14.2: Environmental Exposure and Health Outcomes
By the end of this section, you should be able to:
- Assess environmental hazards and threats to individuals, families, and populations.
- Examine sources and types of environmental agents and how they affect health.
- Discuss strategies to reduce environmental risks, exposures, and injury.
- Explain why individuals, communities, and populations have a right to know about actual or potential environmental risks.
Exposure to hazards in the environment is a growing concern for individuals, families, and populations. Environmental agents are specific substances that can directly interact with, and potentially impact, the health of the environment and humans. Environmental agents can be categorized into biological, chemical, and physical. The sources of environmental agents are diverse, ranging from human activities to natural disasters and biological events. Environmental agents can create environmental health hazards , or conditions that have the potential to cause harm to the environment and humans. The impact of environmental hazards on health can be significant, with potential health outcomes ranging from minor symptoms to severe illnesses and even death. Therefore, it is essential to identify strategies to reduce environmental risks and exposure to injury. Communities and individuals can protect themselves by managing environmental hazards and maintaining safe food and water. Moreover, the right to know about actual or potential environmental risks is crucial for individuals, communities, and populations. This knowledge empowers them to take appropriate actions to protect themselves and their communities.
Environmental Hazards and Impact on Health
Environmental agents have the potential to create hazards by polluting the air we breathe, the water we drink, and the food we eat, affecting our quality of life and overall health. While some of these hazards, such as smoke emanating from stacks, are clearly visible, most are not. For example, small plastic fragments such as microplastics (MPs) and nanoplastics (NPs) are ubiquitous pollutants in water, air, and soil. NPs are more hazardous due to their extremely small size (<1000 nm), which allows them to escape water treatment processes and float long distances in both air and water, contaminating fresh water, oceans, air, and food (Yee et al., 2021). Furthermore, their size enables them to penetrate living tissues and cells more easily. These particles are generated for use in consumer products such as cosmetics, cleansers, and detergents (major sources) and through the degradation of plastics such as tires (Lai et al., 2022). Small plastic contaminants can transport pollutants, microorganisms, and pathogens on their surfaces, which can amplify their physiological and environmental effects (Trevisan et al., 2020). While understanding of the impact of small plastics on human health is only just beginning to emerge, toxicological studies indicate that NPs can cross the blood-brain, intestinal, and placental barriers (Lai et al., 2022).
Human activities are the primary drivers of environmental agents, and societal and lifestyle choices including urbanization, economic activity, recreational pursuits, and food habits play a role. The presence of these agents, or toxins, in the air, water, and land can have deleterious effects on human health across the lifespan. Teratogens such as secondhand smoke and alcohol consumption during pregnancy can cause defects in a developing embryo. Alcohol, tobacco, asbestos, and radon are carcinogens , or cancer-causing toxins. Mutagens such as radioactive substances found in nuclear waste and radon alter a person’s DNA. The ingestion or handling of neurotoxins such as lead or mercury can lead to adverse effects on the nervous system. Finally, endocrine disruptors such as phthalates and bisphenol A (BPA) are found in many modern consumer products and can have a wide range of effects on the endocrine system, impacting human development and reproduction.
Physical agents include noise, temperature, vibrations, radiation, and lighting, which originate from different sources, including the built environment (human-made structures and surroundings) and industry. Chemical agents including heavy metals, pesticides, polychlorinated biphenyls (PCBs), chlorofluorocarbons (CFCs), endocrine-disrupting chemicals (EDCs), and sulfur dioxide (SO 2 ) are used in agriculture, industry, and the burning of fossil fuels for transportation and electricity. Biological agents were the most significant environmental health hazard through much of human history and include molds, dust mites, cockroaches, pollen, bacteria, viruses, protozoa, parasitic worms, and pet dander, saliva, and waste.
Air Pollution
Air pollution is a serious environmental and public health issue that affects people of all ages and backgrounds but most especially the vulnerable, children, older adults, and those with respiratory disorders. Air pollution is caused by the release of harmful substances into the air, such as particulate matter, ozone, and nitrogen dioxide (Figure 14.3). These substances originate from a variety of sources such as factories, vehicles, and industrial plants. When these harmful substances are released, they mix with the air we breathe, potentially causing a range of health problems if inhaled. For example, particulate matter (PM), a mixture of solid particles and liquid droplets, can penetrate the respiratory system, irritating the lungs and exacerbating health conditions such as asthma and bronchitis. Long-term exposure to particulate matter has been associated with an increased risk of cardiovascular diseases, respiratory illnesses, and even premature death. Ozone, a common pollutant formed when volatile organic compounds (VOC) and nitrogen oxides (NOx) react to sunlight, can inflame and damage the lining of the lungs, exacerbating respiratory symptoms. Studies have linked ozone exposure to lower birth weights and decreased lung function in newborns, an increased risk of metabolic and cardiovascular disorders, and potentially lung cancer. Nitrogen dioxide (NO 2 ), produced during fossil fuel combustion, can enter the bloodstream, leading to an inflammatory response such as neuroinflammation; research has linked exposure to NO 2 to an increased risk for neurodegenerative diseases such as Parkinson’s (Jo et al., 2021).
The Air Quality Index (AQI) is a system used to communicate information to the public about air pollution levels and any associated health impacts in a specific location. The EPA sets an AQI for five primary air pollutants including ground-level ozone, particulate matter, carbon monoxide (CO), sulfur dioxide (SO 2 ), and nitrogen dioxide (NO 2 ). The AQI is divided into six categories, each of which corresponds to a different level of health concern. These categories are color-coded for easy understanding, ranging from Good (Green) for air quality that is satisfactory and poses little or no risk to health to Hazardous (Maroon), which indicates a health warning where the entire population may be affected (Air Now, 2023).
Water Pollution
Water, like air, is necessary for life and essential for human health. Water pollution is a serious issue that impacts the health and safety of water bodies, putting both human well-being and the environment at risk. Industrial waste, agricultural runoff, urbanization, sewage, and oil spills are some of the major contributors to water pollution. Factories release wastewater containing harmful chemicals and heavy metal into our waterways. Farms contribute to water pollution when fertilizers and pesticides wash into waterways, referred to as runoff. Agricultural runoff can have a devastating impact on water quality and the creatures that live in our waterways. Excess nutrients from fertilizers can lead to algal blooms, which choke the life out of aquatic ecosystems and create dead zones . Pesticides and herbicides used to protect crops can harm aquatic life. Prolonged exposure to pollutants like lead, arsenic, and mercury can have severe health implications, especially when they build up in the human body.
Lead, a toxic metal, poses a significant threat, even at low levels. Its persistence in the environment allows it to linger for extended periods. Rain from urban areas runs into storm drains, bringing pollutants from streets, parking lots, and roads into nearby streams and rivers.  Drinking water can be a particular concern if contaminated with lead from sources such as lead pipes or plumbing fixtures; additionally, soil and groundwater contamination can also contribute to lead in drinking water. Lead exposure may lead to severe health problems, including developmental disabilities, learning disabilities, neurological damage, premature birth, low birth weight, seizures, and hearing loss (CDC, 2022d). Children are particularly vulnerable to the effects of lead poisoning ; even at low levels, lead exposure can have far-reaching consequences to their health. Recognizing the dangers posed by lead, the Environmental Protection Agency (EPA) established a maximum contaminant level goal (MCLG) of zero for lead in drinking water (EPA, 2023a), meaning that the EPA considers any level of lead in drinking water to be unsafe.
Perfluoroalkyl and polyfluoroalkyl substances (PFAS), also known as “forever chemicals,” are synthetic compounds characterized by a strong carbon-fluorine bond. This unique bond gives PFAS the ability to withstand heat and repel water and fats, leading to their extensive use in various manufacturing industries and consumer goods for more than 70 years (Wylie & Malits, 2022). PFAS are found in nonstick cookware, stain-resistant fabrics, fast-food packaging, personal care products, and more. Due to their resistance to breakdown, PFAS persist in the environment, contaminating water, air, and soil. Furthermore, PFAS are not easily metabolized and can remain in the body for years or even decades (Wylie & Malits, 2022). Due to the persistent nature of PFAS in the environment and their common routes of exposure through drinking and eating, nearly everyone has measurable levels of PFAS in their blood. Individuals working in occupations related to PFAS manufacturing and firefighters might experience higher exposure levels. Infants can also be exposed through transplacental transmission during pregnancy or through breast milk. PFAS exposure has been associated with various health effects, including obesity, elevated cholesterol, cancers, thyroid problems, colitis, learning difficulties, delayed puberty, and adverse pregnancy outcomes (Wylie & Malits, 2022). For example, a study of more than 10,000 individuals showed that those with higher PFAS exposure had a 40 percent greater likelihood of developing preeclampsia than those with lower exposures (Braun, 2023). The EPA proposed national standards in March 2023 to address concerns about PFAS in public drinking water supplies. The proposed standards aim to limit concentrations of six PFAS compounds in drinking water (Braun, 2023).
Finally, water pollution also affects human health indirectly by degrading the ecosystem. Polluted water harms aquatic life, disrupts food chains, and causes declines in fish populations that communities depend on for sustenance and livelihoods. The impact of water pollution is wide-ranging and can profoundly affect human health as well as that of the environment.
A recent report from the Government Accountability Office (GAO) examined the presence of PFAS in the drinking water systems of several states, including Illinois, Massachusetts, New Hampshire, New Jersey, Ohio, and Vermont. The overall findings indicated that out of the 5,300 water systems analyzed, approximately 29 percent of the population served by these systems had drinking water with PFAS levels that exceeded the safety standards set by the EPA (U. S. Government Accountability Office, 2022).
