Tuesday, April 26, 2011

Breathing process

1. Breathing control centre are:
  • located in two major regions (medulla oblongata + pons).
  • in medulla - sets the basic rhythm,
  • in pons - moderates it smoothing out the transition between inhalation + exhalation.
  • send impulses to the diaphragm + external intercostals muscle.

2. The central chemoreceptors (lies near the breathing control centers):
  • detet the changes in pH of the cerebospinal fluid (CSF).
  • stimulate the breathing centre
  • slow down or speed the rhythmic discharge of nerve impulses

3. Carotid bodies are
  • found in the carotid artery in the neck.
  • chemoreceptor with nerve endings in the wall of carotid artery
  • monitors the changes of blood pH in the carotid artery.

4. Aortic bodies are
  • found in aorta.
  • chemoreceptors that monitor the changes of blood pH.
  • nerve endings in the wall of aorta.

5. Aortic and carotid bodies:
  • also called peripheral chemoreceptors.
  • impulses are relayed to the breathing control centres.
  • change of CO2 conc. in the blood triggers a series of chain reactions.
  • blood CO2 conc. back to normal,
  • negative feedback loop.

6. In the blood plasma:
  • CO2 released by cellular respiration 
  • reacts with H2O to form carbonic acid (H2CO2)
  • dissociates to form hydrogen carbonate ions (HCO3+) and hydrogen ions (H+).
  • increase in hydrogen ions (H+) conc.
  • increase the acidity of the blood plasma,
  • decreasing the pH.

7. In the region of medulla
  • CO2 diffuses into CSF from the surrounding capillary.
  • then reacts with H2O in the fluid to form carbonic acid (H2CO3).
  • dissociates to form hydrogen carbonate (HCO3+) and hydrogen ions (H+).
  • The acidity in the CSF increases
  • resulting in the decreases in the pH.

8. When blood flows through Peripheral Chemoreceptors (from aortic + carotid bodies) + Central Chemoreceptor

à detect increase in H+ conc
à send impulses to breathing control centre (in medulla oblongata)
à sends impulses to diaphragm + external intercostals muscles to contract faster
à breathing rate increases (to expel excess CO2)
à lungs expand (for faster breathing)
à stimulates stretch receptors (in lungs)
à send impulses to the breathing control centre
à sends impulses (via parasympathetic nerve) to the diaphragm + external intercostals muscle
à to slow down the contraction
à breathing rate returns to normal
à negative feedback reaction.

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