CHAPTER 7(c) - BREATHING CYCLE

BREATHING MECHANISM

-Events that bring inhaled air to the alveoli and removes exhaled air in a process called ventilation
-ventilation helps to maintain gaseous exchange and blood pH levels
-inspiratory (inhalation) and expiratory (exhalation)
-lungs rely on the diaphragm and the rib cage during breathing

INHALATION AND EXHALATION

-Lungs are not attached to the rib cage by tissues but are separated from it by a thin film of pleural fluid which holds the pleural membrane

-and lubricates it when the lungs expand during inspiration

-medulla oblongata and pons in the hindbrain control this automatic action

RECEPTORS OF BREATHING MECHANISM

1. CENTRAL CHEMORECEPTOR

-In the medulla region of the hind-brain

-sensitive to the pH of the cerebrospinal fluid (indicator of blood Co2)

-the higher the blood CO2 concentration, the lower the pH of cerebrospinal fluid

2. PERIPHERAL CHEMORECEPTOR 

-located in carotid and the aortic bodies

-both bodies are also sensitive to blood pH

-indicates the changes in arterial CO2 concentration

3. MECHANORECEPTOR (STRETCH RECEPTOR)

-In the bronchial tree 

-help maintain any expansion in the lungs and size of airways

-they send impulses to the expiratory centres to shorten inspiration

**respiratory muscles will react to increase or decrease alveolar ventilation as required by regulating amplitude and depth of each breath**

BREATHING RECEPTORS

DURING VIGOROUS EXERCISE

1.Increase in the partial pressure of co2 in the body

2.Drop in the pH of blood

3.Rise in the carbon dioxide partial pressure is detected by chemoreceptors in the carotid artery

4.Impulse are send to stimulate the inspiratory and the cardiovascular center in the brain

5.Inspiratory cente then sends out impulse through

6.Intercostal nerve to stimulate the contraction of the external intercostal muscle of the rib cage

7.Phrenic nerve to stimulate the contraction of the radial muscle of the diaphragm

8.Both contractions bring the rib cage outwards and upwards

9.Air inhaled to the lungs

10.Inhalation and Exhalation are carried out more frequently to increase the rate of alveolar ventilation for faster gaseous exchange in the body.

11.Too much oxygen can cause an increase in the metabolic rate of carbohydrate, fats and protein which will result in accumulation of co2 causing an increase in the rate of ventilation as well as cardiac frequency