The authorities then investigated potential disparities related to PFAS contamination, focusing on large community water systems. The results showed that disadvantaged communities in New Jersey were more likely to have PFAS-contaminated drinking water compared to other communities (Suran, 2022).
Nurses can educate clients on the following measures to reduce PFAS exposure:
- Replace old, chipped, or damaged nonstick cookware. When using nonstick cookware, use a low to medium heat setting.
- Limit intake of fast food, which often comes in PFAS-coated packaging.
- When possible, use filters that remove PFAS from drinking water.
- Vacuum frequently, especially for older carpeting.
- Limit intake of microwave food such as popcorn and foods in microwavable packaging.
Land Pollution
Soil pollution is a serious problem with potentially devastating consequences for both the environment and human health. It occurs when harmful substances contaminate soil through industrial processes, agricultural practices, improper waste disposal, and the use of hazardous chemicals. Common soil pollutants include heavy metals such as lead, mercury, cadmium, and arsenic as well as pesticides, herbicides, industrial chemicals, and petroleum products. These substances can persist in the soil for an extended period, making the problem long-lasting and challenging to remediate. For instance, improper waste disposal is a significant contributor to land pollution. When non-biodegradable waste materials like plastics are deposited in landfills or open areas without proper management, they can release toxic chemicals and contaminants into the soil. Industrial activities are another major cause of land pollution. Factories and manufacturing plants often release hazardous substances directly into the soil or air. Agricultural practices, while essential for food production, can also contribute to soil pollution. Chemical fertilizers, pesticides, and herbicides can accumulate in the soil, negatively impacting soil fertility and potentially seeping into water sources. Urbanization and construction projects further exacerbate land pollution. The clearing of land for buildings, roads, and infrastructure can cause soil erosion, deforestation, and habitat loss, disrupting the ecosystem’s equilibrium. The consequences of land pollution are extensive. Contaminated soil can negatively affect plant growth, reduce agricultural yields, and harm wildlife, leading to a decline in biodiversity. For humans, polluted soil poses significant health risks in several ways. Crops grown in polluted soil can absorb toxins, contaminating food and potentially impacting health. Contaminated soil may release harmful substances such as particulate matter into the air or nearby water bodies, further spreading pollution and significantly impacting air quality and water safety.
Due to the dangers posed by contamination, the EPA administers programs to identify, evaluate, and potentially redevelop polluted sites. The Superfund program is a federal government initiative overseen and managed by the EPA. Superfund sites are locations where substantial hazardous substances have been released into the environment, posing risks to human health and the ecosystem. These sites are regulated by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund (EPA, 2023n), which provides the legal framework for the cleanup and remediation. The program aims to identify, prioritize, and assess sites as well as facilitate decontamination, often a multiphase process involving federal and state agencies, responsible parties, and the affected community. You can search for superfund sites in your community and elsewhere here . The EPA also administers a Brownfields program (EPA, 2023l). Brownfields are properties that are, or are suspected to be, contaminated by industrial or commercial activity. Caused by pollution from former businesses such as factories, gas stations, dry cleaners, landfills, and manufacturing facilities, brownfields may have hazardous agents in the soil, groundwater, or structures, posing a risk to both environmental and human health. Unlike Superfund sites, brownfields may not contain severe levels of contamination requiring immediate federal intervention but instead have potential for redevelopment or revitalization. The EPA estimates that there are approximately 450,000 brownfields sites in the United States.
Strategies to Reduce Risk
The Right to Know principle supports access to information held by public organizations and is based on the idea that transparency, openness, and accountability are critical to a healthy society and the protection of human rights. In 1986, the Emergency Planning and Community Right-to-Know Act (EPCRA) was passed to address concerns about the safety and environmental hazards associated with the storage and handling of toxic chemicals. Concerns were sparked by the 1984 Bhopal disaster, in which an extremely toxic pesticide, methylisocyanate, leaked in the middle of the night into the city of Bhopal, India, killing and severely injuring thousands (Chatterjee, 2023). To reduce the likelihood of such a disaster in the United States, Congress imposed certain requirements for emergency planning and reporting of hazards and toxins. The provisions of the Community Right-to-Know initiative serve to enhance the public’s awareness of, and access to, information on the presence, application, and release of chemicals at certain facilities. In 2018, the reporting requirements of EPCRA were revised by the America’s Water Infrastructure Act (AWIA) to provide for notification of state agencies with data on reportable releases of chemicals into water sources (EPA, 2023a).
Reducing the risk of land, air, and water pollution begins with reducing hazardous agents and requires serious commitment on the part of individuals, businesses, communities, regulatory agencies, and governing bodies. Some general strategies include the following:
- Regulation and monitoring to ensure safety and compliance
- Legislation and enforcement to hold polluters accountable
- Incentives for businesses, communities, and individuals to adopt environmentally friendly practices
- Conversion to renewable sources of energy
- Investment in research and development of innovative technologies
- Raising awareness about the effects of the environmental hazards on health
- Reduce, reuse, recycle!
Table 14.2 presents community-level strategies to reduce the risk of land, air, and water pollution.
| Type of Pollution | Strategies to Reduce Risk |
|---|---|
| Soil and land |
|
| Air |
|
| Water |
|
While the strategies in Table 14.2 are effective at the community level, individuals also play an important role in protecting the environment and their health. However, they are often unsure of what they can do to reduce their footprint and live more healthfully in the environment. Nurses can provide clients with the following individual strategies to reduce risk and improve environmental health:
- Compost organic matter to reduce improve soil quality and health
- Dispose of waste, including hazardous materials, medications, and electronics, according to local regulations
- Minimize the use of pesticides, herbicides, and fertilizers
- Purchase food from reputable sources and consider, if possible, organic options
- Support local cleanup and outreach efforts
- Limit use of plastics, especially those that are single use
- Ensure drinking water is from a safe and reliable source
- Avoid swimming or using water that appears polluted or is known to be polluted
- Avoid outdoor activities when air quality is poor
- Use rainwater harvesting, the collection of rainwater to reuse for non-drinking purposes
- Use public transportation, walk, or bicycle
- Reduce contaminants in the home through regular cleaning and maintenance
- Ensure the home is properly ventilated and reduce indoor pollutants such as tobacco smoke
- Use energy-efficient appliances when available
- Maintain personal vehicles to regulatory standards
- Advocate for policies that invest in, develop, and support green practices


9.19: Hypothesis Test for Difference in Two Population Proportions (6 of 6)
Learning Objectives
- Identify type I and type II errors and select an appropriate significance level based on an analysis of the consequences of each type of error.
Review of Type I and Type II Errors
Inference is based on probability, so there is always some chance of making a wrong decision. Recall that two types of wrong decisions can be made in hypothesis testing. When we reject a null hypothesis that is true, we commit a type I error. When we fail to reject a null hypothesis that is false, we commit a type II error.
The following table summarizes the logic behind type I and type II errors.
It is possible to have some influence over the likelihoods of committing these errors, but decreasing the chance of a type I error increases the chance of a type II error. We have to decide which error is more serious for a given situation. Sometimes a type I error is more serious, and other times a type II error is more serious.
Try It
Teens and Antidepressants
Recall the description of a clinical trial in which researchers study the effect of a new antidepressant on teens. Researchers design a randomized, controlled, double-blind experiment to study the effect of the antidepressant Fluoxetine combined with psychiatric therapy. The control group receives a placebo and psychiatric therapy. The response variable is improvement , which means symptoms of depression improve.
The hypotheses are as follows, with p 1 = proportion of teens who improve in the treatment group (Fluoxetine and psychiatric therapy) and p 2 = proportion of teens who improve in the control group (placebo and psychiatric therapy).
- H 0 : p 1 − p 2 = 0
- H a : p 1 − p 2 > 0
Decreasing the Chance of Type I or Type II Error
How can we decrease the chance of a type I or type II error? Because decreasing the chance of a type I error increases the chance of a type II error, we have to weigh the consequences of these errors before deciding how to proceed.
Recall that the probability of committing a type I error is α. Why? Well, when we choose a level of significance (α) , we are choosing a benchmark for rejecting the null hypothesis. If the null hypothesis is true, then the probability that we will reject a true null hypothesis is α. So the smaller α is, the smaller the probability of a type I error.
It is more complicated to calculate the probability of a type II error. The best way to reduce the probability of a type II error is to increase the sample size. But once the sample size is set, larger values of α will decrease the probability of a type II error (while increasing the probability of a type I error).
Following are general guidelines for choosing a level of significance:
- If the consequences of a type I error are more serious, choose a small level of significance (α).
- If the consequences of a type II error are more serious, choose a larger level of significance (α). But remember that the level of significance is the probability of committing a type I error.
- In general, we pick the largest level of significance that we can tolerate as the chance of a type I error.
Note: It is not always the case that one type of error is worse than the other.
Try It
Hormone Replacement Therapy
Recall the experiment that investigated the side effects of hormone replacement therapy (HRT) for women with menopausal symptoms. The experiment randomly assigned over 16,000 U.S. women to receive a hormone treatment or a placebo. The experiment was double blind. After 5 years, a larger proportion of the hormone group had breast cancer and heart disease. This observed difference was statistically significant. Researchers were so alarmed by the results that the experiment was ended early to prevent further harm to the health of the women participating in the hormone group.
