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Vessels and Circ.

Anatomy & Physiology

three types of blood vessels arteries, capillaries, and veins
arteries convey blood from heart to capillaries
capillaries microscopic porous blood vessels that are necessary for exchanging substances between blood and tissues
veins drain blood from capillaries and transport it back to the heart
vessel composition walls composed of layers called tunics surround the inside space of the vessel (arteries, capillaries, and veins differ in specific composition
three tunics tunica intima, tunica media, and tunica externa
purpose of three tunics exchange substances between blood and tissues
lumen inside space of the vessel
tunica intima innermost layer of vessel, has endothelial component (simple squamous epithelium) facing lumen and has subendothelial layer of areolar connective tissue
tunica media middle layer of the vessel, circularly arranged layers of smooth muscle cells with elastic fibers, contraction causing vasoconstriction (narrowing of vessel lumen), relaxation causing vasodilation (widening of vessel lumen)
tunica externa outermost layer of vessel, areolar connective tissue with elastic and collagen fibers help anchor vessel to other structures
comparison of the different vessel types - arteries have thick tunica media and narrower lumen, have more elastic and collagen fibers (can spring back to shape), and are more resistant to changes in blood pressure
veins have thicker tunica externa and larger lumen, less elastic and collagen fibers (wall collapsed if no blood in it) (not as strong with vasoconstriction and vasodilation)
artery branching branch into smaller and smaller vessels extending from heart, decrease in lumen diameter, decrease in elastic fibers, increase in relative amount of smooth muscle, and three basic types
largest artery in body aorta
three types of arteries elastic arteries, muscular arteries, arterioles
elastic arteries largest arteries, conduct blood from heart to smaller muscular arteries, have large proportion of elastic fibers, allow artery to stretch and recoil (helps propel blood through arteries during diastole)
types of elastic arteries aorta, pulmonary trunk, common carotid, common iliac arteries
muscular arteries medium-sized arteries, distribute blood to specific body regions, have greater amounts of muscle, less elastic tissue (better able to vasoconstrict and vasodilate), branch into arterioles
muscular arteries brachial, anterior tibia, coronary arteries
arterioles smallest arteries, have fewer layers of smooth muscles, larger arterioles have three tunics while smaller arterioles have thin endothelium and single layer of smooth muscle, and are needed to regulate systemic blood pressure and blood flow
capillary characteristics smallest blood vessels, connect arterioles to venules, length 1 mm, diameter 8-10 micrometers (just larger than single erythrocyte), consist of endothelial layer on basement membrane (optimal for exchange of substances between blood and tissues)
capillary beds groups of capillaries functioning together, at one time only one-quarter of beds are open, 5% of total blood volume in capillaries at given moment
perfusion amount of blood entering capillaries per unit per gram of tissue
venules smallest veins from 8 to 100 micrometers in diameter, companion vessels with arterioles, smallest, postcapillary venules drain capillaries, largest of these have all three tunic, and these merge to form veins
small, medium-sized, and large veins have numerous valves to prevent blood from pooling in the limbs, that are formed of tunica intimia and elastic and collagen fibers, and have similar structure to heart's semilunar valves
small and medium-sized veins companion vessels with muscular arteries
largest veins travel with elastic arteries
blood locations at rest pulmonary circulation with 18% of blood, heart with 12% of blood, and systemic circulation with 70% of blood
systemic circulation break down of 70% of blood systemic arteries (10%), systemic capillaries (5%), systemic veins (55%)
systemic veins as blood reservoirs relatively large amt of blood w/in veins allows them to function as blood reservoirs, moved back to circulation via vasoconstriction (i.e. if more blood needed during exertion), shifted back to reservoirs via vasodilation (i.e. less blood needed at rest)
total blood flow amount of blood transported through vasculature per time, equal to cariac output, may increase significantly with exercise, if increases, more blood available to tissues, if decreases, less available to tissues
hypertension blood pressure too high and can damage blood vessels and lead to cardiovascular disease
hypotension blood pressure too low, body deprived of nutrients, may cause death if severe
blood pressure maintained by multiple systems (endocrine nervous, urinary)
blood pressure force per unit area of blood against a vessel wall (def.), driving force propelling blood through the vessels, changes from one end to the other, and is highest in arteries and lowest in veins
blood pressure gradient changes in pressure from one end of a vessel to the other
arterial blood pressure blood flow pulsatile (because ventricles contracting and relaxing), systolic pressure, diastolic pressure, pulse pressure
systolic pressure pressure in arteries during ventricular systole, highest pressure generated in arteries, artery maximally stretched
diastolic pressure pressure in arteries during ventricular diastole, lowest pressure generated in arteries, artery maximally recoiled
