What is the chemical identity of endothelium derived relaxing factor (EDRF)?

Question 26

Step 1: Identify Endothelium Derived Relaxing Factor (EDRF). EDRF was the initial term for a substance released by endothelial cells that causes vasodilation. It was later identified as nitric oxide.

Step 2: Evaluate the options.

• a) Nitrous oxide ($\text{N}_2\text{O}$) is laughing gas, an anesthetic.
• b) Nitric oxide (NO) is the chemical identity of EDRF.
• c) Potassium is an ion, not EDRF.
• d) Carbon monoxide (CO) is another gasotransmitter but not EDRF.

Answer: Nitric oxide (b) b

Question 27

Step 1: Understand vasodilator actions. Vasodilators cause blood vessels to widen, increasing blood flow.

Step 2: Evaluate the actions of each substance.

• a) NO (Nitric Oxide): A potent vasodilator.
• b) CO (Carbon Monoxide): Can act as a vasodilator, similar to NO.
• c) Potassium: High extracellular potassium can cause vasodilation in some vascular beds.
• d) Angiotensin III: Part of the renin-angiotensin system, Angiotensin III is a vasoconstrictor, meaning it causes blood vessels to narrow.

Answer: Angiotensin III (d) d

Question 28

Step 1: Understand vasoconstrictors. Vasoconstrictors cause blood vessels to narrow, increasing vascular resistance and blood pressure.

Step 2: Compare the potency of the given vasoconstrictors.

• a) Endothelin 1: Considered one of the most potent vasoconstrictors known.
• b) Angiotensin II: A very potent vasoconstrictor.
• c) Norepinephrine: A potent vasoconstrictor, primarily acting on alpha-adrenergic receptors.
• d) Vasopressin (ADH): A potent vasoconstrictor, especially at high concentrations.

Among these, Endothelin-1 is generally recognized as the most potent.

Answer: Endothelin 1 (a) a

Question 29

Step 1: Analyze the physiological changes upon rising from a supine position. When a person stands up, gravity causes blood to pool in the lower extremities. This leads to a decrease in venous return to the heart.

Step 2: Evaluate the consequences of decreased venous return.

• a) Central blood volume increases: Incorrect. Central blood volume decreases due to pooling in the periphery.
• b) Heart rate decreases: Incorrect. Heart rate increases as a compensatory mechanism to maintain cardiac output.
• c) Central venous pressure decreases: Correct. Reduced venous return leads to a drop in pressure in the central veins.
• d) Discharge from arterial baroreceptors decreases: Correct. The drop in central venous pressure leads to a decrease in cardiac output and arterial blood pressure, which reduces the stretch on arterial baroreceptors, thus decreasing their firing rate.

Both c) and d) are correct physiological responses. However, the decrease in central venous pressure is a direct hemodynamic consequence of blood pooling, which then triggers the baroreceptor response.

Answer: Central venous pressure decreases (c) c

Question 30

Step 1: Recall the mechanism of the chloride shift (Hamburger phenomenon). The chloride shift is a process that occurs in red blood cells (RBCs) to facilitate the transport of carbon dioxide ($\text{CO}_2$) from tissues to the lungs. When $\text{CO}_2$ enters RBCs, it is converted to bicarbonate ions ($\text{HCO}_3^-$).

Step 2: Explain the movement of ions. To maintain electrical neutrality, as negatively charged bicarbonate ions ($\text{HCO}_3^-$) move out of the RBCs into the plasma, negatively charged chloride ions ($\text{Cl}^-$) move into the RBCs.

Step 3: Evaluate the options.

• a) Chloride ions move into RBCs when bicarbonate ions move out: This accurately describes the chloride shift.
• b) Sodium ions move into plasma when $\text{CO}_2$ enters RBCs: Incorrect. Sodium ions are not directly involved in the chloride shift mechanism.

Answer: Chloride ions move into RBCs when bicarbonate ions move out (a) a