Circulatory System

Differentiation of Systems

  • Circulatory System: Refers to the systems of blood circulation, including the cardiovascular and lymphatic system.
  • Cardiovascular System: Comprises the heart and blood vessels that transport blood throughout the body.
  • Lymphatic System: A network that returns lymph—fluid that may contain infection-fighting white blood cells—back to the bloodstream.
  • Immune System: Involves the body's defense mechanisms against pathogens, supported by the lymphatic system.

Cardiovascular System

Design, Function, and Main Components

  • Main Components: Heart, blood, and blood vessels (arteries, veins, and capillaries).
  • Function: Transports nutrients, gases, hormones, blood cells, and waste products to and from cells.
  • Design:
    • The heart acts as a pump.
    • Blood vessels form a continuous circuit throughout the body.

Blood

Components of Blood and Their Major Functions

  • Components:
    • Red Blood Cells (RBCs): Carry oxygen via hemoglobin.
    • White Blood Cells (WBCs): Part of the immune defense against infection.
    • Platelets: Essential for blood clotting.
    • Plasma: Liquid component carrying nutrients, hormones, and wastes.

Comparison of Formed Elements in Blood

  • Origins:
    • All formed elements arise from hematopoietic stem cells in the bone marrow.
  • Histology:
    • RBCs have a biconcave shape; WBCs exhibit diverse structures depending on type (e.g., lymphocytes, neutrophils).
  • Functions:
    • RBCs: Oxygen transport.
    • WBCs: Immune response.
    • Platelets: Clot formation.

Differentiation of Various Blood Components

  • Plasma vs. Serum:
    • Plasma: Liquid component that exists when blood is not clotting.
    • Serum: Fluid that remains after blood coagulation, lacking clotting factors.
  • Blood vs. Lymph:
    • Blood: Circulates nutrients and oxygen.
    • Lymph: Transports immune cells and proteins.
  • RBCs vs. WBCs:
    • RBCs: Erythrocytes, no nucleus, primarily for gas transport.
    • WBCs: Leukocytes, have a nucleus, immune functions.
  • Granulocytes vs. Agranulocytes:
    • Granulocytes: Type of WBC that contains granules (e.g., neutrophils, eosinophils).
    • Agranulocytes: WBCs without granules (e.g., lymphocytes, monocytes).

Heart

Structure of the Pericardium and Heart Wall

  • Pericardium:
    • A double-walled sac that contains the heart.
    • Fibrous Pericardium: Outer layer providing protection.
    • Serous Pericardium: Inner layer with two parts (parietal and visceral) producing serous fluid to reduce friction.
  • Heart Wall:
    • Composed of three layers:
    • Epicardium: Outer layer, connective tissue and epithelium.
    • Myocardium: Middle layer, cardiac muscle responsible for contraction.
    • Endocardium: Inner layer, smooth lining of chambers and valves.

Chambers, Great Vessels, and Valves of the Heart

  • Chambers:
    • Right Atrium, Right Ventricle, Left Atrium, Left Ventricle.
  • Great Vessels:
    • Aorta, Pulmonary Arteries, Pulmonary Veins, Superior and Inferior Vena Cava.
  • Valves:
    • Atrioventricular Valves: Tricuspid (right) and Mitral (left).
    • Semilunar Valves: Pulmonary and Aortic.

Conduction System of the Heart

  • Components:
    • Sinoatrial Node (SA Node): Primary pacemaker.
    • Atrioventricular Node (AV Node): Secondary pacemaker, coordinates contraction.
    • Bundle of His and Purkinje Fibers: Distribute impulses through ventricles.
  • Functional Features:
    • Electrical impulses trigger heartbeats, ensuring synchronized contraction of chambers.

Cardiac Circulation

  • Flow of Blood Through the Heart:
    1. Blood enters the Right Atrium from the Superior/Inferior Vena Cava (deoxygenated).
    2. Flows through the Tricuspid Valve to the Right Ventricle.
    3. Pumped through the Pulmonary Valve into the Pulmonary Arteries to the lungs (oxygenated).
    4. Returns via Pulmonary Veins into the Left Atrium.
    5. Passes through the Mitral Valve into the Left Ventricle.
    6. Blood is pumped through the Aortic Valve into the Aorta to the body.

Vessels

Differentiation of Circulatory Routes

  • Pulmonary Circulation:
    • Circulates blood between the heart and lungs for gas exchange.
  • Systemic Circulation:
    • Transports oxygenated blood from the heart to all body tissues and returns deoxygenated blood.
  • Portal Circulation:
    • Involves veins that drain blood from the gastrointestinal tract to the liver.

Comparison of Structures and Functions of Blood Vessels

  • Arteries:
    • Thick, muscular walls; carry oxygenated blood away from the heart (except pulmonary arteries).
  • Arterioles:
    • Smaller branches of arteries; regulate blood flow and pressure.
  • Capillaries:
    • Microscopic vessels where nutrient and gas exchange occur; wall consists of a single endothelial cell layer.
  • Venules:
    • Small vessels that collect blood from capillaries and converge into veins.
  • Veins:
    • Thinner walls compared to arteries; carry deoxygenated blood back to the heart (except pulmonary veins).

Anatomical Features That Aid Venous Return

  • Valves: Prevent backflow of blood in veins.
  • Skeletal Muscle Pump: Contraction of surrounding muscles helps push blood back toward the heart.
  • Respiratory Pump: Changes in thoracic pressure during breathing draw blood into the heart.

Differentiation of Capillary Types

  • Continuous Capillaries:
    • Have a continuous endothelial lining, permit selective passage of materials.
  • Fenestrated Capillaries:
    • Contain pores (fenestrations) for increased permeability, found in kidneys and intestines.
  • Sinusoidal Capillaries:
    • Have large openings allowing passage of larger molecules and cells, found in liver, spleen, and bone marrow.