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?
-Bone marrow
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?
-Bone marrow
What do all RBCs originate from?
-Common myeloid progenitor cells
What drives haemopoesis?
-Cytokines
What cytokine drives haemopoesis of RBCs?
-Erythropoietin
What cells originate from the common myeloid progenitor?
- Megakaryocytes
- Erythrocyte
- Mast cell
- Myeloblasts
What cell type is derived from megakaryocytes?
-Platelets
What cell types are derived from myeloblasts?
- Basophils
- Neutrophils
- Eosinophils
- Monocytes
What cell type is derived from monocyte?
-Macrophage
What cell types originate from common lymphoid precursor?
- Lymphocytes
- 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?
-Thrombopoietin
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?
- Lymphocytes
- Monocytes
Where does final lymphocyte maturation occur?
- T cells mature in the thymus
- B cells mature in the bone marrow
Describe the structure of erythrocytes
- Anucleate
- 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?
-Maintain elasticity
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?
- Phagocytic
- 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
