MLT GlobePhysiology: Respiratory physiology – page 2
27 Physiology MCQs on Respiratory physiology with answers and explanations.
Peripheral chemoreceptors in the carotid and aortic bodies increase ventilation when stimulated by:
Carotid and aortic bodies respond to low PO2, high PCO2 and high H+ (low pH), increasing breathing. High PO2 or low H+ would reduce their output.
Which condition shifts the haemoglobin–oxygen dissociation curve to the right?
Acidosis (Bohr effect), raised pCO2, heat and raised 2,3-BPG lower Hb oxygen affinity, shifting the curve right. Cold, low 2,3-BPG and HbF shift it left.
Which change in arterial blood most strongly stimulates the carotid body chemoreceptors?
Carotid bodies respond chiefly to hypoxaemia, and also to raised pCO2 and falling pH. Alkalosis and hypocapnia reduce their firing; anaemia with normal pO2 does not stimulate them.
Compared with oxygen, how quickly does carbon dioxide diffuse across the alveolar–capillary membrane?
CO2 is far more soluble in the membrane fluid than O2, so despite its larger molecular weight it diffuses roughly 20 times faster.
Approximately what is the intracellular pCO2 of metabolically active tissue cells at rest?
Cells produce CO2, so intracellular pCO2 (~46 mmHg) exceeds arterial pCO2 (~40 mmHg), driving diffusion into capillary blood. 100 mmHg is roughly alveolar pO2.
Neurones of the pneumotaxic (pontine respiratory) centre mainly:
The pneumotaxic centre limits the duration of inspiration, which shortens each breath and raises the rate. The basic rhythm is generated in the medulla; stretch and pH are sensed by peripheral receptors.
Which brainstem structure is currently regarded as the main generator of the basic inspiratory rhythm?
The pre-Bötzinger complex, within the ventral respiratory column, contains pacemaker-like neurons generating inspiratory rhythm. Pontine centres fine-tune timing; chemosensitive areas adjust ventilation to CO2.