Blood Blood is a specialized connective tissue Consists of several kinds of cells Cells suspended in a liquid matrix called plasma –Cellular elements = 45% of volume –Plasma = 55% of volume

Figure The composition of mammalian blood

Plasma 90% H 2 O 10% Solutes –Nutrients, Wastes, Hormones, Respiratory Gases –Electrolytes Maintain osmotic balance Help buffer blood –Plasma Proteins Acts as buffers Maintain osmotic balance Antibodies (immunoglobulins) Clotting Factors (fibrinogens) Transporters/Carriers

Cellular Elements Red Blood Cells –Function is to transport oxygen White Blood Cells –Function is to fight infections Platelets –Fragments of cells that contain no nuclei –Function in blood clotting

Figure Differentiation of blood cells

Red Blood Cells Also called erythrocytes Most numerous type of cell in blood –5 million cells per mm 3 Small biconcave disks Large surface area for rapid diffusion of oxygen Lack nuclei to make room for hemoglobin, the iron containing protein that transports oxygen Lack mitochondria/ATP by anaerobic metabolism

White Blood Cells Called leukocytes 5,000 to 10,000 per mm 3 Spend most of their time patrolling interstitial fluid and the lymphatic system Five types –Monocytes (a phagocytic cell) –Neutrophils (a phagocytic cell) –Basophils –Eosinophils –Lymphocytes (B cells and T cells)

Stem Cells All red and white blood cells and platelets are derived from pluripotent stem cells –Pluripotent stem cells have potential to differentiate into any type of blood cell Formed in red marrow of bones –ribs, vertebrae, sternum, and pelvis Negative feedback system controls formation of red blood cells –Erythropoietin synthesized in kidney if O 2 level is low and stimulates marrow to produce more red blood cells

Blood Clotting Fibrinogen always present in blood is converted to fibrin when activated by clotting factors released from platelets, damaged cells, and plasma Thrombus = clumping platelets and clot formation in the absence of injury Hemophilia = disease characterized by excessive bleeding due to lack of appropriate clotting factors