Physiology of blood vessel

Blood vessel
Blood vessel
In a general sense, a vessel is defined as a

hollow utensil for carrying something: a cup,

a bucket, a tube. Blood vessels, then, are

hollow utensils for carrying blood. Located

throughout your body, your blood vessels are

hollow tubes that circulate your blood.

There are three varieties of blood vessels:

arteries, veins, and capillaries. During blood

circulation, the arteries carry blood away from the

heart. The capillaries connect the arteries to veins.

Finally, the veins carry the blood back to the heart.

General Pathway of Blood Flow

heart -> arteries -> arterioles ->

capillaries -> venules -> veins -> heart

If you took all of the blood vessels out of an

average child, and laid them out in one line, the

line would be over 60,000 miles long! An adult's

vessels would be closer to 100,000 miles long!

Classification of blood vessels
Arteries

elastic fibers support vessel & allow it to

stretch

large amounts of smooth muscle in

walls, allows stretching & constriction

they have elastic recoil to keep BP

relatively high & flow more uniform

 Arterioles

thinner layers of smooth muscle tissue

thinner layer of elastic fibers
deliver blood to capillaries & regulate flow into

capillaries
constriction or vasoconstriction - slows or limits

capillary blood flow & increases BP in arteries

Arterioles
 Capillaries

very thin & very narrow

site of exchange of nutrients and

wastes between blood & tissues

Capillaries
Veins

large diameter and thin walls

1-way valves

blood reservoir ~ 50% of blood "stored" at

resting condition

valves prevent back flow (gravity keeps

blood in legs)
Veins
valves
 summary
 Windkessel vessels: large arteries

 Resistance vessels: small arteries

 Exchange vessels: formed by a

single layer of endothelial cells

 Capacitance vessels: veins

Arteries and arterial pressure
 Definition

 Determinants

 Normal values
  Definition

Blood pressure means the force exerted

by the blood against unit area of the vessel

wall. Blood pressure in the arteries is called

the arterial pressure.

 Blood pressure is usually measured in

millimeters of mercury(mmHg). A pressure

value of 100mmHg in an artery means that

the force exerted by the blood in this

artery is sufficient to push a column of

mercury up to a level of 100mm high.

Blood pressure
 How is blood pressure measured?

Blood pressure is measured by a quick,painless

test using a medical instrument called a sphygmoma-

nometer. A rubber cuff is wrapped around a person’s

upper arm andinflated. It compresses a large artery in

the arm, momentarily stopping the blood flow.

 Next, air in the cuff is released, and the

person measuring the blood pressure listens

with a stethoscope. When the blood starts to

pulse through the artery, it makes a sound.

Sounds continue to be heard until the pressure

in the artery exceeds the pressure in the cuff.

 The person listening and watching the phygmomanometer

gauge records two measurements. Systolic pressure (the

higher number) is the pressure of the blood flow when the

heart beats (the pressure whenthe first sound is heard).

 Diastolic pressure is the pressure between

heartbeats (the pressure when the last sound

is heard). Blood pressure is measured in

millimeters of mercury, which is abbreviated

mm Hg.

The harder it is for blood to flow, the

higher the numbers will be.
 The value of arterial blood pressure

changes continuously throughout each cardiac

cycle. The pressure rises during cardiac

systole and falls during diastole.

 Systolic arterial pressure: the peak
pressure value reached during systole.
 Diastolic arterial pressure: the minimum
pressure value reached during diastole.
 Pulse pressure: the difference between
the systolic and the diastolic pressures.
 Mean arterial pressure: the mean of the
pressure values during the entire cardiac
cycle.
 Mean Arterial Pressure

Systolic Pressure

Integrated pressure

Mean Arterial
Pressure

Diastolic Pressure

Pulse Pressure = Systolic Pressure – Diastolic Pressure

Mean Arterial Pressure = Diastolic Pressure + (Pulse Pressure)/3
 Normal values

 Systolic pressure : 100 ---120 mmHg

 Diastolic pressure : 60 ---80 mmHg

The arterial pulse pressure can be
affected by the following factors:

 stroke volume

 heart rate

 Peripheral resistance

 Quantity of blood in the arterial system

 Elasticity of the vessel walls

a. HR

 HR increase from 60 to 120 beats/min,

both SP and DP↑, but DP ↑ > SP↑ , PP ↓

 HR decrease from 60 to 40 beats/min,

both SP and DP↓, but DP ↓>SP ↓, PP ↑

 b. SV

 SV is a measure of CO

 SV ↑→ SP ↑ ↑, DP ↑, PP ↑

 SV↓→SP ↓ ↓, DP ↓, PP ↓
c. Compliance of aorta and large ateries.

 Compliance↓, the ability of buffering

dramatic changes in pressure decreases ,

PP↑.
d. Peripheral resistance:

 TRP↑→DP↑↑, PP↓

 Viscocity↑, R ↑, DP ↑.
e. The ratio of circulating volume to

capacitance of circulation

 Circulating volume ↓ ( bleeding) or

capacitance ↑ (vessel relax)

Blood
pressure
meter
Blood pressure measure
New type blood pressure meter
 What is high blood pressure?