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The type I error in this situation is that we conclude that HRT increases the risk of breast cancer and heart disease, but it does not. The type II error is that we conclude that HRT does not increase the risk of breast cancer and heart disease, but it does.
Identify the type of error associated with each consequence.
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https://assessments.lumenlearning.co...sessments/3665
Let’s Summarize
- Hypothesis tests for two proportions can answer research questions about two populations or two treatments that involve categorical data.
-
The null hypothesis for the two-proportions test is always a statement of “no difference.”
- H 0 : p 1 − p 2 = 0
The alternative hypothesis is one of the following.
- H a : p 1 − p 2 < 0, or
- H a : p 1 − p 2 > 0, or
- H a : p 1 − p 2 ≠ 0
-
The test statistic for the two proportions test is similar to the test statistic for one sample proportion tests.
This statistic is approximately normal in its distribution if each sample has at least ten successes and failures. Note that the standard error is estimated with pooled proportion.
- The normal distribution may be used to provide P-values for a two-proportions test if each sample has at least 10 successes and failures.
- When the P-value in a two-proportions test is less than the level of significance (α), we should reject the null hypothesis in favor of the alternative. In this case, we say that the differences are statistically significant.
-
Two types of errors can be made when conducting a hypothesis test.
- A type I error occurs when we reject a true null hypothesis.
- A type II error occurs when we fail to reject a false null hypothesis.
- The level of significance, α, is the probability of a type I error.
- Increasing the sample size lowers the probability of a type II error.
- After considering the consequences of the type I and II errors, we should choose the largest value for α that we can tolerate, because increasing α decreases the probability of a type II error.
-
After conducting a hypothesis test, it is important to consider whether the conclusions are reasonable. We discussed two common pitfalls in drawing conclusions from statistical studies.(1) The conclusion is not appropriate to the study design.
- The study makes an inference based on nonrandom data.
- The study makes inappropriate cause-and-effect conclusions.
- The study overgeneralizes its conclusions.
(2) The conclusion confuses statistical significance with practical importance.
Contributors and Attributions
- Concepts in Statistics. Provided by : Open Learning Initiative. Located at : http://oli.cmu.edu . License : CC BY: Attribution


9.6: Coordination Frameworks
Bridging ligands link metals in multicenter coordination complexes
Some ambidentate and multidentate ligands have the capacity to bridge two metal centers. For instance, the cyano ligands can bridge two metal centers by forming linear links of the type
\[\ce{M-CN-M'} \nonumber \]
Linkages like these can be used to bridge multiple metal centers in a cluster or network solid, the latter of which is sometimes called a coordination framework. When the cyano ligand is combined with octahedral metal centers possessing 90\(^{\circ}\) L-M-L bond angles, a cubic coordination network results. An example is the Prussian Blue coordination framework, which possesses the unit cell depicted in Figure \(\sf{\PageIndex{1A}}\).
The cubic network shown in Figure \(\sf{\PageIndex{1A}}\) reflects the 3D structure of the octahedron, in which the M-L bonds point along the x, y, and z axes. If a square planar metal center is used, a 2D coordination network comprising interlinked squares is produced instead. An example is the Hofmann clathrate shown in Figure \(\sf{\PageIndex{1B}}\), which depicts a Hofmann clathrate in which square planar [Ni(CN) 4 ] 2- units are linked by trans -Ni(NH 3 ) 2 2+ units (which are octahedral but have a square plane of open coordination sites perpendicular to the NH 3 -Ni-NH 3 axis).
The structures of coordination polyhedra and frameworks reflect ligand and metal coordination geometries
As illustrated by the Prussian Blue and Hofmann clathrate coordination networks shown in Figure \(\sf{\PageIndex{1}}\), the structures formed when a bridging ligand links multiple metal centers depends on the geometry of the centers, the ligand, and the metal-ligand bonds formed. Because the directionality of metal-ligand bonding in many types of complexes is well-characterized and predictable, it is possible to design metal complexes and linkers that can serve as building blocks for clusters and networks. In particular
- metal complexes with combinations of labile (substitutable) ligands in particular topologies. These insure that the linking ligand will be arranged around the metal center in those defined directions.
- Ligands that possess binding sites oriented in defined directions so that they link the metal centers together in particular topologies.
Examples of the sort of metal centers that can be used and examples of linking ligands are given in Figure \(\sf{\PageIndex{2}}\).
Examples of how the building blocks shown in Figure \(\sf{\PageIndex{2}}\) might be used to prepare molecular polyhedra and coordination networks are depicted schematically as shown in Figure \(\sf{\PageIndex{3}}\). Among the examples shown in Figure \(\sf{\PageIndex{3}}\), those depicted on the right schematize the Hofmann clathrate (top) and Prussian Blue (bottom) coordination networks of Figure \(\sf{\PageIndex{1}}\).
A wider variety of structures are possible than those hinted at by the building blocks and structures shown in Figures \(\sf{\PageIndex{2}}\) and \(\sf{\PageIndex{3}}\). More may be obtained using the principles of molecular structure outlined in the sections on coordination geometry , ligands , and isomerism . In fact, one of the first coordination polyhedra prepared involved Jean-Marie Lehn's recognition that planar bidentate ligands in a tetrahedral bis-chelate are oriented perpendicular to one another, as shown in Figures \(\sf{\PageIndex{5A}}\). This enabled him to prepare a molecular trigonal prism by combining a source of Cu 2 + with the trigonal planar and linear-capable organic linkers that bind the Cu 2 + in bidentate fashion, as shown in Figure \(\sf{\PageIndex{5B}}\).
Metal Organic Frameworks (MOFs) are porous coordination polymers in which metal "building units" are connected by rigid organic ligand "struts"
One class of coordination frameworks that has received much attention over the past 25 years is the metal organic frameworks (MOFs). These consist of metal centers linked by rigid organic ligands to give a porous structure similar to those of the aluminosilicate-based zeolites. The structure of one MOF, called MIL-53, is given in Figure \(\sf{\PageIndex{6A}}\).
As can be seen from the overall structure of MIL-53 depicted in Figure \(\sf{\PageIndex{6A}}\), the structure possesses large rhombic prismatic voids, represented by the yellow spheres. These voids can in principle be occupied by small molecule substrates. Because of MOF's potential to bind and store substrates, there is considerable interest in developing MOFs that are useful for storing and separating particular gases.
A closer look at the structure of MIL-53 reveals that the carboxylate oxygens in the benzenedicarboxylato (BDU) linkers span two different metal centers rather than binding to only one. As explained in Figure \(\sf{\PageIndex{7}}\), this binding mode enables the formation of rigid stable networks, although it requires the use of metal building blocks in which two or more metal centers are held in close proximity.
In MIL-53, the metal centers that the DBU ligands coordinate are chains of octahedral metal centers bridged by \(\mu_2\) hydroxo ligands. These chains form spontaneously as the network forms under the high temperature conditions of its synthesis. In other cases, metal secondary building units (SBUs) containing the necessary bridging dicarboxylate ligands are used. One common class of metal SBUs used is the paddlewheel carboxylates shown in Figure \(\sf{\PageIndex{8A}}\). These consist of two metals spanned by a square plane of four carboxylates in a paddlewheel arrangment.
The use of paddlewheel carboxylate metal SBUs and bridging organic carboxylate ligands enables the construction of coordination frameworks like that of HKUST-1 shown in Figure \(\sf{\PageIndex{9}}\). The structure of these networks depends on the geometry of the linking ligand. For instance, in HKUST-1 the 1,3,5-benzenetricarboxylato bridging ligands each link three paddlewheel SBUs to give the cubic network shown in Figure \(\sf{\PageIndex{9}}\). Other organic carboxylate ligands give different network topologies. In addition, the ability of some paddlewheel carboxylates to coordinate ligands perpendicular to the carboxylates, represented by the ligands marked L? in Figure \(\sf{\PageIndex{8}}\), affords additional opportunities to use these networks to bind substrates that can coordinate those sites.
Another common metal SBU is the basic zinc acetate structure shown in Figure \(\sf{\PageIndex{10}}\). As shown in Figure \(\sf{\PageIndex{10A}}\), the structure is analogous to those of the basic beryllium acetates and involves an OZn 4 tetrahedron in which the tetrahedrally arranged Zn 2 + are connected by carboxylate ligands spanning the tetrahedron's six edges. When these carboxylate ligands are replaced by rigid dicarboxylates (Figure \(\sf{\PageIndex{10B}}\)), the result is that the Zn 4 O core is surrounded by an octahedral coordination sphere of carboxylate ligands (Figure \(\sf{\PageIndex{10C}}\)).
The structure of MOF-5 also illustrates how the size of the pores in an MOF structure may be tailored by lengthening or shortening the organic linker. In particular, from Figure \(\sf{\PageIndex{11}}\) it can be seen that the size of the MOF-5's cubic unit cell depends on the length of the organic portion of the carboxylate linker. In MOF-5 this linker consists of a single benzene unit and gives 9-Angstrom pores, while the use of two and three benzene rings increases the pore size to 13 and 16 Angstroms, respectively, as shown in \(\sf{\PageIndex{12}}\).
References
1. The structure of Prussian blue is rendered from that reported in Buser, H. J.; Schwarzenbach, D.; Petter, W.; Ludi, A., The crystal structure of Prussian Blue: Fe 4 [Fe(CN) 6 ] 3 .xH 2 O. Inorganic Chemistry 1977, 16(11) , 2704-2710; to simplify depiction of the coordination framework, water molecules were removed. The structure of the Hofmann-type clathrate is rendered from that reported in Rayner, J. H.; Powell, H. M., 688. Crystal structure of a hydrated nickel cyanide ammoniate. Journal of the Chemical Society (Resumed) 1958, 3412-3418.
