what do blood vessels do?
they are dynamic structures that pulsate, constrict, relax and proliferate.
old theory about how blood went through the body?
blood moved through the body like an ocean tide, moving out through the heart and ebbing back into the same vessels
Greek physician Galen
movement of blood through blood vessels description
heart contracts, blood is forced into the large arteries leaving the ventricles. blood then moves into successively smaller arteries and reaching the smallest branches, the arterioles that blood drains from the capillaries into venules (smallest veins) and then into larger and larger veins that merge to form the large veins that empty into the heart.
carry blood away from the heart
are said to branch, diverge or fork as they form smaller divisions
carry blood towards the heart and are said to join, merge and converge into successively larger vessels approaching the heart.
explain the arteries and veins of the systemic circulation
arteries carry oxygenated blood and veins carry oxygen poor blood.
explain the arteries and veins of the pulmonary circuit
arteries carry oxygen poor blood to the lungs and the veins carry oxygen rich blood to the heart.
only the __ have intimate contact with tissue cells and directly serve cellular needs.
this occurs through the gossamer-thin capillary walls
the innermost tunic
has intimate contact with the blood in the lumen
contains the endothelium that lines the lumen of all vessels
tell me about the endothelium that the tunica intima contains?
it is simple squamous endothelium
it is contrinuous with the endocardial lining of the heart, and its flat cells fit closely together, forming a slick surface that minimizes friction as blood moves through the lumen.
what the a subendothelial layer? where is it found?
it is a layer consisting of a basement membrane and loose connective tissue that supports the endotheium
this can be found in vessels larger than 1 mm in diameter
the middle tunic that is mostly circulary arranged smooth muscle cells and sheets of elastin.
what regulates the smooth muscle of the tunica media?
it is regulated by sympathetic vasomotor nerve fibers of the autonomic nervous system and chemicals.
either vasoconstriction or vasodialation ca be effected by this.
what is the role of the tunica media?
is critical in regulation of circulatory dynamics bc small changes in vessels diameter greatly influence blood flow and blood pressure.
sum up the tunica media
it is the bulkiest layer in arteries and bears the chief responsibility for maintaining blood pressure and contrinuous blood circulation.
outermost layer of a blood vessel wall
composed largerly of loosely woven collagen fibers that protect and reinforce the vessel and anchor it to surrounding structures.
is infiltrated with nerve fibers, lymphatic vessels and in larger veins, a network of elastic fibers.
a system of tiny blood vessels found in larger vessels that nourish the more exernal tissues of the blood vessel walls.
how is the innermost (or luminal) portion of the vessel nourished?
it obtains nutrients directly from blood in the lumen.
what are the three types of arteries in terms of relative size and function?
thick walled arteries near the heart (aorta and its major branches).
largest in diameter and the most elastic.
conducting arteries, where does this name come from
elastic arteries are sometimes referred to as conducting arteries bc their large lumen make them low resistance pathways that conduct blood from the heart to medium sized arteries.
which tunic contains the lost elastin?
where the elastin constructs holey laminae (sheets) of elastic conn tissue that look like slices of Swiss cheese between the layers of smooth muscle.
elastic arteries are...
pressure reservoirs, explanding and recoiling as blood is ejected from the heart.
in elastic arteries, blood flows...
continuously rather than starting and stopping with the pulsating rhythm of the heart.
muscular (distributing) arteries definition
deliver blood to specific body organs and account for most of the named arteries from lab.
are distal to the elastic arteries.
what are muscular arteries active in?
they are active in vasoconstriction and are less distensible bc they have more smooth muscle and less elastic tissue than elastic arterioes.
smallest of the arteries.
larger arterioles have all 3 tunics but their tunica media is chiefly smooth muscle with a few scattered elastic fibers
smaller arterioles are a little more than a single layer of smooth muscle cells spiraling around the endothelial lining
what is minute to minute blood flow into the capillary beds determined by?
arteriole diamter, which varies in response to changing neural, hormonal and local chemical influences.
spider shaped smooth muscle cells that stabilize the capillary wall and help control capillary permeability.
