Circulation and Cardiovascular System Overview

Circulatory System

  • The circulatory system is responsible for the internal transport of gases, nutrients, and waste within mammals.
  • It is a closed system, meaning blood is contained within vessels.

Heart Structure

  • Mammals have a four-chambered heart:
    • Two atria (upper chambers) and two ventricles (lower chambers).
    • Right atrium and right ventricle are involved in the pulmonary circuit; left atrium and left ventricle in the systemic circuit.
    • Valves ensure one-way flow of blood through the heart.

Circulatory Pathways

  • Pulmonary Circuit:

    1. Right ventricle pumps deoxygenated blood to the lungs via pulmonary arteries.
    2. Lungs oxygenate blood, which then enters the left atrium via pulmonary veins.

  • Systemic Circuit:

    1. Left atrium to left ventricle.
    2. Left ventricle pumps oxygenated blood to the body through the aorta.
    3. Blood returns to the right atrium via the superior and inferior vena cavae.

Blood Flow Mechanism

  • Diastole: Heart is relaxed; blood fills all four chambers.
  • Systole:
    • Atria contract, forcing blood into the ventricles.
    • Ventricles contract, sending blood out through the pulmonary artery and aorta.
  • Cardiac Output: Average output is about 75 ml per beat or 5.25 liters/min.

Blood Vessels

  • Arteries: Carry blood away from the heart; have thick walls to handle high pressure.
  • Veins: Return blood to the heart; contain valves to prevent backflow, walls are thinner than arteries.
  • Capillaries: Thinnest vessels, only one cell thick, allowing for efficient gas and nutrient exchange.

Blood Composition

  • Average adult has 4-6 liters of blood:
    • 45% cells (red blood cells, white blood cells, platelets)
    • 55% plasma (90% water, 10% dissolved molecules).

Red Blood Cells (RBCs)

  • Approximately 25 trillion RBCs in circulation; lifespan of 3-4 months.
  • Each has a biconcave shape for maximum gas exchange and contains hemoglobin.
  • Levels of RBCs and hemoglobin are regulated by oxygen levels in the tissue. Low levels are known as anemia.

White Blood Cells (Leukocytes)

  • Function: Defense against infection, classified into five types:
    1. Basophils: Release chemicals during infections.
    2. Neutrophils: Phagocytic; ingest bacteria.
    3. Monocytes: Become macrophages, engulf pathogens.
    4. Eosinophils: Fight parasitic infections.
    5. Lymphocytes: B-lymphocytes produce antibodies, T-lymphocytes destroy infected cells.

Blood Clotting

  • Platelets and proteins in blood (e.g., fibrinogen) work together to plug leaks in blood vessels when injured.
  • Blood clotting process involves:
    1. Platelets adhere and activate clotting factors.
    2. Prothrombin is converted to thrombin; fibrinogen converts to fibrin.
    3. Fibrin forms a mesh that traps RBCs, creating a clot.

Heart Health Issues

  • Heart Attack: Caused by blockage of coronary arteries; symptoms include chest pain, sweating, and shortness of breath.
  • Hypertension: Consistently high blood pressure; normal is 120/80 mmHg.
  • Heart Murmur: Occurs when blood flows backward due to malfunctioning valves.
  • Diseases of Blood: Hemophilia and leukemia are examples of blood-related conditions affecting clotting and blood cell production respectively.