methanogenic archaea and some fungi are also present, among many other species of bacteria. These microbes all aid in digestion and contribute to the production of feces, the waste excreted from the digestive tract, and flatus, the gas produced from microbial fermentation of undigested food. They can also produce valuable nutrients. For example, lactic acid bacteria such as bifidobacteria can synthesize vitamins, such as vitamin B12, folate, and riboflavin, that humans cannot synthesize themselves. E. coli found in the intestine can also break down food and help the body produce vitamin K, which is important for blood coagulation.
The GI tract has several other methods of reducing the risk of infection by pathogens. Small aggregates of underlying lymphoid tissue in the ileum, called Peyer’s patches (Figure \(\PageIndex{4}\)), detect pathogens in the intestines via microfold (M) cells, which transfer antigens from the lumen of the intestine to the lymphocytes on Peyer’s patches to induce an immune response. The Peyer’s patches then secrete IgA and other pathogen-specific antibodies into the intestinal lumen to help keep intestinal microbes at safe levels. Goblet cells, which are modified simple columnar epithelial cells, also line the GI tract (Figure \(\PageIndex{5}\)). Goblet cells secrete a gel-forming mucin, which is the major component of mucus. The production of a protective layer of mucus helps reduce the risk of pathogens reaching deeper tissues.
The constant movement of materials through the gastrointestinal tract also helps to move transient pathogens out of the body. In fact, feces are composed of approximately 25% microbes, 25% sloughed epithelial cells, 25% mucus, and 25% digested or undigested food. Finally, the normal microbiota provides an additional barrier to infection via a variety of mechanisms. For example, these organisms outcompete potential pathogens for space and nutrients within the intestine. This is known as competitive exclusion. Members of the microbiota may also secrete protein toxins known as bacteriocins that are able to bind to specific receptors on the surface of susceptible bacteria.
Compare and contrast the microbiota of the small and large intestines.
General Signs and Symptoms of Oral and GI Disease
Despite numerous defense mechanisms that protect against infection, all parts of the digestive tract can become sites of infection or intoxication. The term food poisoning is sometimes used as a catch-all for GI infections and intoxications, but not all forms of GI disease originate with foodborne pathogens or toxins.
In the mouth, fermentation by anaerobic microbes produces acids that damage the teeth and gums. This can lead to tooth decay, cavities, and periodontal disease, a condition characterized by chronic inflammation and erosion of the gums. Additionally, some pathogens can cause infections of the mucosa, glands, and other structures in the mouth, resulting in inflammation, sores, cankers, and other lesions. An open sore in the mouth or GI tract is typically called an ulcer.
Infections and intoxications of the lower GI tract often produce symptoms such as nausea, vomiting, diarrhea, aches, and fever. In some cases, vomiting and diarrhea may cause severe dehydration and other complications that can become serious or fatal. Various clinical terms are used to describe gastrointestinal symptoms. For example, gastritis is an inflammation of the stomach lining that results in swelling and enteritis refers to inflammation of the intestinal mucosa. When the inflammation involves both the stomach lining and the intestinal lining, the condition is called gastroenteritis. Inflammation of the liver is called hepatitis. Inflammation of the colon, called colitis, commonly occurs in cases of food intoxication. Because an inflamed colon does not reabsorb water as effectively as it normally does, stools become watery, causing diarrhea. Damage to the epithelial cells of the colon can also cause bleeding and excess mucus to appear in watery stools, a condition called dysentery.
List possible causes and signs and symptoms of food poisoning.
Key Concepts and Summary
- The digestive tract, consisting of the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine, has a normal microbiota that is important for health.
- The constant movement of materials through the gastrointestinal canal, the protective layer of mucus, the normal microbiota, and the harsh chemical environment in the stomach and small intestine help to prevent colonization by pathogens.
- Infections or microbial toxins in the oral cavity can cause tooth decay , periodontal disease , and various types of ulcers .
- Infections and intoxications of the gastrointestinal tract can cause general symptoms such as nausea, vomiting, diarrhea, and fever. Localized inflammation of the GI tract can result in gastritis , enteritis , gastroenteritis , hepatitis , or colitis , and damage to epithelial cells of the colon can lead to dysentery .
- Foodborne illness refers to infections or intoxications that originate with pathogens or toxins ingested in contaminated food or water.


