Theme 2. - RBCs Flashcards
what do RBCs do in the lungs?
pick up O2 and deposit CO2
how soluble is oxygen in plasma?
poorly soluble
how much more O2 is carried on Hb than dissolved in the blood?
70%
how can hypoxia occur even if PO2 is normal?
most oxygen is carried on Hb so if there is insufficient Hb to carry it there will be hypoxia (eg in anaemia)
what is co-operativity?
Hb can bind O2 in the lungs and release it in tissues
what % of a RBC is Hb?
95%
what makes up a Hb molecule?
4x haem groups, 4x polypeptide globin chains (2xalpha and 2xbeta)
what makes up a haem group?
Porphyrin ring plus an Fe atom
how is Fe bound to the porphyrin ring of haem?
through non covalent bonding
where does the O2 sit in the haem molecule
in the centre of the Fe
what makes Hb red?
the porphyrin rings and movement of electrons in the covalent bonds in response to light
what type of iron is Hb conjugated to?
Ferrous (Fe2+)
how many oxygens can each haem bind?
one
what composition of Hb does HbA and HbM have?
2x alpha and 2x beta
what composition of Hb does HbF (foetal) have?
2x alpha and 2xgamma
which Hb has the highest affinity for oxygen - HbA. HbM or HbF?
HbF
what is the Bohr effect?
increased CO2 in the blood causes a decreased affinity of Hb for oxygen
name two things that decrease Hb affinity for oxygen
Co2 and low pH
what kind of alteration does Co2 make to Hb when it binds?
allosteric - alters conformation to make it want to bind O2 less
what two molecules can bind Hb to make its affinity for oxygen less?
Co2 and H+ - bind at a different site to oxygen so its not competitive inhibition
what is the distribution of dissolved Co2 in the blood, was HCO3- and in carbamino compounds?
10% in blood, 68% asa HCO3- and 22% as carbamino compounds
how do carbamino compounds bind CO2?
CO2 displaces one of the NH3 groups to make COOH
are co2 levels higher outside or inside the cell?
outside
CO2 + carbonic anhydrase = ?
carbonic acid
what does carbonic acid dissociate into
H+ and HCO3-
how does HCO3- exit the RBC?
through the HCO3-/Cl- exchanger (HCO3- moves out so most is dissolved in the plasma)
what is the chloride shift?
in the body - Cl- moves into the cell in exchange for HCO3- so there is no build up of electrical charge
then in the lungs - Cl- moves out of the cell and HCO3- moves in
what is the oxygen storage compound found in muscles?
myoglobin
in an oxygen binding curve what is the partial pressure of oxygen and fractional saturation?
PP of oxygen - concentration of oxygen
Fraction sat - % of haem groups that have oxygen bound to them
does myoglobin or haemoglobin have a higher fractional saturation of oxygen?
myoglobin
- right shift means there will be more oxygen bound to myoglobin than Hb at any given concentration
what does a right shift in an O2 saturation curve mean?
affinity for oxygen is lower
what 4 things cause a right shift of the O2 saturation curve and what are they associated with?
Cl-, 2,3 DPG, H+ and Co2
- associated with increased muscle activity
where is 2,3 DPG found and what does it do?
- found in low concentration in RBCs (5mM)
- it binds Hb and lowers its affinity for O2
Does HbF have a higher or lower affinity for 2,3 DPG than HbM?
lower therefore binds oxygen with a higher affinity
how much oxygen with HbA release in the tissues?
50%
how much oxygen with HbF be bound to?
75% - 50% then picks up half of the 50% that HbA drops in tissue
what is co-operativity in relation to HbA having an S shaped oxygen saturation curve?
can pick up and drop off oxygen where needed
myoglobin, Hb F and HbA - which have the highest affinity for oxygen?
myoglobin then right shift = HbF then right shift = HbA
what is the main control of breathing?
oxygen, Co2 and H+ levels in the blood
- mostly by Co2 or H+ (in CSF)
which two brain structures monitor CSF to control breathing rate?
pons and medulla
how big are RBCs?
7 microns
what is the haematocrit?
% of whole blood taken up by CF once spun
where does erythropoiesis occur in development and after birth?
development - liver, spleen, LNs and yolk sac
post birth - BM only
what is EPO and where is it made?
hormone/cytokine made in the kidneys (in response to hypoxia) that drives erythropoiesis
how long to reticulocytes last?
2 days
what do reticulocyte levels indicate?
bone marrow activity
what is methaemoglobinaemia and what causes it?
defective/pathological met Hb in RBC that cant carry oxygen
- Iron in Hb is ferric (Fe3+) instead of ferrous (Fe2+)
- can be caused by congenital globin mutations or hereditary decreases in NADH or toxic substance exposure
how much stronger does CO bind Hb than O2?
250x
what will PP of O2 in the blood be in CO poisoning?
normal - just not enough O2 being carried by Hb
how is CO poisoning treated?
give patient 95% oxygen and 5% CO2 to drive out CO from binding pocket on Hb
what is polycythaemia and how is it detected?
too many red blood cells
- high PCV - increased viscosity of blood that can clog BVs
when is polycythaemia seen physiologically?
at high altitude
when is polycythaemia seen pathologically?
neoplasm called polycythaemia vera - treat
how much of total iron is found on Hb in adults?
65%
how much iron is stored intracellularly and in what form?
30% - stored as ferritin and haemosiderin
what system is iron stored in the body?
reticulo-endothelial system - liver, spleen, RBC, BM, macrophages/monocytes
