RBC physiology

Question 1

Which lineage are red cells derived from?

Answer 1

Myeloid lineage

Question 2

What is the name given to RBC progenitors in the bone marrow?

Answer 2

Erythroblasts

Question 3

What are reticulocytes?

Answer 3

Immature red blood cells in the circulation. 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) after another 1–2 days. Mature red cells are non-nucleated biconcave discs.

Question 4

What is erythropoeitin?

Answer 4

A hormone which controls erythropoiesis

Question 5

Where is erythropoeitin synthesised?

Answer 5

Produced in the peritubular cells in the kidneys (90%) and in the liver (10%)

Question 6

What determines EPO production?

Answer 6

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

Question 7

What does erythropoeitin do?

Answer 7

Stimulates an increase in the proportion of bone marrow precursor cells committed to erythropoiesis, and CFU-E are stimulated to proliferate and differentiate

Question 8

What is the structure of normal adult haemoglobin?

Answer 8

Adult Hb molecule (HbA) and two α and two β globin polypeptide chains (α2β2)

Question 9

What substances are required for red cell synthesis?

Answer 9

• Iron
• B12
• Folate
• Thiamine
• Vitamins

Question 10

Where is iron normally absorbed in the gut?

Answer 10

Duodenum

Question 11

Once absorbed into enterocytes, how is Iron transported out into the blood stream?

Answer 11

Ferroportin - a transmembrane protein which can be inhibited by hepcidin

Question 12

How is Iron transported in the blood?

Answer 12

Bound to plasma transferrin - β-globulin that is synthesized in the liver. Each transferrin molecule binds two atoms of ferric iron and is normally one-third saturated

Question 13

How is Iron stored in cells?

Answer 13

As Ferritin - intracellular protein that stores iron

Question 14

What regulates iron absorption?

Answer 14

• Recent dietary intake
• Iron body stores
• State of bone marrow erythropoiesis to the intestine

Question 15

What enzyme alters iron from its ferric to ferous form, so that it can be absorbed at the intestine?

Answer 15

Ferric Reductase

Question 16

What is the action of hepcidin?

Answer 16

Regulates the activity of the iron exporting protein ferroportin by binding to ferroportin causing its internalization and degradation, thereby decreasing iron efflux from iron exporting tissues into plasma

Question 17

What can cause high levels of hepcidin production, and thus lowering of iron absoprtion into plasma, and subseuqently lowering stores?

Answer 17

Inflammation

Question 18

What causes increased hepcidin production, and thus increase iron absorption into plasma?

Answer 18

• Anaemia
• Low iron stores
• Hypoxia

Question 19

Where is Vitamin B12 absorbed?

Answer 19

Terminal Ileum

Question 20

What is haemosiderin?

Answer 20

An insoluble iron–protein complex found in macrophages in the bone marrow, liver and spleen. It appears to be a complex of ferritin, denatured ferritin and other material.

The iron within deposits of hemosiderin is very poorly available to supply iron when needed

Question 21

Where are the main sites of iron storage?

Answer 21

• Reticuloendothelial cells
• Hepatocytes
• Skeletal muscle cells

Question 22

How is B12 absorbed?

Answer 22

In combination with Intrinsic factor, which is secreted by gastric parietal cells

Question 23

What is folic acid and what is its purpose?

Answer 23

Folic acid monoglutamate - glutamate which is involved in amino acid metabolism and DNA synthesis