TOB S10 - Blood Cells and Haemopoiesis Flashcards
What are the two stages of haemopoiesis?
Proliferation
Differentiation
Give a brief description of haemopoietic Proliferation
Starting with a stem cell the cell divides in two
One replaces the original stem cell
One will differentiate
Describe the process of haemopoietic differentiation
Haemopoietic progenitor cell will differentiate to either:
- A lymphoid blast which will go on to form immunoresponse cells
- A myeloid blast which will go on to form Erythrocytes, platelets or White blood cells
The progenitor will then differentiate into a certain cell type under the influence of particular cytokines
What cytokine will cause a myeloid blast to differentiate into an erythrocyte and which will cause it to differentiate into a platelet?
Erythrocyte = Erythropoietin
Platelet = Thrombopoietin
What controls rate of erythropoiesis?
Partial pressure of O2
Fall in pO2 will stimulate erythropoietin release from kidney
This stimulates maturation and release of red cells from the marrow
How many RBCs, granulocytes and platelets are produced per day?
RBCs = 2.5 billion/kg/day
Platelets = 2.5 billion/kg/day
Granulocytes = 1.0 billion/kg/day
Where are RBCs, WBCs and platelets produced in the body and how does this change as we age?
Produced in the bone marrow
Widespread throughout the bone marrow in infants
More limited distribution in adulthood:
Pelvis, Sternum, Skull, Ribs, Vertebrae
What are peripheral blood levels of:
Hb
RBCs
WBCs
Platelets
Hb = 130-160g/L
RBCs = 4.4-5.5x10^12/L
WBCs = 7-11x1^9/L
Platelets = 150-400x10^9/L
What are the main functions of a RBC?
To deliver oxygen to tissues and deliver carbon dioxide to the lungs
Carry haemoglobin
Maintain haemoglobin in its reduced state (ferrous)
Maintain osmotic equilibrium
Generate ATP
Describe the form of a RBC
How is this useful?
Biconcave flexible disk
8um in diameter
Facilitates passage through microvasculature which has a minimum diameter of 3.5um
How is Haemoglobin catabolised?
Broken down into constituent parts, Fe2+ is recycled
Haem is converted to bilirubin and conjugated in the liver
Liver releases conjugated bilirubin into the gall bladder/small intestine and it is changed into a variety of pigments, the most important of which are stercobilin and urobilinogen
Stercobilin is excreted in the faeces
Urobilinogen may be passed back into the blood and excreted by the kidneys.
How are the platelets produced?
Megakaryocytes produce platelets
Platelets bud off from the cytoplasm
Describe the features of platelet structure relevant to the clotting process
Phospholipid membrane w/glycoprotein receptors for clotting factors and platelet adhesion
alpha-granules in the cytoplasm produce the glycoproteins
Dense bodies in the cytoplasm produce 5-HT, ADP, catecholamines and calcium for platelet aggregation
How are platelets involved in a blood clot?
Platelets are activated leading to adhesion to the damaged section of membrane via Von Willebrand’s factor
The then aggregate with other platelets
The Fibrin mesh of a blood clot traps platelets (as well as red cells)
Also involved in the clotting cascade, interact with various clotting factors via their phospholipid membrane (particularly factor III, which activates prothrombin into thrombin, resulting in fibrin production)
5-HT from the Dense granules constricts blood vessel
What are the effects of granulocyte - colony stimulating hormone on Neutrophils?
Increases production
Enhances chemotaxis - Attraction of the neutrophil to site of infection
Enhances phagocytosis and killing of pathogens