Chapter 42 Guided Reading Answers

46. Calculate the partial pressure of oxygen. Show work!

Atmospheric pressure at sea level is 760 mm Hg. Because the atmosphere is 21% oxygen by volume, the partial pressure of oxygen is 0.21 × 760, or about 160 mm Hg.

10. What is the function of the atria? What is the function of the ventricles?

Atria are the chambers that receive blood entering the heart. Ventricles are the chambers responsible for pumping blood out of the heart.

37. Write out the equation that shows the formation of carbonic acid and the bicarbonate ion. How does this explain blood pH change as CO2 increases?

CO2 + H2O � H2CO3 � HCO3- + H+ Blood pH decreases when carbon dioxide concentration increases because carbonic acid forms and the hydrogen ion concentration increases as a result.

9. In a circulatory system, exchange occurs in two general places. Blood goes to a respiratory surface (lungs, gills, skin) or to the organs and tissues of the body (systemic circulation). At which type of blood vessels does exchange actually occur?

Capillaries

22. How do structure and function correlate in the capillaries?

Capillaries have thin walls to facilitate the exchange of substances between the blood in capillaries and the interstitial fluid.

12. Why is a four-chambered heart a key adaptation required for endothermy?

Endotherms use about 10 times as much energy as equal-sized ectotherms. Their circulatory systems therefore need to deliver about 10 times as much fuel and O2 to their tissues (and remove 10 times as much CO2 and other wastes). This large traffic of substances is made possible by separate and independently powered systemic and pulmonary circuits and by large hearts that pump the necessary volume of blood.

36. Describe three ways in which the structure of an erythrocyte enhances its function, which is to transport oxygen. This is an excellent example of how structure and function are interrelated.

Erythrocytes are small disks that are biconcave. This shape increases surface area, enhancing the rate of diffusion of O2 across their plasma membranes. Additionally, mammalian erythrocytes lack nuclei, leaving more space in these tiny cells for hemoglobin, the iron-containing protein that transports O2 . Erythrocytes also lack mitochondria and generate their ATP exclusively by anaerobic metabolism, making them more efficient.

39. What is erythropoietin (EPO)? What will stimulate its production?

Erythropoietin is a hormone that stimulates erythrocyte production. EPO is produced by the kidney s if tissues do not receive enough O2

7. Compare and contrast open and closed circulatory systems. Be certain focus on advantages of each.

In an open circulatory system, the blood moves between vessels and open sinuses. In a closed circulatory system, the blood is always within vessels. In an open circulatory system, the circulatory fluid bathes the organs directly. Contraction of one or more hearts pumps the hemolymph through the circulatory vessels into interconnected sinuses, spaces surrounding the organs. In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid.

30. Why does the presence of blood proteins tend to pull fluid back into the capillaries?

Many blood proteins are too large to pass readily through the endothelium, and they remain in the capillaries. These dissolved proteins are responsible for much of the blood's osmotic pressure. The difference in osmotic pressure between blood and the interstitial fluid opposes fluid movement out of the capillaries.

35. Where are the two breathing control centers located in the brain?

Medulla oblongata and pons

Cardiac output

The volume of blood each ventricle pumps per minute. The two factors that determine cardiac output are heart rate and stroke volume.

15. The following figure is vital to your overall understanding of mammalian circulation. Label the following

aorta, pulmonary artery, left lung, right lung, left atrium, left ventricle, aorta, inferior vena cava, superior vena cava, systemic circulation, and pulmonary circulation. Then reread this section in your book, and trace what is happening from Point 1 to Point 11. See page 920 in your text for the labeled figure.

The cardiac cycle - describe in terms of valves opening and closing

One complete sequence of pumping and filling.

25. What is meant by the term countercurrent exchange and why is it an advantage to animals? Without countercurrent exchange, what would be the maximum absorption percentage if O2 simply diffused from water to blood in the gills?

Only 50% of the oxygen could be absorbed without countercurrent exchange because, at this point, the gas concentration would be at equilibrium, and there would be no further net diffusion of oxygen.

24. What is the relationship between blood pressure, velocity and total cross-sectional area? This is a key concept - why would blood flow slow in a capillary just when you think it will speed up because the capillary is narrow?