they are on the outer surface of some capillaries
__ and __ are poorly vascularized
tendons and ligaments
cartilage and epithelial lack capillaries but recieve nutrients by nearby conn tissue. the avascular cornea and lens of the eye receive nutrients from aqueous humor
capillaries are the...
back alleys and driveways that provide direct access to nearly every cell in the body
what is the role of capillaries?
bc of their location and the thinness of their walls they are well suited for exchange of materials (gases, nutrients, hormones, etc) between the blood and the interstitial fluid.
they are abundant in the skin and muscles.
are the most common type of capillaries
they are continuous in the sense that their endothelial cells provide an uninterrupted lining, adjacent cells being joint laterally by tight junctions--but there are intercellular clefts.
intercellular clefts definition
gaps of unjoined membrane that are caused by the tight junctions being incomplete.
they allow limited passage of fluids and small solutes.
how are brain capillaries unique?
the tight junctions of their continuous capillaries are complete and are the structural basis of the blood brain barrier
capillaries were some of the endothelial cells are riddled with oval pores. the pores are usually covered with a delicate membrane (or diaphragm)
are much more permeable to fluids and small solutes than continuous capillaries.
fenstrated capillaries are found wherever...
active capillary absorption or filtration formation occurs.
ex- small intestines, endocrine organs, kidneys
also called sinusoidal capillaries
highly modified leaky capillaries
have large irregularly shaped lumens and are usually fenestrated.
have few tight junctions and larger intrercellular clefts than ordinary capillaries
structurally, sinusoids allow...
large molecules and even blood cells to pass between the blood and surrounding tissue.
describe the sinusoids in the liver
the endothelium is discontinuous and its lining includes large hepatic marcrophages that remove and destroy any contained bacteria.
what are the two types of vessels a capillary bed consists of
1. a vascular shunt (metarteriole-thoroughfare channel)
2. true capillaries
vascular shunt definition
a short vessel that directly connects the arteriole and venule at opposite ends of the bed
describe the flow of blood in microcirculation
a terminal arteriole feeding the bed leads into a metarteriole which is continuous with a thoroughfare channel. the thoroughfare channel joins the postcapillary venule that drains the bed.
true capillaries description
10-100 per capillary bed
branch off the metarteriole and return to the thoroughfare channel.
occassionally spring from the terminal arteriole and empty directly into the venule.
a cuff of smooth muscle fibers surrounding the root of each true capillary at the metarteriole and acts as a valve to regulate blood flow into the capillary.
blood flowing through a terminal arteriole may go either through __ or __
the true capillaries
through the shunt
when the precapillary sphincters are relaxed (open)...
blood flows through the true capillaries and takes part in exchanges with tissue cells.
when the precapillary sphincters are contracted (closed)...
blood flows through the shunts and bypasses the tissue cells.
the amount of blood entering a capillary bed is regulated by...
local chemical conditions and arteriolar vasomotor nerve fibers.
the smallest venules
consist entirely of endothelium with pericytes contracting around them.
extrememly porous- fluid and WBC move easily from the bloodstream through their walls.
larger venules have (structually)
have one or two layers of smooth muscle cells and thin external as well
veins usually have __ distinct tunics
but their walls are thinner and their lumens larger than those of arteries.
lumens normally look slitlike when in prepared slides
structural makeup of veins descriptions
little smooth muscle or elastin in tunica media (which is poorly developed anyway and is thin)
tunica externa is the heaviest wall layer--consisting of thick longitudinal bundles of collagen fibers and elastic networks
capacitance vessels/blood reservoirs
a name for veins bc they accommodate a large blood volume due to their large lumens and thin walls.
up to 65% of the body's blood supply is found in the veins at any time.
explain the difference between vein wall thickness and that of corresponding arteries
walls of veins can be much thinner than arterial walls without danger of bursting bc the blood pressure in veins is low.
adaptations to the low pressure condition to ensure blood returns in the same amount of time it was pumped out (2)
1. large diameter lumens of veins (offers low resistance to blood flow)
2. valves that prevent blood from flowing backward
formed from folds of the tunica intima. resemble the SL valves of the heart in structure and function
prevent blood from flowing backward.
alternate pathways provided by anastomoses for blood to reach a given body region.
