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Respiratory Physiology: Ventilation, Gas Exchange, and Spirometry

← Builds on Respiratory System Gross and Microscopic Anatomy

Terms you will need

  • tidal volumeThe amount of air you breathe in and out with each normal breath.
  • residual volumeThe amount of air that always stays in your lungs even after you exhale as much as you can.
  • alveolar gas exchangeThe process where oxygen moves into your blood and carbon dioxide moves out in the tiny air sacs of your lungs.
  • diaphragmThe main muscle that helps you breathe by moving up and down to change the size of your chest.

How this topic runs

  1. 1Start here
  2. 2How it works
  3. 3At competition depth

Respiratory physiology involves the processes of ventilation, gas exchange, and spirometry, which are essential for maintaining life. The respiratory system includes structures that move air into and out of the lungs, passageways for air movement, and microscopic gas exchange surfaces covered by capillaries. Oxygen is inhaled and transported to cells for energy production, while carbon dioxide is exhaled as a waste product. This system works closely with the circulatory system to deliver oxygen and remove carbon dioxide from the body. The mechanics of breathing, the structure of the respiratory tract, and the efficiency of gas exchange are all vital components of respiratory physiology.

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

Ventilation is the process of moving air into and out of the lungs. This happens through the nose and mouth, where air travels down the trachea and into the bronchi, which branch into smaller airways called bronchioles. At the end of the bronchioles are tiny air sacs called alveoli.

These are where gas exchange occurs. The diaphragm, a large muscle under the lungs, helps control this movement. When it contracts, it creates space for the lungs to expand and draw in air.

When it relaxes, the lungs push air out. Gas exchange is how oxygen and carbon dioxide move between the air in the alveoli and the blood in nearby capillaries. Oxygen moves into the blood, and carbon dioxide moves out.

This happens because of a concentration gradient—gases move from where they are more concentrated to where they are less. The alveoli have a large surface area and thin walls to make this process fast and efficient. The blood carries oxygen to cells and brings carbon dioxide back to the lungs to be exhaled.

It checks how much air a person can inhale and exhale, and how quickly they can do it. This helps doctors diagnose conditions like asthma or COPD. To picture this, imagine a tree with many branches.

The trunk is the trachea, the main branches are the bronchi, and the tiny twigs are the bronchioles. The blood vessels wrap around these balloons, picking up oxygen and dropping off carbon dioxide. The whole system works like a pump, moving air in and out with each breath.

Key Points

  • Tidal volume is the amount of air inhaled or exhaled during a normal breath, typically around 500 ml at rest.
  • Partial pressure is the pressure exerted by a specific gas in a mixture of gases, such as the pressure of oxygen or carbon dioxide in the air or blood.

Terms

Tap a term for a plain-language explanation.

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