2. (a) Fujita, M.; Ogura, K., Transition-metal-directed assembly of well-defined organic architectures possessing large voids: From macrocycles to [2] catenanes. Coordination Chemistry Reviews 1996, 148 , 249-264. (b) Leininger, S.; Olenyuk, B.; Stang, P. J., Self-Assembly of Discrete Cyclic Nanostructures Mediated by Transition Metals. Chemical Reviews 2000, 100(3) , 853-908.
3. Machado, V. G.; Baxter, P. N. W.; Lehn, J.-M., Self-assembly in self-organized inorganic systems: a view of programmed metallosupramolecular architectures. Journal of the Brazilian Chemical Society 2001, 12, 431-462.
4. Yaghi, O. M.; O'Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J., Reticular synthesis and the design of new materials. Nature 2003, 423 (6941), 705-714.


23.5: The Stomach
By the end of this section, you will be able to:
- Label on a diagram the four main regions of the stomach, its curvatures, and its sphincter
- Identify the four main types of secreting cells in gastric glands, and their important products
- Explain why the stomach does not digest itself
- Describe the mechanical and chemical digestion of food entering the stomach
Although a minimal amount of carbohydrate digestion occurs in the mouth, chemical digestion really gets underway in the stomach. An expansion of the alimentary canal that lies immediately inferior to the esophagus, the stomach links the esophagus to the first part of the small intestine (the duodenum) and is relatively fixed in place at its esophageal and duodenal ends. In between, however, it can be a highly active structure, contracting and continually changing position and size. These contractions provide mechanical assistance to digestion. The empty stomach is only about the size of your fist, but can stretch to hold as much as 4 liters of food and fluid, or more than 75 times its empty volume, and then return to its resting size when empty. Although you might think that the size of a person’s stomach is related to how much food that individual consumes, body weight does not correlate with stomach size. Rather, when you eat greater quantities of food—such as at holiday dinner—you stretch the stomach more than when you eat less.
Popular culture tends to refer to the stomach as the location where all digestion takes place. Of course, this is not true. An important function of the stomach is to serve as a temporary holding chamber. You can ingest a meal far more quickly than it can be digested and absorbed by the small intestine. Thus, the stomach holds food and parses only small amounts into the small intestine at a time. Foods are not processed in the order they are eaten; rather, they are mixed together with digestive juices in the stomach until they are converted into chyme, which is released into the small intestine.
As you will see in the sections that follow, the stomach plays several important roles in chemical digestion, including the continued digestion of carbohydrates and the initial digestion of proteins and triglycerides. Little if any nutrient absorption occurs in the stomach, with the exception of the negligible amount of nutrients in alcohol.
Structure
There are four main regions in the stomach : the cardia, fundus, body, and pylorus (Figure \(\PageIndex{1}\)). The cardia (or cardiac region) is the point where the esophagus connects to the stomach and through which food passes into the stomach. Located inferior to the diaphragm, above and to the left of the cardia, is the dome-shaped fundus . Below the fundus is the body , the main part of the stomach. The funnel-shaped pylorus connects the stomach to the duodenum. The wider end of the funnel, the pyloric antrum , connects to the body of the stomach. The narrower end is called the pyloric canal , which connects to the duodenum. The smooth muscle pyloric sphincter is located at this latter point of connection and controls stomach emptying. In the absence of food, the stomach deflates inward, and its mucosa and submucosa fall into a large fold called a ruga .
The convex lateral surface of the stomach is called the greater curvature; the concave medial border is the lesser curvature. The stomach is held in place by the lesser omentum, which extends from the liver to the lesser curvature, and the greater omentum, which runs from the greater curvature to the posterior abdominal wall.
Histology
The wall of the stomach is made of the same four layers as most of the rest of the alimentary canal, but with adaptations to the mucosa and muscularis for the unique functions of this organ. In addition to the typical circular and longitudinal smooth muscle layers, the muscularis has an inner oblique smooth muscle layer (Figure \(\PageIndex{2}\)). As a result, in addition to moving food through the canal, the stomach can vigorously churn food, mechanically breaking it down into smaller particles.
The stomach mucosa’s epithelial lining consists only of surface mucus cells, which secrete a protective coat of alkaline mucus. A vast number of gastric pits dot the surface of the epithelium, giving it the appearance of a well-used pincushion, and mark the entry to each gastric gland , which secretes a complex digestive fluid referred to as gastric juice.
Although the walls of the gastric pits are made up primarily of mucus cells, the gastric glands are made up of different types of cells. The glands of the cardia and pylorus are composed primarily of mucus-secreting cells. Cells that make up the pyloric antrum secrete mucus and a number of hormones, including the majority of the stimulatory hormone, gastrin . The much larger glands of the fundus and body of the stomach, the site of most chemical digestion, produce most of the gastric secretions. These glands are made up of a variety of secretory cells. These include parietal cells, chief cells, mucous neck cells, and enteroendocrine cells.
Parietal cells —Located primarily in the middle region of the gastric glands are parietal cells , which are among the most highly differentiated of the body’s epithelial cells. These relatively large cells produce both hydrochloric acid (HCl) and intrinsic factor . HCl is responsible for the high acidity (pH 1.5 to 3.5) of the stomach contents and is needed to activate the protein-digesting enzyme, pepsin. The acidity also kills much of the bacteria you ingest with food and helps to denature proteins, making them more available for enzymatic digestion. Intrinsic factor is a glycoprotein necessary for the absorption of vitamin B 12 in the small intestine.
Chief cells —Located primarily in the basal regions of gastric glands are chief cells , which secrete pepsinogen , the inactive proenzyme form of pepsin. HCl is necessary for the conversion of pepsinogen to pepsin.
Mucous neck cells —Gastric glands in the upper part of the stomach contain mucous neck cells that secrete thin, acidic mucus that is much different from the mucus secreted by the goblet cells of the surface epithelium. The role of this mucus is not currently known.
Enteroendocrine cells —Finally, enteroendocrine cells found in the gastric glands secrete various hormones into the interstitial fluid of the lamina propria. These include gastrin, which is released mainly by enteroendocrine G cells .
Table \(\PageIndex{1}\) describes the digestive functions of important hormones secreted by the stomach.
Interactive Link
Watch this animation that depicts the structure of the stomach and how this structure functions in the initiation of protein digestion. This view of the stomach shows the characteristic rugae. What is the function of these rugae?
| Hormone | Production site | Production stimulus | Target organ | Action |
|---|---|---|---|---|
| Gastrin | Stomach mucosa, mainly G cells of the pyloric antrum | Presence of peptides and amino acids in stomach | Stomach | Increases secretion by gastric glands; promotes gastric emptying |
| Gastrin | Stomach mucosa, mainly G cells of the pyloric antrum | Presence of peptides and amino acids in stomach | Small intestine | Promotes intestinal muscle contraction |
| Gastrin | Stomach mucosa, mainly G cells of the pyloric antrum | Presence of peptides and amino acids in stomach | Ileocecal valve | Relaxes valve |
| Gastrin | Stomach mucosa, mainly G cells of the pyloric antrum | Presence of peptides and amino acids in stomach | Large intestine | Triggers mass movements |
| Ghrelin | Stomach mucosa, mainly fundus | Fasting state (levels increase just prior to meals) | Hypothalamus | Regulates food intake, primarily by stimulating hunger and satiety |
| Histamine | Stomach mucosa | Presence of food in the stomach | Stomach | Stimulates parietal cells to release HCl |
| Serotonin | Stomach mucosa | Presence of food in the stomach | Stomach | Contracts stomach muscle |
| Somatostatin | Mucosa of stomach, especially pyloric antrum; also duodenum | Presence of food in the stomach; sympathetic axon stimulation | Stomach | Restricts all gastric secretions, gastric motility, and emptying |
| Somatostatin | Mucosa of stomach, especially pyloric antrum; also duodenum | Presence of food in the stomach; sympathetic axon stimulation | Pancreas | Restricts pancreatic secretions |
| Somatostatin | Mucosa of stomach, especially pyloric antrum; also duodenum | Presence of food in the stomach; sympathetic axon stimulation | Small intestine | Reduces intestinal absorption by reducing blood flow |
Gastric Secretion
The secretion of gastric juice is controlled by both nerves and hormones. Stimuli in the brain, stomach, and small intestine activate or inhibit gastric juice production. This is why the three phases of gastric secretion are called the cephalic, gastric, and intestinal phases (Figure \(\PageIndex{3}\)). However, once gastric secretion begins, all three phases can occur simultaneously.
The cephalic phase (reflex phase) of gastric secretion, which is relatively brief, takes place before food enters the stomach. The smell, taste, sight, or thought of food triggers this phase.  This enhanced secretion is a conditioned reflex, meaning it occurs only if you like or want a particular food. Depression and loss of appetite can suppress the cephalic reflex.
The gastric phase of secretion lasts 3 to 4 hours, and is set in motion by local neural and hormonal mechanisms triggered by the entry of food into the stomach. For example, when your sushi reaches the stomach, it creates distention that activates the stretch receptors. This stimulates parasympathetic neurons to release acetylcholine, which then provokes increased secretion of gastric juice. Partially digested proteins, caffeine, and rising pH stimulate the release of gastrin from enteroendocrine G cells, which in turn induces parietal cells to increase their production of HCl, which is needed to create an acidic environment for the conversion of pepsinogen to pepsin, and protein digestion. Additionally, the release of gastrin activates vigorous smooth muscle contractions. However, it should be noted that the stomach does have a natural means of avoiding excessive acid secretion and potential heartburn. Whenever pH levels drop too low, cells in the stomach react by suspending HCl secretion and increasing mucous secretions.