15.10: References
Aetna. (2023). Non-invasive fetal membranes rupture tests. https://www.aetna.com/cpb/medical/da..._799/0757.html
American College of Obstetricians and Gynecologists. (2017a, June). Ultrasound exams . https://www.acog.org/womens-health/f...trasound-exams
American College of Obstetricians and Gynecologists. (2017b). ACOG Practice Bulletin No. 183: Postpartum hemorrhage. Obstetrics & Gynecology, 130 (4), e168–e186. doi.org/10.1097/AOG.0000000000002351
American College of Obstetricians and Gynecologists. (2018). ACOG Committee Opinion No. 757: Screening for perinatal depression. Obstetrics & Gynecology, 132 (4), e208–e212. doi.org/10.1097/AOG.0000000000002927
American College of Obstetricians and Gynecologists. (2020). ACOG Practice Bulletin Summary, No. 222: Gestational hypertension and preeclampsia. Obstetrics & Gynecology, 135(6), 1492–1495. doi.org/10.1097/AOG.0000000000003892
American College of Obstetricians and Gynecologists. (2021, December). Frequently asked questions: Postpartum depression . https://www.acog.org/womens-health/f...tum-depression
American College of Obstetricians and Gynecologists. (2023). Clinical Practice Guideline No. 8: First and second stage labor management. Obstetrics & Gynecology, 135 (1), 144-162. doi.org/10.1097/AOG.0000000000005447
American College of Obstetricians and Gynecologists. (2024). Dictionary. https://www.acog.org/womens-health/dictionary
American Nurses Association. (2023, January 10). Americans continue to rank nurses most honest and ethical professionals . https://www.nursingworld.org/news/ne...professionals/
Bataille, A., Rousset, J., Marret, E., & Bonnet, F. (2014). Ultrasonographic evaluation of gastric content during labour under epidural analgesia: A prospective cohort study. British Journal of Anaesthesia , 112 (4), 703–707. https://doi.org/10.1093/bja/aet435
Begley, C. M., Gyte, G. L., Devane, D., McGuire, W., Weeks, A., & Biesty, L. M. (2019). Active versus expectant management for women in the third stage of labour. Cochrane Database of Systematic Reviews , 2 . doi.org/10.1002/14651858.CD007412.pub5
Bellini, E., Macchi, A., Setola, N., & Lindahl, G. (2023). Sensory design in the birth environment: Learning from existing case studies. Buildings , 13 (3), 604. https://doi.org/10.3390/buildings13030604
Burch, K. (2022, April 27). What is dilation in pregnancy? https://www.verywellhealth.com/dilat...gnancy-5114743
Cohen, W. H., & Friedman, E. A. (2023, July). The second stage of labor. American Journal of Obstetrics & Gynecology, 230 (3, suppl), S865–S875. https://doi.org/10.1016/j.ajog.2022.06.014
Dayal, S., & Hong, P. L. (2023). Premature rupture of membranes . StatPearls [Internet]. www.ncbi.nlm.nih.gov/books/NBK532888
Dent, M., VanOtterloo, L., Brady, M. (2023). Improving nurse management of the second stage of labor. Nursing for Women’s Health, 27 (5), 344–353. https://doi.org/10.1016/j.nwh.2023.03.005
Finlayson, K., Crossland, N., Bonet, M., & Downe, S. (2020). What matters to women in the postnatal period: A meta-synthesis of qualitative studies. PloS One , 15 (4), e0231415. https://doi.org/10.1371/journal.pone.0231415
Gachon, B., De Tayrac, R., Schmitz, T., Mahmood, T., Nizard, J., & Fritel, X. (2020). Should we advise women that pre-labor caesarean section prevents pelvic floor dysfunction? European Journal of Obstetrics & Gynecology and Reproductive Biology, 244 , 31–34. https://doi.org/10.1016/j.ejogrb.2019.10.037
Garbelli, L., & Lira, V. (2021). Maternal position during labor: Midwives’ knowledge and educational needs in northern Italy. European Journal of Midwifery, 5. https://doi.org/10.18332/ejm/136423
Ghi, T., & Dall’Asta, A. (2024). Sonographic evaluation of the fetal head position and attitude during labor. American Journal of Obstetrics and Gynecology, 230 (3, suppl), S890–S900. https://doi.org/10.1016/j.ajog.2022.06.003
Gicheru, M., Mung’ayi, V., Mir, S., & Kabugi, J. (2019). Comparison of weight-adjusted dose versus fixed dose ondansetron in preventing shivering following spinal anaesthesia for caesarean deliveries. African Health Sciences , 19 (3), 2740–2751. https://doi.org/10.4314/ahs.v19i3.50
Grenvik, J. M., Coleman, L. A., & Berghella, V. (2023).  American Journal of Obstetrics and Gynecology, 222 (5), S1270–S1273. doi.org/10.1016/j.ajpg.2023.02.014
Hawkins, M., Misra, D., Zhang, L., Price, M., Dailey, R., & Giurgescu, C. (2021). Family involvement in pregnancy and psychological health among pregnant Black women. Archives of Psychiatric Nursing, 35 (1), 42–48. https://doi.org/10.1016/j.apnu.2020.09.012