blood pressure readings given in a ratio of systolic to diastolic pressure (average adult has about 120/80 mm Hg as pressure)
pulse pressure additional pressure on arteries when heart contracting, difference between systolic and diastolic blood pressure (i.e. blood pressure 120/80, pulse pressure of 40)
pulse pressure measures elasticity and recoil of arteries, highest in arteries closest to heart, may change temporarily with exercise, with age and disease, arteries losing elasticity (makes more difficult for heart to pump blood, may see changes in pulse pressure)
pulse throbbing sensation associated with pulse pressure
mean arterial pressure (MAP) average of blood pressure forces on arteries, provides index of perfusion
MAP = diastolic pressure + 1/3 pulse pressure (i.e. when 120/80, MAP = 80 + (40) (1/3) = 93 (if MAP < 60, indicates insufficient blood flow)
capillary blood pressure when blood here, pulse pressure is 0, needs to be high enough for exchange of substances, needs to be low enough not to damage vessels, arterial end about 40 mm Hg and below 20 mm Hg at venous end, accounts for filtration & reabsorption at respective ends
venous blood pressure venous return, pressure not pulsatile here, 20 mm Hg in venules, almost 0 when reaches right atrium, small gradient (may be insufficient to move blood when standing)
venous return movement of blood from capillaries back to heart
venous blood pressure (cont.) return facilitated by skeletal muscle pump and respiratory pump
skeletal muscle pump assists movement of blood within the limbs, with muscle contraction, veins squeezed to help propel blood, valves helping prevent backflow, blood pumped more quickly back to heart during exercise, with prolonged inactivity, blood pooling in the leg veins
respiratory pump assists movement of blood within thoracic cavity,
respiratory pump during inspiration diaphragm contracts and flattens with inspiration, abdominal cavity (decreasing in volume and increasing in pressure), thoracic cavity (increasing in volume and decreasing in pressure), blood propelled from abdominal cavity to thoracic cavity
respiratory pump during expiration with expiration diaphragm relaxing, decreased intra-abdominal pressure, helps blood move from vessels back into heart, helps move from limbs into abdominal vessels, effect increased with breathing rate
resistance amount of friction blood experienced traveling through vessels, due to contact between blood and vessel wall, and influences and opposed total blood flow, affected by viscosity, vessel length, and lumen size
peripheral resistance resistance of blood in blood vessels (as opposed to heart)
blood viscosity blood resistance to flow (greater "thickness" with greater viscosity), dependent on percentage of particles in fluid (blood with formed elements, proteins, platelets - about 5 times more viscous than water)
change in viscosity causes changes in resistance of blood flow (i.e. in anemia, fewer erythrocytes (blood viscosity lower, blood with less resistance) or i.e. in dehydration, greater percentage of erythrocytes (blood viscosity higher, blood with more resistance))
vessel length resistance increasing with length (greater friction experienced by fluid, shorter vessels with less resistance than longer of same diameter)
vessel radius the major way resistance is regulated, flow is fastest in the central lumen (encounters resistance from nearby vessel wall), different flow rate within vessel (laminar flow)
as diameter of vessel increases... less blood near edges (overall blood flow increases)
resistance usually regulated by arterioles through... vasodilation and vasoconstriction
resistance increased with... atherosclerosis
relationship between flow and radius flow proportional to radius to the fourth (F proportional to r^4 (i.e. radius increases 1 mm to 2 mm, change in flow 16 times greater)
total blood flow total blood moving through cardiovascular system per time, flow proportional to pressure gradient divided by resistance (F proportional to change in P/R
systemic blood pressure gradient blood flow directly related to pressure gradient (as gradient increases, total blood flow is greater, and as gradient decreases, total blood flow is less), and increased cardiac output increases pressure gradient and greater effect needed by heart
resistance blood flow inversely related to resistance (resistance increases, blood flow lessens/ resistance decreases, blood flow increases) [if pressure gradient stays the same]
sustained increased resistance... (i.e. with significant weight gain) generally correlates with elevated arterial pressure, greater pressure needed to overcome higher resistance
blood pressure... needs to be high enough to maintain perfusion, if too high, damages vessels, dependent on cardiac output, resistance, blood volume, and variables regulated through nervous and endocrine system
during exercise increase total blood flow due to faster & stronger heartbeat & blood removal from venous reservoirs... ensures metabolically active tissue receiving adequate blood and increased flow to coronary vessels (helps ensure sufficient O2 reaches cardiac muscles)
during exercise skeletal muscle blood flow increasing... needed to meet high metabolic demands
during exercise increased percentage of blood flow to skin to help dissipate heat
during exercise relatively less blood to... abdominal organs, kidneys, less metabolically active structures
Created by: Nicolekr



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