Red cells

Question 1

What are RBCs derived from?

Answer 1

Myeloid stem cells

Question 2

What is the shape of RBCs and why is this important?

Answer 2

They are biconcave in shape in order to pass through narrow blood vessel such as capillaries.

Question 3

Which growth factor stimulates the production of RBCs?

Answer 3

Stimulated by the growth factor erythropoietin which is a glycoprotein synthesised in the kidney. Low amounts produced normally however higher amounts produced in response to kidney hypoxia.

Question 4

What is Haemoglobin A composed of?

Answer 4

2 alpha and 2 beta chains bound to a haem group. Each haem group contains a Fe2+ ion held in a porphyrin ring which oxygen can bind to.

Question 5

How is iron absorption controlled?

Answer 5

Hepcidin binds to and degrades the transmembrane protein ferraportin in the duodenum enterocyte therefore preventing the movement of iron out of the enterocyte. Hepcidin synthesis is suppressed by erythropoietic activity since iron absorption is needed for making new red cells. Hepcidin is produced by the liver.

Question 6

What is the importance of vitamin B12 and folic acid?

Answer 6

DNA synthesis requires 4 immediate precursors. These are dATP, dTTP, dCTP and dGTP. Vitamin B12 and folic acid are needed for dTTP synthesis therefore a deficiency of vitamin B12 or folic acid inhibits DNA synthesis.

Question 7

How is b12 absorbed?

Answer 7

1. B12 combines with intrinsic factor made in gastric parietal cells.
2. The B12-IF complex can then bind to receptors in the ileum.

Question 8

How long do red cells circulate for?

Answer 8

120 days

Question 9

Meaning of hypochromia?

Answer 9

Hypochromia means that the cells have a larger area of central pallor than normal. This results from a lower haemoglobin content and concentration and a flatter cell. Red cells that show hypochromia are described as hypochromic. Hypochromia and microcytosis often go together.

Question 10

Meaning of polychromasia?

Answer 10

Polychromasia (‘many colours’) describes an increased blue tinge to the cytoplasm of a red cell. It indicates that the red cell is young. Polychromatic cells are larger than normal red cells i.e. polychromasia is one of the causes of macrocytosis.

Question 11

Anisocytosis?

Answer 11

red cells show more variation in size than is normal.

Question 12

Poikilocytosis?

Answer 12

red cells show more variation in shape than is normal

Question 13

What are target cells?

Answer 13

Red cells with an accumulation of haemoglobin in the centre of the area of central pallor