Cardiovascular Lecture 1 Solutions - PHGY 210 2024 - Copy

PHGY 210 2024 USCA Questions Cardiovascular Physiology – Lecture 1 1. Which of the following statements about diffusion is INCORRECT ? a. The rate of diffusion is higher across membranes with greater surface area. b. The rate of diffusion is slower across greater distances. c. Higher temperatures generally lead to greater rates of diffusion. d. Higher solvent densities lead to greater rates of diffusion. e. Molecules with greater mass have lower rates of diffusion. Solution a) Statement (a) is CORRECT; therefore, it is not the right option. b) Statement (b) is CORRECT; therefore, it is not the right option. c) Statement (c) is CORRECT; therefore, it is not the right option. d) Statement (d) is INCORRECT; therefore, it is the right option. Higher solvent densities lead to lower rates of diffusion. Conversely, lower solvent densities lead to higher rates of diffusion. e) Statement (e) is CORRECT; therefore, it is not the right option.

PHGY 210 2024 USCA Questions 2. Fick’s law of diffusion states that: a. The diffusion rate of gas across a membrane is inversely proportional to the surface area of the membrane. b. The diffusion rate of gas across a membrane is inversely proportional to the solubility of the gas. c. The diffusion rate of gas across a membrane is directly proportional to the pressure gradient of the gas. d. The diffusion rate of gas across a membrane is directly proportional to the thickness of the membrane. e. The diffusion rate of gas across a membrane is directly proportional to the molecular weight of the gas. Solution Fick’s law of diffusion is explained by the following equation: Rate of Diffusion = ( P 1 − P 2 ) × A T × Solubility √ MW Where:  P 1 is the partial pressure of the gas outside of the cell.  P 2 is the partial pressure of the gas within the cell.  A is the surface area of the cell membrane.  T is the thickness of the cell membrane.  Solubility is the solubility of the gas.  MW is the molecular weight of the gas. a) Option (a) is INCORRECT. From the equation, we can see that the diffusion rate of a gas across a membrane is directly proportional to the surface area of the membrane. b) Option (b) is INCORRECT. From the equation, we can see that the diffusion rate of a gas across a membrane is directly proportional to the solubility of the gas. c) Option (c) is CORRECT. The quantity ( P 1 – P 2 ) represents the pressure gradient of the gas. From the equation, we can see that the diffusion rate of a gas across a membrane is directly proportional to the pressure gradient of the gas. d) Option (d) is INCORRECT. From the equation, we can see that the diffusion rate of a gas across a membrane is inversely proportional to the membrane thickness.

PHGY 210 2024 USCA Questions e) Option (e) is INCORRECT. Increasing P 1 increases the pressure gradient (represented by the quantity P 1 – P 2 ). Since the diffusion rate is directly proportional to the pressure gradient, increasing the pressure gradient would increase the diffusion rate. 4. If one wished to DOUBLE the diffusion rate of oxygen into a cardiac cell, one could theoretically do so by: a. Halving the thickness of the cell membrane. b. Doubling the partial pressure of oxygen just outside of the cell membrane. c. Doubling the partial pressure of oxygen just inside of the cell membrane. d. Halving the surface area of the cell membrane. e. Halving the solubility of oxygen. Solution The diffusion rate of a gas can be explained with the following equation: Rate of Diffusion = ( P 1 − P 2 ) × A T × Solubility √ MW Where:  P 1 is the partial pressure of the gas outside of the cell.  P 2 is the partial pressure of the gas within the cell.  A is the surface area of the cell membrane.  T is the thickness of the cell membrane.  Solubility is the solubility of the gas.  MW is the molecular weight of the gas. a) Option (a) is CORRECT. Since the diffusion rate is inversely proportional to the membrane thickness, halving T would double the diffusion rate. b) Option (b) is INCORRECT. This option is tricky. It is important to note that the rate of diffusion is directly proportional to the pressure gradient P 1 – P 2 . Therefore, although doubling P 1 would increase the pressure gradient, it will not always double the pressure gradient. Ex: 100 – 50 = 50 but 200 – 50 = 150. In this instance the pressure gradient increased by a factor of 3, rather than 2.

PHGY 210 2024 USCA Questions c) Option (c) is INCORRECT. Doubling P 2 would decrease the pressure gradient rather than increasing it, let alone doubling it. Therefore, this option would not double the diffusion rate. As an aside, if we were to halve P 2 , the pressure gradient will not always double (same rationale as for option (b)) d) Option (d) is INCORRECT. Since the diffusion rate is directly proportional to the surface area of the cell membrane, halving A would halve the diffusion rate. e) Option (e) is INCORRECT. Since the diffusion rate is directly proportional to the solubility of oxygen, halving solubility would halve the diffusion rate. 5. Which of the following statements about comparative physiology is CORRECT ? a. Hemolymph in insects seeps out onto the organs from the posterior end and returns to the circulation through openings called ostia. b. In birds and mammals, the right heart is part of the systemic circulation whereas the left heart is part of the pulmonary circulation. c. Amphibians and most reptiles only have lung capillaries through which they oxygenate their blood. d. The cardiovascular system of fish includes an open, double-loop circulation, and a two-chambered heart. e. Crocodiles and alligators possess a gear-tooth valve that closes when underwater, causing oxygen-poor blood to enter the systemic circulation. Solution a) Option (a) is INCORRECT. Hemolymph in insects seeps out onto the organs from the anterior end rather than the posterior end. b) Option (b) is INCORRECT. In birds and mammals, the right heart is part of the pulmonary circulation whereas the left heart is part of the systemic circulation. c) Option (c) is INCORRECT. In addition to lung capillaries, amphibians and most reptiles also have skin capillaries through which they oxygenate their blood. This is referred to as the pulmocutaneous circulation.