CARDIOVASCULAR SYSTEM BLOOD VESSELS General Organization Arteries Large (Elastic) Arteries Muscular (Distributing) Arteries Arterioles (Small) Arteries Precapillary (Terminal) Arterioles Capillaries Veins Venules Medium Veins Large Veins Lymphatics
General Organization Blood Vascular System Portal System Lymph Vascular System
Tissue Components Endothelium Elastic elements Muscular elements Connective tissue elements
Arteries - General Structural Plan Tunica Intima Tunica Media Tunica Adventitia Arteriosclerosis
Tunica Intima Endothelium Basement membrane Subendothelial connective tissue Internal elastic lamina (IEL)
Tunica Media Smooth muscle Elastic fibers/lamina
Tunica Adventitia External elastic lamina (EEL) Connective tissue Vasa vasorum Sympathetic nerves
Arteriosclerosis - “Hardening of Art.” Atherosclerosis Monckeberg’s Medical Calcific Sclerosis Arteriolosclerosis
Myointimal Cells Intimal smooth muscle cells Potential of fibroblasts, macrophages & SM Foam cells (lipophages)
BV CLASSIFICATIONS Arteries Capillaries Veins Large (Elastic) Medium (Muscular) Small (Arterioles) Capillaries Continuous Sinusoids Lymphatics Veins Small (Venules) Medium Large (Cava)
Large (Elastic) Arteries Tunica intima thicker subendothelial c.t. poorly defined IEL Tunica media - thickest, largely elastic Tunica adventitia EEL poorly defined vasa vasorum
Muscular (Distributing) Arteries Tunica intima - thin with prominent IEL Tunica media - largely smooth muscle Tunica adventitia thick with prominent EEL vasa vasorum, lymphatics, nerves
Arterioles (Small Arteries) Tunica intima - absence of IEL Tunica media - gradual reduction in layers Tunica adventitia - no EEL
Precapillary (Terminal) Arterioles Metarterioles no IEL 1-2 smooth muscle cells serve as AV shunts true capillaries are branches Precapillary Sphincters guard openings of true capillaries
Capillaries - General Structural Plan Endothelium Basement Memb. Pericytes Other Cells
Endothelium Cells elongated along capillary axis Attached by both occluding (tight) and communicating (gap) junctions Oval or elongated nucleus (bulges into lumen) Contractile - cytoplasmic filaments Pinocytotic vesicles and vacuoles
Basement Membranes Continuous in blood vascular system (prominent in brain as BBB) Discontinuous in sinusoids and lymphatics Collagen Type IV Elastic fibers
Pericytes Enclosed in own basement membrane Discontinuous and irregularly spaced Particularly numerous in brain (BBB) Nucleus bulges away from lumen
Other Cells Fixed macrophages Mast cells - secrete heparin Rare nerve fibers
Capillary Function Barrier Exchange Forces Endocapillary layer Endothelium Basal lamina and pericytes Adventitia Exchange Forces Hydrostatic Osmotic Concentration
Capillaries - Structural Types True Capillaries Continuous capillaries Fenestrated capillaries with diaphragms Fenestrated capillaries without diaphragms Sinusoids Lymphatic Capillaries
Venules (Small Veins) Tunica intima - endothelial tube Tunica media Pericytes Isolated smooth muscle cells Tunica Adventitia - minimal
Medium Veins Tunica intima - thin, forms valves Tunica media - scattered smooth muscle Inner layer longitudinally arranged in large veins Tunica adventitia - thick with longitudinal
Large Veins Tunica intima - slightly thicker than medium Tunica media - sparse smooth muscle cells Tunica adventitia - thick with longitudinal bundles of smooth muscle cells
Lymphatics Tunica intima & adventitia only Discontinuous basement membrane Very frequent valves Anchoring filaments Extensive vasa vasorum Lymphangion Interposed lymph node filters Drain into veins
BV CLASSIFICATIONS Arteries Capillaries Veins Large Elastic lamina Medium >10 SM layers Small (Arterioles) <5 SM layers Capillaries Continuous (Fenestrated & Non-Fenestrated) Sinusoids (Liver, spleen, lymph nodes, BM) Lymphatics (Everywhere) Veins Small (Venules) Thin wall, large lumen Medium Few layers of SM, “ Large (Cava) Long. SM in Adv.