15 concise topics with breakdowns: definitions, key facts, and class questions.
The «Respiration» section covers the entire pathway of oxygen from atmospheric air to the tissues and the return transport of carbon dioxide. We will analyze the physical properties of respiratory gases, the biomechanics of the respiratory act, the critical role of surfactant in alveolar ventilation, as well as the laws of diffusion and the specifics of $O_2$ and $CO_2$ transport by the blood.
A separate block is dedicated to process control: how the respiratory center functions, how neurohumoral regulation works, and how all of this integrates into a unified functional system. We will also examine the physiology of respiration under special conditions: the mechanism of the newborn's first breath, altitude hypoxia, and adaptation to decreased or increased atmospheric pressure.
During seminars and exams, instructors most frequently grill students on lung volumes and capacities (the basics of spirometry), the oxyhemoglobin dissociation curve (oxygen transport), and the mechanisms altering the activity of the respiratory center. A firm grasp of these core processes is your key to passing the exam successfully and the foundation for your future clinical practice.
Why is there more oxygen in expired air than in alveolar air?
Upon expiration, alveolar air mixes with a portion of air from the "dead space". The composition of the dead space air is close to atmospheric, so it increases the total proportion of oxygen in the expired mixture.
Why cannot residual volume be determined by spirometry?
A spirometer measures only the air that passes through the device (is inhaled or exhaled). Residual volume is by definition impossible to exhale, which is why an inert gas dilution method (using argon) is employed to calculate it.
Why is pleural pressure negative?
This is due to the specifics of ontogenesis. During growth, the chest cavity increases in size faster than the lung tissue. Because of this discrepancy, the lungs are constantly in a stretched state (elastic recoil tends to compress them), which forms the subatmospheric pressure between the pleural layers.
Why is only one-fifth of the air renewed during quiet breathing?
This is an evolutionary mechanism that avoids sharp jumps in gas concentrations. Such portioned renewal ensures the relative constancy of blood gas composition.
Oxygen diffuses from the alveoli into the pulmonary capillaries because the partial pressure of O2 is higher in the alveoli (102 mmHg) than in the inflowing venous blood (40 mmHg).
Oxygen passes from the alveoli into the blood of the pulmonary capillaries. This occurs along the partial pressure gradient: in the alveoli it is 102 mmHg, and in venous blood it is 40 mmHg.
Does the valence of iron change when binding oxygen?
No, the process is called oxygenation, not oxidation. Iron in the heme remains divalent.
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