Control of breathing (physiology)

Question 1

What part of the brain is responsible for respiration?

Answer 1

Pons and medulla = gives subconscious respiration
Higher centres will give conscious control when needed

Question 2

What nerve innervates the diaphragm?

Answer 2

Phrenic nerve
(from C 3,4,5&raquo_space; C345 keeps diaphragm alive)

Question 3

What is the control of inspiration?

Answer 3

Somatic via phrenic nerve and intercostal nerves
Usually subconscious but can be subject to voluntary modulation

Question 4

How can respiratory centres rhythm be modified? (4)

Answer 4

Emotion - via limbic system in the brain e.g. laughing or crying
Voluntary override - via higher centres in the brain
Mechano-sensory input from thorax - stretch reflex, stops overstretching of alveoli
Chemical composition of blood - PO2, PCO2, pH detected by chemoreceptors

Question 5

What are the 2 classes of chemoreceptors and where are they located?

Answer 5

Central - medulla
Periphery - carotid and aortic bodies

Question 6

What stimulus activates central chemoreceptors?

Answer 6

Respond directly to H+ concentration in CSF (directly reflects on PCO2)

Question 7

What stimulus activates peripheral chemoreceptors?

Answer 7

Responds to PO2 and plasma [H+]
(less so to PCO2)

Question 8

What is the effect on ventilation of central chemoreceptors being activated?

Answer 8

Causes reflex stimulation of ventilation if H+ conc. increases (driven by raised PCO2)

Ventilation inhibited by decrease in arterial PCO2 (reduces CSF [H+])

Question 9

What is the effect on ventilation of peripheral chemoreceptors being activated?

Answer 9

Brings about reflex stimulation of ventilation following significant fall in arterial PO2 (<60 mmHg)

If plasma pH falls ventilation will be stimulated.
If plasma pH increases ventilation will be inhibited.

Question 10

How do central chemoreceptors regulate arterial PCO2 by monitoring the pH of CSF?

Answer 10

They detect changes in pH in CSF around the brain.
If pH falls ([H+]. increases) then ventilation is stimulated.
If pH rises ([H+] decreases) then ventilation is inhibited.

Question 11

How are peripheral chemoreceptors important during hypoxia and acid-based disturbances?

Answer 11

Detect changes in arterial PO2 and H+ conc.

During hypoxia (reduced PO2 < 60mmHg) reflex stimulation of ventilation occurs.

If pH falls ventilation will be stimulated, if it increases ventilation will be inhibited.

Question 12

What is the bodies response to hyperventilating?

Answer 12

Ventilation is reflexly inhibited by an increase in arterial PO2 or a decrease in arterial PCO2/[H+].

Question 13

What is the bodies response to hyperventilating?

Answer 13

Ventilation is reflexly inhibited by an increase in arterial PO2 or a decrease in arterial PCO2/[H+].

Question 14

How does CO2 affect acid-base balance?

Answer 14

CO2 is capable of changing ECF pH because:
CO2 + H2O <> H2CO3 <> HCO3- + H+

Normally pH is stable because all the CO2 produced is eliminated in expired air.
But hypo/hyperventilation will alter plasma PCO2 and plasma [H+] will vary accordingly.

Hypo = CO2 retention = increase [H+] = respiratory acidosis.
Hyper = CO2 loss = decrease [H+] = respiratory alkalosis.

Question 15

What is the equation for pH? (relating lungs and kidneys)

Answer 15

pH inversely proportional to HCO3 (bicarbonate - controlled by kidneys)/ CO2 (controlled by lungs)

Question 16

How do we not get food in respiratory system?

Answer 16

Respiration is inhibited during swallowing to avoid aspiration of food/fluids.

Swallowing follows and expiration in order to dislodge any particles outwards from the region of the glottis.