4: The CV System II Flashcards
arterial system
high pressure system delivering blood away from heart
arterioles = smallest branches of arteries that lead to capillary beds
arterioles useful for blood pressure regulation as they can change drastically in their size
capillary bed
smallest blood vessels with very thin walls (one cell thick for diffusion)
location of exchange between blood and interstitial fluid
thoroughfare channels within capillary bed provides more rapid exchange between arteriole and venous system
precapillary sphincters are muscular structures at opening of capillaries to control rate of blood flow into capillary (stops high pressure)
arteriovenous anastomosis are low resistance channels to bypass the capillary bed, in skin for rapid control of blood flow during temp regulation
venous system
venules are smallest branches of veins that collect blood from capillaries to return to heart
not under high pressure so blood moves slower
nearly 2/3 of blood at any given moment at rest sits in systemic venous system
blood vessel structure
blood vessel walls have three layers: tunica intima, tunica media, tunica externa
common between veins and arteries but have different characteristics
tunica intima
inner layer
encompasses an endothelial lining and connective tissue layer
in arteries it has an internal elastic membrane providing passive elasticity
endothelium
damaged endothelium = more likely to get clots
endothelium provides non-stick surface
chambers of heart have endothelium constant with major blood vessels
releases vasoactive substances which affect vascular tone, blood pressure and blood flow
maintains vascular homeostasis
vasodilators: nitric oxide
vasoconstrictors: endothelin
tunica media
middle layer
contains concentric sheets of smooth muscle in loose connective tissue, accompanied by elastic fibres in arteries and collagen in veins
in arteries, between the tunica media and tunica externa there is an external elastic membrane
tunica externa
outer layer
anchors vessel to adjacent tissues
contains collagen fibres, elastic fibres and in veins smooth muscle cells
vasa vasorum are small arteries and veins in walls of large arteries and veins
types of artery
elastic artery = elastic fibres, e.g. aorta, only artery with internal elastic membrane
muscular artery = thick tunica media, less elastic fibres, femoral artery is example, can change greatly in diameter
arterioles = only made of tunica media, endothelium and basement membrane
capillaries
endothelial tube into thin basement membrane
no tunica media or externa
diameter similar to that of red blood cell
different capillaries for different roles: continuous, fenestrated, sinusoid
continuous capillaries
found in all tissues except epithelia and cartilage
have complete endothelial lining
permit diffusion of water, small solutes and lipid soluble materials
specialised continuous capillaries in CNS and thymus that have very restricted permeability
fenestrated capillaries
have pores in endothelial lining
permit rapid exchange of water and large solutes
found in endocrine glands, kidneys, intestinal tract, choroid plexus
sinusoid capillaries
have gaps between adjacent endothelial cells
permit free exchange of water and large plasma proteins
found in liver, spleen, bone marrow (RBCs move into CV system), endocrine organs
phagocytic cells monitor blood at sinusoids (engulf foreign cells)
venous system
veins collect blood from capillaries and return it to heart
compared to arteries, veins having large diameter, thins walls, low BP
large veins = thick tunica externa
medium veins = less smooth muscle
venules = very thin walls, only has endothelium and tunica externa
venous valves
made of folds of tunica intima
prevent backflow of blood
compression of veins from skeletal muscle pushes blood back to heart (skeletal muscle pump)
when walls of veins near valve weaken, varicose veins may result