Question

For each of the reflex systems A–E, select the most appropriate option from the types of receptors listed below. 

1. Arterial stretch receptors. 

2. Arterial chemoreceptors. 

3. Pulmonary stretch receptors. 

4. Atrial stretch receptors. 

5. Coronary artery chemoreceptors. 

A. The reflex regulation of blood pressure. 

B. The reflex regulation of ventilation. 

C. The reflex regulation of blood volume. 

D. System causing reflex hypotension, bradycardia and apnoea. 

E. The Hering–Breuer reflex.

Answer 1

A. Option 1 Arterial stretch receptors. Stretch of these receptors by a rise in blood pressure results in a reflex reduction in heart rate and vasoconstrictor tone to limit the rise in pressure. 

B. Option 2 Arterial chemoreceptors. A fall in P_O2 or pH or a rise in P_CO2 stimulates the arterial chemoreceptors to cause a reflex increase in pulmonary ventilation. The main stimulation effect of C_O2 on breathing is via the respiratory centre in the medulla oblongata but the stimulatory effect of hypoxia is via the arterial chemoreceptors only. 

C. Option 4 Atrial stretch receptors. Stretch of atrial stretch receptors results in a fall in blood pressure and an increase in urinary output. 

D. Option 5 Coronary artery chemoreceptors. C fibres close to the walls of coronary vessels are stimulated by certain circulating substances such as serotonin and veratridine, to cause hypotension, bradycardia and perhaps apnoea (the Bezold–Jarisch reflex). 

E. Option 3 Pulmonary stretch receptors. When pulmonary stretch receptors are stretched during inspiration, they send impulses to the brain via the vagus nerves that inhibit the inspiratory centre in the medulla oblongata.