Notes on Blood Vessels and Blood

Blood Vessels

  • Blood is transported through three main types of blood vessels:

    • Arteries: Carry blood away from the heart.
    • Veins: Carry blood toward the heart.
    • Capillaries: Facilitate exchange between the bloodstream and tissue cells, also occurring in the lungs.

  • All blood vessels are lined with smooth epithelium but show structural differences.

  • Arterial Blood Pressure:

    • Measured as force exerted by blood against vessel walls during:
    • Systole (contraction)
    • Diastole (relaxation)
    • Normal ranges:
    • Systolic: 90−130extmmHg90 - 130 ext{ mmHg}
    • Diastolic: 60−80extmmHg60 - 80 ext{ mmHg}

  • Hypertension: Condition of abnormally high blood pressure.

Structural Differences Between Veins and Arteries

  • Veins:

    • Thin walls, expandable (less muscle), lower blood pressure, contain valves.

  • Arteries:

    • Thick, muscular, and elastic walls, higher blood pressure, carry blood away from the heart.
Capillary Structure
  • Capillaries form networks (capillary beds) to ensure all cells receive oxygen and nutrients while removing waste.
  • Composed of three layers or "tunics".
Regulation of Arterial Lumen Diameter
  1. Vasoconstriction:
    • Smooth muscle fibers contract, reducing lumen diameter, regulated by the ANS (Autonomic Nervous System).
  2. Vasodilation:
    • Smooth muscle fibers relax, increasing lumen diameter, also regulated by ANS and chemicals (e.g., nitric oxide).
  3. Vasospasm:
    • Occurs upon damage to artery/arteriole, contracting smooth muscle to limit blood flow and reduce blood loss.
Arterioles
  • Very small arteries, delivering blood to capillaries.
  • Play a key role in regulating blood flow:
    • Vasoconstriction: Decreased blood flow and increased blood pressure.
    • Vasodilation: Increased blood flow and decreased blood pressure.
Venous System

  • Venules:

    • Formed by several capillaries uniting, receive blood from capillaries and empty into veins.

  • Venous Return: Volume of blood returning to the heart through systemic veins.

    • Achieved by:
    • Heart's pumping action.
    • Valves to prevent backflow.
    • Skeletal muscle contractions (skeletal muscle pump).
    • Breathing (respiratory pump).
Venous Pumps

  • Respiratory Pump:

    • Changes in thoracic and abdominal pressure enhance venous return, especially during deep ventilation.

  • Skeletal Muscle Pump:

    • Muscles contract, squeezing blood toward the heart through venous valves.
Varicose Veins
  • Caused by faulty valves leading to abnormal venous pooling and swelling.
Capillary Exchange
  • Capillary walls permit exchange between blood and interstitial fluid due to their thin walls (approximately 8 µm in diameter).
  • Precapillary Sphincters:
    • Regulate blood flow into capillary networks.
Summary: Blood Flow Regulation

  • Blood flow and pressure regulated by neural and hormonal negative feedback systems.

    • Controlled by the cardiovascular center in the medulla oblongata, integrating inputs from multiple areas.

  • Neural Input: From cerebral cortex, limbic system, hypothalamus, sensory receptors (proprioceptors, baroreceptors, chemoreceptors).

  • Hormonal Regulation:

    • Hormones like angiotensin II, aldosterone, epinephrine, and norepinephrine raise blood pressure.
    • Atrial natriuretic peptide lowers blood pressure.
Disorders
  • Myocardial Infarction (Heart Attack): Occurs when blood flow to the heart is blocked.
  • Atherosclerosis: Buildup of plaques within arteries leading to blockage.
Homeostasis Functions of the Cardiovascular System
  • Regulation of electrolyte and fluid balance (with kidneys).
  • Regulation of body temperature.
  • Distribution of hormones and biochemicals.
  • Transport of gases, nutrients, and waste.
  • Immune response mediation and defense.