Structure of RBC's & biochemistry

Question 1

What are the properties of RBC’s (erythrocytes)?

Answer 1

• Full of haemoglobin to carry oxygen
• No nucleus & no mitochondria
• No DNA/RNA ==> RBC’s cannot divide
• High Surface area/volume ratio to allow for gas exchange
• Flexible to squeeze through capillaries
• Short-life span = 120 days ==> requiring constant replacement

Question 2

In what specific type of marrow does RBC production take place in ?

Answer 2

Red bone marrow

Question 3

What are RBC’s (going all the way back up the haematopoietic tree) essentially produced from?

Answer 3

Pluripotent stem cells

Question 4

Describe the structure of adult haemoglobin (remember this is not the whole erythrocyte we are talking about here, just the Hb)

Answer 4

• 4 globin chains (protein)
• Each globin chain contains a haem group
• Each haem group contains a single Fe2+ ion which one O2 molecule can bind to
• Haem group also contains a flat protoporphyrin ring ==> Haem = iron (Fe2+) + protoporphyrin ring
• One haemoglobin molecule can only have 4 O2 molecules bound to it

Question 5

What happens to old & damaged RBC’s & what are the main organs involved?

Answer 5

1. Macrophages (Phagocytic cells) of the liver & spleen engulf old RBC’s
2. Golbular haemoglobin proteins are then broken down into amino acids which enter the blood stream (recycled)
3. Haem group (minus iron) is converted into bilirubin (initially biliverdin then converted to uncongugated bilirubin, then to conjugated bilirubin in the liver and then it is secreted into bile and in turn excreted via faeces & urine)
4. Iron fom the haem group binds to transferrin in the blood & is recycled into either the liver for starage, the spleen or bone marrow for more RBC production
   5.

Question 6

What are the 3 main types of Hb & how do they differ from one another ?

Answer 6

1. HbA (97% of Hb in adults) - consists of 2 alpha & 2 beta globin chains (α₂β₂)
2. HbA₂ (α₂𝛿₂) - 2 alpha & 2 delta chains (1.5-3.2%)
3. HbF (foetal Hb) (α₂γ₂​) - 2 alpha & 2 gamma chains (<1% in adults, but obv in the foetus it is the main type)

Question 7

What is the hormone which controls erythropoeisis & where is this hormone produced ?

Answer 7

Erythropoietin (EPO) produced in the kidney & released into the circulation

Question 8

What is the action of EPO?

Answer 8

It stimulates an increase in the proportion of bone marrow precurosr cells comitted to eryrhopoeisis

Question 9

What stimulates EPO production ?

Answer 9

Regulated mainly by tissue oxygen tension, production is increased if there is hypoxia from whatever cause e.g. anaemia, cardiac or pulmonary disease

Question 10

What are the different stages of erythrocyte production starting from pronormoblast

Answer 10

Note - erythroblast excludes nucleus isnt one of the cell stages but it is something which happens

Also note that the names of the stages are in very light writing

Question 11

What precursor cell for erythrocytes has a full complement of Hb in the cytoplasm but still has a nucleus ?

Answer 11

Orthochromatic erythroblast

Question 12

What are the specialised features of mature erythrocytes ?

Answer 12

• Biconcave (disc) shape - maximises the surface to volume ratio & decreases the diffuse distance for O2 or CO2. This therefore allows for more effective uptake & release of O2 & CO2 (gas exchange)
• Has a flexible membrane which allows erythrocytes to deform & ==> squeeze in single file through capillaries

Question 13

What is the most common type of blood cell in the blood ?

Answer 13

Erythrocytes

Question 14

What is meant by haematocrit & what are its normal values ?

Answer 14

It is the percentage of total blood volume which is RBC’s

• Males normal = 40-50%
• Females normal = 36-46%

Question 15

What percentage of blood is plasma & what % is platelets & WBC’s?

Answer 15

• Plasma - 5.5%
• Platelets & WBC’s < 1%

Question 16

What is meant by oxidation & reduction reactions ?

Answer 16

OIL RIG:

• Oxidation = loss of electrons
• Reduction = gain of electrons

Note - electrons are -vely charged

Question 17

What is the RBC ion balance & cell volume actively regulated by & what is the problem with this?

Answer 17

• Ion balance & cell volume is actively regulated by engergy dependant (ATP) Na+/K+ ATPases (sodium potassium pumps)
• Problem is that these pumps are ATP dependant & erythrocytes have no mitochondria, so only route for ATP production is (anaerobic) glycolysis
• Key things erythrocyte needs from pathway are ATP, NADH & NDAPH

Question 18

What is the key function of the NADPH produced in the process of anearobic glyocolysis for the erythrocyte & what is the importance of this ?

Answer 18

• Key function = to help keep iron in Fe2+ state (reduced state ==> possibly a reducing agent?)
• Produced by glycolysis (embden myerhof pathway) (produces ATP & NADH which reverses Fe3+ to Fe2+)
• Important because HbFe3+ (methaemoglobin cannot bind O2)

Question 19

What is NADPH required for in erythrocytes & how is it produced & why is this important ?

Answer 19

• Required for the maintanence of adequate levels of (reduced) glutathione which combats oxidative stress
• GSSG is reduced through gaining an electron from NADPH (which is oxidised through losing a Hydrogen ion & is ==> acting as a reducing agent)

Question 20

How is the NADPH produced in glycolysis ?