The intestinal phase of gastric secretion has both excitatory and inhibitory elements. The duodenum has a major role in regulating the stomach and its emptying. When partially digested food fills the duodenum, intestinal mucosal cells release a hormone called intestinal (enteric) gastrin, which further excites gastric juice secretion. This stimulatory activity is brief, however, because when the intestine distends with chyme, the enterogastric reflex inhibits secretion. One of the effects of this reflex is to close the pyloric sphincter, which blocks additional chyme from entering the duodenum.
The Mucosal Barrier
The mucosa of the stomach is exposed to the highly corrosive acidity of gastric juice. Gastric enzymes that can digest protein can also digest the stomach itself. The stomach is protected from self-digestion by the mucosal barrier . This barrier has several components. First, the stomach wall is covered by a thick coating of bicarbonate-rich mucus. This mucus forms a physical barrier, and its bicarbonate ions neutralize acid. Second, the epithelial cells of the stomach's mucosa meet at tight junctions, which block gastric juice from penetrating the underlying tissue layers. Finally, stem cells located where gastric glands join the gastric pits quickly replace damaged epithelial mucosal cells, when the epithelial cells are shed. In fact, the surface epithelium of the stomach is completely replaced every 3 to 6 days.
Homeostatic Imbalances
Ulcers: When the Mucosal Barrier Breaks Down
As effective as the mucosal barrier is, it is not a “fail-safe” mechanism. Sometimes, gastric juice eats away at the superficial lining of the stomach mucosa, creating erosions, which mostly heal on their own. Deeper and larger erosions are called ulcers.
Why does the mucosal barrier break down? A number of factors can interfere with its ability to protect the stomach lining. The majority of all ulcers are caused by either excessive intake of non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin, or Helicobacter pylori infection.
Antacids help relieve symptoms of ulcers such as “burning” pain and indigestion. When ulcers are caused by NSAID use, switching to other classes of pain relievers allows healing. When caused by H. pylori infection, antibiotics are effective.
A potential complication of ulcers is perforation: Perforated ulcers create a hole in the stomach wall, resulting in peritonitis (inflammation of the peritoneum). These ulcers must be repaired surgically.
Digestive Functions of the Stomach
The stomach participates in virtually all the digestive activities with the exception of ingestion and defecation. Although almost all absorption takes place in the small intestine, the stomach does absorb some drugs, such as alcohol and aspirin.
Mechanical Digestion
Within a few moments after food enters your stomach, mixing waves begin to occur at intervals of approximately 20 seconds. A mixing wave is a unique type of peristalsis that mixes and softens the food with gastric juices to create chyme. The initial mixing waves are relatively gentle, but these are followed by more intense waves, starting at the body of the stomach and increasing in force as they reach the pylorus. It is fair to say that long before your sushi exits through the pyloric sphincter, it bears little resemblance to the sushi you ate.
The pylorus, which holds around 30 mL (1 fluid ounce) of chyme, acts as a filter, permitting only liquids and small food particles to pass through the mostly, but not fully, closed pyloric sphincter. In a process called gastric emptying , rhythmic mixing waves force about 3 mL of chyme at a time through the pyloric sphincter and into the duodenum. Release of a greater amount of chyme at one time would overwhelm the capacity of the small intestine to handle it. The rest of the chyme is pushed back into the body of the stomach, where it continues mixing. This process is repeated when the next mixing waves force more chyme into the duodenum.
Gastric emptying is regulated by both the stomach and the duodenum. The presence of chyme in the duodenum activates receptors that inhibit gastric secretion. This prevents additional chyme from being released by the stomach before the duodenum is ready to process it.
Chemical Digestion
The fundus plays an important role, because it stores both undigested food and gases that are released during the process of chemical digestion. Food may sit in the fundus of the stomach for a while before being mixed with the chyme. While the food is in the fundus, the digestive activities of salivary amylase continue until the food begins mixing with the acidic chyme. Ultimately, mixing waves incorporate this food with the chyme, the acidity of which inactivates salivary amylase and activates lingual lipase. Lingual lipase then begins breaking down triglycerides into free fatty acids, and mono- and diglycerides.
The breakdown of protein begins in the stomach through the actions of HCl and the enzyme pepsin.
Its numerous digestive functions notwithstanding, there is only one stomach function necessary to life: the production of intrinsic factor. The intestinal absorption of vitamin B 12 , which is necessary for both the production of mature red blood cells and normal neurological functioning, cannot occur without intrinsic factor. People who undergo total gastrectomy (stomach removal)—for life-threatening stomach cancer, for example—can survive with minimal digestive dysfunction if they receive vitamin B 12 injections.
The contents of the stomach are completely emptied into the duodenum within 2 to 4 hours after you eat a meal. Different types of food take different amounts of time to process. Foods heavy in carbohydrates empty fastest, followed by high-protein foods. Meals with a high triglyceride content remain in the stomach the longest. Since enzymes in the small intestine digest fats slowly, food can stay in the stomach for 6 hours or longer when the duodenum is processing fatty chyme. However, note that this is still a fraction of the 24 to 72 hours that full digestion typically takes from start to finish.


18.2: Gothic Architecture
Gothic Architecture: The Abbey Church of Saint Denis
The Abbey Church of Saint Denis is known as the first Gothic structure and was developed in the 12th century by Abbot Suger.
Illustrate a timeline of the creation of the Abbey Church of Saint Denis
Key Points
- The Abbey Church of Saint Denis provided an architectural model for cathedrals and abbeys of northern France, England, and other European countries.
- In the 12th century, Abbot Suger rebuilt portions of the church using innovative structural and decorative features that were drawn from a number of sources, resulting in the first truly Gothic building.
- The two architects who worked under Abbot Suger’s direction remain uncredited, identified only by their unique stylistic contributions.
Key Terms
- Abbey Church of Saint Denis : The Cathedral Basilica of Saint Denis is a large medieval abbey church in the commune of Saint Denis, renowned for its Gothic architecture.
- Rayonnant Gothic : The period of French Gothic architecture between c. 1240 and 1350, characterized by a shift in focus away from the High Gothic mode of great scale toward a greater concern for two dimensional surfaces and the repetition of decorative motifs at different scales.
- ambulatory : The round walkway encircling the altar in many cathedrals.
- Romanesque : European architecture containing both Roman and Byzantine elements; sometimes applied to the debased style of the later Roman Empire, but especially to the more developed architecture prevailing from the 8th to the 12th centuries.
The Abbey Church of Saint Denis, also known as the Cathedral Basilica of Saint Denis, is a large medieval abbey church in the commune of Saint Denis, now a northern suburb of Paris. This site originated as a Gallo-Roman cemetery in late Roman times. Around 475 CE, St. Genevieve established a church at this site. In the 7 th century, this structure was replaced by a much grander construction, on the orders of Dagobert I, King of the Franks.
The Basilica of Saint Denis is an architectural landmark, the first major structure of which a substantial part was designed and built in the Gothic style . Both stylistically and structurally, it heralded the change from Romanesque architecture to Gothic architecture . Before the term “Gothic” came into common use, it was known as the “French Style.”
Saint Denis is a patron saint of France and, according to legend, was the first Bishop of Paris. Legend says that he was decapitated on the Hill of Montmartre and subsequently carried his head to the site of the current church, indicating where he wanted to be buried.
Dagobert I refounded the church as the Abbey of Saint Denis, a Benedictine monastery. Dagobert also commissioned a new shrine to house the saint’s remains; it was created by his chief counselor, Eligius, a goldsmith by training.
Abbot Suger
Abbot Suger (circa 1081-1151), Abbot of Saint Denis from 1122 and a friend and confidant of French kings, had been given the abbey as an oblate at the age of 10 and began work around 1135 on rebuilding and enlarging it.
Suger was the patron of the rebuilding of Saint Denis, but not the architect, as was often assumed in the 19th and early 20th centuries. In fact it appears that two distinct architects, or master masons, were involved in the 12th century changes. Both remain anonymous, but their work can be distinguished stylistically. The first, who was responsible for the initial work at the western end, favored conventional Romanesque capitals and molding profiles with rich and individualized detailing. His successor, who completed the western facade and upper stories of the narthex before going on to build the new choir , displayed a more restrained approach to decorative effects, relying on a simple repertoire of motifs , which may have proved more suitable for the lighter Gothic style that he helped to create.
Suger’s western extension was completed in 1140 and the three new chapels in the narthex were consecrated on June 9 th of that year. On completion of the west front, Abbot Suger moved on to the reconstruction of the eastern end. He wanted a choir (chancel) that would be suffused with light. To achieve his aims, Suger’s masons drew on the new elements that had evolved or been introduced to Romanesque architecture: the pointed arch , the ribbed vault , the ambulatory with radiating chapels, the clustered columns supporting ribs springing in different directions, and the flying buttresses , which enabled the insertion of large clerestory windows. This was the first time that these features had all been brought together. The new structure was finished and dedicated on June 11 th of 1144, in the presence of the King.
