Control of breathing

Question 1

What is required for gas diffusion?

Answer 1

1) Large surface area for gas exchange.
2) Large partial pressure gradients.
3) Gases with advantageous diffusion properties.
4) Specialised mechanisms for transporting O 2 and CO 2 between lungs and tissues.

Question 2

Partial pressure defintion

Answer 2

Sum of the partial pressures (mmHg) or tensions (torr) of a gas must be equal to total pressure.

Question 3

Partial pressure equation

Answer 3

Partial pressure of gas (Pgas) = fraction of gas (Fgas) in gas mixture x barometric pressure
Pgas = Fgas x Pb

Question 4

How is oxygen transported in the blood?

Answer 4

1. Dissolved

2. Bound to haemoglobin (Hb)

Question 5

What makes up a haemoglobin (Hb)?

Answer 5

Four heme (iron porphyrin compounds) groups joined to globin protein (two α chains and two β chains polypeptide chains)
Each heme group contains iron in the reduced ferrous form (Fe+++)

Question 6

What is the job of the reduced ferrous form in the heme group?

Answer 6

Site for O2 binding

Question 7

How many O2 groups bind a heme groups

Answer 7

4 O2 molecules

Question 8

What is the oxyhemoglobin dissociation curve?

Answer 8

Curve illustrates relationship between PO2 in blood and number of O2 molecules bound to Hb

Question 9

CO2 Production

Answer 9

Normal healthy conditions:
- 200 ml CO2 / min produced
- 80 molecules CO2 expired by lung for every 100 molecules of O2 entering.
Ratio of expired CO2 to O2 uptake – Respiratory Exchange Ratio.
In normal conditions, respiratory exchange ration = 0.8 (80 CO2 to 100 O2).

Question 10

How is CO2 carried around in the blood?

Answer 10

i) 7% dissolved- other 93% diffuses into red blood cells
ii) 23% (of 93%) bound to haemoglobin (Hb).
iii) 70% (of 93%) converted to bicarbonate and hydrogen ions(created by enzyme carbonic anhydrase)

Question 11

What are mechanoreceptors?

Answer 11

how body detects how much muscles are moving per breath

Sleep, Phonation, Emotion, Cardiovascular, Temperature, Exercise- other variables that effect the brain

Question 12

What is chemoreceptors?

Answer 12

Chemoreceptors are sensory receptors that detect chemical changes in the surrounding environment.
In respiratory system chemoreceptors detect changes in PO2, PCO2 and pH in blood.

Question 13

What are peripheral chemoreceptors?

Answer 13

Peripheral chemoreceptors are small, highly vascularised bodies in region of aortic arch and carotid sinuses (internal and external carotid artery)

Question 14

How is information from peripheral chemoreceptors sent to the brain?

Answer 14

Information sent via the glossopharyngeal and vagus nerves to the nucleus in brainstem called NTS

Question 15

What is the vagus nerve?

Answer 15

Main nerve in the brain

Question 16

What is the glossopharyngeal nerve?

Answer 16

Another carotid nerve

Question 17

What do peripheral chemoreceptors respond to?

Answer 17

• Respond to decreases in PO 2 (hypoxia).
• Reduction in arterial PO 2
• Peripheral chemoreceptors stimulated.
• Neural signals sent from carotid and aortic bodies to NTS in brainstem.
• Ventilation increases to restore PO 2 levels.

Question 18

What happens if PO2 is less than 60 mmHg

Answer 18

Progressive hyperventilation

Question 19

What are central chemoreceptors?

Answer 19

Clusters of neurones in the brainstem that are activated when PCO 2 is increased (hypercapnia) or pH decreased

Question 20

Where does hypercapnia response occur?

Answer 20

Central chemoreceptors in brainstem

Question 21

What is hypercapnia involved in?

Answer 21

Plays a major role in movement to movement control of breathing

Question 22

What are mechanoreceptors?

Answer 22

Sensory receptors that detects changes in pressure, movement and touch
In respiratory system detect movement of lungs and chest wall

Question 23

What neurones generate rhythm of breathing?

Answer 23

Respiratory neurones

Question 24

What do brainstem neurones produce?

Answer 24

Rhythmic neural signals sent to spinal cord

Question 25

Where does the phrenic nerve exit the spinal cord?

Answer 25

Level 3-5

Question 26

What do nerves exiting the thoracic spinal cord do?

Answer 26

Innervate intercostal muscles