See figure 42.10

35. Review figure 42.16. What is blood plasma? What are the cellular elements of blood? What is the relative percentage of each? Then, name each type of cell and give its function. Finally, list the four major constituents of plasma. What are their functions?

See page 928 in your text for the labeled figure and answers.

24. Gills serve as the respiratory organ in many aquatic animals. Figure 42.22 in your text uses arrows to show the flow of water. The most significant part of this figure is the portion that shows the countercurrent flow of water and blood. Study carefully the paragraph that describes countercurrent exchange, and then label this figure to explain how oxygen is taken up over the length of a capillary.

See page 935 of your text for the labeled figure and explanation.

28. Let's look at the anatomy of a mammalian respiratory system. In figure 42.24, label each of the following structures and explain its function or describe it- pharynx, larynx, trachea, left and right lungs, left and right bronchi, bronchioles, and alveoli.

See page 937 in your text for the labeled figure and descriptions.

Venule

Small vessel that flows into larger veins Thin wall; small diameter

Arteriole

Small vessel that leads from the larger arteries; when smooth muscle of wall contracts, blood pressure is affected Smaller in size than arterie; thick muscular wall

Systole

The contraction phase of the cycle

2. Gaining O2 and nutrients while shedding CO2 and other waste products occurs with every cell in the body. However, diffusion is rapid only over small distances. Describe the two general solutions to this problem.

The first solution is a body size and shape that keeps many or all cells in direct contact with the environment. Each cell can thus exchange materials directly with the surrounding medium. Second is a circulatory system that moves fluid between each cell's immediate surroundings and the tissues where exchange with the environment occurs.

31. The capillaries "leak" about 4 liters of fluid each day. How is this returned to the blood?

The lost fluid and proteins return to the blood via the lymphatic system, which includes a network of tiny vessels intermingled among capillaries of the cardiovascular system.

47. A gas always diffuses from a region of _____ partial pressure to a region of ______ partial pressure.

higher, lower

25. As blood vessel diameter decreases, blood velocity will

increase.

Residual volume

the volume of air still remaining in the lungs after the most forcible expiration possible

Stroke volume

the volume of blood pumped from the left ventricle per beat

Heart attack

a sudden and sometimes fatal occurrence of coronary thrombosis, typically resulting in the death of part of a heart muscle

28. If the blood pressure is reported as 110/80, what is the diastolic pressure?

80

36. Study the "Control of Breathing in Humans," page 940. What is a bicarbonate ion? How is it formed?

A bicarbonate ion is a hydrogen and carbon compound formed when carbonic acid dissociates into H+ and HCO3-. Carbonic acid is formed when CO2 is released as a by-product of cellular respiration. Active tissues produce high levels of CO2. This is why exercise causes blood pH to decrease.

5. Larger animals must have a circulatory system to move fluid between cells and the outside environment. What are the three basic components of a circulatory system?

A circulatory system has three basic components: a circulatory fluid, a set of interconnecting vessels, and a muscular pump (the heart).

Stroke

A condition due to the lack of oxygen to the brain which may lead to reversible or irreversible paralysis. The damage to a group of nerve cells in the brain is often due to interrupted blood flow, caused by a blood clot or blood vessel bursting

27. How does a sphygmomanometer is used to measure blood pressure. Explain the three key "listening points" involved in determining blood pressure. See page 925 in your text for the labeled figure.

A sphygmomanometer, an inflatable cuff attached to a pressure gauge, measures blood pressure in an artery. The cuff is inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery. The cuff is allowed to deflate gradually. When the pressure exerted by the cuff falls just below that in the artery, blood pulses into the forearm, generating sounds that can be heard with the stethoscope. The pressure measured at this point is systolic pressure. The cuff is allowed to deflate further, just until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure.

29. Explain the exchange of fluid at the two ends of a capillary. Include these terms in your discussion-interstitial fluid, osmotic pressure, and blood pressure. See page 927 in your text for the labeled figure.

