Circulation

Circulatory System Overview

  • The circulatory system has two main functions:

    • Transport: Facilitates the movement of oxygen, nutrients, hormones, and waste products.

    • Defense against diseases: Protects the body through immune responses mediated by white blood cells.

Components of Blood

  • Blood composition:

    • Red Blood Cells (RBCs):

    • Function: Transport oxygen from the lungs to tissues.

    • Adaptations:

      • Biconcave shape increases surface area for oxygen absorption.

      • Absence of nucleus maximises space for haemoglobin, which contains iron and binds oxygen.

    • White Blood Cells (WBCs):

    • Function: Immune defence against pathogens.

    • Types:

      • Lymphocytes: Produce antibodies specific to pathogens, causes clumping of microbes.

      • Phagocytes: Engulfs and digests foreign particles in a process called phagocytosis.

    • Platelets:

    • Function: Involved in blood clotting by converting fibrinogen to fibrin, forming a mesh that traps blood cells and helps scab formation.

    • Plasma:

    • Function: Liquid component of blood, transports blood cells, nutrients, hormones, and urea.

Blood Smear Examination

  • When using a microscope to examine a blood smear:

    • Recognize the effect of placing RBCs in hypotonic solutions, leading to cell lysis (bursting due to water influx by osmosis).

Blood Vessel Structure and Function

  • Types of Blood Vessels:

    • Arteries:

    • Carry oxygenated blood away from the heart (except pulmonary arteries which carry deoxygenated blood).

    • Characteristics:

      • Thick walls (muscle and elastic fibers) to handle high pressure.

      • Small lumen diameter.

    • Veins:

    • Carry deoxygenated blood back to the heart (except pulmonary veins which carry oxygenated blood).

    • Characteristics:

      • Thinner walls with less muscle, low pressure, larger lumen.

      • Valves present to prevent backflow and maintain unidirectional blood flow.

    • Capillaries:

    • Link arteries and veins, allowing for material exchange.

    • Characteristics:

      • One-cell-thick walls facilitate diffusion of oxygen, glucose, and waste materials.

Double Circulation

  • Heart and Circulation:

    • Blood passes through the heart twice during each circulation:

    • Right atrium -> Right ventricle -> Lungs (via pulmonary arteries).

    • Lungs -> Left atrium -> Left ventricle -> Body (via aorta).

  • Path of Blood Flow:

    • Major vessels include:

    • Vena Cava: Returns blood from body to right atrium.

    • Pulmonary Artery: Carries deoxygenated blood to lungs.

    • Pulmonary Vein: Returns oxygenated blood from lungs to left atrium.

    • Aorta: Distributes oxygenated blood from left ventricle to body.

Heart Structure and Function

  • Chambers of the Heart:

    • Atria: Upper chambers; receive blood.

    • Ventricles: Lower chambers; pump blood away from the heart.

    • Left ventricle has a thicker muscular wall to pump blood throughout the body under high pressure.

  • Valves: Prevent backflow, ensuring unidirectional flow of blood.

  • Coronary blood vessels supply the heart muscle with oxygenated blood, reducing risk of heart attacks.

Blockages in Blood Vessels

  • Causes and Effects:

    • Blockages often caused by cholesterol deposits leading to clot formation:

    • Restricted blood flow results in reduced oxygen and glucose delivery to cells, causing cellular death:

      • Coronary artery blockage can lead to heart attacks.

      • Brain artery blockage can lead to strokes.

Treatments for Cardiovascular Disease

  • Medical Interventions:

    • Angioplasty: A procedure using a balloon to widen narrowed arteries, often placing a stent to keep them open.

    • Medications:

    • Statins: Reduce cholesterol, decreasing blockage risk.

    • Aspirin: Thins blood to reduce clotting risk.

Lifestyle Factors Impacting Heart Health

  • Certain habits can increase the risk of heart disease and strokes:

    • High dietary fats, smoking, stress, and lack of exercise contribute to cardiovascular issues.

Exercise and the Circulatory System

  • Benefits of Regular Exercise:

    • Strengthens the heart muscle, increasing cardiac output and reducing resting heart rate.

    • Enhances overall cardiovascular health, shortening recovery time post-exercise.

Summary of Key Terms

  • Cardiac Output: Volume of blood pumped by the heart per minute.

  • Cell Lysis: Process of a cell bursting due to excess water intake by osmosis.

  • Lumen Diameter: The width of the hollow part of blood vessels; varies among arteries, veins, and capillaries.