HISTOLOGY OF CIRCULATORY SYSTEM II

DIVISIONS MACROVASCULATURE: > 0.1µm, large arterioles, muscular & elastic arteries, muscular veins MICROVASCULATURE: < 0.1µm, arterioles, capillaries, post capillary venules Exchange vessels

TISSUE COMPONENTS Endothelium Muscular tissue Connective tissue (Elastic elements)

STRUCTURAL PLAN OF BLOOD VESSELS TUNICA INTIMA Endothelium Basal lamina Sub endothelial connective tissue Internal elastic lamina TUNICA MEDIA Smooth muscles Elastic lamellae, reticular fibers Ground substance elements External elastic lamina

TUNICA ADVENTITIA Collagen & elastic fibers VASA VASORUM Vessels of vessels Arterioles, capillaries, venules in adventitia INNERVATION Sympathetic fibers (norepinephrine) Vasoconstriction Arteries in Skeletal Muscles- cholinergic vasodilator fibers

ENDOTHELIUM: Semi permeable barrier Nonthrombogenic surface; Monitor bidirectional exchange Nonthrombogenic surface; heparin, tissue plaminogen activator & Von Willibrand factor Regulate Vascular tone & Blood flow; Contraction: endothelin 1 & ACE Relaxation: NO & Prostacyclin Inflammation & Local Immune response; Adhesion of WBCs, expression of P-Selectin, Weibel Palade Bodies Growth Factors; VEGF in Vasculogenesis, Angiogenesis, role of Angiopoeitins Lipolysis Produce Vasoactive substances Thrombosis, emboli (Role of TPA)

VASCULAR SMOOTH MUSCLES Present in all vessels EXCEPT capillaries and post capillary venules Enclosed in basal lamina & connective tissue Arranged helically Connected by gap junctions VASCULAR CONNECTIVE TISSUE Variable proportion Collagen, IV, III, I Elastic fibers Ground substance; heterogenous gel

Medical Application Arteriosclerosis Thickening of walls of small arteries Monkeberg’s calcific sclerosis Atherosclerosis

LARGE ELASTIC ARTERIES T. INTIMA Intima is thicker; smooth muscles in sub endothelial connective tissue Internal elastic lamina, though present not prominent T. MEDIA Concentric lamellae of elastic fibers (40-70) Reticular fibers, smooth muscles T. ADVENTITIA Less developed

Arterial Sensory Receptors Carotid & Aortic Sinus: Baroreceptors Tunica Media is thin--- allows distension Afferent impulses via 9th cranial nerve Vasomotor center in brain Efferent adjust lumen to control BP Carotid & Aortic Bodies: Chemoreceptors Para ganglia with rich capillary network Glomus type I cells; dense core granules containing Dopamine, Ach Supported by Satellite Type II cells Ion channels in Glomus cells respond to Low Oxygen, High CO2 or Acidosis Afferents to brain efferents to cvs or respiratory system