biochem of RBCs

Question 1

sites of hamatopoiesis

Answer 1

Embryo
o Yolk sac then liver then marrow
o 3rd – 7th month -> spleen
At birth - Mostly bone marrow, liver + spleen when needed

Birth to maturity
o Number of actives sites in bone marrow decreases but retain ability for haematopoiesis
Adult
o Not all bones contain bone marrow
o Haematopoiesis restricted to skull, ribs, sternum, pelvis, proximal ends of femur (axial skeleton)

Question 2

neutrophils

Answer 2

• Most numerous

Structure
- Segmented nucleus (polymorph)
- Neutral staining granules

Function
- Short life in circulation – transit to tissues
- Phagocytose invaders
- Kill with granule contented and die in the process
- Attract other cells using small molecules released
- Increased by body stress – infection, trauma, infarction

Question 3

eosinophils

Answer 3

Structure
- Usually bi-lobed
- Bright orange/red granules

Function
- Fight parasitic infections
- Involved in hypersensitivity – allergic reactions
- Often elevated in patients with allergic conditions – asthma, atopic rhinitis
- Other functions – immune regulatory

Question 4

basophils

Answer 4

Structure
- Quite infrequent in circulation
- Large deep purple granules often obscuring nucleus

Function
- Circulating version of tissue mast cell
- Role remains unclear
- Mediates hypersensitivity reactions
- FcReceptors binds IgE
- Granules contain histamine

Question 5

do monocytes + granulocytes share a common precursor?

Answer 5

yes

Question 6

monocytes

Answer 6

Structure
- Large single nucleus
- Faintly staining granules, often vacuolated

Function
- Circulate for a week + enter tissues to become macrophages
- Phagocytose invaders
o Kill them
o Present antigen to lymphocytes
- Attract other cells
- Much longer lived than neutrophils
o Means they can access their code/DNA -> cells that can do this have big nuclei

Question 7

structure + function of red cells

Answer 7

Full of haemoglobin to carry oxygen - High oncotic oxygen rich environment (oxidation risk)

No nucleus makes it more deformable, and more room for Hb molecules - Can’t divide, can’t replace damaged protein – limited cell lifespan

No mitochondria either - Limited to glycolysis for energy generation (no Krebs cycle)

High surface area/volume ratio to allow for gas exchange - Need to keep water out

Flexible to squeeze through capillaries - Specialised membrane require than can go wrong

Question 8

how do red cells maintain specific ion conc / keep water out?

Answer 8

sodium-potassium pump
- requires ATP

Question 9

structure of haemoglobin

Answer 9

A tetrameric globular protein

HbA(Adult) has 2 alpha + 2 beta chains

Heme group is Fe2+ in a flat porphyrin ring
- One heme per subgroup
- One oxygen molecule binds to one Fe2+ - oxygen does NOT BIND TO Fe3+

Question 10

function of haemoglobin

Answer 10

deliver oxygen to tissues

act as a buffer for H+

CO2 transport

Question 11

red cell production

Answer 11

occurs in bone marrow as a result of proliferation + differentiation of haematopoietic stem cells (HSCs) regulated by erythropoietin

• hypoxia sensed by kidneys which then produces erythropoietin
• this stimulates red cell production
• EPO levels drop

Question 12

red cell destruction

Answer 12

occurs in spleen (+liver)
aged red cells taken up by macrophages - (taken out of circulation)

red cell contents are recycled
- globin chains recycled to amino acids
- heme group broken down to iron + bilirubin
– bilirubin taken to liver conjugated then excreted in bile

Question 13

why are red cells so at risk of free radicals + why is this bad

Answer 13

lots of oxygen about - free radicals easily generated

bad
- can oxidise Fe2+ to Fe3+ which doesnt transport oxygen
- free radicals damage proteins - RBCs can’t repair/replce protein (no nucleus)

Question 14

relevance of embden-myerhof pathway

Answer 14

Anaerobic glycolysis pathway generates ATP + NADH (reverses Fe3+(metHb) to Fe2+(Hb))

