Transport of O2 and CO2 in blood Flashcards
In blood, what generates the partial pressure to drive diffusion?
DISSOLVED GAS only!
How much O2 content in blood is dissolved?
.3%
Its there to provide O2 when needed
How much O2 in blood is conjugated to Hb?
99.7%
What is the composition of Hb?
2 alpha, 2 beta chains,
each chain bound to a heme group
Each heme group can bind 1 O2 molecule using Fe2+
Meaning adult Hb can bind 4 O2 molecules
What is Methemoglobin?
when iron is Fe3+ rather than Fe2+
DOES NOT BIND O2!
This oxidation happens due to Nitrates and sulfonamides OR a deficiency in methemoglobin reductase
What is different about Fetal Hb (HbF)?
Two beta chains, two gamma chains
Higher affinity for binding O2 than Hemoglobin A
l
What is Hemoglobin S?
Causes sickle cell disease
Alpha subunits normal, BETA subunits abnormal
Lower affinity for O2 than HbA and can change shape
What is O2 binding capacity?
The maximum O2 volume that can combine with Hb
1.34 mLO2/gHb
Blood Hb concentration = 15g/dL
1.34x15=20.1 mLO2/dL
All this depends on Hb concentration and binding properties
What is O2 content mean?
The ACTUAL amount of O2 per volume of blood
O2 content=O2 binding capacityxSaO2+Dissolved O2
How do you calculate O2 delivery?
O2 delivery = Cardiac Output x O2 Content
What are the axes for the Hb dissociation curve?
Hemoglobin saturation (y) and PO2 (x)
Why is the top of the Hb dissociation curve flat?
ensures a relatively contant oxyhemoglobin saturation despite changes in PO2
Starts at about 40 mmHg
Why is the bottom of the Hb dissociation curve steep?
At decreased amount of PO2, O2 gets dumped from the Hb.
In tissues this is important
15-40mmHg
Under normal conditions, How much O2 is transported from the lungs to the tissues per 100mL blood flow?
5 mL
PO2 is about 40 mmHg
Hb saturation is about 75
What is the upper limit that Hb sets on tissue PO2?
40mmHg
divides flat upper from steep lower
below this point O2 is automatically delivered to the tissues
What is the P50 of O2-Hb dissociation curve?
The PO2 when Hb is 50% saturated with O2
Normal value is 27mmHg
Used as an indicator for affinity of Hb for O2
Value changes depending on location in teh body
What does increased P50 value mean?
Weaker affinity of Hb for O2
HbO2 releases O2 more easily
What does decreased P50 mean?
Higher affinity of Hb for O2
HbO2 less ready to release O2
How does temperature affect the Hb dissociation curve?
Increased temperature (fever) shifts the curve to the right = weaker affinity Decreased temperature (hypothermia) shifts curve to the left = higher affinity, preserve O2
How does pH affect the Hb dissociation curve?
Decreased pH = shift right
increased pH = shift left
Exercise = increased lactic acid production
also hypoxemia, kidney failure, ketoacidosis dec pH
How does the PCO2 level affect the Hb dissociation curve?
CO2 Bohr effect
Increased CO2 levels = shift right
Think of anything that happens in the tissues shifts the curve to the right = release of O2
CO2 binds with higher affinity to Hb and kicks it off
How does 2/3-DPG levels affect Hb dissociation curve?
Increased levels = shift right, less affinity
What is 2/3-DPG?
an end product of RBC metabolism
Increased in Chronic hypoxia, anemia, high altitude
DECREAsED IN STORED BLOOD
What are the toxic effects of Carbon monoxide?
CO binds Hb at the same point on the molecule as O2, but with 250x the affinity
The PaO2 will remain about normal even though O2 content is low.
The Hb that hasnt been bound by CO will bind O2 much more tightly
Tx: hyperbaric chamber