provides an area that has been blocked/cut off with adequate blood supply
arterial anastomoses occur around...
joints- where active movement may hinder blood flow through one channel
also common in abdominal organs, the brain and the heart.
arteries that dont have anastomoses or have a poorly developed collateral circulation supply are in the
retina, kidneys, and spleen.
if their blood flow is interrupted, cells supplied by these vessels die.
shunts of capillary beds that connect arterioles and venules
ex- metarteriole thoroughfare channel
do arteries or veins interconnect more readily?
venous anastomose are abundant so occlusions of a vein rarely block blood flow or lead to tissue death
breakdown of circulation
heart is the pump, the arteries are pressure reservoirs and conduits, the arterioles are resistance vessels that control distribution, the capillaries are exchange sites and the veins are conduits and blood reserviors.
blood flow definition
the volume of blood flowing through a vessel, an organ, or the entire circulation in a given period (ml/min)
under resting conditions its relatively constant.
blow flow through ___ body organs may vary eidely and is related to their immediates needs
blood pressure (BP) definition
the force per unit area exerted on a vessel wall by the contained blood
expressed in millimeters of mercury (mm Hg)
what is a pressure gradient?
the differences in blood pressure within the vascular system always from an area of high pressure to an area of low pressure through the body
the pressure gradient provides what for blood?
it provides the driving force that keeps blood moving
the opposition to flow and is a measure of the amount of friction blood encounters as it passes through the vessels.
another name for resistance because most friction is encountered in the peripheral (systemic) circulation
blood viscosity definition
the internal resistance to flow that exists in all fluids and is related to the thickness of a fluid.
remains fairly constant
the greater the viscosity...
the less easily molecules slide past one another and the more difficult it is to get and keep the fluid moving.
what two of the three sources of resistance normally remain constant?
blood viscosity and vessel length
changes in __ __ __ are frequent and significantly alter peripheral resistance
blood vessel diameter
fluid close to the wall of a tube or channel is what? what is to be said of the opposite?
fluid close to the wall/tube is slowed by friction as it passes along the wall, whereas fluid in the center of the tube flows more freely and faster.
(also called streamlining)
the relative speed and position of fluid in the different regions of the tube's cross section remain constant.
smaller the tube, ___ the friction
bc more of the fluid contacts the tube wall where its movement is impeded.
resistance varies ___ with the 4th power of the vessel radius
meaning the larger arteries do not contribute much to peripheral resistance.
smaller-diameter arterioles, which can enlarge or constrict in response to neural and chemical controls, are the...
major determinants of peripheral resistance.
turbulent flow definition
irregular fluid motion where blood from the different laminae mexes.
dramatically increases resistance
occurs when blood encounters an abrupt change in the tube size or protruding areas of the tube wall
blood flow is directly proportional to the difference in...
blood pressure between 2 points in the circulation
when blood pressure (triangle P) increases, blood flow (F)...
when blood pressure decreases, blood flow declines.
which factor affects blood flow more?
peripheral resistance (R) is more important in influencing local blood flow because R can easily be changed by altering blood vessel diameter.
blood flows through the blood vessels along a..
pressure gradient, always moving from higher to lower pressure areas.
___ blood pressure is highest in the aorta
and declines throughout the pathway to finally reach 0 mm Hg in the right atrium.
where does the steepest drop in blood pressure occur?
they offer the greatest resistance to blood flow
as long as a pressure gradient exists...
blood continues to flow into it completes the circuit back to the heart.
arterial blood pressure reflects 2 factors:
1. how much the elastic arteries close to the heart can be stretched (their compliance or distensibility)
2. the volume of blood forced into them at any time
if the amounts of blood entering and exiting the elastic arteries were equal,
arterial pressure would be constant
however blood pressure rises and falls in a regular fashion
as the left ventricule contracts and expels blood into the aorta, it imparts...
kinetic energy to the blood, which stretches the elastic aorta as aortic pressure reaches its peak
why does blood move forward into the arterial bed?
bc the pressure in the aorta is higher than the pressure in the more distal vessels
what happens during diastole?
the aortic valve closes, preventing backflow of blood into the heart, the walls of the aorta recoil which maintains sufficient pressure to keep the blood flowing foward into the smaller vessels.
elastic arteries are the
keep the blood circulting during diastolic pressure, when the heart is relaxing.
the difference between the systolic and diastolic pressure.
it is felt as a throbbing pulsation in an artery during systole
increased whats cause temporary increases in the pulse pressure?
increased stroke volume and faster blood ejection from the heart (results from increased contractibility)
why is low capillary pressure wanted?