Holmes, M. R., & Kim, J. (2019). Prenatal exposure to domestic violence: Summary of key research findings. Case Western University. https://case.edu/socialwork/traumace...PrenatalDV.pdf
Hoyert, D. L. (2023, March 16). Maternal mortality rates in the United States: 2021. National Center for Health Statistics. https://www.cdc.gov/nchs/data/hestat...rates-2021.htm
Huang, J., Zang, Y., Ren, L. H., Li, F. J., & Lu, H. (2019). A review and comparison of common maternal positions during the second-stage of labor. International Journal of Nursing Sciences, 6 (4), 460–467. https://doi.org/10.1016/j.ijnss.2019.06.007
Hundley, V., Downe, S., & Buckley, S. J. (2020). The initiation of labour at term gestation: Physiology and practice implications. Clinical Obstetrics & Gynaecology, 67 , 4–18. https://doi.org/10.1016/j.bpobgyn.2020.02.006
Khaskheli, M., Baloch, S., Baloch, A. S., & Shah, S. G. S. (2021). Vaginal discharge during pregnancy and associated adverse maternal and perinatal outcomes. Pakistan Journal of Medical Sciences , 37 (5), 1302–1308. https://doi.org/10.12669/pjms.37.5.4187
March of Dimes. (2019). Stages of labor . https://www.marchofdimes.org/find-su...h/stages-labor
Marcos-Rodríguez, A., Leirós-Rodríguez, R., & Hernandez-Lucas, P. (2023). Efficacy of perineal massage during the second stage of labor for the prevention of perineal injury: A systematic review and meta-analysis. International Journal of Gynecology and Obstetrics, 162 (3), 802–810. doi.org/10.1002/ijgo.14723
Martin, C., Viky, M., Rokibullah, & Sofinia, H. (2022). The physiological changes in the postpartum period after childbirth. Asian Journal of Humanities and Sciences, 1 (3). doi.org/10.59888/ajosh.v1i03.19
McEvoy, A., & Sabir, S. (2022). Physiology, pregnancy contractions . StatPearls [Internet]. www.ncbi.nlm.nih.gov/books/NBK532927/
Merriam-Webster. (n.d.). Labor. In Merriam-Webster.com dictionary. https://www.merriam-webster.com/dictionary/labor
Murakoshi, T. (2020). "En caul" cesarean delivery for extremely premature fetuses: Surgical technique and anesthetic options. Surgery Journal, 16 (6), Suppl 2, S104–S109. https://doi.org/10.1055/s-0040-1712927
Olarinoye A. O., Olaomo N. O., Adesina, K. T., Ezeoke, G. G., & Aboyeji, A. P. (2021). Comparative diagnosis of premature rupture of membrane by nitrazine test, urea, and creatinine estimation. International Journal of Health Science, 15 (6):16–22.
Olsen, N. S., & Ramus, R. M. (2022, October 7). Abnormal labor . Medscape: Drugs & Diseases. emedicine.medscape.com/artic...73053-overview
Olza, I., Uvnas-Moberg, K., Ekström-Bergström, A., Leahy-Warren, P., Karlsdottir, S. I., Nieuwenhuijze, M., Villarmea, S., Hadjigeorgiou, E., Kazmierczak, M., Spyridou, A., & Buckley, S. (2020). Birth as a neuro-psycho-social event: An integrative model of maternal experiences and their relation to neurohormonal events during childbirth. PloS One , 15 (7), e0230992. https://doi.org/10.1371/journal.pone.0230992
Pattinson, R. C., Cuthbert, A., & Vannevel, V. (2017). Pelvimetry for fetal cephalic presentations at or near term for deciding on mode of delivery. The Cochrane Database of Systematic Reviews. 3 . doi.org/10.1002/14651858.cd000161.pub2
Pergialiotis, V., Bellos, I., Antsaklis, A., Papapanagiotou, A., Loutradis, D., & Daskalakis, G. (2020). Maternal and neonatal outcomes following a prolonged second stage of labor: A meta-analysis of observational studies. European Journal of Obstetrics, Gynecology, & Reproductive Biology, 252 , 62–69. https://doi.org/10.1016/j.ejogrb.2020.06.018
Raines, D. A., & Cooper, D. B. (2023). Braxton Hicks contractions . StatPearls [Internet]. www.ncbi.nlm.nih.gov/books/NBK470546/
Rich, C. Y. (1976). Born with the veil: Black folklore in Louisiana. The Journal of American Folklore , 89 (353), 328–331. doi.org/10.2307/539446
Ronca, D. (2021). What’s a birth caul, and why are people superstitious about it? https://people.howstuffworks.com/bir...l-superstition
Sæther, K. M., Berg, R. C., Fagerlund, B. H., Glavin, K., & Jøranson, N. (2023). First-time parents’ experiences related to parental self-efficacy: A scoping review. Research in Nursing and Health , 46 (1), 101–112. doi.org/10.1002/nur.22285
Shanahan, M. M., Martingano, D. J., & Gray, C. J. (2023). External cephalic version . StatPearls [Internet]. www.ncbi.nlm.nih.gov/books/NBK482475/
Sherwood, G., Barnsteiner, J. (Eds.) (2021). Quality and safety in nursing: A competency approach to improving outcomes (3rd ed.). Wiley-Blackwell.
