Lecture 19 resp physio O2 and CO2 transport

Question 1

O2 transport

O2 is carried in the blood in two forms:
what are they?

Answer 1

1. Dissolved O2

2. Combined with haemoglobin (Hb)

Question 2

1. Dissolved O2

Answer 2

very ineffective for O2 transport

Need to use Haemoglobin (Hb) to carry O2

Question 3

why is dissolved O2 very ineffective for O2 transport?

Answer 3

• For each mmHg, PO2 can only dissolve 0.03 ml of O2 per litre of blood
• Arterial blood with PO2 ~100mmHg contains only 3 mL of dissolved O2 per litre of blood

Question 4

combined with Hb

Answer 4

O2 forms an easily reversible combination with Hb to give oxyhemoglobin

O2 + Hb ⟷ HbO2

binding depends on PO2 - dissociation curve - saturation

Question 5

O2 saturation (“How full is the Hb?”)

whats O2 saturation of Hb?

Answer 5

percentage of the available binding sites that have O2 attached.
Varies with PO2

Question 6

O2 saturation (“How full is the Hb?”)

Arterial blood: PaO2 = 100 mm Hg

whats the SaO2?

Answer 6

~ 97%.

Question 7

O2 saturation (“How full is the Hb?”)

Venous blood: PvO2 = 40 mm Hg

whats SvO2?

Answer 7

~ 75%.

Question 8

what curve is Oxygen hemoglobin?

Answer 8

sigmoidal

Question 9

Oxygen-haemoglobin curve

what does the Upper flat part of the curve explain?

Answer 9

moderate changes in PO2 around the normal value (~100 mm Hg) have only small effects on the % saturation

the amount of O2 carried by arterial blood.

i.e some reserve capacity.

Question 10

Oxygen-haemoglobin curve

what does the Steep part of curve at lower PO2 explain?

Answer 10

helps with loading of Hb in lungs AND unloading of O2 to the tissues.

Small changes in PO2 result in large changes in amount of O2 bound to Hb.

Question 11

O2-Hb dissociation curve varies with

Answer 11

conditions to improve O2 uptake / delivery

Question 12

O2-Hb dissociation curve

what effects results in a right shift in curve?

Answer 12

Increase PCO2
Decrease pH bohr effect
Increase Temperature (exercise)

Question 13

O2-Hb dissociation curve

what effects results in a left shift in curve?

Answer 13

Increase PCO2
Increase pH bohr effect
Decrease temperature (exercise)

Question 14

O2 Content (How much O2 is the blood carrying?)

whats the equation?

Answer 14

O2 content = O2 capacity x saturation ( + dissolved)

Question 15

O2 content = O2 capacity x saturation ( + dissolved)

Answer 15

O2 content of the blood
- ml O2 / litre blood

Hb is the [haemoglobin]
- g/litre

Sat percentage saturation of Hb
- PaO2 is in mm Hg

Question 16

O2 Content (How much O2 is the blood carrying?)

O2 content = O2 capacity x saturation ( + dissolved)

Answer 16

= 1.34 x Hb x (Sat / 100) + 0.03 x PaO2

O2 carrying capacity
- 1.34 x Hb x (Sat / 100)

O2 dissolved
- 0.03 x PaO2

Question 17

O2 content of the arterial blood

Assume 150g of Hb/litre; PaO2 100 mm Hg; SaO2 98%

Answer 17

1.34 x Hb x (Sat / 100) + 0.03 x PaO2

O2 content of arterial blood (ml O2/litre blood) = 200 Arterial O2 content

Question 18

O2 content of the venous blood

Assume 150g of Hb/litre; PvO2 40 mmHg; SvO2 74%

Answer 18

1.34 x Hb x (Sat / 100) + 0.03 x PvO2

O2 content of venous blood (ml O2 /litre blood) = 150 Venous O2 content

Question 19

whats the Arterial (a) - Venous (v) O2 difference?

Answer 19

amount of O2 extracted by tissues

Question 20

Arterial content = 200 ml O2 /litre blood
Venous content = 150 ml O2 /litre blood

whats the a-v difference?

Answer 20

50 ml O2 /litre blood

50 ml O2 was extracted from each litre of blood by the tissues and used in metabolism

Question 21

Arterial (a) - Venous (v) O2 difference

How many litres/min flow to tissues?
CO = 5 litres/min
a - v difference = 50 ml O2 /litre blood

Answer 21

(5x50)

Total O2 extracted by tissues = 250 ml/min (VO2)

Question 22

CO2 transported in 3 forms

what are they?

Answer 22

1. Dissolved in plasma - 20 times more soluble than O2 (~7%)
2. As bicarbonate (70%)
3. Combined with proteins as carbamino compounds (23%)

Question 23

Formation of bicarbonate (70%)

Answer 23

CO2 + H20 ⟷ H2CO3 ⟷ H+ + HCO3-

⟷
- Carbonic anhydrase

Question 24

what do you NEED to maintain normal levels of for metabolic and biochemical stability (e.g pH)?

Answer 24

PaO2 and PaCO2

Question 25

O2 uptake and CO2 production quite variable so how is PaO2 and PaCO2 normally kept within close limits?

Answer 25

tight control of ventilation.

Question 26

Effectors ⟶ Sensors ⟶ Central controller ⟶ Effectors
Triangle

what are the effectors?
what are the sensors?
what is the central controller?

Answer 26

• Respiratory muscles
• Chemoreceptors, Lung and other receptors
• Pons, medulla, other part of brain

Question 27

where are central chemoreceptors located?

Answer 27

Located medulla (brainstem)

Ventrolateral surface of medulla

Question 28

what are Central chemoreceptors?

Answer 28

respond to pH change

Sensitive to the PCO2 but not PO2 of blood

Question 29

Central chemoreceptors

CO2 diffuses out of the cerebral capillaries what does this do?

Answer 29

→ changes pH of the cerebrospinal fluid (CSF)

→ central chemoreceptors respond to pH change

Question 30

where are peripheral chemoreceptors located?

Answer 30

Carotid and aortic bodies

Question 31

what are peripheral chemoreceptors?

Answer 31

responds to decrease arterial PO2

limited response to PCO2 changes

Rapidly responding