Blood pressure tends to drive fluid out of the capillaries, and it is higher at the arterial end. The osmotic pressure exerted by blood proteins (not shown in this figure) tends to pull fluid back in. The interstitial fluid will also exert osmotic pressure. For example, if the osmotic pressure of the blood is low, more fluid will accumulate in the surrounding tissues, leading to edema. This diagram shows a hypothetical capillary in which blood pressure exceeds osmotic pressure throughout the entire length of the capillary. In other capillaries, blood pressure may be lower than osmotic pressure along all or part of the capillary.

Artery

Carries blood away from the heart, Thick muscular wall

Vein

Carries blood toward the heart Thin wall; valves inside veins maintain a unidirectional flow of blood

Capillary

Connects arterioles and venules; because these vessels are only a single cell in thickness, all diffusion occurs here Smallest blood vessel; only a single cell thick; endothelium is simple squamous

43. What causes the development of a plaque in atherosclerosis?

Damage or infection can roughen the lining of the arteries and lead to inflammation. Leukocytes are attracted to the damaged lining and begin to take up lipids, including cholesterol. A fatty deposit, called a plaque, grows steadily, incorporating fibrous connective tissue and additional cholesterol. As the plaque grows, the walls of the artery become thick and stiff, and the obstruction of the artery increases.

1. What are the limits to diffusion as a means of transport for living organisms?

Diffusion is slow for longer distances.

4. Flatworms (phylum Platyhelminthes) such as planaria have a slightly different solution to this problem. What is it?

Flatworms' combination of a gastrovascular cavity and a flat body is well suited for exchange with the environment. A flat body optimizes diffusional exchange by increasing surface area and minimizing diffusion distances.

13. Use the four-chambered hearts of birds and mammals to explain the concept of convergent evolution.

Four-chambered hearts arose independently in the distinct ancestors of mammals and birds and thus reflect convergent evolution. The selective pressure for increased efficiency in circulation in these endotherms drove the evolution of four chambers independently in these lineages; thus, the four chambered heart did not only arise in a single lineage that led to birds and mammals.

18. What does the SA node do?

Heartbeat rhythm is maintained by electric impulses that are generated from modified cells found in the wall of the right atrium, called the sinoatrial (SA) node.

37. What is the role of hemoglobin? What mineral is required to make it?

Hemoglobin is the iron-containing protein that transports O2.

6. What is hemolymph?

Hemolymph is the circulatory fluid and interstitial fluid that bathes body cells in animals with an open circulatory system.

38. What has greater effect on the rate of respiration, low levels of O2 or high levels of CO2? Explain why.

High levels of CO2 are detected by the breathing control centers in the medulla oblongata. Sensors in major blood vessels detect a decrease in blood pH, and the medulla receives the signals from these sensors. Signals from the medulla to the rib muscles and diaphragm increase the rate and depth of breathing. Because high levels of CO2 lower the pH, this has a greater effect on the rate of respiration.

11. Contrast the vertebrate circulatory systems of fish, amphibians, non-avian reptiles and mammals/birds. Focus on heart chambers, blood flow, and level of oxygen in the blood as it flows through the heart and systemic circuits. See page 919 in your text for the labeled figure and explanation.

In bony fishes, rays, and sharks, the heart consists of two chambers- an atrium and a ventricle. Blood entering the heart at the atrium has passed through a system of blood capillaries throughout the body, where there has been a net diffusion of oxygen out of the blood for delivery to mitochondria and a net diffusion of carbon dioxide into the blood, also from cellular respiration. Contraction of the ventricle pumps blood toward the capillary bed of the gills, where there is a net diffusion of oxygen into the bloodstream and a net diffusion of carbon dioxide out of the gills into the surrounding water. The oxygen-rich blood then travels through another system of capillaries before it reaches the heart again. Amphibians, reptiles, and mammals have two circuits, an arrangement called double circulation. In amphibians, blood passes through a pulmocutaneous circuit where blood travels to capillaries in the skin and lungs, whereas in reptiles and mammals this circuit is called the pulmonary circuit because blood only passes through the lung capillaries. An interesting comparison of heart chamber evolution is seen in ectotherms, such as amphibians and reptiles, and endotherms like birds and mammals. Endotherms use about 10 times as much energy as equal-sized ectotherms; therefore, their circulatory systems need to deliver about 10 times as much oxygen and remove 10 times as much carbon dioxide. This more efficient traffic of substances in endotherms is enabled by the separate and independently powered systemic and pulmonary circuits and by large hearts that pump the required volume of blood.