Thus, the Abbey of Saint Denis became the prototype for further building in the royal domain of northern France. Through the rule of the Angevin dynasty , the style was introduced to England and spread throughout France, the Low Countries, Germany, Spain, northern Italy, and Sicily.
The dark Romanesque nave , with its thick walls and small window openings, was rebuilt using the latest techniques, in what is now known as Gothic. This new style, which differed from Suger’s earlier works as much as they had differed from their Romanesque precursors , reduced the wall area to an absolute minimum. Solid masonry was replaced with vast window openings filled with brilliant stained glass and interrupted only by the most slender of bar tracery—not only in the clerestory but also, perhaps for the first time, in the normally dark triforium level. The upper facades of the two much-enlarged transepts were filled with two spectacular rose windows . As with Suger’s earlier rebuilding work, the identity of the architect or master mason is unknown.
The abbey is often referred to as the “royal necropolis of France” as it is the site where the kings of France and their families were buried for centuries. All but three of the monarchs of France from the 10th century until 1789 have their remains here. The effigies of many of the kings and queens are on their tombs, but during the French Revolution , those tombs were opened and the bodies were moved to mass graves.
Gothic Architecture: La Saint-Chapelle
Louis IX’s patronage of the arts drove much innovation in Gothic art and architecture, exemplified by his commission of La Saint-Chappelle, an example of Rayonnant Gothic architecture.
Discuss the innovations in Gothic art and architecture seen in La Saint-Chappelle
Key Points
- Louis IX established the Gothic chapel Sainte-Chapelle to house his collection of Christian relics in the mid-13th century.
- Louis IX’s artistic and architectural patronage was both innovative and highly influential among European royalty.
- Louis IX was made a saint in 1297, and remains the only French monarch to have been canonized.
- Sainte-Chapelle epitomized the Rayonnant Gothic style of architecture.
Key Terms
- Rayonnant Gothic : The period of French Gothic architecture between c. 1240 and 1350, characterized by a shift in focus away from the High Gothic mode of great scale and height toward a greater concern for two dimensional surfaces and the repetition of decorative motifs at different scales. Rayonnant structures tend to be smaller than High Gothic Cathedrals. This style is also known as Court Style.
- Sainte-Chapelle : A chapel in the courtyard of the royal palace on the Île de la Cité, built to house Louis IX’s collection of Holy relics.
Louis IX ruled during the so-called “golden century of Saint Louis,” when the Kingdom of France was at its height of power in Europe, both politically and economically. The king of France was regarded as a primus inter pares among the kings and rulers of the continent. He commanded the largest army, and ruled the largest and most wealthy kingdom of Europe, which was the European center of arts and intellectual thought (La Sorbonne) at the time. The prestige and respect for King Louis IX resulted more from his benevolent personality than from his military domination. For his contemporaries, he was the quintessential example of the Christian prince, and embodied the whole of Christendom in his person. The King was later recognized as a saint by the Catholic Church.
The style of Louis’ court radiated throughout Europe through the purchase of art objects from Parisian masters for export and by the marriage of the King’s daughters and female relatives to foreign husbands. Louis’ personal chapel, La Sainte-Chapelle in Paris, was copied more than once by his descendants elsewhere.
La Sainte-Chapelle (The Holy Chapel) is one of the only surviving buildings of the Capetian royal palace on the Île de la Cité in the heart of Paris, France. It was commissioned by King Louis IX of France to house his collection of relics of the passion, including the Crown of Thorns—one of the most important relics in medieval Christendom. Begun some time after 1239 and consecrated on April 26, 1248, the Sainte-Chapelle is considered among the highest achievements of the Rayonnant period of Gothic architecture . Although damaged during the French revolution and heavily restored in the 19 th century, it retains one of the most extensive in-situ collections (collections that are still in their original positions) of 13 th century stained glass anywhere in the world. The glass depicts stories from the Old Testament and focuses heavily on the depictions of biblical kings, both good and bad. Scholars believe the inclusion of “bad” kings, along with the good, were meant as a lesson for the royal viewer to learn from both good and bad examples of rulership.
La Sainte-Chapelle is a prime example of the phase of Gothic architectural style called “Rayonnant Gothic,” also known as Court Style, and is marked by its sense of weightlessness and strong vertical emphasis. Rayonnant structures tend to be smaller than the High Gothic Cathedrals that came before them. La Sainte-Chapelle stands squarely upon a lower chapel, which served as parish church for all the inhabitants of the palace, which was the seat of government. However, the chapel proper was a private royal chapel and scholars have noted how the structure almost looks like metalwork , as if the chapel itself is a reliquary .
English Gothic Architecture
English Gothic architecture (c. 1180–1520) is defined by pointed arches, vaulted roofs, buttresses, large windows, and spires.
Define the characteristics and particular styles of English Gothic architecture
Key Points
- The Gothic style originated in France with the choir of the Basilique Saint-Denis, built by Abbot Suger and dedicated in June 1144.
- The lancet , a pointed arch , was the most crucial development of the Early Gothic period (c. 1180–1250), resulting in graceful buildings with thinner walls and more light.
- While French Gothic Cathedrals were built to be increasingly tall, English Gothic Cathedrals tended to emphasize the length of the building rather than the height.
- The Decorated Gothic Period (c. 1250–1350) is subdivided into the earlier Geometric Period and later Curvilinear Period, differentiated by styles of window tracery .
- Known for emphasizing vertical lines , the austerity of the Perpendicular Gothic Period was a response to the pandemic Black Death , which emerged in England in 1348.
Key Terms
- Decorated Gothic Period : A name given specifically to a division of English Gothic architecture, which was broken into two periods: the Geometric style (1250–1290) and the Curvilinear style (1290–1350).
- choir : The part of a church where the singing group assembles for song.
- Early English Gothic Period :A period in the late 12th century, characterized by pointed arches, that superseded the Romanesque style.
Gothic architecture flourished in England from approximately 1180 to 1520. This style is defined by pointed arches, vaulted roofs, buttresses , large windows, and spires . The Gothic style was first developed in France, where the various elements had first been used together within a single building at the choir of the Basilique Saint-Denis north of Paris, built by Abbot Suger and dedicated in June 1144. The English adopted the Gothic style, however, they adapted it to their own regional preferences. While French Gothic Cathedrals were built to be increasingly tall, English Gothic Cathedrals tended to emphasize the length of the building rather than the height.
Many of the largest and finest works of English architecture, notably the medieval cathedrals of England, are largely built in the Gothic style. The earliest large-scale applications of Gothic architecture in England are at Canterbury Cathedral and Westminster Abbey . Castles, palaces, great houses, universities, parish churches, and many smaller unpretentious secular buildings, including almshouses and trade halls, were also built in this style.
Early English Gothic Period
The Early English Gothic period lasted from the late 12th century until midway through the 13th century, according to most modern scholars. By 1175, the Gothic style had been firmly established in England with the completion of the Choir at Canterbury Cathedral by William of Sens.
The most significant characteristic development of the Early English period was the pointed arch known as the lancet . Compared with the rounded Romanesque style, the pointed arch of the Early English Gothic is aesthetically more elegant and is more efficient at distributing the weight of stonework, making it possible to span higher and wider gaps using narrower columns . It also allows for much greater variation in proportions.
Using the pointed arch, walls could become less massive and window openings could be larger and grouped more closely together, so architects could achieve more open, airy, and graceful buildings. At its purest, the style was simple and austere, emphasizing the height of the building, as if aspiring heavenward. In the late 12th century the Early English Gothic style superseded the Romanesque style, and during the late 13th century it developed into the Decorated Gothic style, which lasted until the mid 14th century.
Decorated Gothic Period
The Decorated period in architecture is traditionally broken into two periods: the Geometric style (1250–1290) and the Curvilinear style (1290–1350). Decorated architecture is characterized by its window tracery, which are elaborate patterns that fill the top portions of windows. The tracery style was geometric at first, and flowing in the later period during the 14th century. Vaulting also became more elaborate, with the use of increasing numbers of ribs , initially for structural and later for aesthetic reasons.
Examples of the Decorated style can be found in many British churches and cathedrals. Principal examples are the east ends of Lincoln Cathedral and of Carlisle Cathedral and the west fronts of York Minster and of Lichfield Cathedral.
Perpendicular Gothic Period
The Perpendicular Gothic period is the third historical division of English Gothic architecture, and is characterized by an emphasis on vertical lines. The Perpendicular style began under the royal architects William Ramsey and John Sponlee, and lasted into the mid 16th century.
The Perpendicular style grew out of the shadow of the Black Death, a disease that killed approximately half of England’s population in 18 months between June 1348 and December 1349 and returned in 1361–62 to kill another fifth of the population. This epidemic dramatically impacted every aspect of society, including arts and culture , and designers moved away from the flamboyance and jubilation present in the Decorated style. Architects were also responding to labor shortages resulting from the plague, and therefore relied on less elaborate designs.
Perpendicular linearity is particularly obvious in the design of windows, which became immense, allowing greater scope for stained glass craftsmen. Some of the finest features of this period are the magnificent timber roofs: hammerbeam roofs, such as those of Westminster Hall (1395), Christ Church Hall, Oxford, and Crosby Hall, appeared for the first time. Gothic architecture continued to flourish in England for 100 years after the precepts of Renaissance architecture were formalized in Florence in the early 15th century.
German Gothic Architecture
Gothic architecture flourished during the high and late medieval period in the Holy Roman Empire, from approximately 1140–1400.
Summarize the principal features of German Gothic architecture
Key Points
- The Gothic style first developed in France. Territories that constitute modern day Germany adopted the French Gothic and developed regional distinctions to this style.
