Blood Cells - Functions

Fundamentals of Physiology and Anatomy Blood Cells Functions Transport of: • Blood gases • Ions • Metabolites • Hormones • Heat Help maintain homeostasis. Defence • Immune defence • Haemostasis Main Components Separated by centrifugation Plasma (55%) • ECF o Dissolved substances o Inc. gases, metabolites, ions and lipoproteins • Blood-specific proteins o Serum albumin (osmotic pressure) o Fibrinogen – raw material for co-agulation o Clotting factors (haemostasis) Cells • • White blood cells and platelets (5%) Red blood cells (45%) Blood Smear Monocyte Neutrophil Basophil Eosinophil Fundamentals of Physiology and Anatomy Haematopoiesis • • • • • • • • • The making of blood cells Haematopoietic tissue contains: o Haematopoietic stem cells (multipotent) o Erythrocytes o Leukocytes o Thrombocytes 100 billion new cells formed each day During early embryogenesis o BC arrive from yolk sac At foetal stage o Liver makes BC Adults o Made in red bone marrow o Head of the humerus and femur, sternum, ribs, vertebra and pelvis. Bone marrow o Found in spongy bone o Red and yellow bone marrow. Red makes blood cells. o Consists of spicules of bone o Haematopoiesis occurs in spaces o Many vascular sinuses among haematopoietic cells All BC arrive from haematopoietic stem cells o Essential component during bone transplant Subsequent cell divisions -> proliferation and gradual differentiation of cell progenitors and precursors Fundamentals of Physiology and Anatomy Erythrocytes • • • • • • • • • 3 million RBC made/sec 4-6 million/µl in peripheral blood Cell life = 120 days Packed with Hb Biconcave shape o Gives large SA:V ratio o Facilitates gas exchange All the Hb sits on the outer rim. 6-9 µm in diameter 2.6 µm thick at rim 0.8 µm thick at centre • • • • Anucleate No organelles Highly deformable Flexibility allows: o Adaption to capillaries o Them to never leave circulatory system • • Cytoplasm has no discernible organelles Cytoskeletal proteins o Actin and spectrin o Maintain shape Without organelles, RBC cannot synthesise proteins that are lost. • Erythropoiesis Last few steps of making RBC requires: • Fe, B12, folate • B12 and folate is used to make nucleic acids • A deficiency in these nutrients -> anaemia Erythropoietin • Made in kidney • Increases mitosis • Reduces cell death • Cells release erythropoietin during hypoxia (low oxygen levels) Fundamentals of Physiology and Anatomy RBC – End of Life Bone marrow has macrophages that help make RBC. Spleen contains macrophages - they digest old RBC. Hb parts that cannot be recycled -> turned into bilirubin -> excreted as bile -> urine Leukocytes • • • • Use circulatory system to reach destinations Defend tissues against foreign matter. Conc. In blood is 4-11 x 109 per litre o But increases in response to infections Three groups: o Granulocytes o Lymphocytes o Monocytes Neutrophils • • • • • Most common WBC 12 – 14 µm diameter Multi-lobed nucleus o Each lobe linked by highly condensed chromatin Cytoplasmic granules o Neutral in colour Granules contain: o Microbicidal agents – kill engulfed bacteria o Enzymes – degrade ECM o Lysosomes – degrade phagocytosed pathogens Fundamentals of Physiology and Anatomy • • • • • Leave circulation quickly to reach damaged areas First to arrive Live only for a few days outside circulatory system Remove microorganisms and debris via phagocytosis During death, lysosomes are released -> liquefaction of surrounding material (pus) Chemotaxis – cell moves along chemical gradient to source of infection Phagocytosis Ingest foreign pathogens. 1. Pathogen is engulfed by internalisation. 2. Membrane fusion with formation of phagosome. 3. Lysosomes fuse with phagosome. 4. Lysosomes release phagocytic enzymes to destroy foreign particle. Eosinophils • • • • • • Constitute 2-4% of leukocytes in normal blood Bilobed nucleus Acidophilic granules = pink Larger than neutrophils 12-17 µm diameter Are phagocytic but not as active as neutrophils • • • Numbers increase in parasitic infestations and asthma Major role in modulating inflammatory reactions Contain oval granules o Have major basic protein o Eosinophil peroxidase o Other lysosomal enzymes Basophils • • • • • • • Least common Large, basophilic granules May be precursors of mast cells When allergens present -> granules are exocytosed 14-16 µm diameter Bilobed nucleus o Which is obscured by granules. Granules contain o Sulphated proteoglycans o Heparin (anti-clotting) o Chondroitin sulphate o Histamine (vasodilator) Fundamentals of Physiology and Anatomy Monocytes • • • • • • • Largest WBC 15-20 µm diameter Nucleus is eccentrically placed o Often kidney shaped Has surveillance role in cells. Travel in blood stream -> enter peripheral tissues -> become macrophages Precursors of macrophage lineage cells Macrophages are found in tissues throughout the body o Have specific names in some organs. E.g. Kupffer cells in liver, microglia in CNS o Antigen-presenting cells ▪ Each one is specific to one pathogen and one antigen. Lymphocytes • • • • • • Spherical cells Similar morphological characteristics Nuclei are oval shape with dense chromatin Two types: B and T lymphocytes o B lymphocytes produce antibodies Account for 20-40% of leukocytes 7-12 µm diameter Lymphocytes and bone marrow Primary Lymphoid Tissues Where immature lymphocytes acquire capacity for antigen recognition • Bone marrow – T cell development and B cell development and maturation • Thymus – T cell maturation Secondary Lymphoid Tissues Site of lymphocyte activation • Lymph nodes – screens lymph • Spleen – screens blood borne antigens • Mucosa Associated Lymphoid Tissue (MALT) – screens mucosa Thrombocytes/ Platelets • • • • • • • Small cell fragments 2-4 µm Derived from megakaryocytes Important in haemostasis Contains cell organelles and granules Adhere to collagen Release granules, when needed, to activate blood clotting cascade Fundamentals of Physiology and Anatomy Thrombopoiesis • Making platelets • Megakaryocyte found in bone marrow o It buds off fragments of cytoplasm to make platelets. Platelets help repair damaged blood vessels Haemostasis 1. 2. 3. 4. Starts with vessel damage Platelet adhesion Activated platelets release factors (ADP and thromboxane) to recruit more platelets. Clot forms = platelet plug a. Clotting factors induce formation of thrombin b. Thrombin converts fibrinogen -> fibrin 5. Thrombin triggers further platelet activation 6. During repair, clot dissociates by factors (plasmin) PRIMARY HAEMOSTASIS – formation of platelet plug Platelet plug isn’t stable on its own. Secondary haemostasis is required – this is activated by the platelets. Clot Components Blood Cell Summary