Chemical Control Of Ventilation

Question 0

What factors determine ventilation ?

Answer 0

Rate and depth of breathing - under neural control

Question 1

What are the central controllers of ventilation, the effectors and sensors ?

Answer 1

Pons, medulla and other brain areas
Respiratory muscles
Chemoreceptors, lungs and other receptors

Question 2

What do chemoreceptors do and where are they located ?

Answer 2

Detect changes in the chemical composition of the blood and they are in the systemic arterial system and the brain

Question 3

What are the central chemoreceptors ?

Answer 3

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

Question 4

What do central chemoreceptors respond indirectly to ?

Answer 4

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

Question 5

What are central chemoreceptors not sensitive to ?

Answer 5

Arterial partial pressure of oxygen

Question 6

Where are peripheral chemoreceptors in the body ?

Answer 6

Carotid bodies(these are the most important ones) and aortic bodies

Question 7

What do peripheral chemoreceptors respond to ?

Answer 7

Arterial partial pressure of carbon dioxide(increases) oxygen(decreases)and pH (decreases)

Question 8

How is a low partial pressure of oxygen detected by carotid bodies ?

Answer 8

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

Question 9

Are the chemoreceptors more responsive to changes in oxygen or carbon dioxide ?

Answer 9

Carbon dioxide - only a small increase causes a rise in ventilation whereas oxygen has to decrease to 60 before response is significant

Question 10

What partial pressure of carbon dioxide leads to coma ?

Answer 10

90 mmHg

Question 11

Under normal conditions what is the average pH of ECF ?

Answer 11

7.4

Question 12

What is the pH range which causes deleterious effects ?

Answer 12

Anything outside 7.35-7.45

Effects: nerve excitability, decrease in enzyme activity and alterations in while body potassium levels

Question 13

What 2 systems work together to regulate blood pH ?

Answer 13

Respiratory and renal

Question 14

What does the Henderson hasselbalch equation tell us about blood pH ?

Answer 14

Dependent upon carbon dioxide concentration and bicarbonate concentration
So blood pH altered by blood carbon dioxide pressures and bicarbonate concentration

Question 15

What is metabolic acidosis and how is it compensated for ?

Answer 15

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

Question 16

What are some causes of metabolic acidosis ?

Answer 16

Diabetic ketoacidosis - abnormal fat metabolism
Diarrhoea - loss of bicarbonate ions
Heavy exercise - production of lactic acid
Renal failure - reduced proton excretion

Question 17

What is metabolic alkalosis and how is compensated for ?

Answer 17

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