Circulatory System

Circulatory System

  • The circulatory system facilitates the transport of materials within the internal environment, enabling exchange with cells at the cell, tissue, and organ levels.

Structure of the Heart

  • Exterior View of the Heart

    • Pulmonary Artery
    • Left Atrium
    • Pulmonary Vein
    • Left Ventricle
    • Right Ventricle
    • Inferior Vena Cava
    • Superior Vena Cava
    • Aorta
    • Right Atrium

  • Section through the Heart

    • Aorta
    • Left Atrium
    • Aortic Semilunar Valve
    • Pulmonary Vein
    • Bicuspid Valve
    • Left Ventricle
    • Right Atrium
    • Right Ventricle
    • Inferior Vena Cava
    • Superior Vena Cava
    • Pulmonary Artery
    • Semilunar Valve
    • Tricuspid Valve
    • Septum

The Chambers of the Heart

  • The heart is composed of four muscular chambers:
    • Upper Chambers (Atria):
    • Receive blood.
    • Lower Chambers (Ventricles):
    • Act as pumping chambers.
    • The two left chambers are separated from the two right chambers by the septum.

Blood Vessels

  • Major blood vessels include:

    • Aorta
    • Pulmonary Vein
    • Inferior Vena Cava
    • Superior Vena Cava
    • Pulmonary Artery

  • Blood Flow:

    • Vena Cava:
    • Carries deoxygenated blood from the body to the right atrium.
    • Pulmonary Artery:
    • Carries deoxygenated blood from the right ventricle to the lungs.
    • Pulmonary Vein:
    • Carries oxygenated blood from the lungs to the left atrium.
    • Aorta:
    • Carries oxygenated blood from the left ventricle to the body.

The Valves of the Heart

  • Blood flow is controlled by four valves:
    • Aortic Semilunar Valve
    • Bicuspid Atrioventricular Valve
    • Pulmonic Semilunar Valve
    • Tricuspid Atrioventricular Valve
    • Chordae Tendinae:
    • Strong tendons that hold atrioventricular valves in position.
    • Heart sounds, known as "lubb-dubb," result from the snapping shut of the valves.

Blood Circulation Through the Heart

  • Blood flows:
    • To the body
    • From the lungs

Heartbeat Regulation

  • The heart contains specialized conductive tissue which regulates the heartbeat.
    • Sinoatrial Node (SA Node):
    • A cluster of specialized cardiac cells in the wall of the right atrium, initiating the heartbeat (the pacemaker).
    • Atrioventricular Node (AV Node):
    • Secondary pacemaker regulating the beating of the ventricles.

Blood Vessel Types

  • Arteries
    • Muscular blood vessels that carry blood away from the heart.
  • Arterioles
    • Small arteries that direct blood flow to various tissues.
  • Capillaries
    • Microscopic blood vessels connecting arterioles and venules, facilitating the exchange of substances between blood and surrounding tissues.
  • Venules
    • Small veins.
  • Veins
    • Blood vessels that carry blood toward the heart.

Structure of Blood Vessels

  • Layers of Blood Vessels:

    • Tunica Interna: Inner layer.
    • Tunica Media: Middle layer, well developed in arteries, less so in veins.
    • Tunica Externa: Outer layer, well developed in veins.

  • Differences Between Arteries and Veins:

    • Arteries have thick muscular walls, while veins have thinner walls and larger lumens.

Double Circulation in Humans

  • Humans possess a double circulation consisting of two main circuits:
    • Pulmonary Circulation:
    • Takes deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium.
    • Systemic Circulation:
    • Takes oxygenated blood from the left ventricle to the tissues and returns deoxygenated blood to the right atrium.

Cardiac Cycle

  • Definition:
    • The cardiac cycle is the period beginning with atrial contraction and ending with ventricular relaxation.
  • Systole:
    • The period when the heart contracts and pumps blood into circulation.
  • Diastole:
    • The period of relaxation when the chambers fill with blood.
  • Atria and ventricles undergo coordinated systole and diastole to ensure efficient blood pumping.

Cardiac Output

  • Definition:
    • Cardiac output is the amount of blood leaving one ventricle each minute.
  • Formula:
    • extCardiacOutput(mL/min)=extStrokeVolume(mL)imesextHeartRate(beats/min)ext{Cardiac Output (mL/min)} = ext{Stroke Volume (mL)} imes ext{Heart Rate (beats/min)}

Blood Pressure Categories

  • Categories:
    • Normal: Systolic < 120 mm Hg and Diastolic < 80 mm Hg
    • Elevated: Systolic 120-129 mm Hg and Diastolic < 80 mm Hg
    • High Blood Pressure (Hypertension) Stage 1: Systolic 130-139 mm Hg or Diastolic 80-89 mm Hg
    • High Blood Pressure (Hypertension) Stage 2: Systolic 140 mm Hg or higher or Diastolic 90 mm Hg or higher
    • Hypertensive Crisis: Systolic higher than 180 and/or Diastolic higher than 120, consult a doctor immediately.

