Medical Sciences 3999A/B/Y Lecture Notes - Lecture 28: Tunica Intima, Tunica Externa, High Endothelial Venules
2 Mar 2020
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Document Summary
Veins: vessels that conduct blood back to heart. Gradually increase in caliber and walls become thicker as they progress towards heart. More numerous and of larger caliber than arteries. More than 70% of total blood volume of cvs. Walls are thinner and less elastic than arteries. Distensible enough to adopt variations in volume and blood pressure = capacitance/reservoir vessels. Histological section: collapsed structure with irregular slit-like lumen (unless specially fixed to distension) Valves of veins: prevent blood from flowing away from heart; mostly present in medium caliber veins in the extremities. Valve sinus: thinner walled blood vessel located between valve and wall of vein. Muscular and elastic tissue is not nearly as well developed in veins as in arteries (due to lower venous blood pressure); however, ct component is more prominent. Tunica media forming a cylindrical vessel (15-20 um); wall structure not very different from capillary, but of larger caliber.
