Respiratory System - Chemical Regulation of Breathing

Question 1

What are the components of the respiratory system?

Answer 1

Higher centres - cerebral cortex, hypothalamus
Respiratory centre - brainstem, medulla, receives input from pons
Sensors - chemoreceptors, stretch receptors and proprioceptors
Effectors - respiratory muscles

Question 2

What are central chemoreceptors?

Answer 2

Central chemoreceptors are specialised cells located in the central nervous system, primarily in the medulla oblongata
Primarily respond to changes in the pH of the cerebrospinal fluid (CSF)
Role in the regulation of breathing by integrating information about the levels of CO2 and pH in the CSF
They work in concert with peripheral chemoreceptors to maintain appropriate levels of blood gases and pH, ensuring efficient oxygen delivery and carbon dioxide removal from the body

Question 3

What are peripheral chemoreceptors?

Answer 3

Peripheral chemoreceptors are specialised cells located in the carotid bodies and aortic bodies in neck and aorta
Function is to sense changes in levels of oxygen, carbon dioxide and pH in the blood.
When stimulated by changes in these parameters, peripheral chemoreceptors send signals to the respiratory centres in the brainstem (medulla oblongata) to adjust the rate and depth of breathing accordingly

Question 4

Describe how peripheral chemoreceptors respond to changes in oxygen, CO2 and pH.

Answer 4

Oxygen sensing - peripheral chemoreceptors are sensitive to decrease in partial pressure of oxygen PO2 in the blood and when it drops below a certain threshold they’re stimulated
Carbon dioxide sensing - less sensitive to changes in PCO2 than PO2, an increase in PCO2, (hypercapnia) stimulates peripheral chemoreceptors and lead to increased respiratory rate and depth, helping to eliminate excess CO2 from the body
pH sensing - when blood pH decreases (acidosis) due to conditions like metabolic acidosis, peripheral chemoreceptors are stimulated, leading to an increase in respiratory rate in an attempt to compensate for the acidosis by increasing CO2 elimination

Question 5

What is the ventilatory response to carbon dioxide?

Answer 5

Central chemoreceptors detect changes in cerebrospinal fluid pH as a result of increase PaCO2
Central chemoreceptors signal medulla oblongata to stimulate a hyperventilation response facilitating the removal of CO2 from the blood through expiration
This lowers blood PCO2 and restores acid-base balance

Question 6

What is the ventilatory response to H+ ?

Answer 6

Central chemoreceptors detect changes in cerebrospinal fluid pH reflected in changes to blood pH by excess H+ ions
A decrease in blood pH (acidosis) stimulates central chemoreceptors, leading to hyperventilation which eliminates excess CO2 thereby raising blood pH
Respiratory alkalosis, caused by decreased blood CO2 levels, can lead to hypoventilation to retain CO2 and restore blood pH
The ventilatory response to H+ ions plays a crucial role in buffering metabolic acid-base disturbances and maintaining pH balance

Question 7

What is the ventilatory response to oxygen ?

Answer 7

Decrease in PaO2 results in increased ventilation primarily due to peripheral chemoreceptors
Peripheral chemoreceptors are sensitive to hypoxemia signal respiratory centres to increase the rate and depth of breathing via medulla oblongata
Results in increased ventilation which increases oxygen uptake causing a rise in PaO2
The hyperventilation response to hypoxemia is crucial for ensuring adequate tissue oxygenation in conditions such as high altitude or lung diseases

Question 8

How is oxygen regulated using negative feedback loop ?

Answer 8

When PO2 decreases peripheral chemoreceptors in carotid and aortic bodies detect it and the information is relayed to medulla oblongata
Respiratory centres increase rate and depth of breathing increasing ventilation
Results in increase PO2, thus the stimulus for increased ventilation diminishes and negative feedback loop returns to normal

Question 9

How is carbon dioxide regulated using negative feedback loop ?

Answer 9

When PCO2 increases (hypercapnia) central chemoreceptors detect changes in cerebrospinal fluid pH
Information from central chemoreceptors is integrated with input from peripheral chemoreceptors to increase ventilation thereby removing CO2 and lowering PCO2
As blood PCO2 levels decrease, feedback loop returns to normal

Question 10

What are the principle neuronal connections associated with chemoreceptor reflexes ?

Answer 10

• Peripheral chemoreceptors detect changes in blood levels of O2, CO2 and pH
• Afferent sensory neurones carry signals from peripheral chemoreceptors via the glossopharyngeal nerve and vagus nerve to the CNS
• Sensory signals are integrated in the medulla oblongata where respiratory centres are located
• Input from peripheral chemoreceptors may interact with signals from central chemoreceptors in the medulla oblongata
• Efferent signals are sent from respiratory centres to motor neurones controlling respiratory muscles via phrenic nerve (diaphragm) and intercostal nerves
• Motor neurones activate respiratory muscles causing changes in respiratory rate and depth to maintain blood gas homeostasis