Blood Components and Functions

• Blood and lymph facilitate circulation in humans
• These fluids transport nutrients, gases, and waste

Blood

• A fluid connective tissue: plasma and formed elements
• The average adult has roughly 5 liters

Plasma

• The fluid matrix of blood is 55% of blood volume
• Contains water, proteins, electrolytes, nutrients, gases and wastes
• Major plasma proteins: albumin, globulins, and fibrinogen
• Albumin helps maintain osmotic balance
• Globulins participate in immune responses
• Fibrinogen essential for blood clotting

Formed Elements

• Erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (thrombocytes) are the formed elements of blood

Erythrocytes

• Red blood cells are the most abundant blood cells
• Biconcave shape; lacks a nucleus when mature; packed with hemoglobin
• Hemoglobin is an iron-containing protein that transports oxygen
• Red blood cells are produced in red bone marrow
• Lifespan: approximately 120 days

Leukocytes

• White blood cells assist in immune response
• Nucleated cells; categorized as granulocytes and agranulocytes
• Granulocytes: neutrophils, eosinophils, and basophils which feature granules in the cytoplasm
• Agranulocytes: lymphocytes and monocytes which lack granules in the cytoplasm
• Neutrophils are phagocytic and the most abundant leukocytes
• Eosinophils are involved in allergic reactions and parasitic infections
• Basophils release histamine and are involved in inflammatory reactions
• Lymphocytes are B and T cells involved in immune responses
• Monocytes differentiate into macrophages, which are phagocytic

Platelets

• Platelets are cell fragments from megakaryocytes in bone marrow
• Critical role in blood clotting

Blood Groups

• ABO and Rh are the two major blood grouping systems in humans

ABO Blood Groups

• ABO blood groups are based on the presence or absence of A and B antigens on the surface of red blood cells
• Blood type A, B, AB, or O
• Blood type A has A antigens and anti-B antibodies in the plasma
• Blood type B has B antigens and anti-A antibodies in the plasma
• Blood type AB has both A and B antigens and no antibodies in the plasma (universal recipient)
• Blood type O has no antigens and both anti-A and anti-B antibodies in the plasma (universal donor)
• Blood transfusions must be compatible to prevent agglutination (clumping) of red blood cells

Rh Blood Groups

• Based on the presence or absence of Rh factor (D antigen) on red blood cells
• Individuals with the Rh factor are Rh-positive (Rh+)
• Those without are Rh-negative (Rh-)
• Rh incompatibility can occur during pregnancy if an Rh-negative mother carries an Rh-positive fetus
• The mother may develop anti-Rh antibodies, which can attack the red blood cells of subsequent Rh-positive fetuses (erythroblastosis fetalis)

Coagulation of Blood

• Blood clotting (coagulation) prevents excessive blood loss after injury
• Cascade of reactions with clotting factors (proteins) in the blood
• Platelets adhere to the site of injury and release factors that initiate the clotting process
• Fibrinogen is converted to fibrin
• Fibrin forms a mesh-like network that traps blood cells and platelets, forming a clot
• Calcium ions play an important role in the clotting process

Lymphatic System

• A network of vessels and tissues
• Helps maintain fluid balance and protect the body against infection
• Consists of lymph, lymph vessels, lymph nodes, and lymphoid organs (spleen, thymus, tonsils)

Lymph

• Fluid similar to blood plasma but with fewer proteins
• It is formed from interstitial fluid that enters lymphatic capillaries

Lymph Vessels

• Similar to blood vessels, transporting lymph throughout the body
• Lymph capillaries are small, permeable vessels that collect interstitial fluid
• Lymph vessels have valves to prevent backflow of lymph

Lymph Nodes

• Small, bean-shaped structures along lymph vessels
• Filter lymph and contain lymphocytes and macrophages that help remove pathogens and cellular debris

Lymphoid Organs

• The spleen filters blood, removing old or damaged red blood cells
• The thymus is involved in the maturation of T lymphocytes
• Tonsils are lymphoid tissues in the throat that help protect against infection

Functions of the Lymphatic System

• Draining excess interstitial fluid and returning it to the bloodstream
• Transporting dietary lipids and lipid-soluble vitamins absorbed from the digestive system
• Carrying out immune responses by filtering lymph and housing lymphocytes and macrophages