5. Gas transport & Respiratory control

Question 1

What are the two forms of oxygen transports?

Answer 1

• 1.5% Dissolved in plasme

- 98.5% Bound to haemoglobin

Question 2

What contributes to circulating partial pressures?

Answer 2

Only dissolved gas

Question 3

Structure of Hb

Answer 3

• Tetrameric globular protein

* 4 Haem groups (each contain 1 Fe2+ ion)

Question 4

How much of O2 is transported in blood by Hb?

Answer 4

98.5%

Question 5

Function of Hb

Answer 5

Greater oxygen carrying capacity

Question 6

Hb-O2 Dissociation curve

Answer 6

Question 7

Changes in affinity of Hb for oxygen

Answer 7

Question 8

3 forms of carbon dioxide transport and percentage

Answer 8

• Dissolved – 10%
• Bound to hg – 30%
• Bicarbonate (HCO3-) – 60%, mostly in plasma

Question 9

Gas exchange diagram

Answer 9

Question 10

What does hypoxia mean?

Answer 10

Insufficient cellular O2

Question 11

Hypoxic hypoxia

Answer 11

Low PaO2 (hypoxemia) → ↓ %Hb Sat 
– Inadequate gas exchange
– ↓ PB (altitude)
– Cyanosis (skin bluish tint) = <70% Hb Sat

Question 12

Anaemic hypoxia

Answer 12

↓ total blood O2 content with normal PaO2
– ↓ circulating rbc’s; ↓ rbc Hb content
– CO poisoning (no cyanosis – HbCO is pink, pale skin)
• CO: 24 times more affinity with Hb than O2.

Question 13

Circulatory hypoxia

Answer 13

↓ supply of oxygenated blood with normal O2 content and PaO2

– Vessel blockage, congestive heart failure

Question 14

Histotoxic hypoxia

Answer 14

O2 delivery to tissues normal, but cells unable to use it.

– Cyanide poisoning (cyanide blocks essential enzymes for cellular respiration)

Question 15

Hyperoxia meaning

Answer 15

Above-normal arterial O2 (i.e. O2 toxicity)

Question 16

Hyperoxia effect in a healthy person

Answer 16

No big effect (Hb saturation almost to the max)

Question 17

When does disease occur with hyperoxia?

Answer 17

When ↓PaO2

Question 18

What could­­ ↑O2 cause?

Answer 18

Can damage brain, cause blindness

Question 19

When O2 is the main driver of ventilation: ­O2 can increase the risk of …..

Answer 19

↓peripheral chemoreceptor sensitivity.

Question 20

Hypercapnia meaning

Answer 20

Excess PaCO2

Question 21

What does hypercapnia occur via/with x 3?

Answer 21

– via hypoventilation (under breathing)
– Occurs with most lung diseases
– Occurs in conjunction with reduced PaO2

Question 22

Hypocapnia meaning

Answer 22

Below normal PaCO2

Question 23

What does hypocapnia occurs occur with?

Answer 23

Anxiety and fear

Question 24

What does hypocapnia occur via?

Answer 24

Via hyperventilation (over breathing)

Question 25

Does hypocapnia have an impact on PaO2?

Answer 25

Not normally

Question 26

When is the only time that PaO2 has an impact on PaO2?

Answer 26

At low PB (e.g. altitude) where low PaO2 stimulates a hyperventilation

Question 27

What is hyperpnea?

Answer 27

Increased breathing / ventilation to match metabolic demand (e.g. exercise)

Question 28

Effect of hypoventilation on Minute Ventilation diagram

Answer 28

Question 29

Effect of hyperventilation on Minute Ventilation diagram

Answer 29

Question 30

How does PCO2 have an effect on ventilation?

Answer 30

Effects mediated through both central and peripheral chemoreceptors, but CO2 must be converted to H+ first

Question 31

Effects of arterial PCO2 on ventilation diagram

Answer 31

Question 32

Effects of Arterial O2 on Ventilation diagram

Answer 32

Question 33

Why is there a change in effects of arterial O2 on ventilation after PO2

Answer 33

Due to activation of peripheral chemoreceptors only (assuming no changes in PCO2 or pH are also occurring)

Question 34

Breath tests x 3

Answer 34

Test 1 - Breath normally: count the number of breaths your take in 30 seconds Test 2 - Hold your breath for about 40 seconds: then, count the number of breaths you take in the subsequent 30 s. Were they deeper or shallower? Test 3 - Breath very fast for 30 seconds: then, count the number of breaths you take in the subsequent 30s. Were they deeper or shallower?

Question 35

Respiratory control centres in brain stem

Answer 35

Question 36

Location of central chemoreceptors

Answer 36

In medulla

Question 37

Function of central chemoreceptors

Answer 37

``` • Directly respond to: • CSF [H+] – Derived via PaCO2 • NOT circulating [H+] – Cannot cross BBB • Therefore, • indirectly respond to PaCO2 • Provide 80% respiratory drive ```

Question 38

What detects PO2 and PCO2 changes?

Answer 38

Chemoreceptors

Question 39

What do Pulmonary stretch receptors (Hering-breuer reflex) detect?

Answer 39

Inflation and deflation

Question 40

What detects dust and pollutants (and trigger coughing/sneezing)?

Answer 40

Irritant receptors

Question 41

Model of Respiratory Control During Quiet Breathing diagram

Answer 41

Question 42

Location of Peripheral Chemoreceptors.

Answer 42

- Carotid bodies (near baroreceptors in carotid sinus) | - Aortic bodies (aortic arch)

Question 43

Function of peripheral chemoreceptors

Answer 43

Respond to ↓PaO2 (<60mmHg) – Important at altitude • Respond to ↑PaCO2 & ↑H+ – Provide 20% respiratory drive • Aortic bodies respond to (although rarely): ↓ total arterial O2 content – Important: Anaemia, Carbon monoxide poisoning

Question 44

Increase and decrease arterial PCO2 diagram

Answer 44