NADH acts as electron donor preventing oxidation of Fe2+ to Fe3+ (generates NAD+ in process)

Question 15

relevance of hexose monophosphate shunt

Answer 15

generates NADPH
- protects against oxidative stress
- regenerates glutathione - a key protective molecule

Question 16

relevance of rapapoport-lubering shunt

Answer 16

generates 2,3, DPB that right shifts oxygen disassociation curve + allows more oxygen to be released

Question 17

what is metHb

Answer 17

Hb with Fe3+

-> doesnt carry oxygen

Question 18

glutathione (GSH)

Answer 18

protects us from free radicals with unpaired electrons (hydrogen peroxide) by reacting with it to form water + an oxidised glutathione product (GSSG)
–> this maintains the redox balance

-> this can be replenished by NADPH which in turn is generated by the hexose monophosphate shunt

Question 19

what is the rate limiting enzyme in the regeneration of glutathione?

Answer 19

glutathione is regenerated by NADPH which in turn is generated by the hexose monophophate shunt

–> the rate limiting enzyme in this process = G6PD

Question 20

why is oxygen dissociation curve for Hb graph sigmoidal?

Answer 20

as 1st o2 binds to haem in one subunit the Hb shape changes
- increasing affinity for next o2 to bind to haem in next subunit

cooperative binding -> allosteric effect

Question 21

how do foetal haemoglobin + myoglobin dissociation curves differ to normal?

Answer 21

FHb - 2alpha2gamma, saturates more at the same pO2 so effectively takes O2 from maternal circulation (1 up form normal)

myoglobin - monomeric myoglobin takes O2 from red cells + has different kinetics (2 up from normal)

Question 22

why do certain small molecules affect oxygen dissociation curve?

Answer 22

can interact with Hb subunits whihc can alter structure of globin subunit
- can alterposition of haem unit in globin unit + so the ability of oxygen to bind to it
- this in turn can affect the shape of the dissociation curve + so how much o2 is delivered to the tissues at a certain pO2

(2,3 DPG can “get in” between chains + change O2 affinity – so less is bound (ie more is released) at the same pO2)

Question 23

what shifts the dissociation curve to the left?

Answer 23

• Higher Hb-O2 affinity
• Lower CO2
• Higher pH / decreased H+
• Lower temp
• Decreased 2-3 BPG/DPG

Question 24

what shifts the dissociation curve to the right?

Answer 24

• By molecules that interact with Hb – H+, CO2, 2,3 BPG
• Result in more O2 being delivered to tissues
• Reduced Hb-O2 affinity
• Higher CO2
• Lower pH / increased H+
• Higher temp
• Increased 2,3 BPG/DPG – (increased also in chronic anaemia)

Question 25

important differences between dissociation curves of HbA, HbF + myoglobin

Answer 25

At the same pO2, HbF (and myoglobin) bind more O2
o Explains how O2 is transferred to fetus in utero + to muscles

Critical part of the curve clinically is 5.3 (venous) to 13.3 (arterial) partial pressures

Question 26

modulation of saturation at critical low pO2 pressures improved o2 delivery

Answer 26

Curve is shifted right by molecules that interact with Hb – H+, CO2, 2,3 DPG
o This results in more O2 delivered to tissues
o Think of why CO2 + H+ may be increased – good to have more O2 around in these conditions

Question 27

what makes RBC membrane flexible

Answer 27

protein rich
genetic mutation in these proteins = bad (hereditary spherocytosis)

Question 28

erythropoietin feedback loop

Answer 28

-Interstitial fibroblasts near to the peritubular capillaries + the proximal convoluted tubule detect hypoxia in the blood flowing through the kidney
–>Results in increased production of hormone erythropoietin

This stimulates cell division of red cell precursors + recruits more cells to red cell production in the marrow
–> result is erythroid hyperplasia = more machinery to produce red cells