Phy Of Blood Vessels

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

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Resistance vessels: small arteries

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Exchange vessels: formed by a single layer of endothelial cells

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Capacitance vessels: veins

Arteries and arterial pressure

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Definition

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Determinants

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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 sphygmomanometer. A rubber cuff is wrapped around a person’s upper arm and inflated. 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 ↓

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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 ↑

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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 Category

Systolic (mmHg)

Diastolic (mm Hg)

Normal

Less than 120

And

Less than 80

Prehypertension

120-139

or

80-90

Hypertension,

140-159

or

90-100

160 or higher

or

100 or higher

stage 1 Hypertension, 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!