Factors Affecting Blood Pressure

  • Key factors influencing blood pressure include:
    • Vasoconstriction/vasodilation
    • Salt intake
    • High fat intake
    • Genetics
    • Heart disease
    • Water intake

Functions of Blood

  • Blood components facilitate various functions:
    • Transport: Nutrients, oxygen, and hormones to tissues, removal of wastes like carbon dioxide and urea.
    • Regulation: Maintains body’s pH and temperature.
    • Protection: Clotting to prevent blood loss and immune response against pathogens.

Features of Blood

  • Temperature: 38°C
  • pH: 7.35-7.45
  • Salinity: 0.9%
  • Total Body Weight: 8%
  • Volume:
    • Men: 5-6 L
    • Women: 4-5 L

Composition of Blood

  • Approximately:
    • Plasma: ~55%
    • Platelets: ~1%
    • Red Blood Cells: ~40%
    • White Blood Cells: ~4%

Blood Plasma

  • Description:
    • A clear, pale yellow liquid constituting 46-63% of whole blood.
  • Composition:
    • Water (92%)
    • Dissolved organic/inorganic solutes (1%)
    • Dissolved plasma proteins (7%)

Blood Cell Functionality

  • Red Blood Cells (Erythrocytes):
    • 4-6 million/mm³, responsible for the transport of O₂ and some CO₂.
  • White Blood Cells (Leukocytes):
    • Granular leukocytes:
    • Neutrophils: 2,000-7,000/mm³, phagocytes.
    • Eosinophils: 100-400/mm³, phagocytes & anti-inflammatory response.
    • Basophils: 20-100/mm³, inflammatory response.
    • Agranular leukocytes:
    • Monocytes: 100-900/mm³, phagocytes.
    • Lymphocytes: 1,500-3,000/mm³, immune response.
  • Platelets (Thrombocytes):
    • 200,000-500,000/mm³, involved in blood clotting.

Blood Clotting

  • Process:
    • A blood clot forms a jelly-like mass at a wound site to stop bleeding, consisting of a mesh of protein fibers and trapped blood cells.
  • When solidified, it forms a scab.
  • Thrombus: If a clot forms inside a blood vessel, it can lead to serious conditions like heart attacks or strokes if it becomes dislodged.

The Thrombin System

  • Clotting Cascade:

    1. Blood platelets and injured cells release thromboplastin.
    2. Thromboplastin interacts with Ca²⁺ and prothrombin to form thrombin.
    3. Thrombin converts fibrinogen to fibrin.
    4. Fibrin forms a mesh at the injury site to trap cells and prevent bleeding.
    5. Clot contracts over the wound to help close it.

  • Serum: The clear fluid that escapes from the clot is plasma minus fibrinogen.

  • Fibrinolysis: The breakdown of the clot initiated by an enzyme in the clot a few days after formation.

Summary of the Thrombin System

  • Formula Elements:
    • Thromboplastin + prothrombin + Ca²⁺ = thrombin
    • Thrombin + fibrinogen = fibrin
    • Fibrin + blood cells = clot

Lymphatic System

  • The lymphatic system serves two primary functions:
    • Returns tissue fluid to the circulatory system.
    • Assists in protecting the body from disease.

Structure of the Lymphatic System

  • Comprised of:
    • Lymph Vessels: One-way drainage system transporting lymph.
    • Lymph Nodes: Bean-shaped structures with high concentrations of macrophages and lymphocytes.

Functions of the Lymphatic System

  • Filtering:
    • Removes cellular materials including pathogens and cancer cells.
  • Immune Activation:
    • Activates the immune response through lymphocyte action.

Relation of Blood Pressure and Lymphatic System

  • High Blood Pressure Effects:
    • Increased diffusion, potential swelling of feet and ankles due to insufficient drainage by the lymphatic system.

Blood Transfusions and Blood Types

  • Blood Types:
    • Various antigens and antibodies define blood types:
    • A: A antigen, B antibody.
    • B: B antigen, A antibody.
    • O: No antigens, A and B antibody (universal donor).
    • AB: A and B antigens, no antibodies (universal receiver).

Types of Transfusions

  • Whole Blood: Added clotting components for severe blood loss.
  • Red Cell Concentrates: Primarily red blood cells.
  • Platelet Concentrates: Aid in coagulation.
  • Plasma Transfusions: Frozen and defrosted for clotting factors.
  • Immunoglobulins: Help patients combat infections.
  • Autologous Transfusions: Blood taken from the patient for use during surgery.