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
When pH decreases, the firing rate of the neurons in carotid and aortic bodies ____.
Increases
Increases respiratory rate and tidal volume
True r false: Carotid bodies receive among the highest blood flows in the body
True
They account for 20% of the ventilatory drive, and ablation of the carotid bodies results in loss of compensatory ventilatory response to hypoxia and about 30% reduction in ventilatory response to high carbon dioxide.
Central Chemoreceptors
Located on ventral surface of the medulla near cranial nerves 6-10 and 12. Cells have no direct contact with arterial blood, but are bathed in CSF. The CSF in this brain area is in close proximity to the choroid plexus. Blood flow is high and carbon dioxide equilibrates rapidly so that CSF PCO2 is close to arterial PCO2.
Respond directly to H+, but indirectly to carbon dioxide.
The blood-brain barrier is permeable to ___ but not ___.
Carbon dioxide,
H+
Causes of metabolic acidosis
Hyperchioremic:
Diarrhea, Acetazolamid, IV hyperalimentation, Interstitial renal disease, Renal tubular acidosis
Increased Undetermined anion:
Generalized renal failure, diabetic ketoacidosis, alcoholic ketoacidosis, lactic acidosis
Causes of metabolic alkalosis
Vomiting, nasogastric suction, diuretics, alkali treatment, corticoid treatment, severe K+ depletion, Cl- restriction
Causes of respiratory acidosis
Respiratory failure (Obstructive lung disease, chest wall disease, mechanical hypoventilation), CNS depression, Severe pulmonary edema, status asthmaticus, primary hypoventilation, pneumothorax, abdominal distension
Causes of respiratory alkalosis
Hyperventilation, Gram-negative sepsis, pulmonary emboli, pnemonia, hepatic failure, high altitude, and severe anemia
When inhaled carbon dioxide levels are above ___, arterial PCO2 rises rapidly, resulting in ____.
7%, CNS depression (and eventually carbon dioxide narcosis and coma)
Carbon monoxide poisoning
CO binds to hemoglobin forming carboxyhemoglobin. The affinity between hemoglobin and CO is 230 times stronger than the affinity to oxygen. Binding of CO to one of the four O2 binding sites on hemoglobin results in the retnetion of O2 at the other sites and the failure of O2 release to the tissues. THere is a shift of the O2 dissociation curve to the left
Acute blood loss can lead to ___.
loss of oxygen carrying capacity
Hypoxia at high altitude leads to ___.
compensation with erythrocytosis
Nonchemical influence on ventilation
Proprioceptors and stretch receptors:
Located in muscle, tendons, and joints. Can stimulate ventilation in response to physical disturbance (slap and tickle) and possibly as anticipatory to physical exercise
Irritant receptors:
Stimulated by chemical or mechanical irritants, or histamine and bradykinin during an allergic reaction. Receptors in trachea and extrapulmonary bronchi cause coughing. In lungs, these receptors cause rapid shallow breathing and bronchoconstriction.
Other pulmonary receptors:
Stretch receptors in the smooth muscle of the airways excite sensory neurons running in the vagus, which will inhibit respiration. This is known as the Hering-Breuer reflex. In adults it functions at tidal volumes above 1 liter (ie during very strenous exercise. It is important in normal breathing in human infants and other mammals. Deflation receptors stimulated rapid, shallow breathing. These may contribute to ventilatory response during pulmonary congestion or edema.
Reticular activating system
diffuse network of neurons in midbrain and medulla that contribute to many of the autonomic functions. Parts of the RAS form the DRG and VRG while specialized receptors feed into these structures.
Off-switch neurons
Inhibited for most of inspiration, but this inhibition decreases with time and eventually helps to terminate respiration.
