Control Of Respiration

Question 1

What is the rhythm of respiration?

Answer 1

Inspiration followed by expiration.

Question 2

What generates the rhythm of respiration?

Answer 2

A network of neutrons called the pre-botzinger complex. These neutrons display pacemaker activity. They are located near the upper end of the medullary respiratory centre.

Question 3

Describe the neuron process that gives rise to inspiration.

Answer 3

1. Rhythm generated by pre-botzinger complex.
2. This excites the DORSAL respiratory group of neurons
3. They fire in bursts
4. The firing leads to contraction of the inspiratory muscles
5. When firing stops, there is passive expiration

Question 4

Is inspiration active or passive?

Answer 4

Active

Question 5

Is expiration normally active or passive?

Answer 5

Passive

Question 6

How does the diaphragm change the volume of the thorax during inspiration?

Answer 6

The volume of the thorax is increased vertically due to the contraction of the diaphragm.

Question 7

Which nerve controls the diaphragm?

Answer 7

Phrenic nerve from cervical 3, 4, and 5.

Question 8

How does the intercostal muscles change the volume of the thorax during inspiration?

Answer 8

The contraction lifts the ribs and pulls out the sternum.

Question 9

What is the neuron process behind active expiration?

Answer 9

1. There is increased firing of dorsal neurones which excites ventral respiratory group neurons.
2. These then fire to excite internal intercostal and abdominal muscles for forceful expiration.

Question 10

How can the rhythm of firing from the medulla be modified by the Pneumotaxic Centre?

Answer 10

Stimulation of the PNEUMOTAXIC CENTRE by dorsal respiratory neurons terminates inspiration. This regulates respiration as it prevents prolonged inspiration.

Question 11

How can the rhythm of firing from the medulla be modified by the Apneustic Centre?

Answer 11

This has the opposite effect to the pneumotaxic centre. It sends impulses to excite the inspiratory area of the medulla. This results in prolonged inspiration.

Question 12

Where else does the respiratory system receive stimulation from?

Answer 12

Higher brain centres
Stretch receptors in the walls of the bronchi and bronchioles
Juxtapulmonary receptors - affected by pulmonary conditions
Joint receptors
Baroreceptors
Central and peripheral chemoreceptors - chemical control

Question 13

What are some of the involuntary modifications of breathing?

Answer 13

1. Pulmonary Stretch receptors in the Hering-Breur Reflex
2. Joint Receptors in exercise
3. Stimulation or the respiratory centre by temperature, adrenaline, or impulses from the cerebral cortex.
4. Cough reflex

Question 14

How do pulmonary stretch receptors work?

Answer 14

They are activated during inspiration and afferent discharge inhibits inspiration. This is the HERING-BREUER REFLEX

Question 15

How do joint receptors work?

Answer 15

They send impulses when the limbs move reflexly increasing breathing. They contribute to increased ventilation during exercise.

Question 16

Name some factors that increase ventilation during exercise.

Answer 16

Reflexes originating from body movement
Adrenaline release
Impulses from the cerebral cortex
Increase in body temperature
Later accumulation of CO2 and H+ generated by active muscles.

Question 17

What is the cough reflex?

Answer 17

This helps to clear dust, dirt or excessive secretions out of the lungs and is activated by irritation of airways or tight airways by a centre in the medulla.

Question 18

What is the process of the cough reflex?

Answer 18

1. Short intake of breath
2. Closure of the larynx
3. Contraction of abdominal muscles to increase intra-alveolar pressure.
4. Opening of the larynx and expulsion of air at a high speed.

Question 19

What is the chemical control of respiration?

Answer 19

This is an example of negative feed back control. It is controlled by variables in the blood gas tension, especially relating to carbon dioxide. Chemoreceptors sense the values of gas tension in the blood.

Question 20

Describe peripheral chemoreceptors.

Answer 20

They are located in the carotid bodies and aoritc bodies and they mainly sense tension of O2 (and some CO2) and [H+] in the blood.

Question 21

Describe central chemoreceptors.

Answer 21

They are situated near the surface of the medulla of the brainstem and respond to [H+] in the cerebrospinal fluid.

Question 22

What is cerebrospinal fluid?

Answer 22

This is separated from the blood by the blood-brain barrier. It is relatively impermeable to H+ and HCO3- and CO2 diffuses readily across the barrier.
It contains less protein than blood and is therefore less buffered than blood.

Question 23

What is the hypoxaemic drive of respiration?

Answer 23

This is carried out by the peripheral chemoreceptors and is stimulated by low PO2.
This drive is important in patients with chronic CO2 retention and at high altitudes

Question 24

Why do we give COPD patients with hypoxaemia and chronically elevated CO2 less O2?

Answer 24

These patients have lost sensitivity to the hypercapnic drive and are therefore dependent on hypoxaemic drive, if their hypoxia is corrected, they will lose some of their hypoxaemic drive and CO2 will therefore accumulate.

Question 25

What causes hypoxia at high altitudes?

Answer 25

Decreased partial pressure of inspired oxygen. This results in hyperventilation and increased cardiac output.

Question 26

What are some of the chronic adaptations the high altitude hypoxia?

Answer 26

Increased - RBC production, 2,3 BPG production in RBC, number of capillaries, number of mitochondria
The kidneys will also conserve acid

Question 27

What is the H+ drive of respiration?

Answer 27

This effect id via the peripheral chemoreceptors because H+ cannot cross the blood brain barrier. They are stimulated by increased H+ causing hyperventilation and increased elimination of CO2.