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Respiratory Physiology: Ventilation, Gas Exchange, and Spirometry

See how long you can hold your breath as you continue reading…How long can you do it? Chances are you are feeling uncomfortable already. A typical human cannot survive without breathing for more than 3 minutes, and even if you wanted to hold your breath longer, your autonomic nervous system would take control. This is because every cell in the body needs to run the oxidative stages of cellular respiration, the process by which energy is produced in the form of adenosine triphosphate (ATP). For oxidative phosphorylation to occur, oxygen is used as a reactant and carbon dioxide is released as a waste product.

Figures (10)

Typical breathing effort when breathing through a diving regulator
Fig. 2. A comparison between the operations and effects of a cocurrent and a countercurrent flow exchange system is depicted by the upper and lower diagrams respectively. In both it is assumed (and indicated) that red has a higher value (e.g. of temperature or the partial pressure of a gas) than blue and that the property being transported in the channels therefore flows from red to blue. Note that channels are contiguous if effective exchange is to occur (i.e. there can be no gap between the channels).
Fig. 4. A histological cross-section through an alveolar wall showing the layers through which the gases have to move between the blood plasma and the alveolar air. The dark blue objects are the nuclei of the capillary endothelial and alveolar type I epithelial cells (or type 1 pneumocytes). The two red objects labeled "RBC" are red blood cells in the alveolar capillary blood.
Fig. 10. Inhalation-exhalation cycle in birds.
Fig. 11. A stylised cross-section of a euphyllophyte plant leaf, showing the key plant organs involved in gas exchange
Complete respiratory system
Parts of the lower respiratory tract
This is a diagram showing how inhalation and exhalation is controlled by a variety of muscles, and what that looks like from a general overall view.
Inhaled air is warmed and moistened by the wet, warm nasal mucosa, which consequently cools and dries. When warm, wet air from the lungs is breathed out through the nose, the cold hygroscopic mucus in the cool and dry nose re-captures some of the warmth and moisture from that exhaled air. In very cold weather the re-captured water may cause a "dripping nose".
The lower airways:TracheaMainstem bronchusLobar bronchusSegmental bronchusBronchioleAlveolar ductAlveolus

Key Points

  • At sea level, where the ambient pressure is about 100 kPa, oxygen constitutes 21% of the atmosphere and the partial pressure of oxygen (PO2) is 21 kPa (i.e. 21% of 100 kPa).
  • The diaphragm is also the main muscle of respiration involved in breathing, and is controlled by the sympathetic nervous system.

Terms

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