1. capillaries are fragile and high pressures would rupture them
2. most capillaries are extremely permeable and even low cap pressure forces solute containing fluids out of the blood stream into the interstital fluid.
fluids flowing into the capillaries are important why?
they are continually refreshing the interstitial fluid
what is the problem with venous pressure?
despite structural modifications of veins (large lumens and valves), venous pressire is normally too low to promote adequate venous return.
three functional adaptations critical to venous return:
layer of smooth muscle around veins
created by pressure changes occurring in the ventral body cavity during breathing.
moves blood up toward the heart
explain how the respiratory pump works
as we inhale, ab pressure increases, squeezing local veins and forcing blood toward the heart.
at the same time, pressure in the chest decreases and thoracic veins expand and speed blood entry into the right atrium
how does the muscular pump work?
as the skeletal muscles surrounding the deep veins contract and relax, they milk blood toward the heart
once blood passes each successive valve, it cannot flow backwards.
layer of smooth muscle thats an adaptation for venous return
it constricts under sympathetic control, increasing venous return.
a way in which the sympathetic nervous system increases cardiac output
what homeostatic mechanisms regulate cardiovascular (and mainly BP?)
how do cardiac output and peripheral resistance relate to blood pressure?
F = blood pressure/peripheral resistance
CO = blood pressure/resistance
blood pressure = cardiac output x peripheral resistance
blood pressure also varies directly with
blood volume bc cardiac output depends on blood volume (heart cant pump out what it doesnt have)
what is in charge of the heart rate most of the time?
the cardioinhibitory center in the medulla via the parasympathetic vagus nerves
maintains a resting heart rate
tell me about the short term controls of blood pressure
are mediated by the nervous system and bloodborne chemicals
they counteract moment to moment fluctuations in blood pressure by altering peripheral resistance and CO
what are the two main goals of the nerual controls of peripheral resistance
1. maintaining adequate MAP by altering blood vessel diameter. (note: small changes in blood vessel diameter causes substantial changes in peripheral resistance and systemic blood pressure)
2. altering blood distributing to respond to specific demands of various organs.
how do most neural controls operate?
by reflex arcs involving baroreceptors and associated afferent fibers, thhe vasomotor center of the medulla, vasomotor fibers and vascular smooth muscle.
occasionally also imputs form chemoreceptors and higher brain centers
the neural center that oversees changes in the diameter of blood vessels.
is a cluster of neurons in the medulla.
transmots impulses along the vasomotor fibers
made of the vasomotor center and the cardiac center
intergrates blood pressure control by altering cardiac output and blood vessel diameter.
sympathetic efferents that exit from the T1 and L2 levels of the spinal cord and run to innervate the smooth muscle of blood vessels (mainly arterioles).
get trasmitted impulses from the vasomotor center
what receives impulses more frequently?
arterioles of the skin and digestive viscera receive vasomotor impulses more frequently and tend to be more strongly constricted than those of the skeletal muscles.
what does increase in sympathetic activity do?
produces generalized vasoconstriction and a rise in blood pressure.
what does decreased sympathetic activity do?
allows the vascular muscle to relax somewhat and causes blood pressure to decline to basal levels
what inputs modify vasomotor activity?
