Wednesday, December 19, 2012

Answers to Chapter 31 DYUC and ATC

Do You Understand Concept 31.1?
List the differences between innate and adaptive immunity.

Innate immunity is nonspecific. It may be present all the time or activated in response to an injury or invasion. Innate systems include the skin and toxic molecules, which provide a rapid first line of defense, and phagocytic cells that ingest foreign particles. Adaptive immunity is specific and distinguishes between substances as self or nonself. Found only in vertebrates, adaptive immunity is slow to develop and involves proteins such as antibodies and T cell receptors that can recognize and destroy foreign particles.

Rarely, a person is born with a genetic disease and has no lymphocytes. What would be the consequences of this situation for the immune system? Explain why such a person would have to be very careful about going outdoors.

Lymphocytes include both B cells and T cells and are involved in adaptive immunity. A person without them would not develop immunity over time to pathogens in the environment, and thus would be at risk for infections when going outdoors. The immune system would have to rely on less-specific innate responses, which might not be as effective.

Do You Understand Concept 31.2?

Outline the sequence of innate defenses encountered by a pathogenic bacterial cell if it is ingested in food. Similarly, outline the defenses encountered by a bacterial cell that lands in the nose.

A bacterial cell that is ingested in food will encounter mucus in the body cavities, which may trap it. In the stomach it will also be exposed to gastric juices containing hydrochloric acid and proteases. A bacterial cell that lands in the nose will encounter mucus, lysozymes that can cleave bacterial cell walls, and defensins. Defensins can insert themselves into the bacterial membrane and increase its permeability to water and all solutes.

Antihistamines are used to treat the symptom of sneezing due to inflammation caused by irritants in the airways. How do you think antihistamines might work?

Antihistamines block the action of histamine, a substance that increases permeability of blood vessels to white blood cells and other molecules and allows these to move into tissues that are challenged. If these cells and molecules are blocked they will not be able to initiate the responses of inflammation and sneezing.

A massive inflammation due to a food allergy can be treated with an injection of epinephrine. Refer to the description of epinephrine’s effects in Concept 30.2. How do you think this hormone relieves the inflammation symptoms?

Epinephrine is involved in the fight-or-flight response. Some of its effects include increased heart rate and blood flow, and increases in fuel in the blood. These responses can combat the inflammation caused by a food allergy. Epinephrine also constricts blood vessels. This results in less flow in the capillaries and a reduction of inflammation.

Do You Understand Concept 31.3?

Make a table describing the four key features of the adaptive immune system.


Focuses responses on pathogens that are actually present
Responds to novel pathogens
Distinguishes self from non-self
Doesn't destroy self-cells
Has immunological memory
Responds effectively to the same pathogen in later exposures

In 2009, the H1N1 strain of influenza was a worldwide epidemic. Notably, very old people, who had been alive during the 1918 flu outbreak, had low rates of H1N1 infection. Explain this in terms of immunological memory.

The immune system remembers a pathogen after an earlier exposure through the adaptive immune response. Older people who had been exposed to that pathogen in the first epidemic and survived would have mounted a stronger and more rapid immune response to the subsequent exposure.

Insulin-dependent diabetes (Type 1) results from a destruction of the cells in the pancreas that make the hormone insulin (see Concept 39.4). One hypothesis for this disease is that it is caused by an autoimmune reaction. Explain how this might happen and how you would investigate your hypothesis.

During development, B cells that fail to recognize self-cells usually undergo apoptosis, called clonal deletion. If clonal deletion doesn't occur, it can lead to an autoimmune disease, in this case destruction of the pancreatic cells that make insulin. One way to test this would be using molecular mimicry to see if exposure to an antigen very similar to the suspected self antigen, the pancreatic cells, would lead to an immune response.

Do You Understand Concept 31.4?

Sketch an IgG antibody, identifying the variable and constant regions, light and heavy chains, and antigen-binding sites.

Refer to textbook Figure 31.7A.
The bacterium that causes diphtheria (refer to textbook Figure 31.4) synthesizes a toxic protein. You have probably not been exposed to this bacterium or its toxin. At the present time, are you making B cells and antibodies that bind specifically to diphtheria toxin? Explain your answer.

