L17 Flashcards
O2 is carried in the blood in two forms. what are these
- Dissolved O2
2. Combined with haemoglobin
per 100mL of blood how much O2 can be dissolved
0.3mL
arterial blood has a PO2 of about 100 mmHg. how many mL of O2 could be dissolved in the blood
only 3 ml dissolved O2 / litre
describe the structure of hemoglobin
it is a protein complex with 4 subunits (tetramer)
it subunits known as globin (2 alpha and 2 beta)
there is 1 heme group
attached to each subunit (therefore 4 heme groups in total)
each heme group has a iron atom which is what allows O2 to bind
describe the structure of the Heme in relation to haemoglobin ability to carry O2
Each heme can ’bind’ one O2 molecule
there are 4 Heme’s in each Hb molecule therefore each Hb molecule can carry 4 O2
O2 forms an easily reversible combination with Hb to give
oxyhaemoglobin:
O2 + Hb ↔ HbO2
what does a lack of iron result in
anemia
which affects O2 binding/carrying
capacity
what makes up hemoglobin
4 Heme + Globin (4 peptides) = hemoglobin (Hb)
what does binding of O2 to Hb depend on
Binding depends on 𝑃𝑂2 - dissociation curve - saturation
what is the real colours of oxygenated and deoxygenated blood
Oxygenated/arterial blood = bright red
Deoxygenated/venous = dark red
no O2 = black
what contributes to the colour of blood
Heme group and its
iron atom account
for color ± O2
in clinical setting if you were to take arterial blood and it had a dark red colour, what would this mean
there is something wrong with the patients partial pressure
what does the Oxygen-haemoglobin dissociation curve tell us
Tells us how much hemoglobin is bonding to the O2 and how that depends on the PP of oxygen
As the pressure increases so does the hemoglobin O2 saturation
describe the Oxygen-haemoglobin dissociation curve shape
sigmoidal
the curve has 2 parts
The flat part
And the steep low part
describe the upper flat part of the Oxygen-haemoglobin dissociation curve
moderate changes in
𝑃𝑂2 around the normal value (~100 mmHg) have only
small effects on the % saturation and therefore the
amount of O2 carried by arterial blood
therefore the upper part provides some reserve capacity.
describe the steep part of the oxygen-haemoglobin dissociation curve at lower 𝑃𝑂2
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.
why can the Oxygen-haemoglobin dissociation curve
shift left or right
because of the Bohr effect
what could cause the Oxygen-haemoglobin dissociation curve to shift to the right
natural right shift occurs as blood flows through the capillaries of the tissues (because of high metabolic demand and therefore high CO2 and H+) to facilitate O2 release.
increased 2,3 BPG (DPG), H+, temperature and CO2
what does a right shift cause in terms of Hb’s affinity for O2
more likely to release O2
favors the release of O2 from Hb to the
tissues (offloading).
Right = Release
what does a left shift cause in terms of Hb’s affinity for O2
more likely to bind O2
favors the binding of O2 to Hb
(onloading)
Left = Loading
what could cause the Oxygen-haemoglobin dissociation curve to shift to the left
natural left shift occurs as blood flows through the lung capillaries (Less CO2
and H+)
facilitates the uptake of O2 from the alveoli into the blood
decreased 2,3 BPG (DPG), H+, temperature and CO2
what is the main factor that cases the Oxygen-haemoglobin dissociation curve to shift left or righ
the partial pressure of CO2
what is 2,3 BPG (DPG)
Di or bi phosphoglycerate
it is a byproduct of glycolysis
what is the result of the Bohr effect
it improves both the pick up and delivery of O2 by Hb
describe CO-hemoglobin disassociation
the curve is vertical as Hb has a much higher affinity for CO than it does for O2
affinity is 200x more
what does binding of CO to Hb cause
less O2 can be bound therefore less O2 is carried around the body
it also shifts the O2-Hb dissociation curve to the left causing the release O2 in the tissue only at very low PO2
what is the O2 carrying capacity
The maximal amount of O2 that can be combined with Hb is called O2 carrying capacity
i.e Amount of O2 carried when Hb 100% saturated
one gram can combine with how many moles of O2
1.34
what is O2 content
How much O2 is the blood carrying
how do you calculate O2 content
O2 content = O2 capacity x saturation
+( O2 dissolved)
calc O2 content of the arterial blood
(Assume 150g of Hb/litre; PaO2 100 mmHg; SaO2 98%).
O2 content = O2 capacity x saturation
+( O2 dissolved)
1.34 x 150 x 98/100 +(0.03 x 100) = 200mL O2/litre blood
what are the units for O2 content
mL O2/litre blood
what is the a-v difference
amount of O2 extracted by tissues
compare the normal a-v difference to the a-v difference when excersizing
why does this happen
More oxygen is extracted and used by tissues when exercising. therefore the a-v O2 difference will increase
Normal a - v difference = 50 ml O2/L blood
Exercise a - v difference might be 150 ml O2/L
the steeper part of the O2-Hb disassociation curve allows for this
what does anemia do to the O2-Hb dissociation curve
Saturation curve stays same as there are no problems with the saturation part it has to do with the content
O2 content reduced (because of low hemoglobin level)
Exercise problems from a-v difference
e.g Can’t remove 150 ml/L when only have 100
what does anemia become a problem
at rest the individual will usually be fine
however when they start exercising is when the problem presents itslef
this is because of issues with the a-v difference eg you can’t remove 150 ml/L when only have 100
therefore in anemia you loose the steep part of the O2-Hb dissociation curve
CO2 is transported in 3 forms. what are these
- Dissolved in plasma
- As bicarbonate
- Combined with proteins as carbamino compounds
how many x more soluble is CO2 in the plasma compared to O2
20x
what % of CO2 is transported dissolved in plasma
10%
what % of CO2 is transported as bicarbonate
(70%)
what % of CO2 is transported in hemoglobin
20%
what is it called when Co2 is bound to Hb
carbaminohemoglobin
what causes the increase in H+ when CO2 is transported
when CO2 is transported in Hb it interacts with N, when it does this it knocks off a H+ making the blood more acidic (decreasing the pH)
when bicarbonate is made H+ is a byproduct
how is CO2 converted into bicarbonate (HCO3-)
CO2 + H2O –> H+ + HCO3-
carbonic anhydrase catalyzes this reaction
what catalyses the bicarbonate reaction
carbonic anhydrase
what is the difference between the CO2 and the O2-Hb disassociation curve
CO2 is more linear and it gets shifted up and down instead of left and right
what causes the upward shift of the CO2-Hb dissociation curve
a decrease in O2 partial pressure (PO2)
what causes the downward shift of the CO2-Hb dissociation curve
a increase in O2 partial pressure (PO2)
what is the result of the upward shift of the CO2-Hb 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
what is the result of the downward shift of the CO2-Hb 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
The majority of CO2 transport in the blood occurs as:
A. dissolved.
B. Carbamino-hemoglobin.
C. Combined with heme.
D. HCO3-
E. A and B.
D