Shuman, C. J., Peahl, A. F., Pareddy, N., Morgan, M. E., Chiangong, J., Veliz, P. T., & Dalton, V. K. (2022). Postpartum depression and associated risk factors during the COVID-19 pandemic. BMC Research Notes, 15 (102). https://doi.org/10.1186/s13104-022-05991-8
Singata, M., Tranmer. J., & Gyte, G. L. (2013). Restricting oral fluid and food intake during labour. Cochrane Database of Systematic Reviews, 8, CD003930. doi.org/10.1002/14651858.CD003930.pub3
Smith, J. R. (2020, November 25). Management of the third stage of labor . Medscape: Drugs & Diseases. emedicine.medscape.com/artic...75304-overview
Sobczak, A., Taylor, L., Solomon, S., Ho, J., Kemper, S., Phillips, B., Jacobson, K., Castellano, C., Ring, A., Castellano, B., & Jacobs, R. J. (2023). The effect of doulas on maternal and birth outcomes: A scoping review. Cureus, 15 (5), e39451. https://doi.org/10.7759/cureus.39451
Thumm, B., Walsh, G., & Heyborne, K. (2020). Diagnosis of rupture of membranes: AmniSure, clinical assessment, and the Food and Drug Administration warning. American Journal of Obstetrics & Gynecology MFM, 2 (4), 100200. https://doi.org/10.1016/j.ajogmf.2020.100200
Tilden, E. L., Snowden, J. M., Bovbjerg, M. L., Cheyney, M., Lapidus, J., Wiedrick, J., & Caughey, A. B. (2022). The duration of spontaneous active and pushing phases of labour among 75,243 US women when intervention is minimal: A prospective, observational cohort study. EClinical Medicine, 22 (48), 101447. https://doi.org/10.1016/j.eclinm.2022.101447
Udompornthanakij, P., Kongsomboon, K., & Hanprasertpong, T. (2020). Accuracy and factors influencing Leopold’s manoeuvres in determining vertex presentation during late third trimester of pregnancy. Journal of Obstetrics & Gynaecology, 40 (5):639–643. doi.org/10.1080/01443615.2019.1645102
Vanderlaan, J., & Givens, S. (n.d.). Evidence-based childbirth education: An essential step in shared decision-making for maternity care. Lamaze International. https://www.lamaze.org/Portals/0/LI_...ecision_r3.pdf
VanSickle, C., Liese, K. L., & Rutherford, J. N. (2022). Textbook typologies: Challenging the myth of the perfect obstetric pelvis. The Anatomical Record , 305 (4), 952–967. doi.org/10.1002/ar.24880
Vittner, D., McGrath, J., Robinson, J., Lawhon, G., Cusson, R., Eisenfeld, L., Walsh, S., Young, E., & Cong, X. (2018). Increase in oxytocin from skin-to-skin contact enhances development of parent-infant relationship. Biological Research for Nursing, 20 (1), 54–62. https://doi.org/ 10.1177/1099800417735633
Weiss, R. E. (2022). What is the mucus plug? https://www.parents.com/mucus-plug-8619269
World Health Organization. (2024, April 26). Maternal mortality. https://www.who.int/news-room/fact-s...rnal-mortality
Young, J. (1960). John Braxton Hicks (1823–1897). Medical History, 4 (2), 153–162. https://doi.org/10.1017/S0025727300025230