Red Cells Flashcards
Where and how are red and white cells produced?
- Red cells (erythrocytes) and white cells (leukocytes, (granulocytes, monocytes and platelets)) produced in bone marrow
- Derived from multipoint haemopoietic stem cells (HSCs) 3. Haemopoiesis=prduction of blood cells
What are red cells produced under the influence of?
- erythropoietin
2. synthesised in the kidney 3. reduced oxygen supply to the kidney is a stimulus to erythropoietin synthesis
What is the production of white cells under the influence of?
Bone marrow production of granulocytes (neutrophils, eosinophils and basophils) and monocytes is under influcend of multiple cytokines such as the interleukins and granulocyte- and granulocyte-macrophage colony stimulating factors (G-CSF and GM-CSF)
What is the production of platelets under the influence of?
thrombopoietin
What is the function of HSCs?
- Average person produces more than 500 billion blood cells every day and this needs regulation the number of each blood cell type in circulation
- HSCs give rise to all of the different mature blood cell types and tissues
- HSCs are self renewing cells: when they differentiate, at least some of their daughter cells remain as HSCs, so the pool of stem cells is not depleted
- The other daughter of HSCs (myeloid or lymphoid progenitor cells) can follow any of the other differentiation pathways that lead to the production of one or more specific types of blood cell, but cannot renew themselves
Describe the process of erythropoiesis
- The myeloid stem cell/ precursor can give rise to a pro-erythroblast
- This in turn gives rise to erythroblasts and then erythrocytes
- Erythrocytes are biconcave shape, help manoeuvrability through small blood vessels to deliver oxygen
- Normal erythropoiesis required presence of growth factor erythropoietin
- Erythropoietin is a glycoprotein that is synthesised mainly in the kidney in response to hypoxia
- Erythropoietin stimulates the bond marrow to produce more red blood cells
How is iron absorbed?
- Excess iron is potentially toxic to organs such as the heart and liver
- Excess iron cannot be excreted
- Only 1-2mg per day is absorbed from the diet
- Absorption of iron in the gut is carefully regulated according to body sores by hepcidin
How do duodenal enterocytes alter iron absoprtion?
- Hepcidin synthesis is suppressed by erythropoietin
- In duodenum ferroportin on enterocytes transfers iron from cell into blood stream
- When storage iron is high or inflmsmotry response in body, hepcidiin synthesis is increased 4. Hepcidin degrades ferroportin
- This prevents the efflux of iron from the enterocyte, so it is lost when the cell is shed into the gut lumen
How is vitamin b12 and folate needed for rbc development?
- DNA synthesis needs 4 immediate precursors: dATP, dTTP, dCTP, dGTP
- Vitamin B12 and folate are needed for dTTP synthesis necessary for the synthesis of thymidine
- Deficiency of Vitamin B12 or folate inhibit DNA synthesis
Vitamin B12 and folate deficiency affects all rapidly dividing cells:
-Bone marrow: cells can grow but are unable to divide normally
-Epithelial surfaces of mouth and gut
-Gonads
How is vitamin B12 absorbed?
- Stomach: B12 combines with intrinsic factor (IF) made in the gastric partial cells
- Small intestine: B12-IF binds to receptors in the ileum
- Vitamin B12 deficiency may result from:
- Inadequate intake e.g. veganism
- Inadequate secretion of IF: pernicious anaemia (an autoimmune disorder)
- Malabsorption
What is hypochromia?
- Hypochromia means that the cells have a larger area of central pallor than normal
- This results from a lower haemoglobin continent and concentration and a flatter cell
- Red cells that show hypochromia are described as hypo chromic
- Hypochromia and microcytosis often go together
What is polychromeasia?
- Polychromasia describes an increased blue tinge to the cytoplasm of a red cell
- Indicates that red cell is young
- Polychromatic cells are larger than normal red cells, I.e. polychromasia is one of casues of macrocytosis
What are target cells?
-Are red cells with an accumulation of haemoglobin int he centre of the area of central pallor
-Target cells may occur in a number of different conditions:
Obstructive jaundice
Liver disease
Haemoglobinopathies
Hyposplenism
What are sickle cells?
- Sickle cells are sickle or crescent shape
- They result from the polymerisation of haemoglobin S which in the deoxygenated form is much less soluble than haemoglobin A
- Haemoglobin S occurs when one or two copies of an abnormal Beta globin gene (Beta subscript S) are inherited
- Caused by mutation in beta globin gene: a charged glutamic acid residue in position 6 is replaced by an uncharged valine molecule
What cells become what?
- Monocytes become macrophages
- Megakaryocytes become platelets, erythrocytes are RBCs, 3. B cells become plasma cells, granulocytes are basophils, neutrophils, and eosinophils
