Cardiovascular Lecture 3 Solutions - PHGY 210 2024

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PHGY 210 2024 USCA Questions Cardiovascular Physiology – Lecture 3 1. Which statement about the various classes of blood vessels is FALSE ? a. The average speed of blood flow is greater in the arteries than in the arterioles. b. The total combined cross-sectional area of all veins is smaller than the total combined cross-sectional area of all venules. c. The diameter of the average capillary is smaller than the diameter of the average venule. d. The length of the average capillary is greater than the length of the average vein. e. The total number of capillaries is greater than the total number of venules. Solution a) Option (a) is INCORRECT. The statement is true, and not false. b) Option (b) is INCORRECT. The statement is true, and not false. c) Option (c) is INCORRECT. The statement is true, and not false. d) Option (d) is CORRECT. The length of the average capillary is LESS than the length of the average vein. Therefore, statement is false. e) Option (e) is INCORRECT. The statement is true, and not false.
PHGY 210 2024 USCA Questions 2. Which statement about the various classes of blood vessels is TRUE ? a. All arteries and arterioles make up the resistance blood vessels. b. Venules, veins, and vena cava make up the capacitance blood vessels. c. Arterioles and venules make up the exchange blood vessels. d. The aorta and large arteries make up the capacitance blood vessels. e. Arterioles and capillaries make up the resistance blood vessels. Solution a) Option (a) is INCORRECT. Not all arteries make up resistance blood vessels. Larger arteries are classified as distribution vessels. Small arteries and arterioles make up the resistance vessels. b) Option (b) is CORRECT. Venules, veins, and vena cava are vessels with greater compliance. They can accommodate greater blood volumes and are therefore classified as capacitance blood vessels. c) Option (c) is INCORRECT. Capillaries are the type of blood vessel that are responsible for gaseous exchange. d) Option (d) is INCORRECT. The aorta and large arteries are classified as distribution vessels. The large amounts of smooth muscle around these vessels make them less compliant and less accommodating of larger blood volumes. e) Option (e) is INCORRECT. Despite their small diameter, capillaries do not make up resistance blood vessels. They are more involved in gaseous exchange. Small arteries and arterioles make up resistance blood vessels and are the means by which we can quickly regulate blood pressure through autonomic control of smooth muscle contraction/relaxation to induce vasoconstriction/vasodilation.
PHGY 210 2024 USCA Questions 3. Which of the following is NOT involved in the control of resistance in blood vessels? a. Local metabolites b. Hormones c. Plasma proteins d. Neurotransmitters e. Endothelial cells Solution a) Option (a) is INCORRECT. Local metabolites, such as adenosine and hydrogen ions (you don’t need to memorize these), play a crucial role in regulating vascular resistance. When tissues are metabolically active, they produce these substances, which cause vasodilation, reducing resistance in blood vessels and increasing blood flow to meet the metabolic demands of the tissues. b) Option (b) is INCORRECT. Hormones like epinephrine, norepinephrine, and angiotensin II can influence vascular resistance by either constricting or dilating blood vessels. For example, epi and norepi released during the fight-or-flight response cause vasoconstriction, increasing resistance, and raising blood pressure. c) Option (c) is CORRECT. Plasma proteins are not directly involved in the control of resistance in blood vessels. While proteins in the plasma play essential roles in maintaining osmotic pressure and transporting substances, they do not regulate vascular resistance like other factors such as local metabolites, hormones, or neurotransmitters. d) Option (d) is INCORRECT. Neurotransmitters released by sympathetic nerve fibers such as norepinephrine, can cause vasoconstriction in response to neural signals. The vasoconstriction increases vascular resistance and regulates blood flow to different organs and tissues based on physiological needs. e) Option (e) is INCORRECT. Endothelial cells lining the inner walls of blood vessels produce various substances, including nitric
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PHGY 210 2024 USCA Questions oxide (NO), which regulates vascular tone and resistance. For example, NO released by endothelial cells causes vasodilation, reducing resistance, and increasing blood flow. 4. Which of the following statements regarding laminar flow in a blood vessel is TRUE ? a. The resistance to flow is inversely proportional to the fourth power of the radius of the vessel. b. The velocity of flow is slowest in the middle of the vessel. c. The resistance to flow is inversely proportional to the length of the vessel. d. The resistance to flow is independent of the viscosity of the blood. e. NONE OF THE ABOVE ARE TRUE. Solution Consider Poiseuille’s Law for this question. The equation is as follows: R = 8 νL π r 4 Where v is the viscosity of the blood, L is the length of the vessel, and r is the radius of the vessel. a) Option (a) is CORRECT. This statement correctly describes the relationship between resistance and the radius of the blood vessel. b) Option (b) is INCORRECT. The velocity of flow is fastest in the middle of the vessel. This is because there is fewer contact with the walls of the vessel. At the walls of the vessel, there is more contact, and thus more friction, which slows the blood down. c) Option (c) is INCORRECT. As seen by the equation describing Poiseuille’s Law, the resistance to flow is directly proportional to the length of the vessel. d) Option (d) is INCORRECT. As seen by the equation describing Poiseuille’s Law, viscosity is indeed a factor that determines resistance. Therefore, resistance is not independent of viscosity.
PHGY 210 2024 USCA Questions e) Option (e) is INCORRECT. 5. Which of the following statements is TRUE ? a. The combined resistance of blood vessels in parallel is greater than the resistance through each individual vessel. b. Compliance can be calculated by the change in volume within a blood vessel divided by its change in pressure. c. The flow of blood through a vessel can be calculated by dividing the resistance of the vessel by the perfusion pressure through the vessel. d. The combined resistance of blood vessels in a series is less than the resistance through each individual vessel. e. Arteries and arterioles are more compliant than veins and venules, respectively. Solution a) Option (a) is INCORRECT. The combined resistance of blood vessels in parallel is less than the resistance through each individual vessel. 1 R total = 1 R 1 + 1 R 2 + … + 1 R n = ¿ R total < R 1 ,R 2 ,…, R n b) Option (b) is CORRECT. This is the correct method by which to calculate the compliance of a blood vessel. c) Option (c) is INCORRECT. The flow of blood through a vessel is calculated by dividing the perfusion pressure through the vessel by the resistance of the vessel. d) Option (d) is INCORRECT. The combined resistance of blood vessels in series is greater than the resistance through each individual vessel.
PHGY 210 2024 USCA Questions R total = R 1 + R 2 + … + R n = ¿ R total > R 1 , R 2 ,…,R n e) Option (e) is INCORRECT. Veins and venules have less smooth muscle around them, rendering them more compliant and better capable of accommodating larger volumes of blood compared to arteries and arterioles.
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