Vessels

Anatomy of Blood Vessels

  • Layers of Blood Vessel Walls:
    • Endothelium (Tunica Intima) - Simple squamous epithelium.
    • Smooth Muscle (Tunica Media) - Involved in vasoconstriction and vasodilation.
    • Connective Tissue (Tunica Externa) - Composed of areolar connective tissue; contains vasa vasorum.

Types of Blood Vessels

  • Arteries: Carry blood away from the heart.

    • Elastic Arteries - Large, dense elastic tissue, near the heart.
    • Muscular Arteries - Most common, thick smooth muscle layer, active in vasoconstriction.
    • Arterioles - Smallest arteries, no connective tissue, significant for capillary blood flow.

  • Capillaries: Connect arterioles to venules.

    • Single layer of endothelium allows easy diffusion.
    • Supported by basal lamina.
    • Types of Capillaries:
    • Continuous - Most common, leaky junctions.
    • Fenestrated - Large pores, found in kidneys and small intestine.
    • Sinusoidal - Large pores, allows large molecules to pass.

  • Capillary Beds: Composed of metarterioles and capillaries, controlled by precapillary sphincters.

Capillary Exchange

  • Mechanisms:
    • Diffusion through endothelium and between cells (paracellular).
    • Transcytosis - Vesicular transport of materials.
    • Bulk Flow - Driven by hydrostatic or osmotic pressure; filtration at arterial end, absorption at venous end.

Edema

  • Causes include:
    • Inadequate lymph drainage (e.g., elephantiasis).
    • Imbalance in filtration and absorption due to hydrostatic pressure or plasma protein levels.

Veins and Venules

  • Venules: Drain capillaries, increase smooth muscle as they enlarge.
  • Veins: Thinner muscle layer, act as blood reservoir. Blood flow assisted by skeletal muscle and respiratory movements.

Circulatory Systems

  • Pulmonary Circulation: Carries deoxygenated blood from the right ventricle via pulmonary arteries to lungs, returns oxygenated blood through pulmonary veins to left atrium.
  • Systemic Circulation:
    • Ascending aorta from left ventricle; branches to coronary arteries.
    • Aortic Arch: Supplies blood to upper body.
    • Descending Aorta: Thoracic and abdominal aorta with various branches.

Blood Flow and Pressure

  • Pressure Created by Ventricular Contraction: Blood flows due to pressure gradients.
  • Blood Vessel Diameter: Affects pressure; vasodilation decreases pressure, vasoconstriction increases.
  • Blood Pressure: Highest in arteries; systolic average 120 mm Hg, diastolic average 80 mm Hg.

Regulation of Blood Pressure

  • Main Factors: Blood volume, cardiac output, peripheral resistance.
  • Short-Term Response: Cardiovascular control via cardiac and vasomotor centers, baroreceptor reflex.
  • Long-Term Control: Renal mechanisms regulate blood volume to maintain pressure balance.