High blood pressure in an adult is defined as a

systolic pressure of 140 mm Hg or higher and/or a
diastolic pressure of

90 mm Hg or higher for an extended time. A systolic

pressure of 120 to 139 mm Hg or a diastolic pressure
of 80 to 89 mm Hg is “prehypertension” and needs to
be watched carefully. Blood pressure of less than 120
over 80 mm Hg is considered normal for adults.
 Blood pressure classification for adults age 18 and older
Blood Pressure Systolic (mmHg) Diastolic (mm Hg)
Category
Normal Less than 120 And Less than 80

Prehypertension 120-139 or 80-90

Hypertension, 140-159 or 90-100

stage 1
Hypertension, 160 or higher or 100 or higher

stage 2
∗ Unusually low readings should be evaluated for clinical significance.
 Why is the high blood pressure harmful?

High blood pressure causes the heart to

work harder than normal. Both the heart

and arteries are then more prone to injury.
High blood pressure increases the risk of
heart attacks, strokes, kidney failure, eye
damage, congestive heart failure and
atherosclerosis.
 If high blood pressure isn’t treated, the
heart may have to work harder and harder to
pump enough blood and oxygen to the body’s
organs and tissues. A heart forced to work
harder than normal for a long time tends to
enlarge and weaken. A slightly enlarged heart
may work well, but one that’s enlarged a lot has
a hard time doing its job.
High blood pressure also hurts arteries and

arterioles. Over time they become scarred,

hardened and less elastic. This may occur s people

age, but high blood pressure accelerates this

process, probably because it speeds

therosclerosis.
Arterial damage is bad because hardened or
narrowed arteries may not be able to supply
enough blood to the body’s organs. And if the
organs don’t get enough oxygen and nutrients,
they can’t work properly. Another risk is that a
blood clot may lodge in an artery narrowed by
fatty buildups, shutting off normal blood
supply to part of the body.
People with mitral or aortic valves that

don’t fully close find that their heart

becomes overactive during vigorous work

or play, or during emotional excitement.

The lungs of people with mitral valve

stenosis are under more pressure. This puts

an extra burden on the heart’s right side,

since it must pumpagainst the raised

ressure. The added pressure in the lungs also

causes fluid retention (pulmonary edema)

and hortness of breath.

Venous pressure and

venous return
  Venous pressure

Venous Valves = one way flap valves that prevent

the backflow of blood caused by the force of
gravity. These valves are needed as the venous
blood pressure is considerably lower than the
arterial blood pressure. Blood is forced through
the valves by skeletal muscle action. Veins run
between skeletal muscle fibers and as the fibers
contract, blood is forced through the veins.
Veins have larger diameters than arteries so

that there is less resistance to flow in veins.

The total cross-sectional area of the veins

gradually decreases as smaller veins converge

into progressively fewer, but larger vessels.

Thus, the velocity of blood flow increases as

blood approaches the heart.

Systemic veins act as a blood reservoir. Veins

have a tremendous ability to store blood. Veins

have much thinner walls with less smooth muscle

than arteries, so veins stretch much more easily.

Additional blood volume is easily accomodated by

the veins with only a small increase in venous

blood pressure.
When blood demand is low, the veins can

store extra blood in reserve. At rest, the

veins usually contain about 60% of the blood.

If the blood is needed (as during exercise) it

can be driven out of the veins and to the

heart (increased venous return = increased

cardiac output)
Center venous pressure: 4-12cm H2O

Peripheral venous pressure:

 Venous return

Venous return refers to the volume of blood

entering each atrium per minute from the

veins.
By the time blood enters the veins, the pressure
is quite low, but still greater than atrial pressure
so blood will flow into the atria. If atrial pressure
is abnormally high, as when the AV valves are
leaky, there is a decrease in venous return and
blood will dam up in the venous system
(congestive heart failure).
 There are five factors which can
increase venous return to the heart:

1. Sympathetic nerves can cause the veins to

vasoconstrict (smaller diameter).

2. Skeletal muscle activity. Many large veins in

the extremeties lie between skeletal muscles so
when the muscles contract, the veins are
compressed. This helps increase venous return
during exercise.
3. veins are equipped with one way valves so
blood only flows forward. The valves also help
counteract the gravitational effects of standing
upright by minimizing backflow. - Varicose veins
form when the venous valves can no longer support
the blood above them. Usually seen in people who
stand for long periods and/or have unusually thin
walled veins. Blood can pool and the veins will not
function properly. The only serious problem with
having varicose veins, is an increased risk of blood
clot formation (which could break loose = embolism)
in the pools of blood.
4. Respiratory actions help pull blood from
the lower regions of the body toward the
heart. Increased respiratory activity
increases venous return during exercise.

5. When the AV valves first open, the

atria become larger. This lowers the atrial
pressure and increases the venous to atrial
pressure gradient so more blood flows into the
heart. Basically, the heart sucks blood from the
veins.
Thank you!