There are millions of naïve B cells in circulation, each one specific to a particular antigen, even if not previously exposed. A small number of the B cells make an antibody on their cell surface that binds to the diphtheria toxin. Once a B cell is activated by antigen-binding (exposure) only then will it begin antibody production.

When an antigenic protein such as diphtheria toxin (see above) enters the bloodstream, numerous clones of B cells are activated. Explain.

The original antigen binding stimulates the B cell to divide and create a clone of cells. These are genetically identical to the B cell and will all produce or secrete antibodies with the same specificity as the B cell and will bind to the free antigen in the bloodstream. Because an antigen, such as a protein, usually has several groups of atoms that themselves are antigens (antigenic determinants), there will be numerous B cell clones activated.

Do You Understand Concept 31.5?

Compare the T cell receptor and B cell receptor in terms of structure, diversity, and function.

T cell and B cell receptors are similar in structure, each with a variable and a constant region, though the T cell receptors are smaller and are glycoproteins instead of immunoglobulins. The two types are equally diverse and specific to a particular antigen. B cells function as part of the humoral response to produce antibodies. T cells are of two types: TH and TC. TH cells can bind to an antigen and stimulate other immune cells, including B and TC cells, to divide. TC cells bind to and destroy cells that bear the antigen on their surface.

What are the similarities and differences in function between class I and II MHC proteins?

Class I MHC proteins are present on the surfaces of nucleated mammalian cells. They present fragments of antigens to TC cells. Class II MHC proteins are on the surfaces of macrophages, B cells, and dendritic cells. They ingest antigens and bind fragments for presentation to TH cells.

What are the roles of TH cells in cellular and humoral immunity?

TH cells with specific receptors bind to antigen-presenting cells and then release cytokines, which stimulate B cells to divide in the humoral immune response and TC cells to divide in the cellular immune response.

Since MHC proteins are highly variable and almost always differ between unrelated people, an organ transplant between such people will generally provoke a cellular immune response, and the organ will be rejected. Patients receiving organ transplants are treated with cyclosporin, a drug that inhibits T cell development. How do you think cyclosporin prevents rejection? What side effects might you expect in treated people?

Blocking the production of T cells would interfere with the immune responses at several stages immediately following recognition. Without T cell activity, the transplanted organ would not be treated as an antigen or be subject to rejection or attack. However, the patient would also not be able to mount an immune response to real pathogens and so would be susceptible to disease.

Apply the Concept for Chapter 31

Concept 31.1 The Adaptive Immune Response Is Specific, p. 629



2. An immune response is mounted in the mother to the Rh+ fetal cells. But the fetus has been born and so is not affected. After the mother’s response, immune cells specific for Rh+ remain as memory cells. The next time a fetus carries the Rh+, there is a massive response by the mother, only this time the fetus has not yet been born and hemolytic disease can result.

3. Antibodies against Rh+, given to the mother, “tie up” antigens that may pass to the mother, and shield the mother’s immune system, with its memory cells, from the antigen so an immune response is not mounted.


Answers to Chapter 38 DYUC and ATC

Do You Understand Concept 38.2?

Draw sketches of circulatory systems showing a single and a double circuit design. Label all of the parts.

Refer to textbook art on pages 748 and 750.

Why can a mammalian circulatory system have different pressures in the pulmonary and the systemic circuits, and why do you think this is important?

Although the pulmonary and the systemic circuit are in series, they are separated by the heart, which provides a separate pump for each. The right ventricle pumps blood through the pulmonary circuit, and the left ventricle pumps blood through the systemic circuit. This anatomy enables the heart to create a higher pressure in the aorta than in the pulmonary artery, which is important because the total length of blood vessels, and hence the total resistance, is greater in the systemic circuit.

Do You Understand Concept 38.3?

A red blood cell is flowing through the superior vena cava. List all of the heart chambers, valves, vessels, and organs it will pass through before it leaves the heart in the aorta.

The blood cell will enter the right atrium, flow through an atrioventricular valve into the right ventricle and be pumped through the pulmonary valve into the pulmonary artery, flowing to the lung. After oxygenation, the blood cell will return to the heart via the pulmonary vein and enter the left atrium. It will pass through another atrioventricular valve into the left ventricle and be pumped into the aorta, passing through the aortic valve.

Why do the atria contract before the ventricles? What would happen if they contracted at the same time?

