Functions and Characteristics of Blood

Functions of Blood

  • Transports oxygen from the lungs to body tissues.

  • Carries carbon dioxide from tissues back to the lungs for removal.

  • Delivers nutrients from the digestive system to body cells.

  • Transports hormones from endocrine glands to target tissues.

  • Carries metabolic wastes away from cells.

  • Protects the body through immune responses involving white blood cells.

  • Prevents excessive blood loss through clotting involving platelets.

Components of Blood

  • Blood composition:

    • Plasma: Approximately 55% of blood volume; liquid portion containing water, proteins, nutrients, and waste products.

    • Formed elements: Comprise about 45% of blood; includes red blood cells (RBCs), white blood cells (WBCs), and platelets.

  • Hematocrit: Percentage of whole blood made up of red blood cells, indicating the blood's oxygen transport capability.

    • Normal hematocrit levels:

    • Males: 42–56%

    • Females: 38–46%

  • Average ratio of blood components:

    • Plasma: approximately 55%

    • Buffy coat (white blood cells and platelets): less than 1%

    • Red blood cells: about 44%

Physical Characteristics of Whole Blood

  • Color:

    • Oxygenated: Bright red

    • Deoxygenated: Dark reddish-brown

  • Temperature: Slightly higher than normal body temperature (helps with heat distribution).

  • Viscosity: About five times more viscous than water due to RBCs and plasma proteins.

  • pH: Alkaline, normal range of 7.35 to 7.45; arterial blood (less CO₂) is closer to higher range, while venous blood (more CO₂) is closer to lower range.

Plasma Functions, Components, and Characteristics

  • Makes up about 55% of total blood volume.

  • Composition:

    • Water: About 92%

    • Proteins:

    • Albumin: Maintains fluid balance and blood pressure.

    • Globulins: Involved in transport and immune defense.

    • Fibrinogen: Plays a role in blood clotting.

    • Other constituents: Electrolytes, nutrients, and waste products for homeostasis.

  • Considered a colloid as proteins remain suspended in the fluid, drawing water into the bloodstream.

Formed Elements and Their Characteristics

  • Definition: Cellular components of blood.

  • Includes:

    • Red blood cells (erythrocytes)

    • White blood cells (leukocytes)

    • Platelets

  • Whole cells: Only white blood cells are considered whole because they contain nuclei.

  • Red blood cells: Lose nucleus during development; platelets are cell fragments from megakaryocytes.

  • Formed elements: About 45% of whole blood, aiding in oxygen transport, immune defense, and clotting.

Structure and Function of Erythrocytes

  • Shape: Biconcave discs without a nucleus.

    • Importance: Shape allows flexibility to pass through small capillaries; increased hemoglobin capacity.

  • Function: Transport oxygen and, to a lesser extent, carbon dioxide.

Erythropoiesis Control Factors

  • Controlled by blood oxygen levels and hormone erythropoietin (EPO).

    • EPO Release: Triggered by low oxygen levels, stimulates red bone marrow to produce more red blood cells.

    • Feedback: EPO production decreases once normal oxygen levels are restored.

Red Blood Cell Lifecycle

  • Lifespan: Approximately 120 days.

  • Destruction:

    • Removed from circulation by macrophages in the spleen and liver.

    • Hemoglobin breakdown:

    • Protein portion broken into amino acids (reused).

    • Iron recycled (stored in liver or used to form new hemoglobin).

    • Heme converted to bilirubin (excreted in bile).

Blood Typing and Significance

  • ABO Blood Group:

    • Type A: A antigens, anti-B antibodies.

    • Type B: B antigens, anti-A antibodies.

    • Type AB: Both A and B antigens, no antibodies.

    • Type O: No antigens, both anti-A and anti-B antibodies.

  • Significance: Incompatible blood transfusions can lead to hemolysis (clumping and breaking apart of red blood cells).

  • Rh Blood Group:

    • Presence of D antigen: Rh positive; absence: Rh negative.

    • Rh negative individuals may develop antibodies after exposure to Rh positive blood.

  • Erythroblastosis Fetalis:

    • Condition occurring in Rh negative mothers with Rh positive fetuses, leading to potential destruction of fetal red blood cells and complications such as anemia and jaundice.

Anemia and Polycythemia

  • Anemia:

    • Definition: Condition with inadequate red blood cells or hemoglobin.

    • Symptoms: Fatigue, weakness, shortness of breath.

    • Causes: Iron deficiency, blood loss, vitamin deficiencies.

  • Polycythemia:

    • Definition: Excessive red blood cells.

    • Consequences: Increased blood viscosity, risk of clots and hypertension.

    • Causes: Low oxygen levels, increased EPO production, bone marrow disorders.

Types of Leukocytes

  • Five types of leukocytes:

    • Neutrophils: Phagocytosis of pathogens.

    • Eosinophils: Combat parasitic infections and allergic reactions.

    • Basophils: Release histamine, promote inflammation.

    • Lymphocytes: Immune responses (antibody production, cell-mediated immunity).

    • Monocytes: Phagocytosis of pathogens.

  • Definitions:

    • Chemotaxis: Movement of leukocytes toward infection sites in response to chemicals.

    • Margination: Adhesion of leukocytes to blood vessel walls near infection.

    • Diapedesis: Process of leukocytes leaving bloodstream and entering tissues.

    • Phagocytosis: Ingestion and destruction of pathogens by phagocytes.

Conditions Related to White Blood Cells

  • Leukopenia:

    • Definition: Abnormally low white blood cell count.

    • Consequences: Weakened immune system, increased infection risk.

    • Causes: Viral infections, bone marrow disorders, autoimmune diseases, chemotherapy, medications.

  • Leukemia:

    • Definition: Cancer of white blood cells originating in bone marrow, producing abnormal leukocytes.

    • Consequences: Crowding of normal blood cells, leading to anemia, frequent infections, excessive bleeding.

    • Causes: Genetic factors, radiation, chemicals, viral infections.

Platelets and Hemostasis

  • Platelets (Thrombocytes): Small cell fragments from megakaryocytes, crucial for clotting.

  • Thrombocytopenia:

    • Definition: Low platelet count.

    • Consequences: Impaired clotting and increased bleeding risk.

Hemostasis Process

  • Definition: Process preventing blood loss from damaged blood vessels.

  • Steps:

    1. Vascular Spasm: Smooth muscle contraction in blood vessels reduces blood flow.

    2. Platelet Plug Formation: Platelets adhere to damage and release chemicals to attract more platelets, forming a plug.

    3. Coagulation: Clotting factors convert fibrinogen into fibrin, forming a stable mesh.

  • Post-Clotting:

    • Clot Retraction: Platelets contract, pulling vessel edges together for repair.

    • Fibrinolysis: Breakdown of the fibrin mesh after healing, restoring normal blood flow.

Thrombosis and Related Conditions

  • Thrombosis: Formation of abnormal blood clot within a vessel.

  • Definitions:

    • Thrombus: A clot that remains attached to vessel wall.

    • Embolus: A clot or part thereof that travels through the bloodstream, potentially blocking vessels.

  • Hemophilia:

    • Definition: Genetic disorder causing deficiency in clotting factors, leading to prolonged bleeding.

    • Cause: Genetic mutation affecting clotting factor production.