Blood gas transport

Question 1

Oxygen exchange from lung to Hb

Answer 1

1. O2 exchange at lung
2. O2 dissolved in plasma
3. O2 bound to Hb

Question 2

What is plasma?

Answer 2

The aqueous portion of blood

Question 3

What is CO2 transported as?

Answer 3

CO2 transported as HCO3- or bound to Hb

Question 4

CO2 transportation to lungs

Answer 4

1. CO2 transported as HCO3- or bound to Hb
2. CO2 dissolved in plasma(PaCO2)
3. CO2 exchange at the lung

Question 5

CO2 transportation from tissues

Answer 5

1. CO2 produced by tissues
2. CO2 dissolved in plasma(PaCO2)
3. CO2 transported as HCO3- or bound to Hb

Question 6

Why is haemoglobin critical to O2 transport?(Solubility)

Answer 6

Oxygen has low solubility in plasma therefore Hb overcomes this problem by enabling O2 to be concentrated within the blood

Question 7

What are the 3 ways the oxygen content of blood is measured?

Answer 7

1. O2 partial pressure (PaO2), expressed as kPa
2. Total O2 content (CaO2), expressed as mL of O2 per L of blood
3. O2 saturation (SaO2 = measured directly in arterial blood, SpO2 = estimated by pulse oximetry), expressed as %,

Question 8

Why does the oxygen-haemoglobin that shape?

Answer 8

1. Starts of with cooperative binding of O2 to Hb

2. The reason the graph plateau’s is due to the saturation of O2 binding sites

Question 9

Why is Hb so effective at transporting O2 within the body?(Structure)

Answer 9

The structure of Hb produces high O2 affinity, therefore a high level of Hb-O2 binding (and saturation) is achieved at relatively low PO2.

Question 10

When is HbO2 saturation substantially affected?

Answer 10

PaO2 must be really low(below 7.5kPa)

Question 11

Why is Hb so effective at transporting O2 within the body?(Conc of Heme and Hb)

Answer 11

Concentration of heme groups and Hb contained in RBC’s enables high carrying capacity

Question 12

How many binding sites does each Hb molecule have?

Answer 12

4(O2 binding) heme groups per Hb molecule

Question 13

What does a leftward shift in the oxyhen-Hb binding curve result in?

Answer 13

higher Hb-O2 affinity = Hb binds more O2 at a given PO2

Question 14

What does a Rightward shift in Oxygen-Hb binding curve result in?

Answer 14

lower Hb-O2 affinity = Hb binds less O2 at a given PO2

Question 15

What is a leftward shift in the oxygen-Hb curve caused by?

Answer 15

• Decrease in CO2
• Increase in pH
• Decrease in 2,3-DPG
• Decrease in temperature

Question 16

What is a rightward shift in the oxygen-Hb binding curve caused by?

Answer 16

• Increase in CO2
• Decrease in pH
• Increase in 2,3-DPG
• Increase in temperature

Question 17

What is the effect of CO2 and pH on Hb-O2 affinity known as?

Answer 17

Known as the Bohr effect

Question 18

What does Hb O2 affinity depend on?

Answer 18

Depends on the local environment

Question 19

O2 saturation in lungs

Answer 19

In lungs:
-Increased PO2
-Decreased PCO2
-Increased pH
therefore increased O2 saturation

Question 20

O2 saturation in resting tissue

Answer 20

In resting tissue:
-Decreased PO2
Therefore decreased O2 saturation and O2 moves from Hb to tissue

Question 21

O2 saturation in working tissue

Answer 21

In working tissue:
-Decreased PO2
However anaerobic respiration and hypoxia also produces lactic acid, CO2 and 2,3-DPG
-Therefore increases O2 demand
-Theres an increase in CO2 and a decrease in pH and 2,3-DPG
-There’s a decrease in Hb-O2 affinity and binding
Therefore a decrease in O2 saturation

Question 22

What does myoglobin act as in the muscle tissue?

