Aortic Histology

Aorta ●​ Largest elastic artery ●​ From left ventricle ●​ Starts at aortic valve ●​ Distribution of oxygenated blood to systemic circulation ●​ Conduction of oxygenated blood with high pressure ●​ Pressure reservoir through elastic recoil ●​ Maintainment of continuous blood flow in diastole Ascending Aorta ●​ Starts at left ventricle after aortic valve ●​ Upward extension from heart ●​ Right coronary artery ●​ Left coronary artery ●​ Functions for supplying myocardium through coronary circulation Aortic Arch ●​ Curvature posteriorly + left over the heart ●​ Branchiocephalic trunk ○​ Right common carotid artery ○​ Right subclavian artery ●​ Left common carotid artery ●​ Left subclavian artery ●​ Responsible for supplying head, neck, and upper limbs Descending Thoracic Aorta ●​ Traveling downwards to posterior mediastinum ●​ Posterior intercostal arteries ●​ Bronchial arteries ●​ Esophageal arteries ●​ Pericardial/mediastinal branches ●​ Superior phrenic arteries ●​ Responsible for supplying thoracic wall and thoracic organs Abdominal Aorta ●​ Starts after passing diaphragm at T12 ●​ Ends at L4 ○​ Bifurcating into common iliac arteries ●​ Celiac trunk ●​ Superior mesenteric artery ●​ Renal arteries ●​ Gonadal arteries ●​ Inferior mesenteric artery ●​ Lumbar arteries ●​ Common iliac arteries ●​ Responsible for supplying abdominal organs, pelvis, and lower limbs Region Location Major Branches Supplies Ascending Aorta From LV upward Coronary arteries Heart Aortic Arch Curved superior portion Brachiocephalic, L common carotid, L subclavian Head, neck, upper limbs Thoracic Aorta Descending in thorax Intercostal, bronchial, esophageal Thorax Abdominal Aorta Below diaphragm Celiac, mesenteric, renal, iliac Abdomen, pelvis, lower limbs Aortic histology ●​ Elastic artery = wall has large amount of elastic tissue ○​ Allows for stretch in systole ○​ Recoil in diastole ○​ Assist in maintaining blood pressure ⇒ continue blood flow during heartbeat Vessel Type ex) Key Histologic Feature Elastic Artery Aorta, pulmonary trunk Numerous elastic lamellae in tunica media Muscular Artery Radial artery, femoral artery Smooth muscle-dominant tunica media Arteriole Small resistance vessels 1–2 layers of smooth muscle Aortic wall layers ●​ Tunica Intima ○​ Simple squamous endothelium in lumen ○​ Basement membrane under endothelium ○​ Subendothelial connective tissue ■​ Collagen ■​ Elastic fibers ○​ Internal elastic lamina ■​ Could be present ■​ Indistinct since there are many elastic layers in media ○​ Gives smooth surface for blood flow ○​ Regulation of vascular tone/signaling through endothelial mediators ○​ Barrier between blood and vessel wall ○​ In sense of histology, thin innermost layer is adjacent to lumen ○​ Hard to identify in routine section ●​ Tunica Media ○​ Thickest in the aorta ○​ 40-70 concentric fenestrated elastic lamellae ■​ Could be different by age and location ○​ Smooth muscle cell could be seen in elastic sheets ○​ Contains collagens + ground substance ○​ Expanding during ventricular systole possible ○​ Elastic recoil in diastole will maintain blood pressure ○​ Extreme pulse pressure is prevented ○​ Histologically could see multiple dark and light wavy concentric layers ○​ Laminated appearance in microscopy ○​ Smooth muscle nuclei could be seen in elastic sheets ●​ Tunica Adventita ○​ Outer layer of connective tissue ○​ High level of collagen + elastic fibers ○​ Vasa vasorum ○​ Nervi vasorum ■​ Vessel wall supplying autonomic nerve ○​ Anchoring of aorta to other surrounding tissues ○​ Supply outer wall with nutrition/oxygen ○​ Support structurally ○​ In histology slide, could see loose connective tissue on the outer layer ○​ Small blood vessel could be seen ■​ Vasa vasorum Histologic features of Aorta ●​ Elastic Lamellae ○​ Elastin sheets, arranged concentrically ○​ Fenestrated ■​ Diffusion between layer is possible ○​ Significant for classification of elastic artery ●​ Vasa Vasorum ○​ Small blood vessels ■​ Supplying walls of large vessels ○​ Diffusion of lumen tends to be insufficient for aortic wall which is thick ○​ Must need dedicated blood supply ■​ Outer media ■​ Adventita ●​ Nervi Vasorum ○​ Autonomic nerve fibers on innervating vessel wall ○​ Used for regulation of smooth muscle tone ○​ Assist in vessel diameter/vascular function