How can we help?

You can also find more resources in our Help Center.

100 terms

Anatomy Chapter 19: Blood Vessels

STUDY
PLAY
blood vessels
a closed delivery system that starts and ends at the heart, three types of blood vessels (arteries, capillaries, veins)
arteries
carry blood away from the heart "branch", always carry oxygenated blood
veins
carry blood to the heart "merge" always carry oxygen poor blood (with the exception of pulmonary veins)
lumen
central blood containing space of a blood vessel
tunica intima
inner most layer of a blood vessel, contains endothelium which minimizes friction
endothelium
simple squanmous that lines the lumen of all vessels, it is continuous with the endocardial lining of the heart
tunica media
middle layer of blood vessel wall, mostly made of smooth muscle cells and elastin, its activities are critical in regulating circulatory dynamics, it also maintains blood pressure
vasoconstriction
reduction in lumen diameter as the smooth muscle contracts
vasodialation
increase in lumen diamneter as the smooth muscle relaxes
tunica externa
outer layer of the blood vessels, is composed largely of loosely woven collagen fibers, that protect and reinforce the vessel and anchor it to its surroundings- infiltrated with lymphatic vessels and nerve fibers
vasa vasorum
system of tiny vessels located in the tunica externa of large blood vessels to ensure that they get enough blood supply themselves
elastic arteries
thick walled arteries near the heat (the aorta and its major branches), largest in diameter from 2.5-1 cm, most elastic/low resistance, "conducting arteries", many elastin sheets among the smooth muscle of the tunica media, relatively inactive to vasoconstriction
conducting arteries
elastic arteries
muscular or distributing arteries
deliver blood to specific body organs, internal diameter ranges from 1cm-0.3mm, thickest tunica media of all vessels, there is an elastic lamina on each face of the tunica media, branch form elastin arteries
arterioles
smallest of the arteries, have a lumen diameter ranging from 0.3mm-10micom, tunica media is mostly smooth muscle with few elastic fibers, lead to capillary beds
capillaries
smallest of the blood vessels (microscopic)- just a tunica intima, length is about 1m, diameter 8-10microm (RBCs flow through single file), exchange materials (gases, nutrients, hormones) between blood and IF
pericytes
spiper shaped smooth muscle cells on the outside of the capillary wall that help control capillary permeability
continuous capillaries
abundant in the skin and muscles, are the most common endothelial cell joined by tight junctions
intercellular clefts
gaps of unjoined membrane created by incomplete gap junctions- allow limited passage of fluids and small solutes
fenestrated capillaries
similar to continuous yet they contain pores, usually covered by a thin membrane, found wherever active capillary absorption or filtrate formation occurs, in the small intestines (allows nutrients to pass) in the endocrine organs (allows hormones to pass), kidneys (rapid filtration of plasma
sinusoids or sinusoidal capillaries
highly modified leaky capillaries found only in the liver, bone marrow, spleen and adrenal medulla- large irregular shaped lumens with pores- fewer tight junctions and larger intercellular clefts than ordinary capillaries- allow large molecules to pass
hepatic macrophages
located in the endothelium of sinusoids in the liver, remove and destroy any contained bacteria
capillary beds
interweaving networks of capillaries, consists of two types of vessels- a vascular shunt (metarteriole-thoroughfare cahnnel), a short vessel that directly connects the arteriole and venule at opposite ends- true capillaries, the actual vessel (exchange)
microcirculation
flow of blood from arteriole through capillary bed to venule
terminal arteriole
feeds the capillary bed
metarteriole
a vessel structurally intermediate between an arteriole and a capillary, continuous with the thouroughfare channel
thoroughfare channel
intermediate between a capillary and a venule, joins the postcapillary venule that drains the bed
post capillary venule
drains the bed
true capillary
branches off of the metarteriole proximal end of the shunt) and return to the thouroughfare channel (distal end)- about 10-100 per capillary bed
precapillary sphincter
a cuff of smooth muscle fibers that surrounds the root of each true capillary at the metarteriole and acts as a valve to regulate blood flow into the capillary
venules
ranging from 8-100 microm in diameter, are formed when capillaries unite, thick tunica media
capitance vessels
(or blood reservoirs) veins- because up to 65% of the bodies blood supply is formed in the veins at anytime
venous valves
folds of the tunica media, resemble semilunar valves, abundant in limbs- prevent blood from flowing backwards (against gravity)
varicose veins
veins that have become tortuous and dilated because of incompetent (leaky) valves, vein walls stretch and become "floppy" causing blood to pool, generally occurs in the legs
venous sinuses
highly specialized flattened veins with extremely thick walls consisting of only endothelium, supported by surrounding structures
vascular anastomes
interconnections where vascular channels unite
arterial anastomes
when arteries supplying the same area come together, provide alternate pathways, located around the joints
collateral channels
alternate pathways for blood to reach a given body region, can supply adequate blood supply if there is a cut or a clot
arteriovenous anastomoses
the metarteriole- thoroughfare channel shunts of capillary beds that connect arterioles and venules
blood flow
is the volume of blood flowing through a vessel, an organ or the entire circulation in a given period of time (mL/min.)
