21-1: Arteries, which are elastic or muscular, and veins, which contain valves, have three-layered walls; capillaries have thin walls with only one layer

measuring pressure

blood pressure (BP): arterial pressure (mm Hg) capillary hydrostatic pressure (CHP): pressure within the capillary beds venous pressure: pressure in the venous system

arteries

carry blood away from the heart

veins

collect blood from capillaries and return it ti the heart compared to arteries, veins have larger diameters, thinner walls, and lower blood pressure

capillary beds (capillary plexus)

connect one arteriole and one venule pre capillary sphincter, which guards entrance to each capillary, and opens and closes causing capillary blood to flow in pulses

vasoconstriction

contraction of smooth muscle in arteriole walls increases blood pressure

thoroughfare channel

direct connection between arterioles and venules within the capillary bed

vascular resistance

due to friction between blood and the vessel wall dependent on vessel length (constant) and diameter (adjustable): resistance (R) increases as vessel diameter decreases

arteries

elasticity: allows arteries to absorb pressure waves that come with each heartbeat contractility: arteries change diameter controlled by sympathetic division of ANS vasoconstriction vasodilation

capillary structure

endothelial tube, inside thin basement membrane no tunica media or externa diameter is similar to that of a red blood cell

total capillary blood flow

equals cardiac output is determined by: pressure (p) and resistance (r) in the cardiovascular system

venous valves

folds of tunica intima prevent backflow of blood compression of veins pushes blood toward heart when walls of veins near the valves weaken, varicose veins or hemorrhoids may result

angiogenesis

formation of new blood vessels stimulated by vascular endothelial growth factor (VEGF) occurs in the embryo as organs develop occurs in response to factors released by cells that are hypoxic, or oxygen-starved which is most important in cardiac muscle, in response to a chronically constricted or occluded vessel

continuous capillaries

found in all tissues except epithelia and cartilage have complete endothelial lining permit diffusion of water, small solutes, and lipid soluble materials, which block blood cells and plasma proteins specialized continuous capillaries in CNS and thymus have very restricted permeability (e.g. blood brain barrier)

from heart to capillaries, arteries change

from elastic arteries to muscular arteries to arterioles

pressure (P)

generated by the heart to overcome resistance absolute pressure is less important than pressure gradient

large veins

have all 3 tunica layers thick tunica externa thin tunica media

sinusoids (sinusoidal capillaries)

have gaps between adjacent endothelial cells permit free exchange between water and large plasma proteins found in liver, spleen, bone marrow, endocrine organs proteins phagocytic cells monitor blood at sinusoids

fenestrated capillaries

have pores in endothelial lining permit rapid exchange of water and larger solutes found in choroid plexus, endocrine organs, kidneys, and intestinal tract

the distribution of blood

heart, arteries, & capillaries: 30-35% of blood volume venous system: 60-65%: 1/3 of venous blood is in the large venous networks of the liver, bone marrow, and skin

systemic veins constrict (vasoconstriction) in response to blood loss...

increasing amount of blood n arterial system and capillaries

elastic arteries (conducting arteries)

large vessels (e.g., pulmonary trunk and aorta) tunica media has many elastic fibers and few muscle cells elasticity evens out pulse force transport large volumes of blood away from the heart.

capillary function

location of all exchange functions of cardiovascular system materials diffuse between blood and interstitial fluid

muscular arteries (distributing arteries)

most arteries are medium-sized muscular arteries tunica media has many muscle cells

collateral

multiple arteries that contribute to one capillary bed allow circulation if one artery is blocked arterial anastomosis, which is the fusion of two collateral arteries arteriovenous anastomoses, which is a direct connection between arterioles and venues, and bypasses the capillary bed

circulatory pressure

must overcome total peripheral resistance: resistance (R) of entire cardiovascular system ∆P across the systemic circuit is about 85 mm Hg

tunica externa

outer layer of a blood vessel which connects it to surrounding tissues contains collagen fibers, elastic fibers, and smooth muscle cells vaso vasorum ("vessels of vessels") are small arteries in walls of large arteries and veins, they serve cells of tunica media and tunica externa

flow (F)

proportional to the pressure gradient (∆P), divided by resistance (R)

vasodilation

relaxation of arterial smooth muscle enlarging the lumen

blood viscosity

resistance (R) caused by molecules and suspended materials in a liquid whole blood viscosity is about 4x that of water

veins

return blood to the heart

arterioles (resistance walls)

small vessels have little or no tunica externa have thin or incomplete tunica media

capillaries

smallest blood vessels with thin walls location of exchange between blood and interstitial fluid

arterioles

smallest branches of arteries that lead to capillary beds

venules

smallest branches of veins that collect blood from capillaries

capillaries

smallest vessels with thin walls microscopic capillary networks permeate all active tissues

turbulence

swirling action that disturbs smooth flow of liquid occurs in heart chambers and great vessels atherosclerotic plaques cause abnormal turbulence

capacitance of a blood vessel

the ability to stretch relationship between blood volume and blood pressure veins (capacitance vessels) stretch more than arteries, which act as blood reservoirs

pressure gradient (∆P)

the difference in pressure from one end of a vessel to the other

tunica intima

the innermost layer of a blood vessel, composed of a single layer of squamous epithelial cells over a sheet of connective tissue its smooth, frictionless surface allows blood to flow smoothly through the vessel

tunica media

the middle and thickest layer of tissue of a blood vessel wall, composed of elastic tissue and smooth muscle cells that allow the vessel to expand or contract in response to changes in blood pressure and tissue demand

medium-sized veins

thin tunica media and few small smooth muscle cells tunica externa contains longitudinal bundles of elastic fibers

vessel walls have three layers

tunica intima, tunica media, tunica externa

total peripheral resistance is affected by

vascular resistance blood viscosity turbulence

venules

very small veins collect blood from capillaries

aneurysm

a bulge in an arterial wall caused by weak spot in elastic fibers pressure may rupture vessel

vasoconstriction and vasodilation affect...

after load on heart, peripheral blood pressure, capillary blood flow

differences between arteries and veins

arterial walls are thicker than a vein's walls arteries have higher blood pressure than veins a constricted artery has a small, round lumen and the endothelium is folded whereas a vein has a large, irregular lumen arteries are generally smaller in diameter than veins arteries are more elastic than veins arteries do not have valves, veins have valves