Blood Prepared by Amara Sundus Senior Lecturer Objectives • • • • • • • • By end of this session student will be able to; Explain characteristics of blood Explain function of blood Define volume and composition of blood Explain clotting mechanism Explain blood group Explain Rh system Explain blood pressure Introduction • Fluid connective tissue • Composed of plasma and serum • Average human has 5 liters of blood ( 4-6 liters) Characteristics of blood • Blood makes up 6–8% of our total body weight. • pH must remain between 7.35–7.45 • Blood temperature is slightly higher than body temperature (38 C) Characteristics of blood • Color range: • Oxygen-rich blood is scarlet red • Oxygen-poor blood is dull red • Sticky and metallic taste • Composed of formed elements Functions of blood • Major function of blood is transport: • Oxygen • Nutrients • Hormones • Heat • Antibodies and cells of immune system • Clotting factors • Wastes Functions of blood • Homeostatic: • Maintenance of water content and acid-base balance • Protective: • Immunity and non-specific resistance; - blood coagulation • Maintenance of body temperature: • As a result of a redistribution of blood volume between skin and the internal organs at high and low temperature of external environment. Composition of blood •Composed of clear, straw-colored, watery fluid called plasma •Plasma constitutes of • 55% volume of blood • 45% formed elements Formed elements •Formed elements includes: • Erythrocytes- Red Blood Cells • Leukocytes – White Blood Cells • Thrombocytes- Platelets- Erythrocytes or RBCs •Most abundant cell of human body (4 million – 6 million per microliter of blood) • Formed in the bone marrow • Mature forms do NOT have a nucleus • Shaped as biconcave disks Erythrocytes or RBCs • Life span of about 120 days • Hemoglobin (iron protein)is found in the RBC • Hemoglobin carries oxygen from the lungs to the rest of the body and carbon dioxide binds to the RBC and is taken to the lungs to be exhaled. Hemoglobin • Iron-containing protein • Binds strongly, but reversibly, to oxygen • Each hemoglobin molecule has four oxygen binding sites • Each erythrocyte has 250 million hemoglobin molecules Leukocytes or WBCs • Largest sized blood cells • Lowest numbers in the blood (4,500 – 11,000 per microliter) • Formed in the bone marrow and some in lymph glands • Primary cells of the immune system, fights disease and foreign invaders • Contain nuclei with DNA, the shape depends on type of cell Leukocytes or WBCs • Certain WBCs produce antibodies • Life span is from 24 hours to several years • There are five different types of WBCs • • • • • Neutrophils Eosinophils Basophils Lymphocytes Monocytes Thrombocytes • • • • • Formed in the bone marrow Fragments of megakaryocytes Smallest of the blood cells Shape can be round, oval, or appear spiky Life span of around 8-12 days Thrombocytes • Involved in the clotting process • Seal wounds and prevent blood loss • Help repair damaged vessels • 150,000 – 400,000 per microliter of blood • Platelets stain bluish with reddish or purple granules Hemostasis • Platelets plays a vital role in healing of damaged blood vessels and prevent loss of blood • More the damage of blood vessels, faster is the beginning of coagulation (*15 sec after injury) Stages of Clotting Clotting Cascade • The clotting cascade occurs through two separate pathways that interact, the intrinsic and the extrinsic pathway. • Extrinsic Pathway The extrinsic pathway is activated by external trauma that causes blood to escape from the vascular system. This pathway is quicker than the intrinsic pathway. • Intrinsic Pathway The intrinsic pathway is activated by trauma inside the vascular system, and is activated by platelets, exposed endothelium, chemicals, or collagen. This pathway is slower than the extrinsic pathway, but more important. Thromboplastin released by damaged tissue cells enters the blood Platelets adhere to damaged blood vessel lining Extrinsic Pathway Intrinsic Pathway Prothrombin activator Prothrombin Thrombin Fibrinogen The Final common pathway in blood clotting Loose fibrin threads Stabilised fibrin clot ABO System •Use to denote the presence of one, both, or neither of the A and B antigens on erythrocytes.
