Red Cell Structure and Function

Question 1

List five properties of red cells?

Answer 1

Full of Hb to carry oxygen
No nucleus 
No mitochondria
High surface area/ volume ratio
Flexible

Question 2

What is the consequence of red cells being full of Hb?

Answer 2

Means they have a high oncotic pressure and high oxidation risk

Question 3

What is the consequence of red cells having no nucleus?

Answer 3

means they can’t divide, can’t replace damaged proteins so have a limited cell lifespan

Question 4

What is the consequence of red cells having no mitochondria?

Answer 4

limited to glycolysis for energy generation (no Kreb’s cycle)

Question 5

What is the consequence of red cells having a high surface area/ volume ratio?

Answer 5

they have a bigger area to keep water out of

Question 6

What is the consequence of red cells being flexible?

Answer 6

this requires a specialised membrane that can sometimes go wrong

Question 7

What does haemoglobin do?

Answer 7

Performs the main functions of red cells carrying O2 to the tissue and CO2 from the tissues to the lungs

Question 8

What does Adult haemoglobin (HbA) consist of?

Answer 8

2 alpha and 2 beta global chains
each globin chain has a heme group attached (prosthetic group)
the heme group consists of Fe2+ in a flat porphyrin ring
one oxygen molecule binds to Fe2+

Question 9

Does oxygen bind to Fe2+ or 3+?

Answer 9

oxygen binds to Fe2+ (ferrous iron)

it does not bind to Fe3+ (ferric iron)

Question 10

Red cell production occurs in the bone marrow as a result of ________1__________ cells get __2______ as they mature and the amount of ____3_____ increases and the amount of RNA in the cytoplasm _____4_________

Answer 10

1) proliferation and differentiation of HSCs
2) smaller
3) Hb
4) decreases

Question 11

Describe reticulocytes?

Answer 11

These contain residual ribosomal RNA and are still able to synthesise Hb, they remain in the marrow for about 1-2 days and are released into the circulation where they lose their RNA and become mature red cells (erythrocytes)

Question 12

Describe how red cell production is regulated?

Answer 12

It is regulated by the hormone erythropoietin (EPO) produced by the kidneys
The kidneys sense hypoxia and produce EPO which then stimulates the bone marrow to produce more red cells

Question 13

Red cell destruction normally occurs in the ___1______, the average red cell lifespan is ___2_____

Answer 13

1) spleen and liver

2) 120 days

Question 14

Describe the process of red cell destruction?

Answer 14

Aged red cells are sensed and taken out by macrophages
the red cell contents are destroyed
the globin chains are recycled to amino acids
the heme group is broken down to iron and bilirubin (broken down porphyrin ring)
bilirubin is taken to the liver and conjugated and then excreted in bile (this colours the faeces and urine)
the iron is recycled and returned to the storage pool for reuse

Question 15

What is the Embden-Myerhof Pathway? What is its significance?

Answer 15

fancy name for main type of glycolysis
glycolysis produces 2ATP, 2NADH and 2 pyruvate
the production of NADH in this anaerobic pathway reverses Fe3+ (metHb) to Fe2+ (Hb_
this is important because metHb is non-functional

Question 16

What is the hexose monophosphate shunt/ pentose phosphate pathway? What is its significance?

Answer 16

parallel pathway to glycolysis that produces NADPH which regenerates glutathione
both NADPH and glutathione protect the RBC against oxidative stress
This pathway’s activity is limited by the enzyme G6PD
some people ca have a faulty enzyme (X linked disorder) resulting in more oxidative stress to cells and premature red cell destruction

Question 17

Describe the role of the red cell in carbon dioxide transport?

Answer 17

10% CO2 is dissolved in solution, 30% bound directly to Hb, 60% gets there as bicarbonate which the red cell plays a role in generating
at the tissue CO2 combines with H2O catalysed by carbonic anhydrase to form carbonic acid
A H+ can then be removed by deoxygenated Hb
HCO3- can then exit the cell in exchange for Cl- entering the cell
at the lungs the opposite happens

Question 18

Describe the shape of the oxygen dissociation curve?

Answer 18

it does not follow michaelis-menten kinetics but is sigmoidal

Question 19

Why is the oxygen dissociation curve sigmoidal?

Answer 19

because of Hb cooperativity

Question 20

Explain what is meant by Hb cooperativity?

Answer 20

the binding of oxygen to one subunit increases the affinity of the remaining subunits for oxygen, equally removal of oxygen decreases affinity

Question 21

What are the advantages of the sigmoidal oxygen dissociation curve?

Answer 21

it means that when travelling to the tissues little oxygen is lost as the top part of the curve is fairly flat but at the tissues can deliver lots of oxygen with only a small drop in PO2 due to the steeper lower part of the curve

Question 22

Explain the difference between adult and fetal Hb?

Answer 22

fetal haemoglobin contains two alpha and two gamma chains
adult haemoglobin contains two alpha and two beta chains
the dissociation curve for fetal haemoglobin is shifted to the left meaning it has a higher affinity for oxygen allowing it to take O2 from the maternal circulation

Question 23

Explain why the myoglobin dissociation curve is different to that of haemoglobin?

Answer 23

myoglobin in muscles is monomeric so does NOT show co-operativity and the curve is therefore hyperbolic

Question 24

What is the Rapapoport- Lubering Shunt?

Answer 24

this generates 23-BPG that shifts the oxygen dissociation curve to the right allowing more oxygen to be released

Question 25

Explain what can shift the oxygen dissociation curve?

Answer 25

the curve is shifted to the right by increased H+, CO2, 23BPG (23BPG is unregulated in chronic anaemia by the RPL shunt) and temperature, also shifted to right by decreased pH
all these would be present when higher rates of respiration are present so it makes sense that oxygen would be offloaded more readily