1. baroreceptors (pressure sensitive mechanoreceptors that respond to changes in arterial pressure and stretch)
2. chemoreceptors (receptors that respond to changes in blood levels of carbon dioxide, H+ and oxygen)
3. higher brain centers
neural receptors located in the carotid sinuses, in the aortic arch and in the walls of every large artery of the neck and thorax
are stretched when arterial blood pressure rises
what happens when baroreceptors are stretched?
a stream of impulses are sent to the vasomotor center. it inhibits the vasomotor center resulting in vasodialation of the arterioles and veins. and a decline in BP
what does venodilation do
shifts blood to the venous reservoirs- causing a decline in venous return and cardiac output.
what happens when afferent impulses reach the cardiac centers?
impulses stimulate parasympathetic activity, inhibit cardioacceleratory center, reduce heart rate and contractile force.
what happens as the whole thing gets unbalanced and there is a decline in MAP?
reflex vasoconstriction is initiated which increases cardiac output, causing BP to rise.
peripheral resistance and cardiac ouput are regulated in response.
what is the function of rapidly responding baroreceptors?
to protect the circulation against short term (acute) changes in BP
baroreceptors help maintain adequate blood pressure in the systemic circuit as a whole
receptors that respond to changes in blood levels of carbon dioxide, H+ and oxygen
in the aortic arch and large arteries of the neck
what is the process of chemoreceptors in short?
transmit impulses to the cardioacceleratory center, increases CO, and to the vasomotor center, which causes reflex vasoconstriction.
rise in BP speeds the return of blood to the heart and lungs
what are the most prominent chemoreceptors?
carotid and aortic bodies in the carotid sinuses and aortic arch.
tell me about the significance of the cerebral cortex and hypothalamus
they are not involved in routine controls of BP, but can modift arterial pressure via the medullary centers.
the hypothalamus mediates what?
the redistribution of blood flow and other cardiovascular responses that occur during exercise and changes in body temperature.
how do hormones help regulate BP?
in the short term, but changes in peripheral resistance and in the long term, by changes in blood volume
how do paracrines help regulate BP?
serve to match the amount of blood flow to the metabolic need of a particular tissue.
massive release of paracrines can affect blood pressure.
explain the effect of adrenal medulla hormones
the AM releases NE and E to the blood; both enhance the sympathetic fight or flight response in periods of stress.
what is E's role?
increases cardiac output and promotes generalized vasoconstrrction (except in cardiac and skeletal muscle)
what does nicotine do?
causes vasoconstriction by directly stimulating ganglionic sympathetic neurons and by promoting release of large amounts of NE and E
explain the angiotension II effect
when BP or blood volume is low, kidneys release renin. renin acts as an enzyme that inevitably generates angiotensin II (stimulates intense vasoconstriction and promotes a rapid rise in systemic BP)
also stimulates the release of aldosterone and ADH (long term regulation of BP by enhancing blood volume)
atrial natriuertic peptide effect
produced by the atria of the heart
causes blood volume and blood pressure to decline.
causes generalized vasodialation (antagonizes aldosterone and prods the kidneys to excrete more Na and water form the body)
antidiuretic hormone effect
produced by the hypothalamus
also called vasopressin
stimulates the kidneys to conserve wwater
not important in short term BP regulation
more ADH is release when BP falls dangerously low and helps restore arterial pressure by causing intense vasoconstriction
what are the long term controls of BP mediated by?
the kidneys restore and maintain BP homeostasis by regulating blood volume
problem with baroreceptors
they respond to short term changesin blood pressure and quickly adapt to prolonged or chronic esisodes of high or low BP
blood volume is a major determinant in what?
blood volume influences venous, EDV and stroke volume to have this effect
increase in blood volume is an increase in blood...
also MAP bc there is a greater fluid load in the vascular tree
while increased blood volume means increased blood pressure, thats not the whole story. what happens with the kidneys?
increased blood volume is an increase in BP that stimulates the kidneys to eliminate what which reduces blod volume and in turn BP
the kidneys act directly and incdirectly to regulate what
arterial pressure and provide major long term mechanism of BP control.
direct renal mechanism
alters blood volume independently of hormones.
when either blood volume or blood pressure rises, the rate at which fluid filters blood from the bloodstream in the kidney tubules is speeded up. here, the kidneys cant filter properly and more of it leaves as urine. as a result BP and blood volume lower.
when BP/blood volume is low, water is conserved and returned to the bloodstream and BP rises.
indirect renal mechanism
also called the renin angiotensin mechanism.
when arterial BP declines, the kidneys release the enzymatic hormone renin into the blood. renin triggers a series of reactions that produce angiotensin II
what does angiotensin II do
increase blood pressure
also triggers thirst which enhances water consumption
what are the 3 ways angiotensin increases BP?
