Lecture 20 - Controlling breathing Flashcards
The three things that affect the controlled rhythm of breathing
1) Metabolic (arterial blood gases and pH)
2) mechanical (postural changes)
3) Episodic non-ventilatory behaviours (talking, eating etc)
How are oxygen and carboin dioxide maintained
Oxygen absorption is matched to delivery
Carbon dioxide production is matched to removal
This is done either passively by the local and central centres in breathing
The three local controls of gas transport
1) Tissue concentrations:
When P(O₂) is low and P(CO₂) is high, blood flow is increased to supply more O₂ and remove CO₂ simultaneously
2) Lung perfusion:
When P(O₂) is low, vasoconstriction occurs to send more blood to more oxygen-rich areas in the lungs
3) Alveolar ventilation:
When P(CO₂) is too high, bronchodilation occurs to increase airflow in that part of the lung, removing the CO₂ from the body
Central control of gas ventilation
There are three main parts to the central control:
- Sensors:
Central and peripheral mechanoreceptors and chemoreceptors - Central controllers:
Respiratory centres in the Medulla and Pons - Effectors:
Muscles of ventilation
The three main sensors for gas ventilation
Central chemoreceptors in the medulla
Peripheral chemoreceptors in the aortic and carotid body
Mechanoreceptors in the lungs
Central chemoreceptors in the medulla: what are they, where are they located, and what do they do?
Chemoreceptors detect chemical changes in the blood
Located just beneath the ventral surface of the medulla, close to the entry of VIII and XI cranial nerves
These detect a change in pH and this is how the body detects hypercapnia (high CO₂ levels) but cannot be used to detect hypoxia (low O₂ levels)
Peripheral chemoreceptors in the aortic and carotid body: what are they, where are they located, what nerves innervate them, and what do they do?
Detect chemical changes in the blood
Just before the bifurcation of the carotid arteries and before/after the aortic arch
Carotid: Carotid sinus nerve (CNS) - Glossopharygneal (each of the ninth pair of cranial nerves, supplying the tongue and pharynx)
Aortic - Vagus
Detect P(O₂) (hypoxia), P(CO₂) (hypercapnia), and P(H⁺) levels and these receptors cause an increase in heart rate to counteract any issues
Mechanoreceptors in the lungs: what are they, where are they located, what nerves innervate them, and what do they do?
Mechanoreceptors monitor physical changes in the body
Lungs
Innervated by the vagus nerve
These receptors react to stretching by the lungs and contain C-fibre receptors, involved in the Hering Breuer reflex
Factors that affect the depth and rate of breathing
- Exercise
- Altitude
- Disease
- P(O₂), P(CO₂), and P(H⁺) but action is only taken if P(O₂) falls below 60 millimetres of mercury (mmHg)
Respiratory acidosis: what is it, what causes it, and what is an example of it?
A decrease in blood pH to be more acidic due to higher blood CO₂ concentrations (>43mmHg), causing more H⁺ in the blood due to the reaction:
CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻
An example is the limited gas exchange in emphysema causing a CO₂ build-up
Respiratory alkalosis: what is it, what causes it, and what is an example of it?
An increase in blood pH to be more alkaline due to lower blood P(CO₂) (<37mmHg), causing less H⁺ in the blood due to the reaction:
CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻
An example is hyperventilation removing too much CO₂
What happens if the PO₂ is too high?
It can occur by breathing too much oxygen in oxygen-rich areas
Free radicals may generate, potentially causing coma or death
What happens if the PO₂ is too low?
Once arterial P(O₂) drops below 60mmHg, ventilation is increased and central chemoreceptors are turned off while peripheral chemoreceptors are turned on and breathing rate is increased
Hering Breuer reflex
A reflex that prevents overinflation of the lungs
Slowly adapting stretch receptors in the lungs: what are they part of, where are they found, and what do they do?
Bronchopulmonary receptors that are part of the lung mechanoreceptors and are found in the visceral pleura, bronchioles, and alveoli
Involved in inhibiting respiratory centres when the lungs overinflate