blood pressure
the force per unit area exerted on a vessel wall, by the contained blood, is expressed in mm of mercury (Hg), unless stated otherwise is considered systemic, a change in BP though out the body keeps our blood flowing
resistance
is the opposition of flow and is a measure of the amount of friction blood encounters as it passes through the vessels- three sources of resistance: blood viscosity, vessel length, vessel diameter
peripheral resistance
where most resistance occurs, away from the heart
blood viscosity
the internal resistance to flow that exists in all fluids, thickness or stickyness, the greater the viscosity the more difficult it is to keep moving
total blood vessel length
the longer the length the more resistance
blood vessel diameter
changes frequency, smaller diameter greater friction, varies inversely with the fourth power of the vessel radius, small arteries constrict more than large arteries
laminar flow or steamlining
smooth constant flow
turbulent flow
irregular fluid motion which increases resistance
systolic pressure
pressure peak- BP in the aorta, averages 120 mm HG in healthy adults
diastolic pressure
lowest pressure 70-80 mm Hg
pulse pressure
difference between systolic and diastolic pressure, pulse is felt during systolic
mean arteriole pressure (MAP)
the pressure that propels the blood to the tissues
respiratory pump
pressure changes occurring in the ventral body cavity during breathing create the respiratory pump that moves blood towards the heart
muscular pump
consists of skeletal activity, muscles surrounding the deep veins contract and relax squeezing blood to the heart with the help from the valves
vasomotor center
a cluster of neurons in the medulla, neural center that oversees changes in diameter of blood vessels
cardiovascular center
integrates blood pressure control by altering cardiac output and blood vessel diameter
vasomotor fibers
sympathetic efferents which exit from the T1-L2 levels of the spinal cord, receive impulses from vasomotor center and innervate the smooth muscle of the blood vessels
vasomotor tone
constant state of moderate constriction, almost always arterioles
baroreceptors
pressure sensitive mechonoreceptors that respond to changes in arteriole pressure and stretch- neural receptors located in the carotid sinuses (dilations in the internal carotid arteries which provide the major blood supply to the brain) in the aortic arch, and in the walls of nearly every large artery of the neck and throrax
carotid sinus reflex
protects blood supply to the brain
aortic reflex
maintains adequate BP in the systemic circuit as a whole
chemoreceptors
located in the aortic arch and large arteries of the neck- transmit impulses to the cardioacceletory center, which then increases cardiac output and vasocontriction- causes BP to rise and speeds return of blood- carotid and aortic bodies
norepinephrine (NE) and epinephrine
adrenal medulla hormones, are released at times of stress into the blood and enhance fight or flight response- both promote vasocontriction, epinephrine increases cardiac output
angiotensin II
stimulates intense vasocontriction, promoting a rapid rise in systemic BP, also stimulates release of aldosterone and ADH, which acts in long-term regulation of BP by enhancing blood volume
atrial natriuretic peptide (ANP)
hormone produced by the atria of the heart- causes BP and blood volume to decline, causes general vasodialation
antidiuretic hormone (ADH) or vasopressin
(vasopressin), produced by the hypothalamus, stimulates the kidneys to conserve water- can cause intense vasocontriction in emergencies
direct renal mechanism
alters blood volume independently of hormones, when BP or BV is high kidneys filtrate out extra fluid, and it is excreted in the urine , lowering BP and BV
indirect renal mechanism
renin- angiotensin mechanism
renin-angiotensin mechanism
when arterial BP declines , the kidneys release the enzymatic hormone renin into blood, renin triggers a series of reactions that produce angiotensin II
aldosterone
a hormone that enhances renal absorption of sodium, as sodium moves into the blood stream water flows, as a result blood volume is conserved
vital signs
body temp., pulse, blood pressure, respiratory rate
pulse
the alternating expansion and recoil of arteries during each cardiac cycle- a pressure wave is created, the radial pulse is located on the wrist
pressure points
arterial pulse, they are compressed to stop blood flow into distal tissues during hemorrhage
