What happens in the heart at the start of ventricular diastole?
▶️ Answer/Explanation
Ans: B
At the start of ventricular diastole, the ventricles relax causing pressure to drop below atrial pressure. This pressure difference forces the atrioventricular valves (mitral and tricuspid) to open, allowing blood to flow from atria to ventricles. Semilunar valves (A) close at this stage, not open.
Which statement is correct?
▶️ Answer/Explanation
Ans: B
Carbonic anhydrase is indeed the enzyme that catalyzes the reversible reaction between CO2 and H2O to form carbonic acid (H2CO3). Option A is incorrect because CO2 forms carbaminohaemoglobin, not haemoglobinic acid. Option C is backwards – carbonic acid breaks down to release CO2 in the lungs. Option D is incorrect as higher CO2 actually decreases haemoglobin’s oxygen affinity (Bohr effect).
An increase in carbon dioxide in human blood shifts the oxyhaemoglobin dissociation curve to the right.
What is the explanation for this effect?
▶️ Answer/Explanation
Ans: D
Increased CO2 lowers blood pH (more H+ ions), reducing haemoglobin’s oxygen affinity (Bohr effect). This rightward shift helps oxygen unloading in tissues needing it most. Other options describe different phenomena unrelated to the curve shift.
Which reactions will be taking place in blood in a capillary that is next to an alveolus?
1. \( \text{Hb} + 4\text{O}_2 \to \text{HbO}_8 \) Key: Hb = haemoglobin
2. \( \text{H}_2\text{O} + \text{CO}_2 \to \text{H}_2\text{CO}_3 \)
3. \( \text{H}_2\text{CO}_3 \to \text{H}^+ + \text{HCO}_3^- \)
▶️ Answer/Explanation
Ans: B
In capillaries near alveoli, oxygen binds to haemoglobin (Reaction 1: \( \text{Hb} + 4\text{O}_2 \to \text{HbO}_8 \)) for transport. Reaction 2 (\( \text{CO}_2 \) hydration) and Reaction 3 (carbonic acid dissociation) primarily occur in tissues, where \( \text{CO}_2 \) is released, not in alveolar capillaries. Thus, only Reaction 1 is correct here.