Histology - Circulatory System

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circulatory flow
elastic arteriestomuscular arteriestoarteriolestocapillariestopostcapillary venulesto medium-sized veintolarge vein
blood vessel composition (3 layers)
1 - tuncia intima2 - tunica media3 - tunica adventitia
tunica intima
*delimits the vessel wall towards the lumen of the vessel and comprised its endothelial lining (typically simple squamous with many tight junctions) and connective tissue (basal lamina and loose connective tissue)*beneath the connective tissue there is...
tunica media
*formed by a layer of circumferential smooth muscle and variable amounts of connective tissue*a second layer of elastic fibers - the external elastic lamina - is located beneath the smooth muscle away from the tunica intima*ite of histological specialization...
tunica adventitia / externa
* outter most layer; surrounds tunica media*consists mainly of connective tissue fibers (COLLAGEN which serves to anchor blood vessle to nearby organs - stability)*blends in with surrounding connective tissue surrounding the vessel*hard to indicate precisely...
*3 types (large elastic, medium muscular, small arteries/arterioles)*specialization of arterial walls depend on: (i) pressure pulses generated during contractions of heart (systole), and (ii) regulation of blood supply to target tissues of arteries*tunica...
elastic arteries
*large*tunica intima of elastic arteries thicker than in other arteries*layer of subendothelial connective tissue allows the tunica intima to move independently from other layers as the elastic arteries distend with the increase in systolic blood pressure*in...
vasa vasorum
blood vessels in tunica adventitia that nourish cells of tunica media and tunica adventitia
muscular arteries
*tunica media thinner than in elastic arteries*subendothelial connective tissue other than the internal elastic lamina often hard to discern*internal elastic lamina appears as well defined layer*tunica media dominated by numerous concentric layers of...
*diameter less than 0.1 to 0.5mm *endothelium still rests on internal elastic lamina - which may be incomplete and which is not always well-defined in histological sections*tunica media consists of 1-3 concentric layers of smooth muscle cells that regulate...
*sum of diameters of all capillaries is significantly larger than that of the aorta - which decreases the blood pressure and flow rate*capillary diameter ranges from 4 to 15 micrometers*functions of capillaries: -provides nutrients and oxygen to surrounding...
*@capillaries*incomplete layer of cells surrounding capilaries*contractile properties*regulate blood flow in capillaries by surrounding the tunica intima*during vascular remodeling and repair they differentiate into endothelial and smooth muscle cells
*walls of veins are thinner than walls of arteries*diameter is larger than that of arteries*layering in the wall of veins is NOT distinct*tunica intima is very thin; only the largests veins contain subendothelial connective tissue*internal and external...
vein valves
*loose, pocket-shaped folds of tunica intima*extends into the lumen of the vein*opening of the pocket will point in the direction of blood flows towards the heart
lymphatic vessels
parts of the blood vessels with exude from the blood vessels into the surrounding tissues because of transport across the endothelium or due to blood pressure*role of lymph vessels is to return surplus liquid (lymph) to blood circulation*UNIDIRECTIONAL...
lymph capillaries
*larger than blood capillaries*very irregularly shaped*begin as blind-ending tubes in connective tissue*basal lamina almost completely absent*endothelial cells do not form tight junctions - thereby facilitates flow of liquids into lymph capillary*temporary...
lymph vessel
*formed from merging lymph capillaries*larger than lymph capillaries - though otherwise very similar*have valves*lymph moved via compression of lymph vessels by surrounding tissues - little lymh moves without this muscular activity*empty into lymph nodes...
lymph ducts
*one or two layer of smooth muscle cells in wall*form vales*movement of lymph toward the heart enhanced by (i) peristaltic contractions of smooth muscle, and (ii) compression of ducts by surrounding tissues
thorasic duct
largest lymph duct, 5mm in diameter, drians lymph from the lower half and upper left quadrant of the body, empties lymph into circulation by merging with vascular system close to junction of left internal jugular and subclavian veins

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