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Central control of respiration & acid:base balance (CPG (central…
Central control of respiration & acid:base balance
CPG (central pattern generator)
Automatic + rythmic
Pacemaker neurones in medulla oblongata (CPG)
CPG is network of communicating pathways which work to produce appropriate resp rate and depth
Neurones of dorsal respiratory group stimulate motor neurones innervating muscles of inspiration
Stretch receptors in lung send impulses to the pons (front of medulla) to switch off stimulation and prevent overinflation. (Hering-Breuer reflex)
Expiration usually passive as elastic recoil.
Active expiration:
neurones in ventral respiratory group send impulses to expiratory muscles
Peripheral chemoreceptors
Carotid and aortic bodies
Monitor PaO2, PaCO2 and arterial [H+]
V.high blood supply
Innvervated by:
Carotid by cranial nerve IX
Aortic bodies by CN X (important in foetus)
More sensitive to change in CO2
Central chemoreceptors
Central (in brain)
Monitor PaCO2 only
CO2 crosses BB barrier. Carbonic acid generates HCO2- and H+. Receptors detect this H+
Most important factor governing respiration under normal circumstances
Blood pH
Normal pH = 7.4
Decrease in ECF pH = acidosis (<7.35) Increase in ECF pH = alkalosis (>7.45)
Rebalance
Alkalosis
Need to increase [H+]
Acidosis
Need to decrease [H+]
Mechanisms
Buffering - fastest, least effect
Lungs - middle speed, medium effect
Kidneys - slowest, greatest effect
CO2 is a potential acid (forms carbonic acid which can dissociate)
Accumulation of H+ due to build up of CO2 =
Respiratory acidosis
Breathing out too much CO2 =
Respiratory alkalosis
Build up of fixed acids (accumulation of H+) =
Metabolic acidosis
(Vice versa for alkalosis)
Buffering
Carbonic acid system most important buffer for pH other than those of respiratory origin
If bicarbonate normal/top range and pH lowered then respiratory acidosis uncompensated. If bicarbonate elevated and pH normal, compensated resp acidosis