Cardiac Histo Flashcards
Layers of vascular wall (innermost to outer)
Tunica intima
Tunica media
Tunica adventitia
Tunica intima
Single layer of endothelial cells (simple squamous epithelium)
Subendothelial layer of loose CT - containing fibroblasts and myointimal cells (which accumulate lipids w/ age)
Tunica media
Circularly oriented smooth muscles
Collagen type III (reticular fibers)
Elastic fibers in large arteries
Tunica adventitia
Collagen type I fibers
Longitudinally oriented smooth muscles in large veins
Vasa vasorum: system of vessels that supplies blood to the vascular walls of large arteries and veins
Nervi vasorum: network of autonomic nerves that control contraction of the smooth muscle in the vessel walls
Elastic lamina of arteries and large arterioles
Internal elastic lamina b/w intima and media
External elastic lamina b/w media and adventitia
Large elastic arteries
Aorta, Pulmonary trunk (artery), and their direct branches
*Tunica media most prominent
Concentric sheets of elastic membranes (fenestrated membranes) - in tunica media
These elastic laminae are sheets of fenestrated elastic material produced by smooth muscle cells in the tunica media
These help to minimize changes in BP w/ ventricular systole and diastole; highly pulsatile blood flow
W/ advancing age the arterial system becomes less elastic thereby increasing peripheral resistance and thus arterial BP
Medium muscular arteries
(Most named arteries)
*Tunica media most prominent
Main function: regulate blood flow to individual organs/parts of the body (by contracting or relaxing the smooth muscles)
Tunica media may contain up to 40 layers of smooth muscle cells
Prominent internal elastic lamina
Arterioles
Internal elastic lamina usually absent
Tunica media: 1-2 layers of smooth muscles
No external elastic lamina
*Arteriole has thicker wall and smaller diameter lumen than venules
The endothelium of arterioles is able to sense changes in BP, blood flow, and O2 tension and to respond to these changes by releasing signals - ex: endothelin (vasoconstrictor) and NO (vasodilator)
Metarterioles
Arise from arterioles and give rise to capillaries
Possess precapillary sphincters (bands of smooth muscle) - regulate blood flow into true capillaries
*These vessels are responsible for maximum peripheral resistance
Thoroughfare channel: distal portion of metarteriole, lacks smooth muscle cells and merges w/ the postcapillary venule
True capillaries: the smallest vessels, branch from the metartiole and thoroughfare channel - lack smooth muscle cells (although may have pericytes)
Pericytes
Only along capillaries and post-capillary venules
Cells w/ long cytoplasmic processes
Contractile functio - contain actin, myosin, tropomyosin, desmin
Controlled by NO
If tissue injury: pericytes and proliferate and differentiate to form new blood vessels
Capillary
Single layer of endothelial cells rolled up in form of a tube
All true capillaries branch off of metarterioles and thoroughfare
Endothelial cells joined by fasciae occludentes (tight junctions) and characteristically contain pinocytic vesicles
Endothelium surrounded by a basal lamina and occasional pericytes
Lumen just large enough to allow the passage of RBCs one at a time
3 types: continuous, fenestrated, discontinuous
Continuous/Somatic capillaries
No fenestrae in its wall
Continuous basal lamina
Pinocytic vesicles +++ (except CNS)
Tight junctions - tightly regulate materials
Cell junctions are frequently marked by cytoplasmic (marginal) folds that protrude into the lumen
*Muscle, CT, lungs, CNS, exocrine glands
Fenestrated/Visceral capillaries
Large fenestra in wall - bridged by a diaphragm (glycocalyx) - except in renal glomerulus
Continuous basal lamina
Fewer pinocytic vesicles
*SI, gallbladder, endocrine glands
Discontinuous/Sinusoidal capillaries
Endothelial cells form a discontinuous layer Multiple fenestrations w/o diaphragm Discontinuous basal lamina Lack pinocytic vesicles *Liver, bone marrow, spleen
AV Anastomosis/Shunts
AV shunts serve in thermoregulation at body surface
Closing AV shunt in skin: causes blood to flow through capillary bed, enhancing heat loss
Opening AV shunt in skin: reduces blood flow to skin capillaries, conserving body heat
Erectile tissues (penis) - closing AV shunt directs blood flow into corpora cavernosa