Red Blood Cells

Question 1

What are the histological characteristics of a red blood cell?

Answer 1

Biconcave disc

Anucleate, lack organelles

7 um diam, 2 um height

Contain haemoglobin

Red when oxygenated; Out of body - O2

Question 2

What are the differences between an erythrocyte, a reticulocyte, and a blast forming unit?

Answer 2

Erythrocyte is the smallest, reticulocyte is slightly bigger, and a blast forming unit is the biggest. Erythrocyte is completely anucleate, reticulocyte has pieces of nuclear material, but does not have a functioning nucleus, and blast forming unit has a functioning nucleus. Erythrocyte is the definitive version, reticulocyte is partway to that version and blast forming unit is still fully dividing. Neither the erythrocyte or the reticulocyte are still dividing.

Question 3

Describe the stages of Erythropoiesis in terms of cell division and development.

Answer 3

Erythropoiesis starts with a stem cell and then goes down the myeloid pathway, which commits to the red blood cell through a blast forming unit, until it reaches a colony forming unit. Then it becomes a pronormoblast (which is partially committed to making erythroid cells) – that divides and becomes smaller and eventually loses the nucleus while going from normoblast to late normoblast and then becoming a reticulocyte, finally terminally differentiating into the definitive red blood cell.

Question 4

Name the cells that arise from lymphoid progenitors and those that arise from myeloid progenitors.

Answer 4

Lymphoid progenitors: natural killer cells, B cells, T cells Myeloid progenitors: eosinophils, basophils/mast cells, neutrophils, monocytes/macrophages, megakaryocytes/platelets, erythrocytes The macrophages/monocytes and neutrophils are both primary phagocytes, are related and share a common precursor

Question 5

What are the normal values for the PCV, the MCH, blood Hb, and MCV?

Answer 5

Haematocrit (PCV) M 40-52% F 36-48% Hb = 13-17 g/dL (male), = 12-16 g/dL (female) Mean Cell Haemoglobin (MCH) 27-34 pg Mean Corpuscular Volume (MCV) = 80-100 fL

Question 6

What are the differences between myoglobin, foetal haemoglobin, and maternal haemoglobin?

Answer 6

Myoglobin is a single peptide and has a very high affinity, which is rapidly maximised, whereas both foetal and maternal haemoglobin have lower levels. Foetal haemoglobin has slightly less right-shifted binding and it’s sigmoid-shaped. Maternal haemoglobin is even more right-shifted and it too is sigmoid-shaped.

Question 7

What are the effects of the following on haemoglobin’s affinity for oxygen: CO2, H+, 2,3-DPG, Cl-

Answer 7

CO2 lowers haemoglobin’s affinity for oxygen. H+, 2,3-DPG and Cl- also rightshift it.

Question 8

What is methaemoglobinaemia?

Answer 8

Fe in haemoglobin is oxidized (Fe3+) instead of usual ferrous (Fe2+) - Cannot transport O2 Does not release O2 in tissues Due to: Congenital globin mutations (Hb M) Hereditary decrease of NADH Toxic substances

Question 9

What are the symptoms and complications of polycythaemia?

Answer 9

Increase in number of RBCs (PCV) - increases blood viscosity. Clog blood vessels a/k/a erythrocytosis Physiologic polycythaemia Due to living at high altitude Polycythaemia vera Often asymptomatic Risk of thrombotic events No cure, venesection All ages, increases with age

Question 10

When would polycythaemia not be considered pathological?

Answer 10

Polycythaemia would not be considered pathological if there was a need for polycythaemia, such as a response to high altitude.

Question 11

Which of the following cells are from a myeloid precursor: reticulocyte, normoblast, erythrocyte, monocyte, plasma cell?

Answer 11

They are all from the myeloid precursor EXCEPT The plasma cell is from the lymphoid precursor

Question 12

Iron depletion results in what type of anaemia?

Answer 12

Iron deficiency: hypochromic microcytic anaemia - the cells keep dividing but they cannot fill up with Hb

Question 13

Vitamin B12 depletion leads to what type of anaemia.

Answer 13

B12 deficiency: megaloblastic anaemic - the cells keep filling up, but they cannot divide fast enough

Question 14

Folic acid depletion leads top what type of anaemia?

Answer 14

Folic acid deficiency: megaloblastic anaemic - the cells keep filling up, but they cannot divide fast enough

Question 15

Why are RBCs biconcave discs?

Answer 15

It allows for the cells to fold, allows the maximisation of the surface area, but without having villi or extensions that might be destroyed by shearing forces.

Question 16

Why aren’t RBCs flat discs (like a coin)?

Answer 16

Such discs would be relatively unsuccessful at folding.

Question 17

Why don’t erythrocytes have microvilli?

Answer 17

Such small extensions would be ripped away by shearing forces of going through blood at high velocity and the cell would not be able to maintain or repair itself due to the fact that there is no nucleus.

Question 18

Explain what is haemoglobin cooperativity.

Answer 18

Haemoglobin cooperativity is a phenomenon whereby increasing levels of oxygen saturation in one subunit lead the other three sub-units of haemoglobin to have increased oxygen binding. Loss of oxygen would cause the other three subunits of haemoglobin to lose more oxygen rather than if they were acting independently.

Question 19

What is the meaning of a leftward shift in saturation curve?

Answer 19

Increase in affinity

Question 20

Draw how CO2 is transported by haemoglobin.

Answer 20

Question 21

Explain how haemoglobin transfers oxygen between mother and baby.

Answer 21

Haemoglobin has a tendency for oxygen to bind to it and this tendency is determined by the partial pressure of the blood around it. Because the foetal haemoglobin is left-shifted, that means for any partial pressure foetal haemoglobin would tend to absorb more oxygen than maternal haemoglobin. That means when the two blood supplies are near each other, foetal haemoglobin will tend to attract oxygen away from the maternal plasma. This will thereafter cause the maternal haemoglobin to drop more oxygen into the maternal plasma, which will lead to a feedback loop, until they finally equilibrate with the foetal haemoglobin losing extensive amounts of oxygen, while the maternal haemoglobin is able to bind to it.

Question 22

Explain how the chemical environment in working muscles leads to gas exchange based on haemoglobin.

Answer 22

• O2 is low
• CO2 is high
• Blood is slightly acidic
• Temperature is higher
• All contribute to causing the following:

–O2 leaves the Hb

–CO2 and H+ bind to Hb and reduce the affinity of Hb for O2

–High temperature reduces the affinity of Hb for O2

–This is a negative feedback loop maintaining set point for O2 levels (which active muscle consume) and CO2 levels (which active muscle dump out)

Question 23

Explain how changes in plasma pH, CO2 and O2 levels affect respiratory rate and respiratory minute volume.

Answer 23

CO2 has a very strong effect on breathing rate

Changing O2 levels has only a modest effect on the strong increase CO2 has on breathing.

The O2 in air would have to decrease dramatically to affect breathing rate.

If the CO2 in arteries is increased (eg during exercise), then arterial O2 levels do affect breathing significantly.

Question 24

Explain why haemoglobin cooperativity (ie the sigmoidal shaped binding curve) aids in the delivery of oxygen to tissues (ie to myoglobin).

Answer 24

The haemoglobin curve cooperativity results in a substantially right-shifted and also lower slope saturation curve. This means that first of all, it is more likely to release oxygen, when myoglobin is still binding to oxygen and the release of oxygen is over a wider range of O2, which means that it’s more suited to delivery of oxygen to a range of different tissues, rather than simply maintaining and absolute setpoint and releasing it when the setpoint is exceeded.