Lecture 17 Flashcards
(68 cards)
1
Q
What are the two ways that O2 is dissolved in the blood?
A
- dissolved in the plasma
2. combined with haemoglobin
2
Q
At 100mmHg, PO2 can only dissolve how much O2 per 10mL of blood? This means that arterial blood with PO2 of 100mmHg contains how much dissolved O2 per litre?
A
0.3mL
3mL
3
Q
Is O2 dissolved in O2 an effective way of transporting O2?
A
no, it only transports 3mL/L x 5L = 15mL/min of O2 but we need it to be about 250mL/O2
4
Q
How many subunits does haemoglobin have?
A
4
5
Q
What are the names of the 4 subunits of Hb?
A
there are 2 α and two β subunits
6
Q
Each subunit is known as a what?
A
a globin
7
Q
Each subunit is attached to a what?
A
a heme
8
Q
Each heme it attached to what atom?
A
Fe
9
Q
O2 binds to what?
A
the Fe in the heme
10
Q
What is the issue with a lack of iron?
A
this is a form of anemia and it affects O2 binding/carrying capacity
11
Q
How many O2 does each Hb carry?
A
4
12
Q
O2 forms an ________ ________ combination with Hb to give oxyhaemoglobin
A
easily
reversible
13
Q
Why is it important that O2 forms an easily reversible combination wit Hb to give oxyhaemoglobin?
A
Because this means that it can easily pick up O2 at the alveoli and easily release it at the tissue
14
Q
The binding of O2 to the haemoglobin depends on the what?
A
PO2
15
Q
What colour is blood when O2 is bound to Hb?
A
red
16
Q
Deoxygenated blood is what colour?
A
blue
black (no O2)
17
Q
What does dark arterial blood indicate?
A
a problem with PO2
18
Q
What does haemoglobin saturation do mean?
A
this is how many O2 can be bound to Hb or how much Hb is saturated with O2
19
Q
As PO2 increases, the __________ _________ increases
A
Hb saturation
20
Q
At the systemic artery PO2 of 100mm/Hg, what is the Hb saturation?
A
almost 100%
21
Q
At the systemic venous PO2 of 40mmHg, what is the Hb saturation?
A
77%
22
Q
What is the P50?
A
This is PO2 required for Hb to be 50% saturated (normally 25mmHg)
23
Q
What shape is the oxygen-haemoglobin dissociation curve?
A
signmoidal
24
Q
What are the two parts of the sigmoidal oxygen-haemoglobin dissociation curve?
A
- upper flat part
2. steep low part
25
What is good about the upper flat part of the oxygen-haemoglobin dissociation curve?
Normally at 100mmHg, there is 100% saturation. If there is a lung disease, PO2 may drop to 70mmHg and you still have almost 100% saturation. This means that there is some reserve capacity with respect to Hb saturation - even small drops in PO2 doesn't change saturation so you can still deliver to the tissue assuming Hb is at the normal level
26
What is good about the lower steep part of the oxygen-haemoglobin dissociation curve?
This helps with the loading and offloading of O2:
in the tissue, there is decreased PO2 so the affinity decreases so Hb readily gives up O2 whereas in the lungs, the PO2 is increased so the affinity increases so Hb quickly binds to O2
Small changes in PO2 result in large changes in the amount of O2 bound to Hb
27
What effect causes the oxygen-haemoglobin dissociation curve to shift either left or right?
the Bohr effect
28
Right shifting of the oxygen-haemoglobin dissociation curve favours what?
releasing/offloading of O2
29
What does a right shift of the oxygen-haemoglobin dissociation curve mean?
that at the same partial pressure, there is less Hb saturation and lower O2 content
30
What causes a natural right shift of oxygen-haemoglobin dissociation curve?
This occurs as blood flows from through the capillaries of the tissues (high metabolic demand so there is high H+ and CO2) to facilitate O2 release and CO2 binding
31
When does the natural right shift occur and what 4 things can cause it because of this?
during exercise:
- increased PCO2
- increased H+
- increased temp
- increased 2,3 DPG (BPG) which is a by-product of glycolysis
32
Left shifting of the oxygen-haemoglobin dissociation curve favours what?
the binding of O2 to Hb
33
What does a left shift of the oxygen-haemoglobin dissociation curve mean?
For any particular PO2 will have higher Hb saturation and O2content
34
What causes a natural left shift of oxygen-haemoglobin dissociation curve?
as blood flows through the lung capillaries there is less Co2 and more H+ which facilitates the uptake of O2 from the alveoli into the blood
35
What happens to P50 when the oxygen-haemoglobin dissociation curve shifts to the right?
it increases
36
What happens to P50 when the oxygen-haemoglobin dissociation curve shifts to the left?
it decreases
37
What four things cause a shift to the left on the oxygen-haemoglobin dissociation curve?
- decreased PCO2
- decreased H+
- decreased temp
- decreased 2,3 DPG (BPG) which is a by-product of glycolysis
38
What four things cause a shift to the left on the oxygen-haemoglobin dissociation curve?
- decreased PCO2
- decreased H+
- decreased temp
- decreased 2,3 DPG (BPG) which is a by-product of glycolysis
39
How does the affinity of CO to Hb compare to that of O2?
CO has 200x the affinity to Hb compared to O2
40
What is the issue with CO in the arteries?