1. it is a potent vasoconstrictor, so it increases blood pressure by increasing peripheral resistance
2. it stimulates the adrenal cortex to secrete aldosterone.
3. it prods the posterior pituitary to release ADH
how can you test the effeciency of a persons circulation?
by taking pulse and blood pressure measurements.
a person's pulse, blood pressure measurements, respiratory rate measurements and body temperature
a pressure wave that is transmitted through the arterial tree. it is the alternating expansion and recoil of arteries during each cardiac cycle.
how/where can you feel a pulse?
in any artery that lies close to the body surface by compressing the artery against firm tissue.
allows an easy way to count heart rate
the point where the radial artery surfaces at the wrist
used to take pulse measurements
important arterial pulse points that are compressed to stop blood flow into distal tissues during hemmorage.
what does monitoring pulse rate do?
its an easy way to assess the effects of activity, postural changes and emotions on HR
pulse examples of a healthy man in different positions
lying down: 66 beats per minute
sit up: 70
rise to stand: 80
exercise: 140-180 (bc of sympathetic nervous system)
explain the auscultatory method
wrap the BP cuff snugly around the arm just superior to the elbow and inflate until the cuff exceeds systoic pressure. (at this point blood flow into the arm is stopped and a brachial pulse cant be felt/heart. ) as the cuff gradually reduces, listen with a stethoscope for sounds in the brachial artery
the pressure read when the first soft tappig sounds are heard. this is the first point at which small amounts of blood is spurting through the constricted artery.
sounds of Korotkoff
the sounds of spurts of blood as the cuff pressure is reduced
they become louder and more distinct as pressure reduces.
when the artery is no longer constricted and blood flows freely, the sounds cant be heart
what are the normal numbers for systolic and diastolic pressure?
systolic pressure varies between 110 and 140 mm Hg
diastolic pressure varies between 70 and 80 mm Hg
explain to me the cycle of blood pressure
BP cycles over a 24 hour period, peaking in the morning in response to waxing ans waning levels of hormones.
extrinsic factors that play a role in blood pressure
BP varies with age, sex, weight, race, mood, physical activity, posture and socioeconomic status.
low blood pressure
reflects individual variations and is no cause for concern
associated with a long life and being free of cardiovascular illness
occur as normal adaptations during fever, physical exertion and emotional upset
common in obese people for a variety of reasons that cant be completely uderstood.
tissue perfusion is involved in: (4)
1. delivery of oxygen and nutrients to and removal of wastes from tissue cells
2. gas exchange in the lungs
3. absorption of nutrients form the digestive tract
4. urine formation in the kidneys
describe the rate of blood flow to each tissue and organ
it is almost the exact amoung to provide for proper function
what parts of the body get what percentage of blood?
abdominal organs- 24%
skeletal muscle- 20% (but during exercise, blood flow to the kidneys and digestive organs is reduced)
in the arterial system branches what happens to blood flow?
total cross section of the vascular bed increases and the velocity of blood declines proportionally.
its crazy that small arteries.capillaries supposedly have more area. explain this
the individual branches have smaller lumens by their COMBINED cross sectional areas are larger. this means that there can be more volume of blood here than the aorta.
what makes so capillaries such a good thing?
allows adequate time for exchanges between the blood and tissue cells.
explain the cross sectional area of venules and then veins
as capillaries combine to form venules and then veins, total c-s area declines and velocity increases.
the automatic adjustment of blood flow to each tissue in proportion to the tissue's requirement at any instant.
regulated by local conditions and is largely independent of systemic factors.
