physio 5 Flashcards
in a solution, what type of gas molecules generate the partial pressure? How does this relate to oxygen in blood?
- only DISSOLVED GAS
- only 0.3% of oxygen in the blood is dissolved and able to add pressure to the solution -the rest is conjugated with Hgb
- 0.3% exists as a reserve
Hgb A structure. how many o2 molecules can it bind?
- Hgb has 2 alpha and 2 beta polypeptide chains- each bound to a heme group
- each heme group has an Fe that can reversibly bind one oxygen leading to 4 oxygen molecules able to be bound by one molecule of Hgb
methemoglobin? what causes it?
- when the Fe of hemoglobin is Fe+3 vs Fe+2 state
- does not bind oxygen
- cause: deficiency of methemoglobin reductase
fetal hemoglobin
- replaces beta chains of Hgb with gamma chains
- has higher affinity to oxygen
hemoglobin s
- causes sickle cell
- has normal alpha subunits but abnormal beta subunits that causes sickle shaped rods in the RBCs, distorting the shape of the RBCs and can occlude small vessels
- has lower oxygen affinity than hemoglobin A
what’s the oxygen binding capacity
the max oxygen volume that can combine with Hgb
it is 1.34 mL oxygen/ g Hb
-depends on amount of hemoglobin and the oxygen binding properties
ex) if we have 15 g/dL Hgb in blood, we know that 15 x1.34 is 20.1 mL oxygen/dL
how do you calculate the actual amount of oxygen per volume of blood? what is that called?
- called oxygen content
- oxygen content = oxygen binding capacity x SaO2 +Dissolved O2
oxygen binding capacity- maximum amount of oxygen bound to Hgb at 100% saturation
SaO2 = percentage of heme groups bound to O2
Dissolved O2 = unbound O2 in blood (DRIVES DIFFUSION)
how do you calculate the amount of oxygen being delivered to the patient
oxygen delivery = CO x oxygen content (which is oxygen binding capacity x SaO2 +Dissolved O2)
or
CO x (dissolved O2 + conjugated HGb)
what does the oxygen-Hgb dissociation curve look like and what are some important props?
- sigmoidal
- at the top of the curve, changes (decreases) to PaO2 have little effect on the Hgb saturation
- however, once you reach about 40 mmHg, decreases in PaO2 have devastating effect on Hgb saturation and oxygen is released to tissues- on venous side with very little pressure change
As blood moves through the arterial side to the tissues, what occurs
- every 100 mL of blood delivers about 5 mL of oxygen
- after the 5 mL the blood is on the venous side at 40 mmHg and 75 saturation
where does hemoglobin se an upper limit on tissue pO2? when it falls blow this value, what occurs
40 mmHg - flat upper part
after that, Hgb automatically delivers oxygen to tissues at a tight po2 range of PaO2 of 40-20 mmHg
what is p50 and how does it change from the normal value on a PO2/Hb saturation curve
- P50 is the PO2 at which Hgb is 50% Oxygen saturated
- if there is a right shift in the curve, Hgb is less likely to hold on to oxygen and thus it has weaker binding to oxygen
- as the curve moves left, you have tigher bonding of Hgb to oxygen at lower levels of PaO2
what occurs to the Hg-Ox binding curve when the pt is running a fever? in hypothermia?
fever- shifted to the right for oxygen delivery to tissues
hypothermia- shift to the left for oxygen preservation
what occurs with the Hg-Ox binding curve when the pH is decreases? increases?
- decreases- curve shifts to right
- increases- shifts to left
- what occurs when CO2 binds to hemoglobin? why is this important?
- when it binds to Hgb, it decreases the oxygen affinity to Hgb and thus shift the curve to the right
- this is important because tissues have a high amount of CO2 and cause the oxygen to become less bound to Hgb and instead perfuse the tissue
