Respiratory: Control of Breathing L18 Flashcards
What part of the brain uses neural control to control our rate of breathing? What part of the nervous system is this? Is this the only way we can breathe?
The respiratory centre in the brainstem periodically sends out impulses to control the rate of breathing. This is part of the autonomous nervous system, as normal quiet breathing occurs automatically.
This control can be overridden by the brain if we ‘want’ to change our breathing rate (i.e voluntary control can override autonomic control), or if we experience certain emotions.
Briefly describe the negative feedback use in keeping arterial pressure of O2 95mmHg and CO2 40mmHg constant.
Sensors gather information and send signals back to the respiratory control centre. These then integrate the information and send signals to the effectors (respiratory muscles), which alter the depth and frequency of breathing.
Where are the peripheral chemoreceptors found? What do they respond to?
Mostly in the carotid arteries but also in the aortic arch. These peripheral chemoreceptors respond to both high arterial CO2 (hypercapnia) and low arterial O2 (hypoxia) and increased arterial [H+] (decreased pH).
What speed do chemoreceptors act? How responsible are they for the response to gas pressure changes?
Peripheral chemoreceptors are fast responding. They are responsible for responding to hypoxia, and 20-30% responsible for hypercapnia.
Central chemoreceptors are found where?
In the medulla.
How do central chemoreceptors work?
Stimulated by decrease in pH (H+ increase) in the brain extracellular fluid (which indirectly indicates increased CO2). Note they are not sensitive to arterial oxygen pressure.
What are the pulmonary stretch receptors? What is the gamma system?
Pulmonary stretch receptors are mechanoreceptors found in the lungs that monitor the stretch of the lungs and send this information to the respiratory centre via the vagus nerve. The gamma system in muscle spindles senses muscle elongation.
What are the arterial baroreceptors?
Arterial baroreceptors sense change in blood pressure and can send signals that will result in changes in breathing in response.
Describe other receptors besides the pulmonary stretch and arterial baroreceptors, that affect the respiratory system.
Receptors in the nose and upper airways respond to cold air, mechanical or chemical stimuli (dust and smoke), initiating coughing, sneezing or bronchoconstriction.
Joint and muscle receptors drive the increase in ventilation required during exercise.
Stimulation of pain and temperature receptors may cause changes in breathing in response to pain and changes in temperature (e.g you may stop breathing for a brief moment after being startled by exposure to cold air or by being hurt),
Explain the effector response to changes in PaCO2.
PaCO2 is the most important driver of changes in ventilation. As PaCO2 increases the effector response will be an increase in ventilation. (There is a myth that breathing harder is due to lack of oxygen, which is not always true, its more likely due to excess CO2)
Most of the response to raised PaCO2 is driven by central chemoreceptors, but peripheral chemoreceptors also have a role (especially in the initial, rapid response). PaCO2 is usually kept within 3mmHg of its normal value of 40mmHg, but during sleep this increases slightly.
Athletes and divers tend to have a lower sensitivity to changes in PaCO2 and a blunted effector response.
Various drugs (e.g morphine) will depress the respiratory centres and will result in hypoventilation, despite increasing PaCO2.
Hypoxia sensitises peripheral chemoreceptors so if PaO2 is low, the response to an increase in PaCO2 will be magnified.
Explain effector response to changes in O2.
The effector response to hypoxia becomes more important at high altitudes, where the PO2 in atmosphere is significantly lower.
It is also important in chronic lung diseases, where oxygen remains low for a sustained period of time (hypoxaemia)
If PaCO2 remains normal, PaO2 levels must be considerably low (less than 60mmHg) before an increase in ventilation.
However if PaCO2 increases while PaO2 decreases, the response will be much more rapid.
Discuss the reflexive breathing following a breath hold response.
Voluntary apnoea (holding breath):
Increase in alveolar and arterial PCO2, decrease in alveolar and arterial PO2.
Increase in firing of peripheral and central chemoreceptors.
Medullary respiratory neurons fire reflexively when levels become critical.
Contraction of inspiratory muscles.
Increase in ventilation.
Return of arterial PCO2 and PO2.
