lecture 18 physiology

Blood Composition

• Blood is considered a connective tissue.

• Composed of cellular elements and an extracellular matrix (plasma).

  • Extracellular Matrix (Plasma)

    • Mostly water, approximately 92%.

    • Suspends formed elements, allowing circulation through the cardiovascular system.

  • Cellular Elements (formed elements):

    • Red Blood Cells (RBCs): Also known as erythrocytes.

    • White Blood Cells (WBCs): Referred to as leukocytes.

    • Platelets: Fragments of cells involved in clotting.

Plasma Proteins

• Three major groups of plasma proteins:

  • Albumin: Most abundant, produced by the liver, functions as a transport vehicle for fatty acids and steroids.

  • Globulins:

    • Transport iron, lipids, and fat-soluble vitamins (A, D, E, and K).

    • Gamma globulins involved in immunity (antibodies/immunoglobulins).

  • Fibrinogen: Essential for blood clotting.

Red Blood Cells (RBCs)

• Structure:

  • Biconcave disk shape maximizes surface area for gas exchange.

  • No nucleus, cytoplasm packed with hemoglobin (Hb).

• Function:

  • Hemoglobin is responsible for transporting oxygen throughout the body.

  • Each Hb molecule can carry four molecules of oxygen.

Life Cycle of Erythrocytes

• Production:

  • RBCs last about 120 days in the bloodstream.

  • New erythrocytes produced at a rate of 2-3 million per second, triggered by erythropoietin from the kidney in response to low O2 levels.

  • Requires iron, folic acid, and vitamin B12.

• Destruction:

  • Old RBCs are removed by the spleen and converted to bilirubin, excreted in feces and urine.

White Blood Cells (WBCs)

• Differ from RBCs in that:

  • Have a nucleus and mitochondria.

  • Can move in an ameboid fashion and exit the bloodstream to sites of infection.

• Types:

  • Major groups: Granular and Agranular leukocytes.

    • Granular leukocytes (e.g., neutrophils) respond quickly to infection and are efficient phagocytes.

    • Agranular leukocytes (e.g., B cells, T cells) are involved in specific immune responses.

Platelets (Thrombocytes)

• Fragments of megakaryocytes, crucial for blood clotting.

• Function primarily to limit blood loss by forming a clot in response to vessel damage.

• Secrete growth factors for tissue repair.

Blood Typing

• Classification system based on antigens present on RBC surface (ABO and Rh systems).

• Importance of matching blood types to prevent transfusion reactions:

  • ABO System (A, B, AB, O): determined by presence of antigens.

  • Rh Factor: Rh-positive (have the antigen) vs. Rh-negative (do not).

Blood Clotting (Hemostasis)

• Mechanisms to stop bleeding:

  1. Vasoconstriction: Narrowing of blood vessels.

  2. Formation of Platelet Plug: Platelets adhere to collagen exposed by vessel injury.

  3. Fibrin Production: Fibers reinforce the plug, turning it into a stable clot.

The Lymphatic System

• Comprises organs, vessels, and tissues that protect against infection and manage fluid balance.

  • Functions include returning excess fluid to blood, aiding in fat absorption, and immune defense.

  • Structure: Includes lymph nodes, spleen, thymus, and various lymphoid tissues.

• Lymph Nodes: Filter lymph fluid and activate immune responses.

• Spleen: Largest lymphoid organ, filters blood, stores breakdown products of RBCs.

• Thymus: Where T-lymphocytes mature, significant during early life.

Interaction with Other Systems

• Relationship with Cardiovascular System: Lymphatic system returns filtered fluids to the bloodstream.

• Immune System: Major role in immune response by presenting lymph to immune cells.

• Digestive System: Absorbs fats via lacteals in the small intestine.