Answer 20

Through the hexose monophosphate shunt where some glucose is converted to rubulose-5-phosphate producing 2 NADPH molecules

Question 21

Erythrocytes are subject ot a high degree of oxidative stress from exposure to drugs & chemicals & ffrom O2 transport - T or F?

Answer 21

True

Question 22

What are reactive oxygen species (ROS) & what can they cause?

Answer 22

• They are free radicals which are highly reactive molecules with unpaired electrons e.g. superoxide (O2-), hydrogen peroxide (H2O2)
• Excessive free radicals or inadequate antioxidant defence (i.e. inadequate NADPH or GSH) can lead to damage of cellular structures & enzymes
• Both O2- & H2O2 are the 2 main ROS causing oxidative stress & damage in the erythrocyte

Note - O2 can be converted into superoxidases (O2-) by NADH oxidase or xathine oxidase, O2- can then be converted into H2O2 (hyodrgen peroxide) by superoxide dismutase, H2O2 then converted to H20 by reduced glutathione (HSG) resulting in coversion of GSH back to GSSG ==> requiring NADPH to continue the cycle

Question 23

What is the importance of glutathione (GSH)?

Answer 23

• To protect against the toxic effects of ROS (free radicals)
• Reduced gluthathione (GSH) is essential to detoxify H2O2, the primary intermediate in oxidative damage

Question 24

What can a lack of GSH result in ?

Answer 24

e.g. due to glucose-6-phosphate dehydrogenase def. (G6PD) or NADPH insufficiency can lead to cell damage

Question 25

If the erythrocyte cannot maintain GSH levels adequately & ==\> there is an accumulation of perioxidases (mainly H2O2) what problems can arise ?

Answer 25

* Weakening of cell wall & haemolysis * Increased rates of oxidation of Fe2+ to Fe3+ which results in HbFe3+

Question 26

Where is CO2 transported to by erythrocytes & what is CO2 produced by ?

Answer 26

Produced by tissues, it is carried to the lungs in systemic venous blood

Question 27

What are the 3 forms CO2 is transported in the blood ?

Answer 27

1. Physcially dissolved in solution approx 10% 2. Bound to Hb (carbamino-haemoglobin) approx 30% 3. As bicarbonate ion - HCO3- approx 60%

Question 28

What enzyme facilitates the transport of CO2 in the blood & how?

Answer 28

Carbonic anyhdrase (present in RBC's) - by converting CO2 to HCO3-, same enzyme that helps convert HCO3- back to CO2 at the lungs

Question 29

A small proportion of O2 is transported dissolved in the blood but 98.5% of it is transported by Hb so really just know that Hb transports O2.

Question 30

When is 2,3 diphosphoglycerate (2,3 DPG) produced? & through what pathway?

Answer 30

* Produced when PO2 is reduced causing release of O2 from Hb by reducing the affinity of Hb for O2 * Rapapoport lubering shunt - Generates 2,3 DPG that right shifts oxygen disassociation curve and allows more oxygen to be released

Question 31

Describe the effect of O2 binding to Hb & the subsequent curve produced

Answer 31

* When O2 binds to Hb it results in the Hb structure becoming a more relaxaed conformation in which O2 binding sites are more exposed & have a higher affinity for O2. This property is known as co-operativity * This results in a sigmoid curve i.e. starts of slower velocity & lower affinity of O2 binding, then O2 binds increasing affinity for O2 ==\> O2 molecules bind more rapidly & continue to increase the affinity for subsequent O2 molecules, then the curve plateaus * This shows Hb is an allosteric protein meaning its shape is changed when it binds to a particular molecule (2,3 DPG does the opposite of O2, it decreases the affinity for binding of O2)

Question 32

What is the difference in affinity for (O2 & 2,3 DPG) between adult Hb (mainly HbA) & HbF & why is this important ?

Answer 32

HbF has a higher affinity for O2 and a lower affinity for 2,3 DPG ==\> facilitating transfer of O2 from mother to foetus across the placenta

Question 33

Describe what the Bohr effect in realtion to the oxygen-dissociation curve is and state the causes of it

Answer 33

This is the shift of the curve to the right = for given oxygen tension there is reduced saturation of Hb with oxygen i.e. Enhanced oxygen delivery to tissues Causes: (think 'Raised' = Right) * raised [H+] (acidic) * raised pCO2 * raised 2,3-DPG\* * raised temperature

Question 34

Explain how the haladane effect works in synchrony with the Boher effect to facilitate the liberation of O2 and the uptake CO2 at tissue level

Answer 34

They work together to facilitate O2 liberation and uptake of CO2 & CO2 generated H+ at tissues by: 1. The Bohr Effect Facilitating the Removal of O2 from Haemoglobin at Tissue Level by Shifting the O2-Hb Dissociation Curve to the Right 2. In turn the haladane effect means the removal of O2 results in an increased affinity for Hb to bind with CO2 and remove it from the tissues

Question 35

What does the haladane effect do to the oxygen dissociation curve and give examples of causes of it

Answer 35

It shifts the curve to the Left = Lower O2 delivery to tissues Causes: Shifts to Left = Lower oxygen delivery * HbF, methaemoglobin, carboxyhaemoglobin * low [H+] (alkali) (i.e. raised PH) * low pCO2 * low 2,3-DPG * low temperature