Ch23 Vessels

7/31/2019 Ch23 Vessels

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Human Anatomy, First EditionMcKinley & O'Loughlin

Chapter 23 :

Vessels andCirculation


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Blood Vessels An efficient mode of transport for oxygen, nutrients,

and waste products to and from body tissues.

Heart is the mechanical pump that propels the bloodthrough the vessels.

Heart and blood vessels form a closed-loop system.

Blood is continuously pumped to and from the

tissues. Are not rigid and immobile.

Can pulsate and change shape in accordance withthe bodys needs.


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Blood Vessels Naming:

Often share names with either the body region they traverseor the bone next to them.

Some are named for the structure they supply.

Arteries and veins that travel together sometimes share thesame name.

Systemic circulation consists of the blood vessels that extend to and from the

body tissues.

Pulmonary circulation consists of the vessels that take the blood to the lungs for

gas exchange.

Workcontinuously and intandem with each other.


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Three Main Classes of Blood

VesselsArteries convey blood away from the

heart to the body tissues.

Arteries branch, or bifurcate, intosmaller and smaller vessels (arterioles)until they feed into the capillaries,

where gas and nutrient exchangeoccurs.

From the capillaries, veins return blood

to the heart.


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Vessels Arteries become progressively smaller as

they divide and get further from the heart.

Veins become progressively larger as theymerge and get closer to the heart.

Anastomosis: Site where two or morevessels merge to supply the same bodyregion.

arterial anastomoses: alternate route

Veins tend to form many more anastomoses than

do arteries.


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Vessels End arteries

Arteries that do not form anastomoses

Only one route

E.g.: renal artery, splenic artery

Functional end arteries

Have small anastomoses

E.g.: coronary arteries


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Blood Vessel Tunics Tunica Intima, or Tunica Interna

innermost layer

composed of: an endothelium (simple squamous epithelium) subendothelial layer (areolar CT)

Tunica Media middle layer of the vessel wall

composed of: circularly arranged smooth muscle cells

Sympathetic innervation: Increase: vasoconstriction (narrowing of the blood vessel

lumen)

Decrease: vasodilation (widening of the blood vessel lumen)


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Blood Vessel TunicsTunica Externa, or Tunica Adventitia

outermost layer

composed of: areolar connective tissue that contains elastic and collagen fibers

helps anchor the vessel to other tissues

Term adventitia is used to specify outer layer in blood vessels thatare buried in CT

Vasa vasorum : blood vessels that supply large blood vessels

In the externa

Arteries vs Veins: Media largest in arteries, externa largest in veins

Lumen is smallest in arteries

Artery wall have more elastic and collagen fibers

Capillaries: only the Interna


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Arteries In the systemic circulation, carry oxygenated

blood to the body tissues.

Pulmonary arteries carry deoxygenated bloodto the lungs.

Three basic types of arteries:

elastic arteries, muscular arteries, and arterioles

as an arterys diameter decreases

corresponding decrease in the amount ofelastic fibers

relative increase in the amount ofsmooth muscle


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Capillaries Contain only the tunica intima, but this layer consists

of a basement membrane and endothelium only.

Allow gas and nutrient exchange between the bloodand the body tissues to occur rapidly.

Smallest blood vessels, connect arterioles to venules.

Are called the functional units of the cardiovascularsystem.

A group of capillaries (10100) functions together

and forms a capillary bed.


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The Three Basic Kinds of

Capillaries Continuous capillaries

the most common type

Fenestrated capillaries

Sinusoids, or discontinuous capillaries


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Veins Drain capillaries and return the blood to the heart.

Walls are relatively thin and the vein lumen is larger.

Systemic veins carry deoxygenated blood to the rightatrium of the heart, while pulmonary veins carryoxygenated blood to the left atrium of the heart.

Blood pressure is substantially reduced by the timeblood reaches the veins.

Hold about 60% of the bodys blood at rest.

Veins function as blood reservoirs.


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From Venules to Veins Venules merge to form veins.

Venule becomes a vein when its diameter is greater than 100micrometers.

Blood pressure in veins is too low to overcome the forces ofgravity.

To prevent blood from pooling in the limbs, most veins containone-way numerous valves to prevent blood backflow in theveins.

As blood flows superiorly in the limbs, the valves close to

prevent backflow. Numerous valves along its length to assist in moving blood back

to the heart.


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From Venules to VeinsMany deep veins pass between skeletal

muscle groups.

As the skeletal muscles contract, veinsare squeezed to help pump the bloodtoward the heart.

This process is called the skeletalmuscle pump.


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Blood Pressure Force/unit area blood places on the

inside wall of a blood vessel.

Measures in mmHg

Sphygmomanometer: device tomeasure blood pressure.

Systolic blood pressure

Diastolic blood pressure

120/80 mmHg


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Circle of Willis An important anastomosis of arteries around the sella turcica.

Formed from posterior cerebral arteries and posteriorcommunicating arteries (branches of the posterior cerebral

arteries), internal carotid arteries, anterior cerebral arteries, andanterior communicating arteries (which connect the two anteriorcerebral arteries).

Equalizes blood pressure in the brain and can provide collateralchannels should one vessel become blocked.


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Hepatic Portal System A venous network that drains the GI tract and shunts the blood

to the liver for processing and absorption of transportedmaterials.

Blood exits the liver through hepatic veins that merge with theinferior vena cava.

Is needed because the GI tract absorbs digested nutrients, andthese nutrients must be processed and/or stored in the liver.


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Pulmonary Circulation

Responsible for carrying deoxygenated blood from the right sideof the heart to the lungs, and then returning the newlyoxygenated blood to the left side of the heart.

Blood is pumped out of the right ventricle into the pulmonarytrunk.

This vessel bifurcates into a left pulmonary artery and a rightpulmonary artery that go to the lungs.


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Aging and the CardiovascularSystem

Heart and blood vessels become less resilient.

Elastic arteries are less able to withstand the forcesfrom the pulsating blood.

Systolic blood pressure may increase with age.

Apt to develop an aneurysm, whereby part of thearterial wall thins and balloons out.

Wall is more prone to rupture, which can causemassive bleeding and death.

Incidence and severity ofatherosclerosis increases.


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Fetal Circulation Oxygenated blood from the placenta enters through the

umbilical vein.

Blood is shunted away from the liver and directly toward theinferior vena cava through the ductus venosus.

Oxygenated blood in the ductus venosus mixes withdeoxygenated blood in the inferior vena cava.

Blood empties into the right atrium.

Most of the blood is shunted to the left atrium via the foramenovale.

Blood flows into the left ventricle and out the aorta. A small amount of blood enters the right ventricle and

pulmonary trunk, but much of this blood is shunted to the aortathrough ductus arteriosus.

Blood travels to the rest of the body, and the deoxygenated

blood returns to the placenta through umbilical arteries.


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