CPR 56 - Control of Respiration

Question 1

List the respiratory centers, where they are found, and what they control?

Answer 1

Dorsal respiratory group - found in medulla oblongata and is most active during normal inspiration.

Venral respiratory group - aka the pre-Botzinger complex and is found in the medulla oblongata. The VRG is most active during above normal inspiration and active expiration. Neurons spontaneously fire and is thought to be the respiratory pacemaker.

Pontine respiratory group - found in the pons and provides tonic input to the medullary centers to control smooth respiratory rhythm.

Cerebral respiratory centers - voluntary control

Question 2

Describe the concept of ramp activity.

Answer 2

Ramp activity is a term used to describe action potential frequency from the respiratory centers. During inspiration there is an increase in APs from the inspiratory centers that eventually reach a crescendo which corresponds to maximal diaphragm tone. The same is true for the expiratory centers but only for active expiration.

Question 3

List the respiratory reflex pathways.

Answer 3

Pulmonary stretch receptors

Irritant receptors

J receptors

Proprioceptors

Question 4

Where are the pulmonary stretch receptors, what do they respond to, and what is their effect?

Answer 4

They lie in the smooth muscle layer of the airways and they fire in reponse to transmural pressure stretch the airways open. Their firing causes an excitation of the inspiratory off-switch and prolongs expiration.

Question 5

Where are the respiratory irritant receptors located, what do they respond to, and what is their effect?

Answer 5

The are located in the airway epithelium and they respond to touch, noxious substances, histamines, serotonins, prostaglandins, and edema. Their stimulation results in coughing/gasping.

Question 6

What are J receptors, where are they, what do they respond to, and what is their effect?

Answer 6

Juxtapulmonary capillary receptors are nerve endings (C-fibers) located next to pulmonary capillaries in the bronchi and alveoli. The Alveolar C-fibers respond to lung injury, overinflation, edema, and embolism. They are not sensitive to inflammatory mediators. The bronchial C-fibers are sensitive to inflammatory mediators. The stimulation of these fibers causes rapid shallow breathing, bronchoconstriction, airway secretion, and cardiovascular depression.

Question 7

Which proprioceptors are relevant to the respiratory system and how?

Answer 7

The chest wall proprioceptors detect the tension present in the wall and infrom the brain of the breathing effort being produced.

Question 8

Where are the central chemoreceptors located, what do they respond to, what is their effect?

Answer 8

The central chemoreceptors are located on the ventral surface of the medulla oblongata. They respond to pH changes in the CSF. A decrease in CSF pH will cause the central chemoreceptors to increase the rate of breathing.

Question 9

What is the blood brain barrier most permeable to?

Answer 9

O2 and CO2

Question 10

Describe how/why the CSF pH changes in response to pCO2 differ from the plasma’s response.

Answer 10

There is little protein in CSF to act as a buffer. Because of this CSF is much more sensitive than plasma to pCO2 increases. It takes a much smaller increase in CSF pCO2 to drop pH the same amount in plasma.

Question 11

T/F - Metabolic acid/base changes do not affect CSF pH.

Answer 11

False - the changes seen are just much less drastic then the changes caused by respiratory acid/base changes.

Question 12

Where are the peripheral chemoreceptors located, what do they respond to, what is their effect?

Answer 12

There is one located at the bifurcation of each carotid artery and multiple along the aorta. The carotid bodies detect pO2, pH, and pCO2 changes. However, their sensitivity to pCO2 is much lesser than to pO2 and pH. The aortic bodies only detect pO2 changes. A decrease in pO2, increase in pCO2, and decrease in pH all cause these centers to depolarize and stimulate the central respiratories centers to increase respiratory frequency.

Question 13

Which nerves do the peripheral chemoreceptors communicate with the CNS through?

Answer 13

Carotid bodies use the glossopharyngeal nerves

Aortic bodies use the vagus nerve

Question 14

What component of the peripheral chemoreceptors posses the actual site of chemoreception? Describe this mechanism of chemoreception.

Answer 14

The glomus cell possesses a K+ channel that closes in response to decreased intracellular pO2 or decreased intracellular pH. Closure of this K+ channel depolarizes the cell which opens voltage gated calcium channels allowing neurotransmitter release.

The cell is permeable to O2 and CO2 (CO2 will undergoe CA reaction in cell) which is how it senses plasma pO2 and pCO2. The glomus cell also has a Na+/H+ exchanger which increased plasma [H+] will inhibit the action of which will decrease intracellular pH. This allows the glomus cell to detect plasma pH.

Question 15

Which chemoreceptors produce the strongest ventilatory response and via which stimulus?

Answer 15

Central chemoreceptors produce the greatest ventilatory response when high arterial pCO2 levels are detected.

Question 16

Describe how pCO2 and pO2 would change in a person who has developed emphysema. Describe why these changes occured.

Answer 16

pO2 would decrease because of a V/Q mismatch

pCO2 would likely remain normal since the body increases ventilation if pCO2 increases and CO2 is much more easily discharged than O2 is absorbed.

Question 17

Describe the role of the peripheral chemoreceptors in stimulating ventilation in a person with acute moderate hypercapnia.

Answer 17

The increased pCO2 will decrease blood pH but the kidneys will compensate and bring the pH back within normal range. Because of this the peripheral chemoreceptors contribute very little to repiration - r_emeber that the carotid bodies are not very sensitive to pCO2 and the aortic bodies only detect pO2_.

Question 18

Describe the roles of the central and peripheral chemoreceptors in driving ventilation in a person with chronic hypercapnia.

Answer 18

In chronic hypercapnia, the choroid plexus will restore CSF pH by secreting HCO3- into the CSF. Because of this the central chemoreceptors will no longer be the main drivers of ventilation. The increased drive to ventilate will then come from the hypoxemia which the peripheral chemoreceptors will sense. The strongest ventilatory drive will come from the carotid bodies.

Question 19

When do the carotid bodies begin to sense drops in pO2 and at what point does their signaling increase drastically?

Answer 19

Carotid bodies can sense any drop in pO2 below 500 mmHg but their response doesn’t begin to really intensify until it starts to drop below 100 mmHg.

Question 20

Describe the debate concerning oxygen induced hypercapnia in patients with COPD.

Answer 20

Because the primary drive to ventilate in patients with COPD comes from hypoxemia, it is thought that putting a COPD patient on oxygen will depress ventilation enough to cause hypercapnia. Many now say that this notion is overemphasized and that CO2 retention is more likely a consequence of V/Q mismatch.

Question 21

What are the symptoms of hypoxaemia?

Answer 21

• Regional pulmonary vasoconstriction in response to alveolar hypoxia to maintain V/Q ratio. This leads to pulmonary hypertension which leads to right ventricular heart failure
• Peripheral vasodilation and increased CO
• Erythropoiesis increase leading to polycythaemia
• Loss of cognitive & motor functions
• Impaired judgement
• Headace, breathlessness, palpitations, tremor, restlessness
• Loss of consciousness

Question 22

What are the immediate and long term benefits of treating hypoxaemia?

Answer 22

Immediate Benefits - improvement in exercise capacity, reduction in dyspnoea, and sleed consolidation

Long Term Benefits - improved survival and slight reduction in pulmonary artery pressure