Chemical Control Of Ventilation Flashcards
What factors determine ventilation ?
Rate and depth of breathing - under neural control
What are the central controllers of ventilation, the effectors and sensors ?
Pons, medulla and other brain areas
Respiratory muscles
Chemoreceptors, lungs and other receptors
What do chemoreceptors do and where are they located ?
Detect changes in the chemical composition of the blood and they are in the systemic arterial system and the brain
What are the central chemoreceptors ?
Most important chemoreceptors in minute to minute control
Present in ventral medulla
Responds to changes in proton concentration of CSF
- increase in protons stimulates ventilation
What do central chemoreceptors respond indirectly to ?
Partial arterial pressure of carbon dioxide - it is able to cross the BBB and into CSF where it is broken down by carbonic anhydrase which Increases proton concentration
What are central chemoreceptors not sensitive to ?
Arterial partial pressure of oxygen
Where are peripheral chemoreceptors in the body ?
Carotid bodies(these are the most important ones) and aortic bodies
What do peripheral chemoreceptors respond to ?
Arterial partial pressure of carbon dioxide(increases) oxygen(decreases)and pH (decreases)
How is a low partial pressure of oxygen detected by carotid bodies ?
Inactivate membrane potassium channels reducing the potassium efflux
Depolarises the cell activating calcium channels causing influx of calcium, triggering the release of nt
Nt binds to receipts on afferent nerve causing an increase in AP frequency
Are the chemoreceptors more responsive to changes in oxygen or carbon dioxide ?
Carbon dioxide - only a small increase causes a rise in ventilation whereas oxygen has to decrease to 60 before response is significant
What partial pressure of carbon dioxide leads to coma ?
90 mmHg
Under normal conditions what is the average pH of ECF ?
7.4
What is the pH range which causes deleterious effects ?
Anything outside 7.35-7.45
Effects: nerve excitability, decrease in enzyme activity and alterations in while body potassium levels
What 2 systems work together to regulate blood pH ?
Respiratory and renal
What does the Henderson hasselbalch equation tell us about blood pH ?
Dependent upon carbon dioxide concentration and bicarbonate concentration
So blood pH altered by blood carbon dioxide pressures and bicarbonate concentration
What is metabolic acidosis and how is it compensated for ?
Addition of acid in the plasma causing a decrease in pH
Decreased pH stimulates peripheral chemoreceptors to increas e ventilation
Causes a decrease in partial pressure of carbon dioxide driving reaction further to left to decrease proton concentration and increase ph
What are some causes of metabolic acidosis ?
Diabetic ketoacidosis - abnormal fat metabolism
Diarrhoea - loss of bicarbonate ions
Heavy exercise - production of lactic acid
Renal failure - reduced proton excretion
What is metabolic alkalosis and how is compensated for ?
Excessive loss of protons or addition of bicarbonate ions
Causes an increase in ph, the decrease proton concentration decreases ventilation to increase partial pressure of carbon dioxide driving reaction to right to increase proton concentration and decrease the ph
Causes: excessive ingestion of anatacids and vomiting
