MLT GlobePhysiology: Respiratory physiology
27 Physiology MCQs on Respiratory physiology with answers and explanations.
Tissue hypoxia means an inadequate supply of:
Hypoxia is too little oxygen at tissue level, whether from low PaO2, anaemia, poor perfusion or poisoned cell respiration. Hypoxaemia specifically means low blood oxygen.
Gas exchange between air and blood takes place in the:
Alveoli have a thin respiratory membrane and a large surface area in contact with capillaries. Conducting airways such as the bronchi and terminal bronchioles do not exchange gas.
A patient with a massive brainstem stroke stops breathing spontaneously. The basic respiratory rhythm generator is located in the:
Respiratory rhythm arises in medullary centres (pre-Botzinger complex), modulated by the pons. The cortex permits only voluntary override of breathing.
Lung tissue recoils passively during quiet expiration. This recoil depends mainly on its abundance of:
Lung parenchyma is rich in elastic connective tissue, which stretches on inspiration and recoils on expiration. Cartilage is limited to the larger airways.
Oxygen diffusing from alveolar air into blood crosses the respiratory membrane. This membrane consists of:
The respiratory membrane is about 0.5 um thick: type I alveolar cells, shared basement membrane and endothelium. Pleura covers the lung surface and chest wall.
A bronchoalveolar lavage shows large phagocytes containing inhaled dust. These resident 'dust cells' are:
Alveolar macrophages derive from monocytes and ingest particles and microbes in the air spaces. Type II cells secrete surfactant, and goblet cells make mucus.
A preterm infant has respiratory distress due to immature alveolar septal cells. These type II pneumocytes normally:
Type II alveolar cells secrete surfactant, which lowers surface tension and prevents alveolar collapse. Deficiency causes neonatal respiratory distress syndrome.
The exchange of oxygen and carbon dioxide between alveolar air and pulmonary capillary blood is termed:
External respiration is gas exchange in the lungs; internal respiration is exchange between blood and tissues. Ventilation is the movement of air in and out.
Which gas makes up about 78% of dry atmospheric air?
Dry air is about 78% nitrogen, 21% oxygen, 0.9% argon and 0.04% carbon dioxide.
Which instrument is used to record tidal volume and vital capacity?
A spirometer measures inhaled and exhaled air volumes and flows. A sphygmomanometer measures blood pressure, and a bronchoscope is used to look inside the airways.
Total lung capacity in a healthy young adult male is closest to:
TLC is about 6 L in adult males. About 500 mL is tidal volume and about 1200 mL is residual volume.
Roughly what proportion of oxygen carried in arterial blood is bound to haemoglobin rather than dissolved in plasma?
Only ~1.5–3% of oxygen is physically dissolved; the rest is carried as oxyhaemoglobin, which is why haemoglobin concentration dominates oxygen-carrying capacity.
Bronchodilation seen during exercise is mediated mainly by which system?
Sympathetic stimulation and circulating epinephrine act on bronchial beta-2 receptors to relax smooth muscle. Vagal (parasympathetic) activity causes bronchoconstriction.
During quiet breathing the intrinsic laryngeal muscles are relaxed. What is the state of the airway at the larynx?
With the muscles relaxed, the vocal folds lie abducted and the glottis is open for breathing. Adduction and tension are needed to produce sound or close the airway.
The cough reflex is triggered when:
Irritant receptors send vagal impulses to the medulla. A deep breath is taken, the glottis closes, the abdominal muscles contract to build pressure, and then the glottis opens suddenly.
Which change shifts the oxygen-haemoglobin dissociation curve to the LEFT, increasing haemoglobin's oxygen affinity?
Raised CO2, H+, temperature and 2,3-BPG shift the curve right and aid oxygen unloading. Alkalosis, hypothermia, low 2,3-BPG and HbF shift it left.
A patient in severe asthma uses neck muscles that visibly contract to lift the sternum during inspiration. Which is such an accessory muscle of respiration?
Sternocleidomastoid and scalenes are accessory inspiratory muscles used in laboured breathing. The diaphragm and external intercostals are the primary inspiratory muscles.
Most of the carbon dioxide produced by tissues travels to the lungs in plasma as:
About 70% of CO2 is converted by carbonic anhydrase in red cells to bicarbonate, which moves into plasma. Carbamino compounds carry about 20-23% and dissolved gas about 7-10%.
Residual volume can be obtained by which calculation?
Total lung capacity equals vital capacity plus residual volume, so RV = TLC - VC. Inspiratory capacity minus IRV gives tidal volume.
In a healthy adult breathing room air, the PO2 of blood in the pulmonary veins is about:
Pulmonary venous blood equilibrates with alveolar air at about 13.3 kPa. Mixed venous blood returning to the lungs is about 5.3 kPa, and inspired air about 20 kPa.