Flashcards in Blood 1+2: Blood and RBCs Deck (37)
We generally have how much blood (in mls) per Kg body weight?
What are the sites of blood production in the developing fetus?
6 weeks to 7 months - mainly liver with spleen contributing
5th month production begins in red marrow (in all bones).
From birth through adulthood marrow is main site, lymphocytes still formed by spleen and lymphoid tissues
Red marrow (blood producing) is found in which bones in adult
Axial skeleton - mainly veterbrae, skull and upper ends of femur and humerus
Describe pluripotent stem cells
Pluripotent stem cell are uncommitted cells capable of self renewal that give rise to different lineages of progenitor cells which in turn give rise to different precursors of blood cells
List the production line of erythrocytes
Proerythroblast -> erythroblast -> reticulocyte -> reticulocyte leaves marrow into blood - looses last of polyribosomes and become -> erythrocytes
What hormone stimulates erythrocyte production?
Erythropoietin - produced by kidneys, 10-15% produced by liver and acts on stem cells to stimulate differentiation of committed progenitor cells into erythrocyte lineage
How long does erythropoiesis generally take
What takes place for erythroblast to become reticulocyte?
Cell size progressively decreases, haemoglobin content increases, nuclear condensation and finally nuclear extrusion -> thus reticulocyte is formed
When do reticulocytes become erythrocytes?
Mature 1-2 days -> then circulate for 1-2 days continuing to make haemoglobin. Then loose residual polyribosomes and become erythrocytes
What controls erythropoiesis?
Mainly EPO - produced mainly in kidneys (some in liver) mainly secreted in response to hypoxia.
Other factors such as corticosteriods, androgens, GH and thyroxine can also play a part
Haem: 4 iron containing porphyrin rings
Globin: Each porphyrin ring attached to polypeptide chain
What dietary constituents are required for haemoglobin production?
- Vit B6
Where is haemoglobin synthesised?
Haem - mitochondria
Globin - cytoplasm
combine together in cytoplasm
How is iron stored in the body?
60-70% in Hb
4-5% in myoglobin
Rest stored as ferritin or haemosiderin in liver, spleen and bone marrow
How is iron transported
Iron binds to transferrin in blood. Usually only 1/3 saturated. When saturation falls to below 15% bone marrow supply is impaired
How is iron balance regulated?
Absoprtion varies from 5-30% of ingested iron depending on body stores levels.
How is iron lost from the body?
Mainly lost from the gut in exfoliated intestinal cells
Small amounts lost in sweat and urine
Women lose almost twice as much due to menstruation
Where is most iron absorbed in gut?
Duodenum and upper jejunum
What are dietary sources of Vit-B12
Cobalamin is synthesised by bacteria. Mostly in animal protein - liver, kidney, muscle, eggs, dairy
How is Vit B12 absorbed
Intrinsic factor secreted by pareital cells of stomach, combines with B12 and is absorbed as complex in terminal ileum
How long do body stores of B12 last?
3-4 years. Deficiency usually due to decreased absorption (pernicious anaemia, ileal disease, ileal resection
What are dietary sources of folate?
Most foods, especially liver, yeast, vegetables, nuts
Where in gut is folate absorbed?
Duodenum and jejenum
How long do body stores of folate last?
Several months. Deficiency can be from decreased intake or absorption issues or increased demand (eg pregnancy)
Megaloblastic erythropoiesis occurs why?
Increased B12 or folate - > delayed DNA synthesis -> delayed maturatio -> cell continues to grow without division becoming abnormally large
Describe the shape of RBCs and physiological benefits
Biconcave disc - flat shape provides large SA:V ratio for rapid diffusion of respiratory gases
How does RBC maintain high Hb concentration and thus osmotic pressure without lysis?
Membrane extremely low permeability to Na.
Small number of Na/K/ATPase and Ca/Mg/ATPas pumps maintain cation balance
Describe Haemoglobin A compared with Hb F
Hb A - adult Hb - 2alpha units and 2beta units
Hb F - fetal Hb - 2alpha and 2 gamma units - higher affinity for O2
Describe RBC metabolism
No mitochondia or ribosomes
95% anaerobic glycolysis and 5% pentose-phosphate pathway.