RBC physiology Flashcards
Which lineage are red cells derived from?
Myeloid lineage
What is the name given to RBC progenitors in the bone marrow?
Erythroblasts
What are reticulocytes?
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.
What is erythropoeitin?
A hormone which controls erythropoiesis
Where is erythropoeitin synthesised?
Produced in the peritubular cells in the kidneys (90%) and in the liver (10%)
What determines EPO production?
Regulated mainly by tissue oxygen tension. Production is increased if there is hypoxia from whatever cause, e.g. anaemia or cardiac or pulmonary disease
What does erythropoeitin do?
Stimulates an increase in the proportion of bone marrow precursor cells committed to erythropoiesis, and CFU-E are stimulated to proliferate and differentiate
What is the structure of normal adult haemoglobin?
Adult Hb molecule (HbA) and two α and two β globin polypeptide chains (α2β2)
What substances are required for red cell synthesis?
- Iron
- B12
- Folate
- Thiamine
- Vitamins
Where is iron normally absorbed in the gut?
Duodenum
Once absorbed into enterocytes, how is Iron transported out into the blood stream?
Ferroportin - a transmembrane protein which can be inhibited by hepcidin
How is Iron transported in the blood?
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
How is Iron stored in cells?
As Ferritin - intracellular protein that stores iron
What regulates iron absorption?
- Recent dietary intake
- Iron body stores
- State of bone marrow erythropoiesis to the intestine
What enzyme alters iron from its ferric to ferous form, so that it can be absorbed at the intestine?
Ferric Reductase
What is the action of hepcidin?
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
What can cause high levels of hepcidin production, and thus lowering of iron absoprtion into plasma, and subseuqently lowering stores?
Inflammation
What causes increased hepcidin production, and thus increase iron absorption into plasma?
- Anaemia
- Low iron stores
- Hypoxia
Where is Vitamin B12 absorbed?
Terminal Ileum
What is haemosiderin?
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
Where are the main sites of iron storage?
- Reticuloendothelial cells
- Hepatocytes
- Skeletal muscle cells
How is B12 absorbed?
In combination with Intrinsic factor, which is secreted by gastric parietal cells
What is folic acid and what is its purpose?
Folic acid monoglutamate - glutamate which is involved in amino acid metabolism and DNA synthesis
