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1

The vascular system consists of

arteries, capillaries and veins. These vessels must be resilient and flexible to withstand pressure and move with tissues

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Function of vascular system

exchange of material between blood and tissues
transporting blood between the capillaries and the heart

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Three layers of a vessel

1. tunica intima
2. tunica media
3. tunica externa

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tunica intima

smooth, innermost layer made of endothelium and a surrounding layer connective tissue

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tunica media

middle layer, made of smooth muscle and external elastic membrane; structure varies pending vessel; important for maintenance of normal bp in arteries

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smooth muscle allows

arteries to constrict or dilate but is too thick to allow difussion between tissues and blood

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tunica externa

fibrous connective tissue, strong t prevent rupture or larger arteries, thinner in veins

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Arteries and veins run

side by side, arteries have thicker walls and higher bp than veins

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has small rounds lumen (internal space)

collapsed artery

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has a large, flat lumen

vein

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lining contracts

veins

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lining does not contract
lining folds

artery

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more elastic

arteries

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have valves

veins

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Arteries

responsible for vasodilation and vasoconstriction; blood travels through elastic arteries, muscular arteries and arterioles, lrgest vessels that carry blood away from heart

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Elastic arteries

conducting arteries

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artery walls are resillient due to

elastic fibers in the tunica media

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elastic rebound

cushions the sudden rise in pressure during ventricular systole and the recoil during ventricular diastole slows the drop in pressure

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Muscular Arteries

medium sized arteries with thick tunica media, distribution arteries, distributes blood to skeletal muscles and organs

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examples of muscular arteries

exernal carotid artery, brachial artery, mesenteric artery and femoral

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major arterial pressure points

common carotid, radial, brachial, femoral, popliteal, posterior tibial, dorsal pedal

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arterioles

small arteries; resistance vessels with poorly defined tunica externa

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tunica media consists of

smooth muscle to allow vasoconstriction/dialation in response to O2 levels

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arterioles have more resistance to blood flow because

more pressure is required to push blood through a small diameter

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capillaries

exchange vessels, only vessels that permit exchange between blood and tissue, one cell layer thick

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blood flow is slowest in capillaries to

allow time for two-way exchange

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There are no capillaries in

cartilage and epithelial tissue

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capillaries prevent

blood loss and keeps plasma proteins in the blood

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Fenestrated capillaries

contain pores that allow rapid exchange

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sinusoids

large and more permeable than other capillaries to allow exchange of larger molecules like protein and blood cells to leave and enter blood stream

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precapillary sphincters

regulated by smooth muscle cells, found at the beginning of each network, regulate blood flow into capillary network based on the needs of tissue

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collaterals

multiple arteries supplying one capillary bed; the fusion exemplifies an arterial anastomosis to provide alernate routes of blood flow

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metarteriole

precapillary arteriole

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thoroughfare channel

normal passageways of capillary bed

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vasomotion

blood flow in capillaries occurs in pulses

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veins

collect blood from tissues and organs and return it to the heart; LARGER in diameter than arteries, thinner walls because no blood pressure

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venules

small veins that collect blood from capillary beds

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medium sized veins

few smooth muscle cells with a sturdy tunica externa

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large veins

all three layers present

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valves

present in venules and medium veins of the limbs that have to fight gravity to return blood to the heart; prevent backflow

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varicose vein

swollen and distended veins found in superficial veins of the legs...prego=blood pools in veins, valves no longer work=stretched

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hemorrhoids

constipation or child birth...vessels in digestive tract irritated and swollen

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exchange in capillaries, 3 steps

1. diffusion=gasses move from greater to lesser concentration
2. filtration=high pressure forces plasma out of caps to tissue distributing nutrients
3. colloid osmotic pressure=attracting pressure caused by proteins in blood, when blood reaches venous end, proteins pull tissue fluid/waste into capillaries

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venoconstriction

systemic veins constrict to shunt blood to arteries, this maintains normal bp during blood loss

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venous reserve

blood reserved in liver, skin and lungs...taken to general circulation after blood loss

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pressure and resistance

increased pressure=increased flow, increased resistance=decreased flow

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blood pressure

arterial pressure pressure is highest in arterial circulation due to the elevated resistance of the arterioles

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capillary hydrostatic pressure

fluid pressure

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venous pressure

low pressure of venous system

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vascular resistance

friction between blood and the wall of the vessel; length and diameter of vessel affect resistance

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vessel length

longer blood vessels experience more friction which increases resistance

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vessel diameter

smaller diameters increase friction slowing the flow of blood; diameter has more of an affect on resistance than does vessel length

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viscosity

normal blood viscosity is dependent on the presence of protein and RBC friction, too much increases friction, too little lower friction

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turbulence

upsetting the flow of blood die to sudden changes in vessel diameter or vessel wall damage

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blood pressure

the force blood exerts against the walls of the blood vessels

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filtration in capillaries depends on

blood pressure

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pressure is measured in

mmHg

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systolic pressure

blood pressure when the left ventricle is contraction, higher of the two numbers
normal range: 120mmHg or below

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diastolic pressure

when left ventricle is relaxed, the lower bp #
normal range: 80mmHg or below

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pulse pressure

the difference between the systolic and dyostolic pressures

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mean arterial pressure (MAP)

diastolic pressure + (pulse pressure / 3)

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**Hypertension

high blood pressure

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Hypotension

low blood pressure

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brachial artery

most common place to take normal bp. readings. pressure decreases as distance from the heart increases

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capillary beds

bp decreases as it travels through the capillary beds of the organs and tissues. it is high enough for filtration but low enough to prevent rupture