The atria contract when an action potential spreads through gap junctions. They are not coupled through these junctions to the ventricles. Instead, the atrioventricular node generates another action potential when its cells are depolarized and conducts it via the bundle of His to the ventricles. If the chambers contracted at the same time it would be possible for blood to flow in the wrong direction.

Do You Understand Concept 38.4?

List the major components of blood (liquid and cellular) and state their functions.

Plasma is the liquid, extracellular matrix of blood and contains water and solutes, such as nutrients, ions, waste products, hormones, gases, and clotting proteins. Cellular components of blood include: erythrocytes, or red blood cells, which carry respiratory gases; leukocytes, or white blood cells, of the immune system; and platelets, which are involved in blood clotting.

Some competitive cyclists have admitted using erythropoietin as an illegal performance-enhancing drug. How can erythropoietin enhance performance?

Erythropoietin enhances the blood's capacity for carrying oxygen by extending the life of existing red blood cells as well as by stimulating development of new ones in the bone marrow.

Do You Understand Concept 38.5?

In which vessels of the circulatory system does the blood move most rapidly? In which does it move most slowly? Why?

Blood moves most rapidly through the arteries due to higher pressure after ventricular contraction and the elastin and smooth muscle fibers that can stretch and withstand this pressure. Blood moves most slowly through capillaries due to their tiny size and the huge quantity of capillaries, resulting in both lower blood pressure and allow for exchange of material with the interstitial fluid.

Compare and contrast the structure of the walls of arteries, capillaries, and veins. How does the structure of the wall relate to each vessel’s function?

Arterial walls contain elastin fibers and smooth muscle fibers that accommodate the high pressure and also propel the blood forward through elastic recoil. Capillaries are very permeable to allow for exchange with the interstitial fluid. Veins have no elastin layer due to the low pressure and rate of flow through them, but may have one-way valves to prevent backflow of blood.

Certain parasitic worms can block lymph vessels. Suppose the lymph vessels draining a leg were completely blocked by a parasite infestation. What do you think would happen to the leg? Explain your answer.

Lymph capillaries take up excess fluid in the capillary beds and then pass the fluid into larger lymphatic vessels that return it to the heart.. If this system were blocked, the lymph would remain in the capillary beds, and the leg would swell as the fluid accumulated.

Occasionally soldiers or guards standing at attention and not moving will faint. Why do you think that occurs? How could they avoid that embarrassing situation?

Fainting can be due to not enough oxygen circulating in the blood. Soldiers who don't move might increase blood flow returning to the heart by flexing skeletal muscles in their legs to compress the veins. They also might exhale completely and inhale deeply to take in more highly oxygenated air.

Do You Understand Concept 38.6?

What three factors determine the mean arterial pressure?

Mean arterial pressure is equal to the product of the heart rate, the stroke volume, and the total peripheral resistance.

If blood pressure gets too high, will angiotensin levels go up or down? What about ADH levels? Explain your answer.

If blood pressure becomes elevated, angiotensin levels will fall because its function is to raise MAP and blood flow to some organs by constricting arterioles throughout the body. ADH levels would also fall so that kidneys would lower their reabsorption of water, decreasing blood volume and thus pressure.

Apply the Concept for Chapter 38

Concept 38.1 A Beating Heart Propels the Blood, p. 752
1. Systole is the duration of contraction of the ventricles, and it would extend from point B to point D.

2. Diastole is when the ventricles are relaxing and filling, and it would extend from point D through B.

3. The blood pumped each cycle is the difference between the end systolic volume and the end diastolic volume—or 70 ml.

4. The first heart sound occurs when the atrioventricular valves shut at the beginning of systole—point B. The second heart sound is when the aortic valve shuts at the end of systole, at point D.

5. The aortic valve would open at point C, when the pressure in the ventricle exceeds the back pressure in the aorta.

Concept 38.2 Blood Circulates in Arteries, Capillaries, and Veins, p. 758

1. There is no sound at the high cuff pressure because the arteries into the arm are totally occluded by the pressure. As the cuff pressure falls, it will eventually fall below the maximum arterial pressure, and at that time the arterial pressure will squeeze some blood into the artery. The sound is due to the starting and stopping of that flow.

2. When the cuff pressure falls below the lowest arterial pressure, the blood will flow continuously through the artery and no periodic sound will be heard.

