1. Respiratory System
Control of Breathing

2. Respiratory Areas
Groups of neurons in the brain stem which control breathing

3. Respiratory Areas Medullary rhythmicity center
Includes two groups of neurons that extend throughout the medulla oblongata
Dorsal respiratory group
Stimulate muscles for inspiration (primarily the diaphragm)
Control the depth of inspiration (forceful breathing)
Ventral respiratory group
Stimulate other respiratory muscles such as the intercostals and abdominals
Some increase inspiration and some increase expiration
Control the basic rhythm of breathing

4. Respiratory Areas Pontine Respiratory Group
Also located in the brainstem (specifically the pons)
Make connections with the medullary rhythmicity center

5. Factors Affecting Breathing
Partial pressure
The amount of pressure that each gas in air contributes to the total air pressure
Proportional to the concentration of the gas
Ex:
air consists of 21% oxygen
Atmospheric pressure of air is 760 HG
So, .21 x 760 = 160 mm Hg, which is the partial pressure of O2

6. Factors Affecting Breathing
Breathing rate and depth are affected by the partial pressure of oxygen and carbon dioxide in body fluids, the degree to which lung tissues are stretched and emotional state.

7. Factors Affecting Breathing
Changes in partial pressure of carbon dioxide in the blood are mainly detected indirectly by chemoreceptors in the medulla oblongata
(chemoreceptors actually detect increases in hydrogen ions that are released when carbonic acid (formed by carbon dioxide combining with water in the fluid of the brain) is ionized in the brain)
Increases in carbon dioxide (either through breathing in carbon dioxide or as cellular waste) trigger breathing rate and tidal volume to increase which increase alveolar ventilation and return the partial pressure of carbon dioxide to normal

8. Factors Affecting Breathing
Changes in partial pressure of oxygen are detected mainly by peripheral chemoreceptors in specialized structures (carotid bodies and aortic bodies) located in the walls of the carotid sinuses and the aortic arch
When stimulated these structures send impulses to the respiratory system which then increases breathing rate and alveolar ventilation
This process is not usually triggered until the partial pressure of oxygen falls below 50% of normal

9. Factors Affecting Breathing

10. Factors Affecting Breathing
Inflation reflex
Occurs when stretch receptors in the visceral pleura, bronchioles, and alveoli are stimulated by stretching of lung tissue
Sends impulses to the respiratory center which then shortens the duration of inspiratory movements
Prevents overinflation of the lungs during forceful breathing

11. Factors Affecting Breathing
Gasping and rapid breathing are normal responses to stimuli such as fear, anger, and excitement

12. Factors Affecting Breathing
Because control of respiratory muscles is voluntary breathing patterns can be consciously altered

13. Factors Affecting Breathing
Hyperventilation
Rapid and deep breathing
Lowers the blood carbon dioxide level below normal
May result in loss of consciousness due to a decrease in oxygen supply to the brain