Cardiovascular System

Cardiovascular System

1. Arteries

   • Tunica Intima
     • Innermost layer, consisting of a single layer of endothelial cells
     • Endothelial cells are lying on the basement membrane
   • Tunica Media
     • An intermediate layer with variable amounts of smooth muscle cells, elastic laminae and reticular fibres
   • Tunica Adventitia
     • Outermost layer which contains the connective tissue rich in collagen and elastic fibres

2. Large Elastic Artery

   • Tunica Intima
     • Is thicker than in other smaller arteries
     • It is composed of A) endothelium
       • Simple squamous epithelium composed of polygonal, flat endothelial cells
         • Their Nuclei protrude in the vascular lumen
     • B) A thick layer of sub endothelial tissue
       • LCT, contains collagen, elastic fibres, scattered fibroblasts and some smooth muscle
   • Tunica Media
     • Thick, consists of series of 40-60 concentrically arranged perforated elastic laminae
     • Number of elastic laminae increases with age
     • The fenestra allow substances to diffuse to and nourish cells deep in the vessel wall
     • Between elastic laminae are smooth muscle cells, reticular fibres and ground substance

3. Medium Sized Artery

   • Tunica Intima
     • 3 LAYERS!! A) Endothelium
       • Similar to Large Elastic Artery
     • B) Subendothelial Layer
       • Thin layer of LCT:Collagen, Elastic Fibres, Fibroblasts
       • As size of artery decreases, this layer becomes thinner
     • C) Internal Elastic Lamina
       • Thick, prominent and is seen as a refractive wavy band
   • Tunica Media
     • Thick, muscular layer with 20-40 layers of smooth muscle cells arranged circularly
     • Outer border of media is marked by the external elastic lamina
     • Between the layers of muscle there is small amount of CT

4. Medium Sized Vein

   • Thickest part of a vein is TUNICA ADVENTITIA
   • Whereas in Artery is TUNICA MEDIA
   • Tunica Intima just has endothelium and thin sub endothelial layer
   • Tunica Media is relatively thin, small bundles of smooth muscle cells, reticular fibres and fine network of elastic fibres
   • Tunica Adventitia composed of many longitudinal collagen fibres which may be combined with bundles of longitudinally orientated smooth muscle cells