Physiology

Question 1

Where is the respiratory rhythm generated?

Answer 1

In the medulla

Question 2

What part of the brainstem sends signals to modify respiration?

Answer 2

The pons

Question 3

List the receptors/centres which send stimuli to the respiratory centres.

Answer 3

Central chemoreceptors
Peripheral chemoreceptors
Higher brain centres e.g. cerebral cortex, limbic system, hypothalamus
Stretch receptors (in walls of bronchi/bronchioles - guard against hyperinflation)
Juxtapulmonary receptors
- stimulated by pulmonary capillary congestion, pulmonary oedema and PE
Joint receptors (stimulated by joint movement)
Baroreceptors (increased resp rate in response to decreased BP)

Question 4

What are the peripheral chemoreceptors?

What do they monitor?

Answer 4

The carotid bodies
The aortic bodies
They monitor the tension of oxygen, CO2 and H+ in the blood

Question 5

What is the Hering-Breur reflex?

Answer 5

When stretch receptors in the walls of the bronchi and bronchioles stimulate the respiratory centres to guard against hyperinflation.

Question 6

Where are the central chemoreceptors situated?

What do they respond to?

Answer 6

Near the surface of the medulla

They respond to the H+ concentration of the CSF/CO2 of the blood.

Question 7

Is CSF more or less buffered than blood? Why?

Answer 7

Less, it contains less protein

Question 8

How does H+ leave the CSF?

Answer 8

It must be converted to CO2. CO2 diffuses readily across the BBB, whereas the BBB is relatively impermeable to H+ and HCO3-.

Question 9

What is the most potent stimulant of respiration in normal healthy people?

Answer 9

Arterial PCO2 acting on central chemoreceptors (i.e. H+ in CSF).

Question 10

Why does ventilation decrease at very low PaO2?

Answer 10

When hypoxia is very severe, the neurons which stimulate respiration are depressed.

Question 11

At which PaO2 are peripheral chemoreceptors stimulated?

Answer 11

8.0kPa

Question 12

What is the normal PaO2 at pulmonary capillaries?

Answer 12

13.3 kPa

Question 13

Which receptors mediate the hypoxic drive of respiration?

Answer 13

The peripheral chemoreceptors.

Question 14

In which circumstances does hypoxic drive become an important stimulator of respiration?

Answer 14

In patients with chronic CO2 retention (e.g. COPD) or at high altitudes.

Question 15

What receptors mediate the H+ drive of respiration?

Answer 15

Peripheral chemoreceptors

They adjust for acidosis caused by addition of non-carbonic acid to the blood

Question 16

What is the effect of low arterial oxygen pressure on a) the peripheral chemoreceptors and b) the central chemoreceptors?

Answer 16

a) Stimulates at

Question 17

In lactic acidosis, which chemoreceptors will be stimulated to cause increased respiration? Explain why it does not stimulate both.

Answer 17

The peripheral chemoreceptors.
H+ does not cross the BBB - central chemoreceptors are only exposed to CSF, and therefore can only sense carbonic H+ as CO2 can cross the BBB

Question 18

Explain the mechanism behind the following conditions leading to SOB:

a) kyphoscoliosis
b) Pneumothorax
c) Asthma and COPD

Answer 18

a) Decreased compliance of the chest wall
b) Loss of transmural pressure gradient across the lungs
c) Increased airway resistance.