Regulation of Ventilation Flashcards
Henderson-Hasselbach equation
[HA] + [H2O] [H3O+] + [A-]
Reaction rates
v1 = k1[HA][H2O]
v2 = k2[H3O+][HA-]
At steady state, v1 = v2
Equilibrium constant
k = [H3O+][A]/([HA][H2O])
Dissociation constant
[H+]*[A=]/[HA]
pH = ?
pK + log [A-]/[HA]
pH of the blood =
6.1 (pK of CO2 buffer system) + log ([HCO3]/(.03*PCO2))
.03 is the solubility of carbon dioxide, PCO2 is the partial pressure of carbon dioxide
How does COPD affect blood pH?
In COPD, elasticity of the lung is lost. Incomplete exhalation and therefore retention of carbon dioxide occurs. As the concentration of carbon dioxide increases, the pH decreases. This is respiratory acidosis. It also results in less oxygen bound to hemoglobin.
How does hyperventilation affect blood pH?
Carbon dioxide is blown off and pH increases. This is respiratory alkalosis. Carbon dioxide is the primary factor in respiratory control, and when carbon dioxide decreases, respirations slow and may even temporarily stop, leading to hypoxia
What controls speech, voluntary breath holding, fear, and pain?
Neurons in the cerebral cortex that send impulses to respiratory motoneurons via corticospinal tracts
The lower motor neuron cell bodies are located in ____.
The phrenic motor nucleus, extending from the third through fifth cervical segments
Transection of brainstem ____ stops breathing completely.
below the medulla
Transection ____ does not affect breathing greatly, indicating that _____.
above the medulla,
the medulla contains neurons sufficient for rhythmic breathing.
Central pattern generator
A group of neurons capable of rhythmic patterned output in the absence of outside influence or sensory feedback.
Cutting of sensory neurons in the vagus nerve does not block ____.
patterned breathing
Dorsal respiratory group
Primary stimulus for inspiration.
Input from central and peripheral chemoreceptors, pulmonary stretch receptors, and somatic pain receptors, mechanoreceptors. Stimulate DRG. Phrenic nerve activity increases in terms of rate and number of units discharging during inspiration .Causes more and more muscle fibers to be recruited. Increase in number of motor units increases tidal volume. Inspiration is terminated by the natural CPG rhythm modulated by sensory feedback. Expiration is primarily passive, although there is always tonic expiratory output and this may increase and become important in forced exhalation
Ventral Respiratory Group
Contains both inspiratory and expiratory neurons. Inspiratory neurons go mainly to the accessory muscle
Pontine and vagal influences
Transection above pons is without effect on breathing. However, transection at the inferior pons causes sustained gasping breathing. This is due to unregulated output by inspiratory neurons by the apneustic center (near the 4th ventricle), which is normally regulated by the pneumotaxic center in the superior pons.Cutting at the inferior pons causes prolonged inspiration, but if vagus is cut and the proximal stump is stimulated then inspiration can be stopped. Physiologically, this vagal feedback is from stretch receptors in the lung which when activated send efferent impulses via the vagus to inhibit inspiration (Hering-Breuer reflex)
Herin Breuer reflex
(If vagus is cut and the proximal stump is stimulated then inspiration can be stopped.) Physiologically, this vagal feedback is from stretch receptors in the lung which when activated send efferent impulses via the vagus to inhibit inspiration
Carotid and aortic body receptors are responsive to ___.
pH, CO2, and O2
Central chemoreceptors respond to changes in concentrations of ____ in the CSF.
CO2 and H+
Where are carotid bodies located?
At the bifurcation of the common carotid arteries (carotid bodies)
and near the aortic arch (aortic bodies)
Glomus cells
Type I cells that make synapses with the nerve endings. Afferents from the carotid bodies go to medulla via the glossopharyngeal nerve and those from the aortic bodies go to the medulla via the vagus nerve.
Carotid body nerve
Glossopharyngeal nerve
Aortic body nerve
Vagus nerve