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veins-pressure

decreases further and approaches zero as blood enters the right atrium

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pulmonary bp

see notes, pg. 6

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elastic rebound

arteries recoil to their original dimensions during ventricular diastole

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elasticity of large arteries

normal elasticity lower systolic pressure and increase diastolic pressure

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elasticity in the aortic wall

absorbs some of the force of ventricle systole and recoils to maintain diastolic pressure when there is no blood flow

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1. venous return, "starlings law"

the heart pumps only the blood it receives, if venous return decreases, cardiac muscle fibers will not be stretched, cannot contract as forcefully

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2. resistance to blood flow

decreases as it travels through larger veins; increases velocity of blood

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3. constriction of veins

smooth muscle allows veins to constrict and force blood toward the heart and valves prevent backflow

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4. skeletal muscle pump, contraction of leg muscles...

squeeze the veins to force blood to the heart

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5. respiratory pump

inhillation and exhillation of the lungs expand and compress veins to return blood to heart

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6. heart rate and force

if heart rate and force increase, blood pressure increases (exercise)

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7. peripheral resistance

vessels offer to the flow of blood (resistance to blood flow)

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8. blood loss

small loss of blood (donation) temp. drop in pressure, followed by a rapid compensation in the form of a rapid heart rate and greater vasoconstriction

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Diffusion

movement of ions from an area of greater concentrationto an area of lesser concentration

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Use Diffusion

water, ions and small molecules such as glucose

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some ions diffuse through channel in plasma membrane

Na+, K+, Ca+, CI-

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large water souluable compounds diffuse through

fenestrated capillaries

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Plasma proteins are

senusoid, which are very permeable

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Filtration

*driven by hydrostatic pressure
*water and small solutes forced through capillary wall
*leaves larger solutes in blood stream

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reabsorption

*the result of osmotic pressure
*equals pressure to prevent osmosis
* caused by suspended blood PROTEINS that are too lrg to cross capillary walls

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net capillary colloid osmotic pressure is the difference between:

1. blood colloid osmotic pressure
2. interstitial fluid colloid osmotic pressure
(pulls water and solutes into a capillary from interstitial fluid)
*both control filtration and reabsorption through capillaries

87

forces water out of solution

net hydrostatic pressure

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forces water into solution

net osmotic pressure

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capillary exchange at arterial end

fluid moves out of capillary and into interstitial fluid

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capillary exchange at venous end

fluid moves into capillary and out of interstitial fluid

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transition point between filtration and reabsorption is closer to

venous end

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capillaries filter more than

they absorb

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excess fluid enters

lymph vessels

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hemorrhaging

increases reabsorption of interstitial fluid

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dehydration

accelerates reabsorption

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increase in hydrostatic or decrease in colloid osmotic pressure within vessels causes fluid to

move out of blood and build up periphreal tissues=edema (swelling)

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autoregulation of blood flow

factors that promote the dilation of precapillary sphincters are called vasodilators; relax the smooth muscle

98

local vasodilators:

decrease tissue O2 levels
increasee Co2
nitric oxide release from endothelial cells
increase in potassium or hydrogen ions
chemicals release during inflammation
elevated local temp

99

local vasoconstrictors

prostaglandins and thromboxanes; stimulate platelet aggregation and constrition of damaged vessels

100

baroreceptor reflexes

cardiovascular reflex that responds to change in pressure

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chemoreceptor reflexes

cardiovascular reflex respond to changes in chemicals in blood

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antidiuretic hormone

causes vasoconstriction that elevates bp, reabsorbs water from kidneys adding to blood volume

103

angiotensin II

responds to fall in renal bp, stimulates production of aldosterone, stimulates secretion of ADH, stimulates thirst, cardiac output, constriction of atrioles

104

erythropoetin

responds to a drop in blood O2 levels, causes vasoconstriction and stimulates the production and maturation of RBCs

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Natriuretic peptide

respond to excessive stretching of arterial wall during diastole; reduces blood volume and pressure by sodium exchange in the kidneys, increase urine production

106

Norepiniphrine

stimulates vasoconstriction; raises bp

107

epinephrine

stimulates vasoconstriction; increases heart rate and force of contraction increasing bp

108

cardiovascular response to light exercise

*extensive vasodilation occurs increasing circulation
*venous return increases with muscle contraction
*cardiac output increases

109

Cardiovascular response to heavy exercise

*activates sympathetic nev. system
* cardiac output increases to maximum
* restricts blood flow to non essential organs
* redirects blood flow to heart, lungs and muscles
* blood supply to brain is not affected

110

**circle of willis (fig 21-24)

circle of arteries around the pituitary gland

111

**Hepatic portal circulation

blood from abdominal digestive organs and spleen circulate through the liver before returning to the heart
Purpose + anastomosis

112

fetal circulation

1. umbilical vein carries oxygenated blood from placenta to fetus
2. umbilical arteries carry oxygen deficient blood from the fetus to placenta
3. placenta contains fetal and maternal blood vessels that are close to one another but do not mix, but allows gases, wastes and nutrients in and out

113

ductus venosus

from the placenta the blood is taken to the inferior vans cava, after birth, these fetal vessels constrict and become nonfunctional

114

foramen ovale

opening in the interatrial septum that permits some blood flow from the R. atrium to L. atrium in the fetal heart, bypassing the R. ventricals

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ductus arteriosus

a short vessel that diverts most of the blood in the pulmonary artery to the aorta and then to the body, bypassing lungs

116

when an infant is born, the intake of O2 and inflation of lungs

closes a flap over the foramen ovale and constricts the ductus arteriosis

117

Pulse

heartbeat found at an atrial site; the force of ventricular contraction transmitted through the arterial wall

118

Pulse sites, 7

radial=wrist, thumb side
carotid=neck
temporal=temple
femoral=top of thigh
popliteal=back of knee
dorsal pedis=top of foot
apical=the heart