Respiratory System - Control of Respiration
What are the two neuronal clusters found within the medullary respiratory center?
1. dorsal respiratory group (DRG) 2. ventral respiratory group (VRG)
What are the five systems involved in control of respiration?
1. medullary centers 2. pontine centers 3. pulmonary stretch receptors 4. chemoreceptors 5. voluntary cortical center
What are the two respiratory control centers that lie higher in the brain stem than the medullary respiratory center?
1. pneumotaxic center (highest) 2. apneustic center
What three chemical factors have an effect on ventilation?
1. pressure of O2 2. pressure of CO2 3. pressure of H+
How high can the PCO2 reach before this depression of brain activity occurs?
70 to 80 mmHg
What is the % saturation of Hb when the PO2 is 60 mmHg?
90% saturation
What is the formula for used for predicting changes in respiration based on changes of changes of chemical factors?
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- think of it like a balancing scale: - when one end is increased, the other end has to increase to compensate - if O2 is low, CO2 is high, increased ventilation to compensate - if H+ is high, O2 is high, decreased ventilation to compensate
What causes the increased H+ concentration in the ECF?
CO2 diffuses down its pressure gradient from the cerebral blood vessels into the ECF in the brain carbonic anhydrase converts CO2 and water into H+ and HCO3-
What is the level of regulation caused by arterial PCO2 compared to PO2?
PCO2 is minute-to-minute regulation - PCO2 is the most important input regulating the magnitude of ventilation under resting conditions
If arterial PCO2 is high, what happens to PCO2 in the ECF of the brain? [H+]?
PCO2 → high [H+] → high
Do peripheral chemoreceptors respond to PO2 or total O2 content?
PO2 - this is why O2 content can fall dangerously low to fatal levels without the peripheral chemoreceptors responding
What is the total PO2 in the arterial blood in the case of CO poisoning?
PO2 is normal - respiration is not stimulated even though O2 isn't being delivered to the tissues
What part of the respiratory control center has a similar role as the SA node of the heart?
Pre-Botzinger complex
Acidosis ____ respiration, alkalosis _____ respiration.
acidosis → stimulates respiration alkalosis → inhibits respiration
Peripheral chemoreceptors are weakly sensitive to ___.
arterial PCO2
Peripheral chemoreceptors are unresponsive to ____.
arterial PO2 - unless it falls 40% below normal
Peripheral chemoreceptors are highly receptive to ____.
arterial [H+]
How does arterial PCO2 indirectly stimulate the peripheral chemoreceptors?
as arterial PCO2 increases there is a corresponding increase in arterial [H+] - there is a corresponding increase in ventilation
Where is the Pre-Botzinger complex located?
at the upper end (head) of the VRG
What receptors are located in the same vicinity as the peripheral chemoreceptors?
carotid sinus and aortic arch baroreceptors - monitor pressure changes, not chemical changes
Why do CO2 levels continue to increase when you hold your breath?
cell metabolism continually produces CO2 and it accumulates if it isn't breathed off.
What monitors the changes of chemical factors?
central chemoreceptors peripheral chemoreceptors
What receptors respond if arterial PCO2 is elevated?
central chemoreceptors in the medulla near the respiratory center
If arterial PCO2 is low, activity of the central chemoreceptors will be ____, and ventilation will be _____.
central chemoreceptors → decreased ventilation → decreased
What influences the central chemoreceptors? peripheral chemoreceptors?
central → "respiratory drive" or drive to breath peripheral → acute changes in blood gases
What are the central chemoreceptors indirectly sensitive to? Peripheral chemoreceptors?
central → CO2 in plasma peripheral → only directly sensitive
What are the central chemoreceptors directly sensitive to? Peripheral chemoreceptors?
central → pH of CSF peripheral → O2, CO2, and H+ (pH)
Where are central chemoreceptors located? Peripheral chemoreceptors?
central → ventral surface of brainstem peripheral → aortic arch and carotid body
What establishes the rhythmic pattern of breathing?
cyclic neural activity to the respiratory muscles
What is a condition that might cause there to be normal levels of arterial PCO2, but high concentration of arterial H+?
diabetic ketoacidosis
Specifically, what muscles alternate contraction to cause the rhythmic pattern of breathing?
diaphragm external intercostal muscles
What happens to the % saturation of Hb when the PO2 falls below 60 mmHg?
drops drastically from 90%
True or false. Arterial [H+] influences the central chemoreceptors.
false H+ doesn't cross the BBB
True or false. Central chemoreceptors directly monitor CO2.
false they monitor H+ concentration in the ECF that bathes them
In people with severe chronic lung disease, what is their primary drive to breathe?
hypoxia → need for oxygen - not the need to breathe out CO2
Where is the generation of respiratory rhythm thought to reside?
in the Pre-Botzinger complex
Why is the medullary respiratory center called the primary respiratory control center?
in the medulla there are several aggregations of neuronal cell bodies - provide output to the respiratory muscles
Where is the pacemaker activity that establishes breathing rhythm found?
in the respiratory control centers in the brain stem
What is the function of the control centers in the pons?
influence the output from the medullary respiratory center
Except for the peripheral chemoreceptors, the level of activity in all nervous tissues ____ during O2 deprivation?
is reduced
What control center controls contraction and relaxation of inspiratory muscles?
medullary respiratory center
What is the primary respiratory control center?
medullary respiratory center
Where are the pneumotaxic and apneustic centers found?
pons
What causes severe chronic lung disease and loss of sensitivity of central chemoreceptors?
prolonged increase in H+ generation in the brain ECF allows HCO3- to leak across the BBB and buffer the excess H+ in the brain ECF this causes H+ in the brain to return to normal even though arterial PCO2 and brain ECF PCO2 are still high
What is the total O2 content in the arterial blood in anemic states?
reduced
In response to PO2 below 60 mmHg in the arteries, what form of stimulation kicks in to compensate?
reflex stimulation of respiration by peripheral chemoreceptors
What type of muscles are respiratory muscles?
skeletal muscles
What is the effect of very high levels of CO2 on the brain?
they directly depress the entire brain, including the respiratory center - just as very low levels of O2 do
True or false. Aortic and carotid peripheral chemoreceptors are highly responsive to fluctuations in arterial [H+].
true
True or false. Respiratory activity can be voluntarily modified.
true
True or false. It is impossible to suffocate by simply holding your breath.
true as [H+] rises to excessively high levels, the excitatory input on the central chemoreceptors is so powerful that it overrides the voluntary inhibitory respiration
True or false. No important receptors monitor arterial PCO2.
true - peripheral chemoreceptors aren't involved in monitoring PCO2
What causes the H+ in the brain ECF to return to normal levels?
ventilation breathes the elevated CO2 off and H+ drops back to normal levels