3. The cuff pressure at which the tapping sounds are first heard (120 mm Hg) is closest to the systolic pressure and the cuff pressure at which the periodic sounds cease (60 mm Hg) is closest to the diastolic pressure.

Answers to Chapter 29 DYUC

Do You Understand Concept 29.2?

A regulatory system you encounter often is the thermostatically controlled heat and air conditioning system that keeps a building’s temperature constant in changing external conditions. Describe such a system in terms of the regulating system, the controlled system, the set points, feedback information, and effector commands.

The temperature of a building is controlled by the actions of a heater and an air conditioner, which constitute the controlled system. The actions of the heater and air conditioner are turned on or off by effector commands from a regulatory system, or thermostat. The setting on the thermostat is the set point, and the thermostat is sensitive to the surrounding air temperature, which provides feedback information. When the set point is different from the feedback information, error signals are generated that are transduced into effector commands controlling the heater and air conditioner.

Do You Understand Concept 29.3?

What are some cellular processes or events that would lead to the survival of cells being limited to an approximately 40oC range of temperatures?

Above this temperature proteins begin to denature and lose their function. Below this range ice crystals can form in cells, leading to cell death.

Explain how a physiological process can be disrupted by changes in its temperature when its component biochemical reactions have different Q10’s.

A physiological process involves many biochemical reactions that are interlinked, with the products of one being the reactants of another. If the rates of these reactions change differentially with a change in temperature, the integration of the interlinked reactions will be disturbed.

Why does MR of a mammal increase as Tadecreases, whereas MR of a reptile decreases as Tadecreases, in the range of Ta’s below 25oC in the example in the figure?

In Ta’s below 25oC, a mammal’s MR will rise in response to its need to increase metabolic heat production to maintain its internal temperature. The reptile cannot increase its MR to compensate for increasing heat loss as Ta falls, therefore its tissues will cool and its MR will fall because of the Q10’s of its biochemical and physiological processes.

Do You Understand Concept 29.4?

Compare the two foxes in Figure 29.9 and explain how the differences you observe influence each element of the heat balance equation for these two species.

The desert fox has long limbs, short fur, large ears, and a thin, long body to allow heat to escape its body, whereas the arctic fox has long fur, small ears, short limbs, and a compact body. In the arctic fox, the heavier insulation (fur) and smaller surface area (body shape, limb length, ear size) decrease heat loss from radiation, convection, and conduction.

Many newborn mammals have brown fat even if brown fat is not seen in adults of that species. Why is brown fat adaptive for newborns?

Brown fat allows for non-shivering thermogenesis, an efficient and stable source of metabolic heat that does not produce ATP and therefore does not limit the metabolic rate due to the buildup of ATP. Its presence enhances a newborn's chances of surviving cold exposure.

For both hot and cold stress, explain how behavioral adaptations can alter heat exchange through all of the components of the heat budget equation.

When heat stressed, behavior can be used by an animal to find a cooler environment that will decrease absorption of thermal energy and facilitate convective and conductive heat loss. Seeking and ingesting water can support evaporative heat loss; immersion in water can dissipate heat through conductive and convective heat loss to the water. Getting into or creating a convective air stream can increase heat loss by convection. In the cold, behavior can be used to increase insulation (piloerection, huddling, decreasing surface area). Basking can increase radiation absorbed. Activity can increase metabolic heat production.

If sweating and panting are such costly avenues of cooling (due to water loss and metabolic energy expenditure), why haven’t evolutionary mechanisms eliminated them as regulatory mechanisms?

Evaporative heat loss is extremely effective as an emergency means of lowering body temperature because of the very high amount of heat that is required to take water from the liquid to the gaseous phase (heat of vaporization).

Do You Understand Concept 29.5?

Draw a diagram of the mammalian thermostat that includes the effectors, the set points, and the negative feedback.

Sorry, diagram won't translate

Explain at least four sources of feedforward information for the mammalian thermostat that can either keep body temperature constant in spite of changes in the environment, or can cause body temperature to change.

Skin temperature is feedforward information that can prevent rises or falls in body temperature as the animal moves between different ambient temperatures.

The onset of activity is feedforward information that can increase heat loss (sweating or panting) in advance of a rise in body temperature.

Circadian rhythms and the onset of sleep is feedforward information that changes the set points of the thermoregulatory system to achieve increases or decreases in body temperature.