Week 2 Lecture Outlinev

7/23/2019 Week 2 Lecture Outlinev

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Vital Signs: Blood Pressure

Video 2.1: Introduction to the Blood Vessels

Anatomy of the blood vessels

- Five types of blood vessels:o arteries

o arterioles

o capillaries site of gas exchange

o venules

o veins

- Two circulationso Systemic circulation:

arteries carry blood to capillaries

in the capillary beds, oxygen (!"leaves blood and moves to

tissues and carbon dioxide (#!" moves from the tissues to theblood

deoxygenated blood is then brought bac$ to the right side of the

heart through systemic veins

aorta carries blood into the systemic circulation

aorta branches into smaller arteries

branching continues until vessels are small enough thatthey are called arterioles

small arterioles carry blood to capillaries

capillaries converge to form venules

venules converge and form veins

o Pulmonary circulation:

pulmonary trun$ carries deoxygenated blood into the pulmonary

circulation


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it branches into %& ' & pulmonary arteries, which carry

blood to the %& ' & lungs, respectively

gas exchange occurs in pulmonary capillaries

pulmonary veins carry oxygenatedblood bac$ to the left side of

the heart

Video 2.2: Blood Vessel Structure

All blood vessels except the capillaries have walls consisting of ) layers

- tunica intima

o

innermost layer is called endothelium it is continuous withendocardiumof the hearto thin, smooth tissue low friction for blood *ow

o directly surrounds the lumen:

o endothelium is the only tissue layer in capillaries

- tunica media

o contains many elastic and smooth muscle +bers

elastic +bers - able to distend and retract

smooth muscle is arranged in concentric layers around the wallof the vessel

when the smooth muscle contracts, it causes the vessel

diameter to decrease in sie this is calledvasoconstriction

conversely, when the smooth muscle relaxes, the vessel

diameter increases this is called vasodilation-

innervated by the sympathetic nervous system

o even at rest, the sympathetic nervous system is

sending signals to the vascular smooth muscle,causing a baseline level of vasoconstriction

o higher level of sympathetic out*ow, cause greater

stimulation of the smooth muscle which can causegreater amount of vasoconstriction


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- tunica externa

o made of a layer of connective tissue

o anchors the blood vessel in place and helps protect the outside of the

vessel

peci+c Type of .lood /essels- tructure and Function

- ) general types of arteries:o elastic arteries

closest to heart

tunica media contains relatively more elastic +bers

these large arteries have to be able to distend during ventricular

systole to compensate for the surge of blood then, the vessels retract during diastole, maintaining pressure

which allows for a continuous *ow of blood

atherosclerosis

o muscular arteries

tunica media contains more smooth muscle

because there is more smooth muscle in the vessel walls, these

vessels have a greater ability to vasoconstrict or vasodilate,,

which allows them to channel blood to di0erent organs orregions of the body

o arterioles

large amount of smooth muscle in tunica media

very responsive to signals from the sympathetic nervous

system in terms of vasoconstricting or vasodilating

these vessels have a big impact on vascular resistance

- veinso venous walls are always thinner than an arterial wall that is the same

distance away from the heart


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o thin, collapsible walls which distend and collapse easily

o veins have relatively large lumen diameters

o due to the structure of veins, venous pressure is low

Video 2.: Blood !irculation

.lood #irculation- heart beats intermittently yet blood *ows continuously- blood "o# 1volume of blood that moves through a level of the vascular

system per minuteo blood *ow is e2ual to cardiac output (#"

o blood *ow is fairly constant under resting conditions

- blood pressure 1 force exerted per unit of surface area against the innerwalls of a blood vessel

o unit of measurement is millimeters of mercury (mm3g"

o blood *ows from region of high pressure to region of low pressure

- resistance 1 anything that opposes, or impedes, blood *ow

o most resistance is in the systemic circulation, away from heart called

peripheral resistance

o in*uenced by several factors:

vessel diameter

45 factor responsible for changes in vascular resistance arterioles are most responsible for changes in peripheral

resistance

blood viscosity- thic$ness or thinness of the blood


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is fairly constant in healthy people

o anemia

o polycythemia

vessel length

pulmonary vs& systemic circulation-

Video 2.$a: %aintaining Blood &lo#

- pressure gradient di0erence in pressure from one part of the vascular

system to another

o blood *ows down its pressure gradient

- pressure across the systemic circulation

o systolic pressure 'SBP(

generated by ventricular contraction

1 the highest pressure achieved in the large arteries

o diastolic pressure ')BP(

achieved during ventricular relaxation

1 the lowest pressure in the large arteries, achieved at the end

of ventricular diastole during diastole, elastic arteries retract to maintain pressure

diastolic pressure is lower than systolic pressure

o mean arterial pressure '%*P(

highest 6A7 occurs in large arteries

lower in smaller arteries due to increased resistance

decreases across the capillary beds

lowest in the large veins close to the heart


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- 6A7 continues to drop in the veins- several features help to maintain blood*ow through the veins even though pressure is low

o venous valves --prevent bac$ward *ow of blood

o s+eletal muscles muscles bulge when contracted -- pushes on veins to send blood

to heart then, during muscular relaxation, venous valves prevent

bac$*ow

o pressure changes in the thoracic cavity during breathing lower

thoracic cavity pressure during inhalation helps return blood to theheart

Video 2.$b: *ssessing Blood Pressure )emonstration

To ta$e a blood pressure:- gather necessary e2uipment:

o in*atable cu0 attached to a sphygmomanometer

ma$e sure the cu0 is the correct sie if cu0 sie is wrong, the

.7 readings will not be accurate

o stethoscope

- apply the cu0-o line up artery mar$er with brachial artery

o cu0 bottom should be in croo$ of the elbow (i&e&, the antecubital fossa"

- ta$ing the pressureo ideally, ta$e the reading in the left arm and support the arm at the

same level of the heart to get the most accurate readingo in*ate the pump this will cause cu0 to in*ate, occluding arteries

under the cu0

arteries collapse, preventing blood *ow

release gauge to de*ate cu0 listen to brachial artery will be 2uiet until blood *ow is no

longer occluded

,orot+o sounds

note +rst sound and last sound


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systolic pressure corresponds to the +rst 8orot$o0

sound

diastolic pressure sound of turbulent *ow stopsbecause blood is *owing smoothly through the arteryagain

blood pressure reading of 559 over ! (559;!" .7 is

top number, n healthy adults, systolic blood pressure should be no higher than 5!9 mm3gand diastolic should be less than ?9 mm3g

- low blood pressure (hypotension"o typically not a problem unless it interferes with the ability to carry

blood to the tissues

- hypertension---i&e&, high blood pressureo can cause damage to blood vessel endothelium

over time, leads to narrowing of lumen and blood *ow restriction

o damage to heart increased wor$load

structural changes

o one can have hypertension and not experience symptoms because

untreated hypertension can damage the cardiovascular system, it isimportant to have .7 assessed regularly and treat hypertension

Factors a0ecting mean arterial pressure

- cardiac output

- resistanceo arterioles create the most vascular resistance


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o cardiovascular regulatory centers@in brainstem

receive input from baroreceptors these are sensors in blood

vessel walls that detect the level of stretch in the blood vesselwalls

regulate pressure by changing vessel diameter and cardiac

output

- blood volumeo normally is fairly constant

o long term mechanisms involving hormonal regulation and $idney

function can change blood volume which then lead to changes in bloodpressure

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