MAP is the same everywhere but...
homeostatic mechanisms adjust cardiac output as needed to maintain the constant pressure
changes in blood flow through individial organs are controlled...
intrinsically by modifying the diameter of local arterioles feeding the capillaries.
what substances act as an autoregulation system in most tissues?
oxygen, H+, K+, adenosine, and prostaglandins.
many act directly to relax vascular smooth muscle, some may act by causing the release of nitric oxide from vascular endothelial cells
nitric oxide (NO)
powerful vasodilator which acts by a cyclic GMP second messenger system.
its effects are brief bc its destroyed quickly.
can be transported over long distances by being bound to chemical buffers in the blood and is released when vasodilation is needed.
what rules blood vessel diameter?
the sympathetic nervous system's primary role is to produce vasoconstriction
nitric oxide plays the major role in causing vasconstriction.
potent vasoconstrictors released by the endothelium
these are a fmaily of peptides which are the most potent vasoconstrictors known.
what is the net result of metabolically controlled autoregulation
immediate vasodilation of the arterioles serving the capillary beds of the needy tissues and dilation of their precapillary sphincters.
this creates a temporary increase in blood flow to the area
what can also cause vasodilation
inflammatory chemicals (histamines, kinins and prostaglandins) released in injury, infection and ellergic reactions.
this helps defense mechanisms clear microorganisms and toxins to promote health
response of vascular smooth muscle.
prevents problems by responding directly to passive stretch (caused by increased intravascular pressure) with increased tone, which resists stretch and causes vasoconstriction.
reduced stretch promotes vasodilation and increases blood flow into the tissue needed.
the dramatically increased blood flow into a tissue that occurs after the blood supply to the area has been temporarily blocked.
results from myogenic response and acumulation of metabolic wastes.
what happens if long term autoregulation is needed?
the number of blood vessels in the region increases and existing vessels enlarge.
the increase of blood vessels in the region and when the existing vessels enlarge.
common in the heart when a coronary vessel is particularly occluded.
occurs thruout the body in ppl who live in hi altitudes
capillary density and blood flow are greater in what fibers?
greater in red (slow oxidative) fibers than in white (fast glycolytic) fibers.
active or exercise hypermia
when muscle becomes active and blood flow increases in direct proportion to their greater metabolic activity
occurs in response to the decreased oxygen concentration and accumulation of metabolic factors that result in the revved up metabolism of working muscles.
what happens between sympathetic nervous system and local metabolic effectors in skeletal muscle?
they have opposing effects on arteriolar diameter.
during exercise, local controls override sympathetic vasoconstriction. blood flow to sk muscle increases tenfold during physical activity. virtually all capillaries are open to accommodate the increased flow
what is the main factor determining how long muscles can continue to contract vigorously?
the ability of the CV system to deliver adequate oxygen and nutrients and remove waste products.
brain tissue is very sensitive to
declining pH and increased blood carbon dioxide levels which causes a lot of vasodilation. so much CO2 suppresses brain activity and abolishes autoregulatory mechanisms
explaain the myogenic mechanism that protects the brain from possibly damaging changes in BP
when MAP declines, cerebral vessels constrict, prootecting small more fragile vessels further down the line from rupturing under this excessive pressure.
there is a rising in intracranial pressure and the brain regulates flow by triggering a rise in systemic blood pressure
what does blood flow through the skin do? (3)
1. supplies nutrients to cells
2. aids in body temp regulation
3. provides a blood reservoir
what is the function of supplying nutrients to cells served by?
autoregulation in response to the need for O2
explain the blood under the skin
there are extensive venous plexuses under the skin. blood flow can change in these depending on body temperature. (this reflects neural adjustments of blood flow through arterioles and coiled arteriovenous anastomoses)
where are the unique coiled arteriovenous anastomoses located?
fingertips, palms of the hands, toes soles of the feet, ears, nose and lips. they are richly supplied with sympathetic nerve endings and are controlled by reflexes initiated by temp receptors or signals from higher CNS centers.
what happens when the skin surface is exposed to heart or the body temp rises?
the hypothalamic thermostat signals for reduced vasomotor stimulation of the skin vessels.
warm blood flushes into the capillary beds and heat radiates form the skin surface.
protein that stimulates the vessels endothelial cells to release vasodilator NO.
increases vasodilation of the arterioles when we sweat
when ambient temp is cold or body temp drops...
superficial skin vessels are strongly constricted.
blood almost entirely bypasses the capillaries associated with the arteriovenous anastomoses, diverting the warm blood to the deeper more vital organs.
the pulmonary arteries and arterioles are structurally like
veins and venules so they have thin walls and large lumens.
