SLE221: SYSTEMS PHYSIOLOGY TOPIC ONE: HAEMATOLOGY COMPOSITION AND FUNCTIONS OF BLOOD Blood makes up one quarter of the extracellular fluid. In an average 70kg man total blood volume 8 of total blody weight, made up of 2 litres blood cells and 3 litres of plasma. Important functions in transportation, regulation and protection. Blood cells: Erythrocytes (RBC): important in O 2ransport. Leukocytes (WBC): immune systems mobile defence units. Platelets: cell fragments important in haemostasis. Blood composition: Plasma: 55 of whole blood. Plasma is 92 water, 68 proteins and remainder is dissolved organic molecules, ions, trace elements and vitamins and dissolved gasses. Composition identical to interstitial fluid except for the presence of plasma proteins. Plasma proteins: mostly synthesised in the liver. Functions include blood clotting defence against foreign invades, hormones, enzymes and increase osmotic pressure in capillary vs interstitial fluid (causes blood to be pulled into the capillaries). Albumins: most abundant plasma protein Globulins: , and Fibrinogen: key factor in blood clotting Buffy coat: platelets and leukocytes. <1 of whole blood. Erythrocytes: 45 of whole blood Haematocrit: 36 of the whole blood volume. Everything except plasma. ERYTHROCYTE (RBC) STRUCTURE AND FUNCTION No nucleus, organelles or ribosomes. Biconcave disc structure promotes O 2 transport in blood. Larger surface area for diffusion of O across the membrane. 2 Thinness of cell enables O2to diffuse rapidly between the exterior and innermost regions of the cell. Flexible membrane allows RBCs to travel through narrow capillaries without rupturing in the process. Haemoglobin: ironcontaining pigment found only in red blood cells. Appears reddish when oxygenated and bluish + when deoxygenated. Primary role is to carry O 2 also combines with CO ,2acidic hydrogenion portion (H ) of ionized carbonic acid, carbon monoxide and nitric oxide. Molecule consists of 2 parts: Globin: protein composed of 4 highly folded polypeptide chains Heme groups: 4 ironcontaining nonprotein groups. Each is bound to 1 of the polypeptides.