Circulation and Cardiovascular System

Circulation Notes

I. Blood Vessels

  • Arteries

    • Carry blood away from the heart.
    • Have a thick layer of smooth muscle that controls blood pressure and flow.
    • Blood Pressure (BP)
    • Systolic Pressure: Pressure when blood is ejected from the heart (averagely 120 mmHg).
    • Diastolic Pressure: Pressure when the ventricle relaxes (averagely 80 mmHg).
    • Normal BP is described as 120/80 mmHg.

  • Arterioles

    • Small arteries that deliver blood to capillaries.

  • Capillaries

    • One-cell thick walls that allow for the exchange of gases and nutrients.
    • Oxygen and nutrients are delivered to tissues, while waste and CO2 are transported to the blood.

  • Venules

    • Collect blood from capillaries.

  • Veins

    • Carry blood back to the heart.
    • Have thinner walls and lower blood pressure than arteries.
    • Contain valves to prevent backflow of blood.

II. Heart

  • Pericardium: A fibrous sac that encloses the heart.

  • Myocardium: The main muscular portion of the heart, made mostly of cardiac muscle.

    • Composed of branching fibers to allow rapid signal conduction.

  • Atria: Chambers that collect blood from veins and push it into ventricles.

  • Ventricles: Chambers that pump blood into arteries.

  • Valves

    • Atrioventricular valves: Prevent backflow into the atria.
    • Semilunar valves: Prevent backflow into the ventricles.

III. Heart Beat

  • Intrinsic Control:

    • SA Node: Acts as the pacemaker, initiating the heartbeat (approx. 70 beats/min).
    • AV Node: Transmits signals to the ventricles.

  • Extrinsic Control:

    • The autonomic nervous system regulates heart rate.

IV. Vascular Pathways

  • Pulmonary Circuit:

    • Pathway of blood from the right ventricle to the lungs and back to the left atrium via pulmonary veins.

  • Systemic Circuit:

    • Pathway from the left ventricle to the body tissues and back to the right atrium via vena cavae.
    • Coronary Arteries: Supply blood to the heart muscle.
    • Hepatic Portal System: Carries blood from the intestines to the liver.

V. Blood

  • Functions of Blood:

    1. Transport O2, CO2, hormones, nutrients, and wastes.
    2. Control body pH.
    3. White blood cells fight disease.
    4. Regulate body temperature.

  • Blood Composition:

    1. Red Blood Cells (Erythrocytes)
    • No nucleus, carry hemoglobin which transports O2 from lungs to tissues.
    • Created in bone marrow, survive for about 120 days.
    1. White Blood Cells (Leukocytes)
    • Larger and fewer than RBCs, play roles in immune defense by engulfing damaged cells and destroying bacteria.
    1. Platelets
    • Cell fragments involved in clotting, survive for 5 to 9 days.
    1. Plasma
    • Mostly water, contains proteins that transport lipids and fight diseases, as well as various solutes.

VI. Capillary Exchange

  • Arterial Blood Entering Capillaries:

    • High in O2 and nutrients, blood pressure > osmotic pressure, allowing for exit of H2O, O2, and nutrients.

  • Venous Blood Leaving Capillaries:

    • Low in O2 and nutrients, blood pressure < osmotic pressure, allowing for the entry of wastes and CO2.

Key Point Summary

  • Blood vessels include arteries, arterioles, capillaries, venules, and veins, each serving a distinct function in circulation.
  • The heart consists of chambers (atria and ventricles) and valves critical for blood flow regulation.
  • Blood components (RBCs, WBCs, platelets, and plasma) each serve unique functions crucial for transport, immune response, and clotting.
  • Capillary exchange is essential for nutrient and gas exchange between blood and tissues.