Answer 22

Myoglobin acts as O2 reservoir within muscle tissue

Question 23

When does myoglobin release O2?

Answer 23

Releases O2 at low PO2

Question 24

What does foetal Hb have a higher O2 affinity over?

Answer 24

Foetal Hb has higher O2 affinity and effectively steals O2 from maternal Hb

Question 25

What does oxyhaemoglobin appear as?

Answer 25

Oxyhaemoglobin (Hb-O2) appears red

Question 26

What does deoxyhaemoglobin appear as?

Answer 26

deoxyhaemoglobin (Hb) appears blue

Question 27

What is cyanosis and when does it occur?

Answer 27

Purple discoloration of skin and tissue that occurs when deoxyhaemoglobin becomes excessive

Question 28

What is central cyanosis and why is it caused?

Answer 28

Bluish discoloration of core, mucous membranes and extremities
Inadequate oxygenation of blood

Question 29

What is peripheral cyanosis and why is it caused?

Answer 29

Bluish coloration confined to extremities (e.g. fingers)

Inadequate O2 supply to extremities

Question 30

When can hypoxia occur?

Answer 30

Hypoxia can occur despite adequate ventilation and perfusion, if the blood is not able to carry sufficient oxygen to meet tissue demands

Question 31

What are the causes of anaemia?

Answer 31

• Iron deficiency

- Haemorrhage

Question 32

How and why does transport of CO2 differ to O2?(Solubility)

Answer 32

CO2 has a higher H2O solubility than O2 does therefore a greater % of CO2 is transported simply dissolved in plasma

Question 33

How and why does transport of CO2 differ to O2?(Binding sites)

Answer 33

CO2 binds to Hb at different sites than O2 (R–NH2 residues at the end of peptide chains, forming carbamino-Hb, R-NHCOOH) and with decreased affinity. Thus, a lower % of CO2 is transported in this manner

Question 34

How and why does transport of CO2 differ to O2?(Reaction with H2O)

Answer 34

CO2 reacts with water to form carbonic acid, which accounts for the majority (≈70%) of CO2 transported

Question 35

What blood carries more CO2 and what is this known as?

Answer 35

Venous blood carries more CO2 than arterial blood (‘The Haldane effect’).

Question 36

Why does venous blood carry more CO2?

Answer 36

Deoxy-Hb has a higher affinity for CO2 and H+ than oxy-Hb does

Question 37

Intake and Removal of CO2 from tissue

Answer 37

CO2 is produced by respiring cells and dissolves in the plasma + enters RBCs.
Conversion of CO2 + H2O to H2CO3 within RBCs (catalysed by carbonic anhydrase)
The effective removal of CO2 by (2) enables further CO2 to diffuse into the RBC (& more can then enter the plasma).
H2CO3 ionises to HCO3- + H+. The RBC cell membrane is impermeable to H+, therefore H+ cannot leave
Accumulation of H+ within cell, and ∴ cessation of (2), is prevented by deoxy-Hb acting as a buffer and binding H+. Movement of O2 into tissues from RBCs ∴ ↑[deoxy-Hb] and enables more CO2 to be transported.
The increased [HCO3-] creates a diffusion gradient for HCO3- to leave the cell. It is exchanged for Cl- to maintain electrical neutrality.

Question 38

CO2 removal from RBC to lungs

Answer 38

Low PACO2, creates a diffusion gradient for CO2 to diffuse out of the blood into the airspace
Increased PAO2 leads to O2-Hb binding. O2-Hb binds less H+ than deoxy-Hb, increasing free [H+]
Increased free [H+] leads to increased H2CO3 and ultimately CO2 which contributes to CO2 plasma saturation.
The changing equilibrium of carbonic acid reaction, also leads to decreased [HCO3-], as it binds the free H+. This creates a diffusion gradient that allows HCO3- ions to entry the RBC in exchange for Cl-.