tunica intima: endothelial lining and elastic connective tissue
tunica media: smooth muscle with collagen and elastic fibers
tunica externa: sheath of connective tissue that protects vessel, anchor to other tissues
what are the three types of arteries?
elastic: first arteries leaving the heart (pulmonary trunk, aorta)
muscular arteries: external carotid arteries (deliver blood to head and neck) deliver blood to body organs, active in vascoconstriction
arterioles: smallest; leads to capillary beds, control flow by vasodilation and vasoconstriction
what are the functions of capillaries?
exchange of gases, nutrients, wastes, hormones between blood and interstitual fluid
why are capillaries ideal for diffusion between plasma and IF?
thin walls provide short diffusion distance
small diameter slows flow to increase diffusion rate
enormous number of capillaries provide huge surface area for increased diffusion
what are the three types of capillaries?
what are continuous capillaries?
least permable, most common
tight junctions connect endothelial cells
intercellular clefts allowpassage of fluids and small solutes
large fenestrations (pores) increase permeability
occurs in areas of active absorption or filtration
fewer tight junctions; usually fenestrated; larger intercellular clefts; large lumens
blood flow sluggish: allow modification
what is precapillary sphincter?
a band of smooth muscle that regulates entrance to capillary beds
what is a vascular shunt?
connects the terminal arteriole with teh postcapillary venule in a capillary bed
what are capillary beds regulated by?
local chemical conditions and vasomotor nerves
where do true capillaries branch from and return to?
metarteriole, thoroughfare channel (pathway is called a vascular shunt)
what are alternate routes for blood flow?
formed by anastromaosis, a joining of blood vessels
arteriovenous anastomosis: bypasses capillary bed, connective arteriole to venule
arterial anastomosis: occurs where arteries fuse before branching into arterioles (ensure delivery of blood to key areas)
what are the three types of veins?
venules: smallest, some lack tunica media; very porous, allow fluids and WBC into tissues
medium sized venules: tunica media has several smooth muscle layers
large veins: thin tunica media and thick collagenous tunica externa; thinner walls than arteries b/c of low pressure; contain up to 65% of blood supply (called capacitance vessels aka blood reservoirs)
what adaptations ensure return of blood to heart despite low pressure?
large diameter lumens offer little resistance
venous valves present backflow of blood
venous sinuses: flattened veins with extrememly thin walls
how to maintain adequate blood flow?
normally, blood flow equals cardiac output (CO); increased CO leads to increased flow through capillaries
decreased CO leads to reduced flow
capillary flow influenced by pressure and resistance
liquids exert hydrostatic presure in all directions
circulatory pressure, high in aorta vs. low in venae cavae
what is blood pressure
force per unite area exerted on wall of blood vessel by blood
what is peripheral resistance?
any fore that opposes flow/movemnt of blood
measure amount of friction blood encournters with vessel walls, generally in peripheral (systemic) circulation
highest pressure gradient exists in arterioles due to high peripheral resistance
what are three important sources of resistance?
vascular resistance: largest component
viscosity: due ot interactions between moles in liquid
turbulence: eddies and swirts in flow of blood
what is vascular resistance?
caused by friction between blood and vessel walls
amount of friction due to length and diameter of vessel.
arteriolar diameter is primary source of vascular resistance
the smaller the diameter, the greater the distance
varies inversely with fourth power of vessel radius
abrupt changes in diameter or fatty plagues from atheroclerosis increase resistance.