What is the average size of a RBC?
-approx. 8um diameter
What is the average lifespan of RBCs?
-approx. 120 days
Where do RBCs originate?
By what system are RBCs removed?
-Reticulo-endothelial system (spleen)
What is the difference between the amount of bone marrow in infants and adults?
- Extensive throughout skeleton in infants
- Limited distribution in adults (pelvis, sternum, skull, ribs, vertrbrae)
What cell types are produced in bone marrow?
-RBCs, platelets and most WBCs
What is haemopoesis?
-The process of the production of blood cells and platelets which continues throughout life
Where does haemopoesis occur?
What do all RBCs originate from?
-Common myeloid progenitor cells
What drives haemopoesis?
What cytokine drives haemopoesis of RBCs?
What cells originate from the common myeloid progenitor?
- Mast cell
What cell type is derived from megakaryocytes?
What cell types are derived from myeloblasts?
What cell type is derived from monocyte?
What cell types originate from common lymphoid precursor?
- Natural killer cells
Where do common myeloid progenitors and common lymphoid progenitors originate from?
-Multipotent haematopoeitic stem cells
What controls erythropoiesis?
- Reduced pO2 detected in interstitial peritubular kidney cells
- Increased production of erythropoietin
- Erythropoietin stimulates maturation of E-progenitor stem cells
- Release of mature RBCs from marrow
- Hb rises
- pO2 rises
- Erythropoietin production falls
What happens to Hb that is released from lysed RBCs?
- Broken down into bilirubin in liver
- Excreted through bile ducts into small intestine
- Excreted as urobiligen via kidneys when bilirubin is reabsorbed from small intestine
What is the consequence of blockage of the bile duct?
-Accumulation of bilirubin leading to jaundice
What controls haemapoiesis of platelets?
How do platelets form from megakaryocytes?
- Megakaryocyte increases in size and replicates DNA
- Platelets (which are cell fragments) bud from the cytoplasm
Which cells of the body can mobilise, divide and transform after to maturation?
Where does final lymphocyte maturation occur?
- T cells mature in the thymus
- B cells mature in the bone marrow
Describe the structure of erythrocytes
- Bioconcave disc approx 8um in diameter
- Pale centre on blood smears due to shape
- Extremely flexible to allow passage through small BVs
- Contain Hb
What is the function of the glycoproteins attached to spectrins in RBCs membranes?
What is a reticulocyte?
-Newly formed RBC which have only just been released from BM
What is the structure of lymphocytes?
- Very large nucleus which almost fills the cell
- Thin rim of cytoplasm evident around the edge
- Small cytoplasmic projections visible with EM
- T cells expressing CD4+ on their surface are Thelper cells
- T cells expressing CD8+ on their surface are cytotoxic T cells
What are the functions of lymphocytes?
- Fundamental part of adaptive immune system
- Pass through endothelial lining of blood vessels into adjacent tissues in response to infection
- Thelper cells recognise foreign antigens when displayed on MHCII of APCs
- Once activated Th stimulate Tc
- Tc cells recognise and kill infected host cells
- B cells transform to plasma cells and secrete specific Ab
Describe the structure of monocytes
- Largest cell in peripheral blood
- Nucleus irregular in shape (kidney shaped)
- Abundant grey/blue cytoplasm
- Occasional lysozyme vacuoles
Describe the function of monocytes
- Highly motile
- Migrate into tissue in response to infection and differentiate into macrophages (have cytoplasmic projections)
- Both actively phagocytic
- Only remain in circulation 1-3 days
- Reserve in red pulp of spleen
- Macrphages capable of chemotaxis, involved in inflammation and interact with Thelper cells
Describe the structure of Eosinophils
- Bilobed nucleus
- Orange-staining granules
What is the function of an eosinophil?
- Capable of weak phagocytosis
- Release cytotoxic enzymes to damage large invading pathogens
- highly motile -> migrate to epithelial surfaces
- Associated with allergic reactions via ingestion of antigen:antibody complex and release of granules
What are the functions of basophils?
- Involved in inflammatory response
- Granules contain heparin and histamine which are released in response to local tissue damage
- Histamine causes vasodilation of BVs and leakage of fluid into tissues
What is the structure of a neutrophil?
- Multi-lobed nucleus
- Small granules in cytoplasm
- Pale cytoplasm
What are the functions of neutrophils?
- Granules are lysosomes which contain digestive enzymes
- Short lived
- Gross accumulation causes pus
- Capable of oxidative burst
Describe the structure and function of platelets
- Small cellular particles
- Contain granules containing fibrinogen and von willebrand’s factor
- Phospholipid surface to provide binding sites for clotting factors during clotting cascade
- Rich in compounds which cause vasoconstriction eg serotonin
- Accumulate at sites of injury
- Responsible for forming a thrombus
- Rich in factor III starting extrinsic clotting cascade
- Adhere to connective tissue
- Aggregate with other platelets
What is von willebrand’s factor?
-Factor needed to adhere to tissue