Physiology - Control of Respiration

Question 1

Arrangement of brainstem (superior to inferior).

Answer 1

Pons
Medulla oblongata
Spinal cord.

Question 2

Ventilation above and below medulla?

Answer 2

Above - Normal.

Below - Ceases.

Question 3

What is the medulla?

Answer 3

Major rhythm generator.

Question 4

What generates the breathing rhythm?

Answer 4

A network of neurons called pre-botzinger complex.

Question 5

Where is the pre-botzinger complex located?

Answer 5

Upper end of medullary respiratory centre.

Question 6

In what two ways can respiration be controlled?

Answer 6

Neural

Chemical.

Question 7

How does inspiration arise?

Answer 7

Rhythm generated by pre-botzinger complex which excites dorsal respiratory group neurones that fire in bursts. The firing leads to contraction of inspiratory muscles causing inspiration.

Question 8

What happens when firing of dorsal respiratory neurons stops?

Answer 8

Passive expiration.

Question 9

What about active expiration during hyperventilation?

Answer 9

Increased firing from dorsal neurones activate a second group - Ventral neurons. Which excite internal intercostals and abdominals causing forceful expiration.

Question 10

What can rhythm be modified by?

Answer 10

Neurones in the pons.

Question 11

What is the PC in the pons?

Answer 11

Pneumotaxic centre. Stimulation terminates inspiration.

Question 12

When is PC stimulated?

Answer 12

When dorsal neurones fire.

Question 13

What would happen without PC?

Answer 13

Prolonged breathing, gasps with brief expiration. - Apneusis.

Question 14

What are the two centres in the pons?

Answer 14

Pneumotaxic and Apneustic.

Question 15

What does the apneustic centre do?

Answer 15

Impulses from apneustic neurones excites inspiratory area of medulla and prolong inspiration.

Question 16

What are the respiratory centres influenced by?

Answer 16

Stimuli from:
Higher brain centres,
Joint Receptors,
Baroreceptors,
Stretch receptors In bronchioles,
Juxtapulmonary receptors.

Question 17

What is the inflation Hering-Breur reflex?

When do they act?

Answer 17

Pulmonary stretch receptors in the bronchioles that prevent hyperinflation by Inhibiting inspiration.

Only at large tidal volumes.

Question 18

Involuntary modifications of breathing.

Answer 18

Hering-Breuer Reflex

Joint receptors in exercise,

Cough reflex,

Stimulations of resp centre by temp, adrenaline or
impulses from the cerebral cortex

Question 19

What occurs after a period of exercise that will increase ventilation?

Answer 19

Accumulation of CO2 and CO2 generated by active muscles.

Question 20

Describe the process of the cough reflex?

Answer 20

Afferent discharge stimulates a short intake of breath followed by closure of the larynx, then contraction of abdominals which increases intra-alveolar pressure and finally opening of larynx and expulsion of air at high speed.

Question 21

What does the cough reflex protect against?

When is it activated?

Answer 21

Vital part of body’s defense system as it helps clear airways of dust, dirt or excessive secretions.

Activated by irritation/ tight airways (asthma)

Question 22

What type of control system is chemical control of respiration?

Answer 22

Negative Feedback.

Question 23

What are the chemically controlled variables of respiration?

What senses the values of these variables?

Answer 23

Blood gas tensions (especially CO2).

Chemoreceptors.

Question 24

What are the 2 types of chemoreceptors?

Answer 24

Peripheral and central.

Question 25

Where are peripheral chemoreceptors found and what do they do?

Answer 25

Carotid and Aortic bodies.

Sense tensions of O2, CO2 and H+ In blood.

Question 26

Where are central chemoreceptors found and what do they do?

Answer 26

Situated near surface of the medulla.

Respond to H+ conc of cerebrospinal fluid (CSF).

Question 27

How is CSF separated from the blood?

Answer 27

Blood brain barrier - CO2 diffuses readily but relatively impermeable to H+ and HCO3-

Question 28

Hypoxic drive of respiration.

Answer 28

Caused by peripheral chemoreceptors.

Stimulated when PO2 falls <8KPa and therefore becomes important in patients with chronic CO2 retention and at high altitudes.

Question 29

What causes hypoxia at high altitudes?

Acute response.

Answer 29

Decreased PiO2.

Hyperventilation and increased cardiac output.

Question 30

Chronic adaptations to high altitude hypoxia?

Answer 30

> RBC production (Increases O2 carrying capacity in blood)

> 2,3 BPG produced in RBC (O2 offloaded easily onto tissues)

> number of capillaries (blood diffuses easily)

> mitochondria (O2 used efficiently)

Kidneys conserve acid (< arterial pH)

Question 31

H+ drive of respiration?

Answer 31

H+ can’t cross blood brain barrier but CO2 can.

Peripheral chemoreceptors adjust for acidosis due to H+ in blood from lactic acid/diabetic ketoacidosis.
Their stimulation causes hyperventilation increasing elimination of CO2 and therefore H+ in body.

Question 32

Effect of Po2 on peripheral and central chemoreceptors?

Answer 32

Peripheral - Only important if PO2 falls <8 Kpa

Central - Severe hypoxia depresses respiratory centre.

Question 33

Effect of arterial H+ on peripheral and central chemoreceptors?

Answer 33

Peripheral - Stimulation important in acid base balance.

Central - H+ cannot cross blood brain barrier.

Question 34

Effect of arterial PCO2 (H+ in brain CSF) on peripheral and central chemoreceptors?

Answer 34

Peripheral - Weak stimulation.

Central - Dominant control of ventilation.