3. In this part of the course, we have discussed how various animal groups solve the same problem. Cnidarians, which include the hydras and jellyfish, do not have a distinct circulatory system. How have they solved the problem of exchange?

In hydras, jellyfish, and other cnidarians, a central gastrovascular cavity functions in the distribution of substances throughout the body and in digestion. An opening at one end connects the cavity to the surrounding water.

32. Describe the process of inhalation and exhalation with regard to the contraction of the diaphragm - which is an active process and which is passive?

Mammals employ negative pressure breathing, which requires the contraction of the diaphragm, a sheet of muscle that forms the bottom of the thoracic cavity. The diaphragm contracts and expands the thoracic cavity downward and the negative pressure allows the lungs to expand and fill with air from the atmosphere.

32. What is lymph? Is it more like blood or more like interstitial fluid?

Lymph is the fluid lost by the capillaries; its composition is about the same as that of interstitial fluid.

34. Name three places you have lymph nodes. What are two functions of these nodes?

Lymph nodes can be found in your neck, armpit, and groin. Lymph nodes filter the lymph and contain white blood cells that attack viruses and bacteria and are therefore important in the body's defense.

What is the common name for the SA node?

Pacemaker

45. What is meant by the partial pressure of a gas?

Partial pressure is the pressure exerted by a gas in a mixture of gases.

33. We don't have a second heart to pump lymph. What keeps it moving along?

Rhythmic contractions of the vessel walls draw fluid into the small lymphatic vessels. In addition, skeletal muscle contractions play a role in moving lymph.

38. Where are blood stem cells found?

Stem cells are located in the red marrow of bones, particularly in the ribs, vertebrae, sternum, and pelvis.

Tidal volume

The amount of air which enters the lungs during normal inhalation at rest

26. Why does blood slow as it moves from arteries to arterioles to capillaries? Why is this important?

The reason is that the number of capillaries is enormous. Each artery conveys blood to so many capillaries that the total cross-sectional area is much greater in capillary beds than in the arteries or any other part of the circulatory system. The result is a dramatic decrease in velocity from the arteries to the capillaries.

Diastole

The relaxation phase of the cycle.

22. There are several requirements for a respiratory surface. The first is that it must be moist. The second is that it must have a large surface area and be thin. What four different organs satisfy these requirements?

The skin of some animals, such as earthworms; gills; tracheae; and lungs

20. The cells of the heart's pacemaker will respond to other inputs to regulate heart rate. List three additional inputs, and describe a specific example of each.

The sympathetic and parasympathetic nerves function like the accelerator and brake in a car- For example, when you stand up and start walking, the sympathetic division speeds up your pacemaker. When you rest, the parasympathetic division slows down your pacemaker. Hormones secreted into the blood also influence the pacemaker. For example, epinephrine, the "fight-or-flight" hormone, speeds up the pacemaker. A third type of input is body temperature. An increase of only 1 degree Celsius raises the heart rate by about 10 beats per minute.

26. What is the most common respiratory structure among terrestrial animals? What groups have this system?

The tracheal system is the most common; it can be found in insects.

23. What anatomical feature of the veins maintains a unidirectional flow of blood back toward the heart?

Valves inside the veins maintain unidirectional flow of blood despite the low blood pressure.

19. Electrical impulses from the SA node cause the atria to contract and are conducted to a relay station, the atrioventricular (AV) node. When an impulse is generated by the AV node, what contracts?

Ventricles

14. What is the advantage to double circulation?

Vigorous flow of blood because heart repressurizes blood after it passes through capillary beds. Allows for higher blood pressure in systemic circuit.

48. Gas exchange with water as the respiratory medium is much more demanding than exchange with the air. What are three reasons for this?

Water is a much more demanding medium for exchange with the air because of its lower O2 content, greater density, and greater viscosity.

Vital capacity

the greatest volume of air that can be expelled from the lungs after taking the deepest possible breath