Constituents of the Blood Dr K K Hampton University of Sheffield

Blood has two phases 1) Cellular component Red cells White cells Platelets 2) Fluid component Plasma

Blood Cellular = 45% Plasma = 55%Haematocrit 0.45 In anaemia cellular component decreased acute anaemia = bleeding, also loose plasma haematocrit 0.45, Hb low chronic anaemia: only loose cells, plasma compensates haematocrit 20%, Hb low

Blood In Polycythaemia cells > plasma haematocrit > 50% Causes:

Blood In Polycythaemia cells > plasma haematocrit > 50% Causes:Erythropoietin Hypoxia (leading to elevated Epo)

Haematopoiesis (formation of the blood cells) Red cells, white cells and platelets in circulation are mature cells, with finite life span red cell = 120 days(make 2 million/sec) white cell = 6 hours platelet 7-10 days red cells and platelets anucleate

Haematopoiesis Precursor cells of mature cells are in the bone marrow Adult = axial skeleton Child = all bones In utero = yolk sac, then liver and spleen Precursor cells are not found in blood

Haematopoiesis Most primitive cells = stem cells Pluripotent: can replicate and differentiate into RBC, WBC and platelets (stem cells vital for marrow transplantation) In bone marrow primitive cells proliferate and differentiate into mature cells

Haematopoiesis Hormonal growth factors stimulate cells to proliferate and differentiate Epo = red cells G-CSF = white cells Tpo = platelets

Red Cells Simple cells, no nucleus, no mitochondria Membrane to enclose Haemoglobin Enzymes of glycolysis Haemoglobin to carry oxygen Have a lot of them 4 X /l Have 5 litres of blood

Haemoglobin Carries oxygen from lungs to tissues Consists of protein, haem, ferrous 2+ ion Allows oxygen to combine Reversibly with iron in an aqueous environment Haemoglobin is a tetramer of 2 alpha and 2 beta chains

White cells Neutrophils Monocytes (macrophages) Basophils Eosinophils Lymphocytes

Neutrophils Phagocytose bacteria and foreign material increased in bacterial infections Inflammatory cells, release pyrogens that increase temperature Made in bone marrow from primitive cells called myeloblasts

Lymphocytes Immune cells B cells (bone marrow) = 1 make antibodies 2 memory cells T cells helper cells Lack = immunodeficiency HIV virus infects CD4 T cells Make in bone marrow from lymphoblasts

Platelets Small cytoplasmic anucleate cells that block up holes in blood vessels Determine the bleeding time Circulate in inactive state Bind to damaged blood vessel and adhere change shape degranulate aggregate into platelet plug = haemostatic

Platelets Made in bone marrow from cells called megakaryocytes Polyploid cells, cytoplasm buds off to become platelets

Platelet number Normal = 140 – 400 X 10 9 /l Reduced = thrombocytopenia > 80 = increased bleeding > 20 = spontaneous bleeding Increased = thrombocytosis Arterial and venous thrombosis

Plasma proteins Soluble and in plasma component Albumin Carrier proteins for nutrients, hormones Immunoglobulins Coagulation proteins

Albumin Major protein in the plasma Produced in liver Determines oncotic pressure Keeps intravascular fluid in that space Lack of albumin results in oedema Liver disease Nephrotic syndrome

Immunoglobulins Produced by plasma cells = differentiated B lymphocytes Several classes, IgG, IgM, IgA, IgE Produced in response to non-self protein antigens Production of antibodies basis of immunity and vaccination

Coagulation proteins Series of proteins (enzymes) that circulate in inactive form Function is to make blood clot Convert soluble fibrinogen into insoluble fibrin polymer Overactivity = thrombosis Failure = bleeding