Blood Gas Transport

Question 1

What is the oxygen content of arterial blood vs. venous blood?

Answer 1

CaO2 = 20 
CvO2 = 15

each time blood circulates through systemic circulation, 5 ml O2/100ml blood diffuses to tissues

Question 2

What are the units for oxygen content of blood?

Answer 2

ml O2 per 100 ml blood (volume %)

Question 3

What are the two forms of blood in which oxygen is transported?

Answer 3

• physically dissolved (2%)

- chemically bound to hemoglobin molecule (98%)

Question 4

Is O2 soluble in blood?

Answer 4

compared to CO2, O2 is relatively insoluble in blood

at PO2 of 100 mmHg, 100 ml blood contains 0.3 ml of O2

Question 5

What is the key feature of oxygen transport?

Answer 5

Hb can combine rapidly and reversibly with O2

reversibility of this chemical reaction allows O2 to unbind from Hb and be released to tissues

Question 6

Describe what happens when O2 binds to Hb.

Answer 6

O2 coming from air into alveoli → diffuses through tissue → binds and creates O2Hb → transported through blood to tissues → deoxygenates at tissues to unbind → O2 needs to be available to be dissolved in plasma → courses through to tissues down partial pressure gradient

Question 7

What type of structure is hemoglobin?

Answer 7

quaternary structure – 4 components, each with one heme that binds O2

Question 8

What colour is Hb?

Answer 8

colour changes depending on binding state of its heme portion

depending on how many O2 are bound to heme portions of Hb

Question 9

What is a pulse oximeter?

Answer 9

non-invasive method estimating oxygen saturation (SaO2)

• shines 2 beams of light through translucent part of body (finger/earlobe) at different wavelengths, each with different absorptions between O2Hb and Hb
• different absorptions allow measurement of O2 saturation

Question 10

Does oxyhemolgobin participate in diffusion?

Answer 10

NO

once O2 enters RBC (after diffusing down its partial pressure gradient from lungs to plasma), it maintains partial pressure gradient for O2 to enter plasma until all 4 sites of Hb are filled (O2 binds)

once O2 binds to Hb, it does not participate in diffusion

• does not contribute to partial pressure gradient anymore
• acting as sink – takes O2 away, and allows concentration gradient to be maintained until fully saturated

Question 11

Oxyhemoglobin Dissociation Curve

Answer 11

see notes

Question 12

What shifts the oxyhemoglobin dissociation curve left?

Answer 12

↑ affinity of Hb (↓ P50 – PO2 required for 50% of Hb to become O2 bound) for O2

Question 13

What shifts the oxyhemoglobin dissociation curve right?

Answer 13

↓ affinity of Hb (↑ P50) for O2

Question 14

What factors shift the oxyhemoglobin dissociation curve right?

Answer 14

(right shift = easier for O2 to unbind from Hb due to lower affinity) -– Bohr shift

• exercise
• increased temperature
• increased PCO2
• decreased pH (acidic)
• increased 2,3 BPG

Question 15

What is 2,3 BPG?

Answer 15

product of red blood cell glycolysis

increased levels in chronic hypoxia (high altitude dwellers, chronic lung disease, congestive heart failure)

Question 16

How does anemia affect the oxyhemoglobin dissociation curve?

Answer 16

↓ Hb results in ↓ O2 carrying capacity and O2 content of blood

SaO2 remains normal

Question 17

How does carbon monoxide affect the oxyhemoglobin dissociation curve?

Answer 17

• Hb affinity for CO 250x greater than O2
• competes with O2 binding on Hb, reducing O2 content
• left shift – interferes with O2 unloading, leading to tissue hypoxia

Question 18

What are the 3 forms in which CO2 is transported in blood?

Answer 18

physically dissolved in blood (7%)

physically dissolved as bicarbonate ion HCO3- (70%)

chemically bound to Hb molecule (23%)

Question 19

Compare the CO2 content of arterial vs. venous blood.

Answer 19

CaCO2 = 48
CvCO2 = 52

each time blood circulates through systemic circulation, 4ml/100ml CO2 diffuses out of tissues and is delivered to lungs to be exhaled

Question 20

What are the units for carbon dioxide content of blood?

Answer 20

ml CO2 per 100 ml blood (volume %)

Question 21

What is carbonic anhydrase?

Answer 21

key enzyme in transport of CO2 in blood

• accelerates formation of carbonic acid (H2CO3) from CO2 and water over 1000x
• in red blood cells, NOT in plasma

Question 22

What is the Haldane effect?

Answer 22

CO2 dissociation curve is influenced by oxygenation state of Hb

CO2 transport in blood depends on O2 release from Hb

Question 23

What is the molecular basis for the Haldane effect?

Answer 23

Hb is better than O2Hb in binding H+ and CO2 to form CO2HHb (carbaminohemoglobin)

assist blood to load more CO2 from tissues by acting as sink for CO2 – maintains partial pressure gradient for diffusion of CO2 out of tissues into plasma and red blood cells

Question 24

What is arterial blood gas analysis?

Answer 24

invasive method in acute/emergency health care setting

sample of blood drawn from artery (a) to measure: PaO2, PaCO2, arterial blood pH

calculates of oxygen saturation (SaO2), ratio of O2Hb to total hemoglobin (O2Hb+Hb)

some blood gas analyzers incorporate co-oximetry that includes measurement of dyshemoglobins (carboxyhemoglobin (CO-Hb)) and methemoglobin (MetHb) in determining total hemoglobin