CARDIOVASCULAR SYSTEM ppt

CARDIOVASCULAR SYSTEM

Blood Vessels

  • Blood vessels are classified into three types based on function and structure:

    • Arteries

    • Capillaries

    • Veins

  • Blood vessels have three layers (tunics):

    • Tunica adventitia (external)

    • Tunica media

    • Tunica intima (interna)

Arteries (High Pressure System)

  • Function: Carry blood away from the heart; must withstand high pressure and rapid changes in blood velocity.

  • Structure:

    • Thick-walled, contractile, and elastic to accommodate pressure.

Tunica Intima (Tunica Interna)

  • Description:

    • Inner layer exposed to blood, made of sparse fibrous tissue.

    • Acts as a selectively permeable barrier and secretes vasoconstrictors and vasodilators.

  • Components:

    • Endothelium: Simple squamous cells over a basement membrane.

    • Subendothelial layer: Connective tissue and smooth muscle fibers.

    • Internal elastic lamina: Fenestrated elastic fibers prominent in muscular arteries.

Tunica Media

  • Description: Thickest layer consisting predominantly of elastic fibers and/or smooth muscle cells.

  • Contains:

    • External elastic lamina and collagen.

Tunica Adventitia (Adventitia)

  • Description: Outermost layer of the blood vessel.

  • Structure:

    • Composed of loose connective tissue that merges with neighboring vessels and nerves.

    • Anchors vessels and provides passage for nerves and small blood vessels (vasa vasorum) which supply blood to the outer wall.

Types of Arteries

  1. Elastic (Conducting) Arteries

    • Largest arteries, receiving the first surge of blood from the heart.

    • Examples: Pulmonary arteries, aorta, carotid arteries.

    • Structure:

      • Tunica intima: Thick with numerous elastic fibers.

      • Tunica media: Thickest layer with elastic fibers, separated by fenestrated laminae.

      • Tunica adventitia: Network of elastic and collagen fibers.

  2. Muscular (Distributing) Arteries

    • Smaller branches that distribute blood to specific organs.

    • Structure:

      • Tunica intima: Endothelium + basement membrane + thick internal elastic layer.

      • Tunica media: Composed mainly of smooth muscle cells (25-40 layers).

      • Tunica adventitia: Contains elastic and collagen fibers, blending with surrounding connective tissue.

Arterioles (Resistance Arterioles)

  • Description: Smallest branches of the arterial tree.

    • Tunica intima: Endothelium and basement membrane; absent in the smallest.

    • Tunica media: 1-2 layers of smooth muscle cells.

    • Tunica adventitia: Collagen and elastic fibers, blends with surrounding tissue.

Capillaries

  • Description: Uniform diameter, approximately 5µm wide, allowing passage of one RBC at a time.

  • Structure:

    • Composed of endothelial cells, basal lamina, and pericytes.

    • Surrounded by smooth muscle cells forming precapillary sphincters to regulate blood flow.

  • Types:

    • Continuous: Tight junctions; found in muscle and nerve tissue.

    • Fenestrated: Circular openings; more permeable (GIT, endocrine glands).

    • Porous: Allow formation of ultrafiltrate (kidney glomerulus).

    • Sinusoids: Larger, irregular shapes; present in liver and bone marrow.

Veins (Low Pressure System)

  • Function: Carry blood from peripheral organs back to the heart; classified into three sizes: small (venules), medium, and large veins.

  • Venules:

    • Similar to capillaries, with subendothelial structures present. Quite porous for fluid exchange

  • Medium-sized veins:

    • Thinner walls, resist physical stress from gravity.

  • Large veins:

    • Tunica media may be thin or absent; significant tunica externa with smooth muscle and collagen.

    • Contain venous valves to prevent backflow.

Heart Structure

  • The heart wall has three layers:

    1. Endocardium: Inner lining, continuous with tunica intima of large vessels; consists of endothelium, subendothelium, and Purkinje fibers.

    2. Myocardium: Thickest layer, composed of cardiac muscle cells. Contains collagen and elastic fibers forming a supporting structure.

    3. Epicardium: External layer, composed of mesothelium and connective tissue, includes blood vessels and nerves.

Impulse Conducting System

  • SA node: Pacemaker derived from myocardium.

  • AV node: Where signals from the SA node spread.

  • AV bundle (Bundle of His): Pathway for signals to exit the AV node; composed of large conducting cardiac fibers (Purkinje fibers).

  • Extends through the ventricular septum, dividing into right and left bundles.