The Mechanics of Breathing

1. The Mechanics of Breathing • Breathing refers to the process of taking air into the lungs and expelling it. • Respiration refers to the exchange of gases between an organism and its environment. • Two phases: • External Respiration involves the exchanges of gases between the air and the blood stream. • Internal Respiration involves the exchanges of gases between the blood and tissues.

2. A. The Respiratory Cycle • Gas moves from high pressure to low pressure. This applies to air movement, as in ventilation, and also to gas exchange in the tissues. • Changing pressure in the thoracic muscles allows gasses to enter and leave the body.

3. 1.Changes in pulmonary pressure • When pressure of air in lungs is lower than the atmosphere, air rushes through nose, trachea, etc. into lungs. When air pressure in lungs is greater, it rushes out.

4. 2. Inspiration – taking air into lungs. • Diaphragm (dome-shaped muscle at bottom or rib cage) contracts, flattening out in the process. This action increases the volume of the thoracic cavity. • The intercostal muscles move the ribs up and out. This action also increases the volume of the thoracic cavity. • The pleura (parietal and visceral) adhere to each other, causing the elastic lungs to expand along with the thoracic cavity. • The resulting decrease in air pressure inside the lungs, causes air to enter the lungs through the respiratory tract.

5. 3. Expiration – Expelling air from lungs. • Diaphragm and intercostal muscles relax, decreasing the volume of the lungs. • Resulting increase in pressure causes air to be expelled. • Expiration is mostly a passive action.

6. 4. Lung Capacity • 14 – 20 breaths/min. – increased when exercising. • Tidal volume (amount of air moved per breath) = 500 ml. • Expiratory reserve volume (extra air that can be expelled) = 1 500 ml. • Inspiratory reserve volume (amt. that can be inhaled after normal breath) = 2000 – 3000 ml. • Vital capacity (max. air possible to move per breath) = 3 400 – 4 700 ml. • Residual air capacity (Air that remains in lungs after max. respiration) = 1 500 ml.

7. B. Control of Breathing 1.Chemical Factors • Increased CO2 in blood reacts with H2O to form carbonic acid. This stimulates the respiratory centre in the medulla of the brain to increase depth and rate of breathing. • Sensory nerves endings in aorta and carotid arteries respond to lack of O2 and also send impulses to respiratory centre.

8. 2.Nervous Control • Respiratory centre evaluates information and if needed sends signal to increase rate and depth of breathing.

9. C. Gas Exchange • Exchange depends on pressure or concentration of gradients. • Differences between blood in capillaries and alveolar air allow for diffusion across alveolar membranes. • Membranes are very thin and moist.

10. External respiration • Higher concentration of O2 and lower concentration of CO2 in the air allows for O2 to diffuse inward across the membrane into the blood and for CO2 to diffuse outward.

11. Internal respiration • Cell uses up O2 and produces CO2 in making energy. • As a result, the O2 is lower and CO2 is higher in cells than in blood. • This allows for O2 to diffuse across the membrane into the cell and CO2 to diffuse out.

12. Assignment 1 • Read. pp. 186-191; Do #1-6 p. 191 • Describe the function of alveoli in detail. Explain how the structure of alveoli help them to fulfill their function. • (a) Why is exhaled air higher in O2 than alveolar air? (b) Define what you think is meant by “dead air,” in this context. 4. In two to three sentences summarize the mechanical process of breathing. 5. Do the compare and contrast frame for inhalation vs. exhalation.