auscultatory method
systemic blood pressure is measured indirectly in the brachial artery of the arm, a blood pressure cuff or sphygmomanometer is wrapped around arm, just superior to the elbow and inflated until cuff pressure exceeds systolic pressure- blood flow stops, cuff pressure is gradually reduced and brachial artery is heard
hypotensin
low blood pressure-systolic is below 100 mmHg, generally a good thing
orthostatic hypotension
temporary low blood pressure and dizziness, prone in elderly when they rise suddenly from a reclined position
chronic hypotension
due to poor nutrition, inadequate levels of blood protein, hints to Addisons disease, hypothyroidism or severe tissue wasting- acute hypotension hints to poor circulation
hypertension
high blood pressure that may be transient or persistant- transient- elevations in systolic pressure occur as normal adaptations during fever, physical exertion, or emotional upset -persistent- (in obese people) hormones released from adipocytes both increase sympathetic tone and interfere with ability of endothelium to induce vasodialation
chronic hypertension
a common dangerous disease, 30% of people greater than 50 have it, strains the heart and damages arteries, organs do not get proper nourishment- sustained arteriole pressure 140/90 or greater
primary or essential hypertension
when no underlying cause is identified, about 90% or hypertensive people- hereditary predispositions, an environmental factors such as: diet, diabetes mellitus, obesity, age, stress, smoking
secondary hypertension
10% of cases, due to identifiable disorders such as obstruction of the renal arteries, kidney disease and endocrine disorders
tissue perfusion
blood flow through body tissues involves: delivery of O2 and nutrients to, and removal of waste from tissues (gas exchange in lungs, absorption or nutrients in digestive tract, urine formation in the kidneys
autoregulation
the automatic adjustment of blood flow to each tissue on proportion to the tissues requirements at any instant
metabolic
(chemical)
myogenic
(muscular)
nitric oxide (NO)
is a powerful vasodialator which acts via cyclic GMP second messenger system
endothelins
potent vasocontrictors that belong to a family of peptides
myogenic responses
an increase in smooth muscle tone that compensates for changes on systemic pressure
reactive hyperemia
dramatic increased blood flow into a tissue that occurs after the blood supply to the area has been temporarily blocked
angiogenesis
when a number of blood cells in a particular region increase and existing muscles enlarge
active or exercise hyperemia
when muscles become active, blood flow increases (hyperemia) in direct proportion to their greater metabolic activity
bradykinin
produced by a perspiration enzyme, it stimulates the vessels endothelial cells to release the potent vasodialator NO
vasomotion
blood flow through capillary networks- reflects the on/off opening and closing of precapillary sphincters in response to local autoregulatory controls
diffusion
movement along a concentrated gradient, from and area of higher concentration to lower
hydrostatic pressure
is the force exerted by a fluid pressing against a wall- in capillaries it is the capillary blood pressure
capillary hydrostatic pressure (HPc)
tends to force fluids through the capillary walls (process called filtration) leaving behind cells and most proteins- BP drops as blood flows through the capillaries (from 35mm Hg-17mm Hg)
interstitial fluid hydrostatic pressure (HPif)
opposes hydrostatic (HPc)- acting outside of the capillaries and pushing in fluid, however there is usually very little fluid int he interstitial space because lymphatic vessels constantly withdraw it- HPif has an assumed value of 0
colloid osmotic pressure
the force opposing hydrostatic pressure, is created by the presence of fluid of large non-diffusable molecules such as proteins that are unable to cross the wall, these molecules draw water towards themselves (osmosis)
capillary colloid osmotic pressure (OPc)
pressure created by blood proteins (mostly albumin), also called oncotic pressure, about 26 mmHg, interstitial fluid contains few proteins- colliod osmotic pressure (OPif) about .1-5 mm Hg
net filtration pressure (NFP)
considers all forces acting at capillary bed, fluids will leave capillary bed if net HP is greater than net OP and fluids will enter capillary if net OP exceeds net HP