6. Erythropoiesis Flashcards Preview

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Flashcards in 6. Erythropoiesis Deck (29):
1

What are the different sites of erythropoiesis prior to birth?

3rd week of development - yolk sac and mesothelial layers of the placenta

6th week - liver and spleen - this is where they are being

3rd month onwards - bone marrow now becomes the principle source of erythrocytes

2

What are the different sites of erythropoiesis after birth?

Up to 5 years old - bone marrow in all bones

5-25 years - bone marrow of long bones

Over 25 years - Produced in the bone marrow of membranous bones i.e. vertebrae, sternum, ribs, cranial bones, ilium

3

Briefly describe red and yellow bone marrow and what is meant by 'myeloid tissue'

Red bone marrow is the site of erythropoiesis

Yellow bone marrow contains large amounts of fat droplets and cells

Myeloid tissue is another term for bone marrow

4

Give the stages of erythropoiesis

Haemocytoplast (haematopoietic stem cell) in the bone marrow

This differentiates into a common myeloid progenitor cell (proerythroblast) and is committed at this stage

Many transformations then occur to become an erythroblast with a condensed nucleus

The cytoplasm then becomes filled with Hb. and a reticulocyte is formed (immature erythrocyte) once the nucleus is expelled and released into the blood

5

What is a normoblast?

This is a late late erythroblast?

SO haemocytoplast to proerythroblast to normoblast to reticulocyte to erythrocyte

6

How does a proerythroblast appear histologically?

Large, round cell

Large staining nucleus

Bright blue rim of cytoplasm surrounds the large staining nucleus

IMAGE ON THE MILLAR PP

7

How does a normoblast appear histologically?

From the image of the proerythroblast:

The nucleus becomes very condensed (is then finally ejected and the cell becomes a reticulocyte)

8

How can you differentiate reticuloytes from erythrocytes histologically?

There are obvious dark markings visible in reticulocytes

These are ribosomes/ribosomal RNA

9

"Diapedesis"

The passing of erythrocytes through the pores in the capillary membranes into the blood capillaries from the bone marrow

10

What is the RBC in a healthy adult?

Men - 5.2 million per microlitre
Women - 4.7 million per microlitre

Just need to remember that it is around 5 million per microlitre

11

What is the lifespan of an erythrocyte and why?

120+/-30 days - this remains remarkably constant in healthy adults

These wear out quickly due to a developed reduced oxygen carrying capacity - they become rigid and cannot pass through capillaries

12

What is the MCV in normal RBCs and in macro and microcytic anaemia?

Normal RBC - 90 fl

Microcytic anaemia - <80 fl

Macrocytic - >100 fl

13

Describe how the process of erythropoeisis is controlled

Controlled via EPO - erythroprotien

EPO is produced in the kidney via fibroblasts in the proximal tubule of the cortex of the kidney

EPO has an effect once the cell has committed i.e. on myeloid progenitor cells/proerythroblasts - it acts to speed up the maturation of the erythroblasts and increases their release into the circulation

14

Why is erythropoiesis be controlled by EPO?

Because oxygen levels around the proximal tubule of the cortex of the kidney are constant and changes due to e.g. exercise do not have an impact

The EPO releasing cells themselves are sensitive to hypoxia - these can then cause an increased/decreased release of EPO

15

What is the link between kidney damage and anaemia?

Kidney damage can lead to microcytic anaemia

This is because kidney damage will result in reduced EPO production

16

How do erythrocytes produce ATP and why do they require ATP?

Erythrocytes do not have mitochondria so cannot use oxidative metabolism to make ATP

SO produce it via anaerobic glycolysis and also use the pentose phosphate pathway for NADPH

Require ATP for sodium pumps in the membrane and also for GLUT1 transporters which take up glucose

17

What else can a common myeloid progenitor cell differentiate into?

Can differentiate into any of the myeloid red cell family

Megakaryotes
Erythrocytes
Mast cells
Myeloblasts

18

Name the different myeloblasts

Basophil
Neutrophil
Eosinophil
Monocyte which can then differentiate into a macrophage

19

What other cell lineage is there other than myeloid?

Lymphoid - haemoblasts can differentiate into lymphocytes

20

State the different lymphoid cells

Common lymphoid progenitor cell can differentiate into a natural killer cell or a small lymphocyte

A small lymphocyte can then differentiate into T lymphocyte or B lymphocyte

B lymphocyte can then differentiate into a plasma cell

21

How are erythrocytes removed from the body?

Erythrocytes are disposed of as they pass through the spleen

Believed that antigens of old erythrocytes differ to the antigens of young erythrocytes and hence allows their detection by splenic macrophages

OR may be due to increased levels of methaemoglobin in the cell

OR detected by their increased rigidity - become trapped in the splenic capillaries - when trapped, can be engulfed by splenic macrophages

22

Describe the mechanism of action of splenic macrophages

Haem and globin are separated
Globin is broken down into amino acids
Haem prosthetic groups are broken open by haemoxygenase enzyme
The iron atom is removed for reuse
Biliverdin is left as a result - this is green in colour

23

How is biliverdin converted to bilirubin?

Via biliverdin reductase

This process occurs in the macrophage

24

What happens to the bilirubin formed from the biliverdin?

Binds to albubin in splenic macrophages and is released in the blood - is unconjugated

Then reaches the liver and is attached to glucaronic acid which is more soluble
The bilirubin is now conjugated

The conjugated bilirubin passes to the small intestine in bile and is converted to urobilinogen via bacteria

Most urobilinogen passes out of the body in the faeces and about 10% is passed back in the portal vein to the spleen and is passed to the to the kidney and excreted in the urine (provides yellow colour)

25

What is the ESR?

Erythrocyte sedimentation rate

26

What is the charge on an erythrocyte and what does this mean?

Negative surface charge - means that they normally repel one another

27

What alters the ESR?

Inflammation - causes the negative charge to be reduced - erythrocytes can clump together - the ESR is increased

28

What is a raised ESR indicative of?

Raised ESR is a specific marker for infection/inflammation in the blood

29

What is a rouleux?

This is a clump of erythrocytes due to a loss of negative charge - occurs during inflammation