- Brick Gothic is a style of Gothic architecture common in Northern Europe, especially in Northern Germany and the regions around the Baltic Sea without natural rock resources where the buildings are built, more or less, using only bricks.
- Hall churches are another distinctively German adaptation to the French Gothic style.
Key Terms
- nave : The middle or body of a church, extending from the transepts to the principal entrances.
- Middle Ages : The period of time in Europe between the decline of the Roman Empire and the revival of letters (the Renaissance) or, according to Henry Hallam, the period beginning with the sixth and ending with the fifteenth century.
- spire : A tapering structure built on a roof or tower, especially as one of the central architectural features of a church or cathedral roof.
Gothic architecture flourished during the high and late medieval period in the Holy Roman Empire, from approximately 1140–1400. The Gothic style first developed in France. Territories that constitute modern day Germany adopted the French Gothic and developed regional distinctions to this style.
German Gothic architecture is notable for its enormous towers and spires . Sometimes they were so big that they were left unfinished until modern times. The spires are quite different than English spires because they are made of lacy “openwork.” There are also many hallenkirke (or hall churches), which have no clerestorey windows. The nave and the aisles are about the same height.
Freiburg Cathedral was built in three stages, the first beginning in 1120 under the Dukes of Zahringen, the second beginning in 1210, and the third in 1230. Of the original building, only the foundations still exist. It is particularly notable for its 116-meter tower, which is nearly square at the base , and the dodecagonal star gallery at its center. Above this gallery, the tower is octagonal and tapered, with the spire at the top. It is the only Gothic church tower in Germany completed in the Middle Ages (1330) that survived the November 1944 bombing raids that destroyed all of the houses on the west and north side of the market.
Cologne Cathedral is, after Milan Cathedral, the largest Gothic cathedral in the world. Construction began in 1248 and took, with interruptions, until 1880 to complete—a period of over 600 years. It is 144.5 metres long, 86.5 m wide, and its two towers are 157 m tall. Because of its enormous twin spires, it also has the largest façade of any church in the world. The choir of the cathedral, measured between the piers , also holds the distinction of having the largest height to width ratio of any Medieval church.
The building of Gothic churches was accompanied by the construction of guild houses and town halls by the rising bourgeoisie. Examples are the Gothic Town Hall (13 th century) at Stralsund, Bremen Town Hall (1410), and the (reconstructed) city hall of Munster (originally from 1350).
The dwellings of this period were mainly timber-framed buildings, as can still be seen in Goslar and Quedlinburg. Quedlinburg has one of the oldest half-timbered houses in Germany. The method of construction, used extensively for town houses of the Medieval and Renaissance periods, lasted into the twentieth century for rural buildings.
Brick Gothic
Brick Gothic (Backsteingotik) is a specific style of Gothic architecture common in Northern Europe, especially in Northern Germany and the regions around the Baltic Sea that lack natural rock resources. The structures are built, more or less, using only bricks. Stralsund City Hall and St. Nicholas Church are examples of this style. Cities such as Lubeck, Rostock, Wismar, Stralsund, and Greifswald are shaped by this regional style. St. Mary’s in Lübeck, built between 1200 and 1350, was a model for many North German churches.
Hall Churches
Hall churches are another example of German Gothic architecture that is distinct from French Gothic. In hall churches, the aisles and nave are almost the same height and the stained glass windows are typically the full height of the walls, allowing in maximum light and space .
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- Gloucester_Cathedral_High_Altar,_Gloucestershire,_UK_-_Diliff.jpg. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/English_Gothic_architecture#/media/File:Gloucester_Cathedral_High_Altar,_Gloucestershire,_UK_-_Diliff.jpg. License : CC BY-SA: Attribution-ShareAlike
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6.1: Angular Momentum
Back in Chapter 2 we introduced the momentum of an object moving in one dimension as \(p = mv\), and found that it had the interesting property of being conserved in collisions between objects that made up an isolated system. Critical to that discussion was the idea that objects are represented by points, so they have well-defined positions. Of course, in real life, objects are not made up a single points, but are extended . We now want to move the discussion into studying these extended objects, that have real size, and understand how they transfer momentum differently than simple points. The biggest difference between points and extended objects it that extended objects can rotate, as well as move through space .
We want to define a quantity that measures this rotation, in the same way linear momentum measured something about how particles translated in space. This quantity is going to be angular momentum \(\vec{L}\), which we define as
\[\vec{L}=I\vec{\omega}\]
The variables here are the rotational analogues of the linear quantities; \(\vec{\omega}\) is angular velocity (like linear velocity \(\vec{v}\)), and \(I\) is called the moment of inertia, and is analogous to the mass \(m\). In this section we will build up an understanding of each of these quantities, and how they can be used to solve problems dealing with the rotation of extended objects.
The equation above is a vector, so we need to understand it's direction. It's tempting to say "the object rotates counterclockwise" or the like, but is there a vector direction associated to "counterclockwise"? There is, but it's probably not what you're thinking! The direction of counterclockwise (or clockwise) rotation comes from the right hand rule . The most basic version of the right hand rule is shown in the figure below, and the way you use it is:
- Take your right hand...
- ...curl the fingers of your right hand in the direction of rotation...
- ...your thumb points in the direction of \(\vec{\omega}\).
Figure \(\PageIndex{1}\): From the Wikipedia page on this topic. In this case, the arrow along the hand shows the direction of \(\vec{\omega}\), and we might say "the angular velocity is directed up and to the right".
The angular velocity \(\vec{\omega}\) is the exact analog to the linear velocity \(\vec{v}\), although it deserves a little bit of attention. The unit for the angular velocity is angular distance per unit time, and in SI units that's radians per second. What's interesting about this is that for a single object, every point on the object will have the same angular velocity. It really has to be that way - if a hoop is spinning at two revolutions per second, asking what angular speed the outside of the hoop is spinning at had better be the same as every other point. Said another way, if any point on the object is spinning at a different rate (say, one revolution per second), that means the object is tearing itself apart! Those kinds of objects are more complicated, so we will always assume our object are rigid , meaning the entire object rotates at the same rate.
Now let's look at the newest aspect of this formula, the moment of inertia \(I\). Like the mass, this quantity encodes the inertia of an object, but includes information about it's shape. Specifically, for an object made up of a bunch of masses \(m_i\) which are located at distances \(r_i\) from an axis of rotation, the moment of inertia is
\[I=\sum_i m_i r_i^2.\label{eq:MomInert}\]
That looks like a simple formula, but if the shape is complicated, that sum might actually be very difficult or impossible to do 1 . Fortunately, there are simplier expressions for many of the shapes we often encounter in nature. Many of these shapes are shown in the figure below, and many more can be found in Wikipedia .
Table \(\PageIndex{1}\)
In nearly all of these examples (save those that have multiple different dimensions, like the annulus and the slab), the moment of inertia can be written like
\[I=\alpha MR^2,\]
where \(\alpha=1/2\) for a cylinder (or disk), \(\alpha=1\) for a hoop, etc.
Just like with linear momentum, we have a conservation principle associated with angular momentum:
The total angular moment of a closed system is conserved:
\[\sum_j \vec{L}_j=constant.\leftrightarrow \Delta \vec{L}=0\]
In addition, we have all the conditions around using this law that we had for conservation of linear momentum; namely, that the system must be isolated.
Adding Moments of Inertia
Just like the case of linear momentum, the total angular momentum of a system can be found by simply adding up the angular momenta of the individual parts of a system. For example, if object 1 is a spinning hoop (of mass \(M\) and radius \(R\), spinning at \(\omega_1\)), and object 2 is a spinning cylinder (of mass \(m\) and radius \(r\), spinning at \(\omega_2\)), then looking at the figure above we can write the total angular momentum of that system as
\[L_{tot}=L_1+L_2=MR^2\omega_1 + \frac{1}{2}mr^2\omega_2.\]
Here, we are assuming the two objects are not moving together at all. But, it often happens that we want to know the angular momentum of a single object that is made up of shapes found in our figure. For example, see figure 6.3.3 in the examples section at the end of this chapter, which is two disks rotating together. In that case the two disks have the same radius \(R\), but one has three times the mass of the other (\(M\) and \(3M\)). If those two disks are rotating at the same rate, their angular momentum would be
\[L_{tot}=L_1+L_2=\frac{1}{2}MR^2\omega + \frac{1}{2}3MR^2\omega=\frac{1}{2}(M+3M)R^2\omega.\]
Notice this is the same result we would have gotten if we had simply added their moments of inertia together first:
\[I_{tot}=I_1+I_2=\frac{1}{2}MR^2 + \frac{1}{2}3MR^2 = \frac{1}{2}(M+3M)R^2 \rightarrow L_{tot}=I_{tot}\omega=\frac{1}{2}(M+3M)R^2\omega.\]
The lesson here is when adding moments of inertia, do not add their masses or radii together alone - add their moments of inertia .
For another concrete example, consider finding the angular momentum of a rod with a mass on the edge (shown below).
The total moment of inertia of this object is tricky, because the objects are different shapes. The rod has a moment of inertia of \(I_r=\frac{1}{3}MR^2\), while the point mass 2 had \(I_p=mR^2\). It's temping to just add the masses together, \(m+M\), but what fraction do you use out front, \(\frac{1}{3}\) or \(1\)? The answer is that you must add the moments of inertia themselves:
\[I_{tot}=I_r+I_p=\frac{1}{3}MR^2+mR^2=(\frac{1}{3}M+m)R^2.\]
Angular Speed vs Linear Speed
When objects rotate at a particular angular speed (in say, revolutions per second), the entire object moves at the same angular speed. This is because these objects are assumed to be rigid, so when one point on the objects goes around once, so does every other point. However, that doesn't mean that each of these points moves at the same linear speed (in say, meters per second). In fact, each point on the object moves at a different linear speed, depending on how far away it is from the center of rotation.