Because its affinity for Hb is much greater than O2, it binds to Hb more which means that less O2 can be bound to Hb. However, it also means that it doesn't easily release O2 to the tissues, this only occurs at very low PO2
41
How does the carbon monoxide-haemoglobin dissociation curve differ from the oxygen-haemoglobin dissociation curve?
It is shifted much to the left and much steeper which means that it binds much more easily to Hb and doesn't let O2 unbind
42
What can cause an increase in arterial CO?
smoking
43
What is the difference between the O2 carrying capacity and the O2 content?
the carrying capacity is how much O2 the blood could carry (ie. the maximal amount of O2 that can be combined with Hb) and the O2 content is how much O2 to the blood is actually carrying
44
Define carrying capacity
how much O2 the blood could carry (ie. the maximal amount of O2 that can be combined with Hb)
the amount of the O2 carried when Hb is 100% saturated
45
How much Hb is in normal blood?
150g Hb/L
46
One gram of Hb can combine with how much O2?
1.34 mL
47
How can we calculate the carrying capacity of O2 in normal blood?
1.34 x 150 = 200mL/L of blood
48
How can we calculate the O2 content?
O2 capacity x saturation (+ O2 dissolved)
49
How can we calculate the O2 content?
O2 capacity x saturation (+ O2 dissolved)
(1.34 x Hb x saturation%/100) + 0.03 x PaO2
where
Hb = haemoglobin in g/L
Saturation = percentage saturation of Hb
PaO2 = partial pressure of O2 in arteries in mmHg
50
Calculate the O2 content of the arterial blood if there is
| 150g Hb/L, PaO2 100mmHg and Saturation (SaO2) = 98%
(1.34 x Hb x saturation%/100) + 0.03 x Pa
(1.34 x 150 x 98/100) + 0.03 x 100
197+3
200 mL O2/L of blood
51
Calculate the O2 content of the venous blood if there is
| 150g Hb/L, PvO2 40mmHg and Saturation (SaO2) = 74%
(1.34 x Hb x saturation%/100) + 0.03 x Pa
(1.34 x 150 x 74/100) + 0.03 x 40
148.8+1.2
150 mL O2/L of blood
52
What does the arterial-venous difference show?
this is the difference between the O2 content in arterial blood, and the O2 content in the venous blood which shows the amount of O2 extracted by the tissues
53
What is the normal a-v difference?
200-150 = 50mL O2/L of blood
| ie. 50mL of O2 was extracted from each L of blood by the tissues and used in metabolism
54
What is the total amount of O2 extracted by the tissues?
50mL O2/L of blood x Cardiac output of 5L/min = 250mL/min
55
What happens to the a-v difference during exercise?
it increases to about 150mL of O2/L instead of 50mL O2/L of blood
56
What is the effect of low Hb (anaemia) of the a-v difference?
The saturation curve stays the same but the O2 content is reduced (eg. 1.34 x 76 x 0.98 = 100mLO2/L instead of 200mLO2/L). This means we have problems when we are exercising because we can't remove 150mL/L when we only have 100mL/L
57
What are the three ways that CO2 is transported around the body?
- dissolved in plasma
- as bicarbonate
- combined with proteins as carbamino compounds
58
How many times more soluble is CO2 compared to O2?
20 times
59
Which method of CO2 transport is the most common?
transported as bicarbonate
60
Describe the conversion of CO2 to bicarbonate
CO2 and H2O are combined by carbonic anhydrase enzyme to form the unstable carbonic acid. This dissociates into H+ and HCO3-.
61
Are the conversions of CO2 to carbonic acid and then to bicarbonate ion, and the conversion of CO2 to carbamino-haemoglobin when combined with Hb reversible?
yes
62
What is formed as a by-product of the conversions of CO2 to carbonic acid and then to bicarbonate ion, and the conversion of CO2 to carbamino-haemoglobin when combined with Hb?
H+
63
What is the effect of H+ being produced by the the conversions of CO2 to carbonic acid and then to bicarbonate ion, and the conversion of CO2 to carbamino-haemoglobin when combined with Hb?
the oxygen-haemoglobin dissociation curve shifts to the right and O2 is released
64
How does the HCO3- work transporting CO2?
CO2 is combined with H2O in the red blood cell to form carbonic acid which dissociates into H+ and HCO3-. H+ is combined with Hb to go to the alveoli and HCO3- is exchanged for Cl- as it exits the RBC and goes to the alveoli
65
What is the effect that affects the CO2-blood dissociation curve?
Haldane effect
66
What is the effect of an upward shift on the CO2-blood dissociation curve?
CO2 and H+ bind more readily to globin chain when the heme contains less O2
i.e., as arterial blood flows through the tissue capillaries losing O2, the change in molecular configuration of Hb favours the onloading of CO2 onto the globin chain
67
What is the effect of a downward shift on the CO2-blood dissociation curve?
CO2 and H+ bind less readily to globin chain when the heme contains more O2 i.e., as venous blood flows through the lung capillaries gaining O2, the change in molecular configuration of Hb to promote the release of CO2 in the alveoli
68
The majority of CO2 transport in the blood occurs as:
A. dissolved.
B. Carbamino-hemoglobin. C. Combined with heme.
D. HCO3-
E. AandB.
D. HCO3-