__ pressure is needed to propel blood through pulmonary vessels
arterial pressure in the pulmonary circulation is much lower than in the systemic circulation
autoregulation of the pulmonary circulation is __ of that seen in most tissues
low pulmonary oxygen causes local vasoconstriction and high levels promote vasodilation.
further explain the effect of the opposite autoregulation mechanism in the pulmonary circulation
when the lungs air sacs are flooded with O2 rich air, the pulmonary capillaries become flushed with blood and are ready to receive the oxygen load.
if the air sacs collapse the oxygen content is low and blood bypasses those nonfunctional areas
movement of blood thru the smaller vessels of the coronary circulation is influenced by
aortic pressure and the pumping activity of the ventricles.
explain blood flow through the heart
when the ventricles contract and compress the coronary vessels, blood flow thru the myocardium stops. as the heart relaxes, the high aortic pressure forces blood thru the coronary circulation.
an abnormally rapid heartbeat reduces the ability of the myocardium to receive adequate oxygen and nutrients under diastole.
what happend to the coronary vessels during strenuous exercise
the coronary vessels dilate in response to local accumulation of vasodilators. and blood flow increases 3-4 times.
cardiac cells use __% of the oxtgen carried to them in blood
increasing the blood flow is the only way to make sufficient additional oxygen available to a more vigorously working heart.
blood flow through capillary networks being slow and intermittent.
reflects the on/off opening and closing of precapillary sphincters in response to local autoregulatory controls.
movement always occuring along a concentration gradient- each substance moving from an area od high concentration to an area of low concentration.
4 diff routes across capillaries for diff types of molecules
1. lipid soluble molecules diffuse thru the lipid bilayer of the endothelial cell plasma membranes
2. fluid filled intercellular capillary clefts (how small water soluble solutes pass- amino acids and sugars)
4. active transport in pinocytotic vesicles or caveolae (used by larger molecules such as proteins)
capillaries differ in their..
leakiness- some are impermeable and some have large fenestrations (pores)
fluid is forced out of the capillaries through the clefts at the arterial end of the bed, but most of it returns to the bloodstream at the venous end.
relatively unimportant to capillary exchange
bulk flow is used to determine..
the relative fluid volumes in the bloodstream and the interstitial space.
normally approx. 20 L are filtered out of the capillaries each day before returning to the blood
the direction and amount of fluid that flows across the capillary walls reflect..
the balance between two dynamic and opposing forces
what are the two forces that are reflected by direction and amount of fluid across the capillary walls:
hydrostatic osmotic pressure
colloid osmotic pressure
force exerted by a fluid pressing against a wall
in capillaries, it is the same as capillary blood pressure.
capillary hydrostatic pressure (HPc)
forces fluids through the capillary walls leaving behind cells and most proteins.
BP drops as blood flows along the length of a capillary bed, so HPc is higher at the arterial end of the bed than the venous end.
interstitial fluid hydrostatic pressure (HPif)
pressure acting outside of the capillaries and pushing fluid into the capillaries.
the net effective hydrostatic pressures at the arterial and venous ends of the capillary bed are equal to
colloid osmotic pressure
the force opposing hydrostatic pressure.
created by the presence in a fluid of large nondiffusible molecules.
plasma proteins in capillary blood create..
capillary colloid osmotic pressure (OPc)
also called oncotic pressure
to see if there is a net gain or net loss of fluid from blood what do you have to calculate
net filtration pressure (NFP)
which considers all the forces acting at the capillary bed
a negative result of NFP results in
the driving of fluid into the capillary bed (is called reabsorption)
any condition in which blood vessels are inadequately filled and blood cannot circulate normally.
results in inadequate blood flow to mett tissue needs.
cells can die and organ damage can follow if it gets too bad
blood volume is normal by circulation is poor as a result of an abnormal expansion of the vascular bed caused by extreme vasodilation.
cause is loss of vasomotor tone due to anaphylaxis; also failure of autonomic nervous system and septicemia (septic shock- bacterial infection)
a systemic allergic reaction in which bodywide vasodilation is triggered by the massive release of histamine.
occurs when heart is so inefficient it cant sustain adequate circulation
routes blood through a long loop to all parts of the body before returning it to the heart