W1: Red Blood Cells Flashcards
3 features or rbcs (erythrocytes)
*biconcave disc shape
*no nuc/ cytoplasmic organelles in mature rbcs
*contain Hb
what stops rbcs from aggregating?
neg charge of outer surface of rbc membranes
why do rbcs have transmembrane proteins?
to give shape + some rigidity
function of band 3 protein
anion transport e.g chloride + bicarbonate
function of glycophorin A
maintenance of neg charge – electrostatic repulsion to prevent aggregation, sugar transport
function of glycophorin C
regs cell shape, mem
deformability + mem mechanical stability
function of ankyrin
links lipid bilayer to spectrin
function of spectrin
maintenance of bioconcave disc
function of “actin complex”
links lipid bilayer to spectrin
most abundant rbc cytoskeletal protein
spectrin
how do rbcs obtain ATP + why
anaerobic glycolysis bc they do not contain mito
what is MetHb?
a form of haemoglobin that cannot carry oxygen to deliver to tissues, inoperative O2 carrier
what product of glycolysis regulates O2 affinity of Hb?
2,3 DPG (= 2,3 BPG)
define erythropoiesis
prod of new rbcs
what regs rbc prod?
erythropoetin (epo), prod in kidneys
how does no. of rbcs incr?
epo acts on committed erythroid precursors to incr cell division
what’s renal hypoxia + how does it affect epo prod?
low O2 levels (in kidneys)
incr epo prod
what makes rbcs flexible to fit through capillaries?
bc nucleus is extruded + phagocytosed before release from marrow
what’s a reticulocyte?
immature rbc
important role of cytoplasmic organelles of reticulocytes
they continue to synthesise Hb for 1-2d after release into circ
what does a high reticulocyte count indicate?
incr rate of rbc prod - acute bone marrow stress/ malignancy
what organ is described as the rbc quality control organ
spleen
how are rbcs destroyed?
by macrophages in spleen if senescent/ defective
what incr rate of destruction by splenic macrophages in red pulp?
loss of mem pliability
antibody coating
what is recycled by splenic macrophages?
Fe
function of Hb
transportation of:
*O2 from lungs to respiring tissue
*CO2 from respiring tissue to lungs
oxyhaemoglobin vs deoxyhaemoglobin
oxyhaemoglobin - oxygenated state – bright red colour
Deoxyhaemoglobin - deoxygenated state – dark red
what is the main catalysing enzyme for CO2 transportation?
mem-associated carbonic anhydrase
what does mem-associated carbonic anhydrase catalyse?
*CO2 + H2O → H2CO3- (= carbonic acid), rapidly dissociates to H+ & HCO3-
*HCO3- diffuses back into the plasma, (~70% of transported CO2)
*HCO3- dissociates back into CO2 + H2O in alveoli, CO2 released to air
how does Hb act as a buffer?
H+ ions left from dissociation of carbonic acid to bicarbonate bind to globin chains of Hb
maintains stable plasma pH + protects against respiratory acidosis
structure of Hb
terametric molecule
4 globin chains - 2 alpha, 2 beta
4 haem groups
what does a haem group consist of?
an Fe atom in a porphyrin ring (physical not chem interaction)
what’s O2 affinity?
relationship btwn Hb O2 saturation + partial pressure of O2
why is O2 dissociation a curve shaped graph?
bc binding of 1st O2 is difficult but 2nd + 3rd easier
want to conserve O2 in arteries + give it up easily in tissues
what specifically adjusts O2 affinity?
conformational change varies access to/ from haem groups
what does 2,3DPG bind to + cause?
to deoxyHb + reduces O2 affinity further
how does acidosis affect O2 affinity + O2 supply
reduces O2 affinity (Bohr effect) + incr O2 supply
what is increased affinity of HbF due to?
less active binding (by y chains) to 2,3DPG
essential for developing foetus
6 advs of artificial rbcs vs transfused human rbcs
*storage temp + shelf-life
*immediate, universal administration
*no lag in effectiveness unlike natural blood (due to 2,3-DPG (metabolite) + nitric oxide depletion during storage)
*no risk of disease transmission e.g HIV
*not dependant on donors
*avoid religious/ cultural issues e.g. Jehovah’s Witnesses
why can’t Hb transfused in solution?
bc free globin chains are toxic to kidneys, scavenge nitrous oxide - leads to vasoconstriction + hypertension
unfavourable, fixed O2 affinity, short half life (30mins)