It's relatively easy to determine how these two quantities are related to each other, and this will turn out to be a very important formula. First, let's think about how fast a point a distance \(r\) from the center of an rotating object moves. If it takes a time period \(T\) for the object to rotate, such a point moves with speed
\[v=\frac{\text{distance traveled}}{\text{time interval}}=\frac{2\pi r}{T}.\]
Now, let's calculate the angular speed of this point (keeping in mind this is actually the angular speed of the entire object!). Over one rotation, it's angular speed will be
\[\omega=\frac{\text{angular distance traveled}}{\text{time interval}}=\frac{2\pi}{T}.\]
The \(2\pi\) here is just the number of radians the point travels for each rotation. These two formula are valid, but not that interesting because we don't know what the particular time period is here - so let's use the two of them to eliminate the time interval \(T\). Solving the second gives \(T=2\pi / \omega\), so let's plug that into the first:
\[v=\frac{2\pi r}{2\pi / \omega}=\frac{2\pi r \omega}{2\pi}\rightarrow v=r\omega\label{eq:AngLinSpeed}.\]
This very simple formula will be very helpful later; for now, it can give us some insight into how these point move. For example, at a particular angular speed \(\omega\), objects closer to the axis of rotation (smaller \(r\)) will move slower (have smaller \(v\)), while objects farther from the axis of rotation (larger \(r\)) will move faster (have larger \(v\)). This seems counterintuitive, but can be understood by seeing that objects far from the axis of rotation have further to travel then objects closer to the center, and have to do it over the same period of time.
1 In your calculus class you will learn how to calculate this for a wide variety of shapes.
2 The moment of inertia of a point mass is not found in the table above, but it's easy to see the answer by looking at equation \ref{eq:MomInert}; with only one point in the sum it becomes \(mr^2\). This can also be seen by thinking about what a point mass actually looks like when it's rotating - a hoop, which is in the table above.


2.13: Tramp Art Stand
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Tramp Art Stand
Norwegian-American Martin Cliff, c.1910 Wood (used cigar boxes) Gift of Lila Martin MHAHS 1980.001.0006 Photograph by Emily Pfotenhauer |
With ingenuity and skill, even cast-off materials like cigar boxes were transformed into unique and artistic household items. This skillfully executed stand in the “Crown of Thorns” pattern contains hundreds of hand-carved wood pieces held together without the use of glue or nails. A popular vernacular art form, this style is dubbed Tramp Art because of the romantic association with homeless workmen who might trade this work for food. Martin Cliff, the maker of this piece (and also the Hardanger fiddle in this exhibition), was known as an “artist farmer.” He drew his inspiration from both his Norwegian heritage and the popular arts and crafts of the period.
In spite of its name, tramp art was not only made by tramps and other itinerants, but was a popular craft taken up by both hobbyists and professional artisans. Tramp art is the name given to a type of woodworking popular in the United States between about 1865 and 1940, characterized by simple techniques such as chip-carving and whittling and the use of small bits of wood assembled into or applied to larger forms. Very common for small or large pieces like furniture, it was more commonly produced by men.This stand could be use for plants or other purposes in the household.
This stand is constructed from ¼” wide strips of unfinished wood reused from old cigar boxes, whittled to points and layered in a lattice formation. Five long vertical strips (willow saplings) protrude from the four-sided pyramidal base to support the top, which is a shallow basket shape lined with cardboard. This lattice of pointed bits of wood is a style of tramp art known as “Crown of Thorns.” The use of discarded materials was very common with the make-do practice and today can be interpreted as a form of recycling, concept that did not exist by that period.
According to the records of the Mt. Horeb Area Historical Society, this unique design was made by Martin Cliff, descended in the Cliff family of Mt. Horeb. He did not have had a nomadic life, something common among many tramp artists, but he moved from time to time. He was born in March 3, in 1876, son of Siri and Arn Klevgaard, pioneers of the Township of Blue Mounds where he engaged in the carpenter’s trade. In 1904 he got married to Miss Klara Kompelien and set down to a farm near Blue Mounds. In 1911 they bought a new land, establishing in a farm near Sand Rock where they lived until 1936. After that, they moved to Mount Horeb where he worked as treasurer of Lukken school and secretary and treasurer for the Sand Rock Cheese Factory.
He also joined the Blue Mounds congregation where he worked serving the community and helping to keep his ethnic roots and traditions, like Norwegian folk music, alive.
Cliff also is the author of the Hardanger Fiddle in this exhibit, a fine piece very skillfully hand made with techniques that are completely different from the tramp art carving style, with even higher standards of craftsmanship. Martin Cliff’s Hardanger fiddle is unique to his craft.
References
Amy Ortiz-Holmes, Tramp Art: Cultural Expression, Visual Splendor, exhibition catalog,
Robert T. Wright Community Gallery of Art, College of Lake County, Illinois (2004), available online (accessed December 22, 2008): http://gallery.clcillinois.edu/pdf/Trampart2004.pdf
“Tramp art bureau” Virginia Historical Society (accessed October 8, 2010); www.vahistorical.org/trampbureau.htm
DAVIS, Alexander, Martin Cliff’s Hardanger Fiddle: A Epitomic Norwegian Cultural Icon , 2016
HOLMES, Ortiz Amy,2010, Something to keep my hands occupied: Tramp Art in Context, 1860-1940


2.1: Prokaryotic Diversity
Scientists have studied prokaryotes for centuries, but it wasn’t until 1966 that scientist Thomas Brock (1926–) discovered that certain bacteria can live in boiling water. This led many to wonder whether prokaryotes may also live in other extreme environments, such as at the bottom of the ocean, at high altitudes, or inside volcanoes, or even on other planets.
Prokaryotes have an important role in changing, shaping, and sustaining the entire biosphere. They can produce proteins and other substances used by molecular biologists in basic research and in medicine and industry. For example, the bacterium Shewanella lives in the deep sea, where oxygen is scarce. It grows long appendages, which have special sensors used to seek the limited oxygen in its environment. It can also digest toxic waste and generate electricity. Other species of prokaryotes can produce more oxygen than the entire Amazon rainforest, while still others supply plants, animals, and humans with usable forms of nitrogen; and inhabit our body, protecting us from harmful microorganisms and producing some vitally important substances. This chapter will examine the diversity, structure, and function of prokaryotes.
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- 2.1.1: Prokaryote Habitats, Relationships, and Microbiomes
- Prokaryotes are unicellular microorganisms whose cells have no nucleus. Prokaryotes can be found everywhere on our planet, even in the most extreme environments. Prokaryotes are very flexible metabolically, so they are able to adjust their feeding to the available natural resources. Prokaryotes live in communities that interact among themselves and with large organisms that they use as hosts (including humans).
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- 2.1.2: Proteobacteria
- Proteobacteria is a phylum of gram-negative bacteria and are classified into the classes alpha-, beta-, gamma-, delta- and epsilonproteobacteria, each class having separate orders, families, genera, and species. Alphaproteobacteria are oligotrophs. The taxa chlamydias and rickettsias are obligate intracellular pathogens, feeding on cells of host organisms; they are metabolically inactive outside of the host cell. Some Alphaproteobacteria can convert atmospheric nitrogen to nitrites.
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- 2.1.3: Nonproteobacteria Gram-negative Bacteria and Phototrophic Bacteria
- Gram-negative nonproteobacteria include the taxa spirochetes; the Cytophaga, Fusobacterium, Bacteroides group; Planctomycetes; and many representatives of phototrophic bacteria. Spirochetes are motile, spiral bacteria with a long, narrow body; they are difficult or impossible to culture. Several genera of spirochetes contain human pathogens that cause such diseases as syphilis and Lyme disease. Cytophaga, Fusobacterium, and Bacteroides are classified together as a phylum called the CFB group.
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- 2.1.4: Gram-positive Bacteria
- Gram-positive bacteria are a very large and diverse group of microorganisms. Understanding their taxonomy and knowing their unique features is important for diagnostics and treatment of infectious diseases. Gram-positive bacteria are classified into high G+C gram-positive and low G+C gram-positive bacteria, based on the prevalence of guanine and cytosine nucleotides in their genome.
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- 2.1.5: Deeply Branching Bacteria
- Deeply branching bacteria are phylogenetically the most ancient forms of life, being the closest to the last universal common ancestor. Deeply branching bacteria include many species that thrive in extreme environments that are thought to resemble conditions on earth billions of years ago. Deeply branching bacteria are important for our understanding of evolution; some of them are used in industry
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- 2.1.6: Archaea
- Archaea are unicellular, prokaryotic microorganisms that differ from bacteria in their genetics, biochemistry, and ecology. Some archaea are extremophiles, living in environments with extremely high or low temperatures, or extreme salinity. Only archaea are known to produce methane. Methane-producing archaea are called methanogens. Halophilic archaea prefer a concentration of salt close to saturation and perform photosynthesis using bacteriorhodopsin.
Thumbnail: A cladogram linking all major groups of living organisms to the LUCA (the black trunk at the bottom), based on ribosomal RNA sequence data.