Circulatory_system

CIRCULATORY SYSTEM

Overview of the Circulatory System

• Function:

  • Transports oxygen and nutrients to cells.

  • Removes waste materials from tissues.

  • Works in conjunction with the respiratory system to maintain homeostasis.

• Components:

  • Comprises blood, blood vessels, and the heart.

  • Divided into two major systems:

    • Cardiovascular System:

      • Transports blood to and from the heart.

    • Lymphatic System:

      • Transports lymph, fighting infections and maintaining fluid balance.

Structure of Blood Vessels

• Layers of Blood Vessel Walls:

  • Tunica adventitia: Outermost layer, providing structural support.

  • Tunica media: Middle layer, mostly composed of smooth muscle.

  • Tunica intima: Innermost layer, responsible for smooth blood flow.

Blood Components

• Composition of Blood:

  • Plasma (55%): Liquid component of blood (90% water); carries nutrients, hormones, and proteins.

  • Formed Elements (45%): Include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.

• Blood Volume Breakdown:

  • Plasma: 55% (90% water)

  • Erythrocytes: 45%

  • Leukocytes and Platelets: 4.8%

Functions of Blood

• Transportation:

  • Carries oxygen, carbon dioxide, nutrients, waste products, and heat.

• Protection:

  • Involves phagocytosis, antibody formation, and clotting mechanisms.

RED BLOOD CELLS (ERYTHROCYTES)

• Structure:

  • Biconcave discs, no nucleus; contain hemoglobin for oxygen transport.

• Function:

  • Transport oxygen from lungs to body tissues and return carbon dioxide back to lungs.

Production of Erythrocytes

• Erythropoiesis:

  • Stimulated by erythropoietin (EPO), released by kidneys in response to low blood oxygen levels.

  • New erythrocytes enter circulation about 3-4 days after stimulation.

WHITE BLOOD CELLS (LEUKOCYTES)

• Types:

  • Phagocytes: Engulf and digest pathogens and debris.

  • Lymphocytes: Important for immune response (B cells produce antibodies, T cells kill infected cells).

• Function:

  • Protect against infections and diseases.

PLATELETS (THROMBOCYTES)

• Description:

  • Cell fragments involved in blood clotting.

• Function:

  • Form plugs at injury sites, initiating the coagulation cascade.

• Hemostasis Events:

  1. Vessel Spasm: Decrease blood flow in response to injury.

  2. Platelet Plug Formation: Sticky platelets converge at injury sites.

  3. Blood Clotting: Formation of a fibrin clot from prothrombin.

  4. Fibrinolysis: Repair process initiates post-clotting.

BLOOD VESSELS COMPARISON

Arteries

• Carry oxygenated blood away from the heart (except pulmonary artery).

• Thick muscular walls to withstand high pressure.

Veins

• Carry deoxygenated blood to the heart (except pulmonary vein).

• Thinner walls; contain valves to prevent backflow.

Capillaries

• Connect arterioles and venules; site of nutrient and gas exchange.

• Thinnest walls (one cell thick) for efficient diffusion.

HEART STRUCTURE AND FUNCTION

Anatomy of the Heart

• Chambers: Right atrium, left atrium, right ventricle, left ventricle.

• Valves: Bicuspid (mitral) and tricuspid valves; semilunar valves in arteries exiting the heart.

• Position: Thoracic cavity, above the diaphragm; protected by the pericardium.

Cardiac Cycle

• Phases of the Cycle:

  • Systole: Ventricles contract to pump blood.

  • Diastole: Heart muscles relax, filling chambers.

• SA Node: Pacemaker that initiates contraction; influences heart rate alongside other factors (hormones, temperature).

REGULATION OF HEART FUNCTION

• Heart Rate Influencers:

  • SA node regulates heart rate; sympathetic/parasympathetic fibers adjust it based on the body's needs.

• Cardiac Output: Amount of blood pushed into systemic circulation, dependent on stroke volume and heart rate.

CIRCULATORY SYSTEM PATHOLOGY

Heart Attack and Stroke

• Heart Attack: Blocked coronary arteries; loss of blood and oxygen leads to cell death.

• Stroke: Interruption of blood flow to the brain, leading to possible irreversible damage.

LYMPHATIC SYSTEM

• Function: Collects and recycles fluid leaked from the cardiovascular system; plays a critical role in immune response.

• Components: Lymphatic vessels and lymph nodes.

• Role of Lymph Nodes: Swell when fighting infections, indicating immune activity.