LEC 17 Blood Flow & Pressure

8/4/2019 LEC 17 Blood Flow & Pressure

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Copyright 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 17

Disorders of Blood Flow and

Blood Pressure


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Artery Structure

Tunica intima:

endothelium

Tunica media: smoothmuscle

Tunica adventitia:collagen and elasticfibers


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Question

Which vessel layer can expand to accommodate pressurechanges?

a. Tunica intima

b. Tunica media

c. Tunica adventitia

d. Tunica externa


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Answer

b. Tunica media

Rationale:The tunica media is composed of smoothmuscle, which can stretch/expand to accommodatechanges in blood pressure.


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Vascular Endothelium

Food and O2 pass into tissues

Wastes and CO2 pass from tissues into blood

Creates compounds that cause vasodilation orvasoconstriction

Creates growth factors that can stimulatesmooth muscle

Forms a smooth lining of the blood vesselsthat resists clot formation

Creates compounds to promote clot formationin injured areas


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Atherosclerosis

Lipids get into the vascular endothelium

White blood cells try to clear them away foam cells

WBCs and vascular endothelium release growth factorsthat promote plaque formation

Plaques block the arteries


7/23Copyright 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins

Lipoproteins

The more protein,the higher thedensity

The more lipid, thelower the density



Question

Tell whether the following statement is true or false.

LDL is considered to be good cholesterol.



Answer

False

Rationale:LDL (low-density lipoprotein, which has morelipids and less protein) is the bad cholesterol. HDL(high-density lipoprotein) has more protein and less fat,and is considered good cholesterol.



Lipid Transport in the Body

Dietary lipids absorbed aschylomicrons

Adipose and muscle cells take up

lipids from chylomicrons

Chylomicron remnants areintermediate-density lipoproteins



Lipid Transport in the Body(cont.)

IDLs become low-density lipoproteins(bad cholesterol)

These can deliver fatto the liver and byother tissues

LDL receptors arenecessary for the liver

to take them up Some LDLs are taken

up by scavenger cellslike macrophages



Fatty Streaks and Atherosclerotic Plaques



Atherosclerosis

Atherosclerosis develops because scavenger cellsencounter the fatty deposits in the artery lining and

Try to destroy the fats by oxidizing them

Oxidized fats injure the endothelium

Clots form and release growth factors

Smooth muscle grows over the fatty core

Try to remove the fats by eating them

Become foam cells in the core of the plaque



Atherosclerotic Plaque

CAP

CORE

MacrophagesSmooth muscle cells

Endothelial cell

Lymphocytes

Lipid-laden

macrophage(foam cell)



Lipid Transport in the Body

High-densitylipoproteins (goodcholesterol) aremade in the liver

They go out to theperipheral tissuesand pick up lipid

Then they carry itback to the liver



Scenario

A man has several genetic defects in his lipoproteinreceptors.

His liver lacks LDL receptors

His muscle cells lack receptors for the apoproteins onchylomicrons

His scavenger cells have extra LDL receptors

Question:

Why might he develop atherosclerosis?



Stable Plaques

Have thick fibrous caps

Partially block vessels

Do not tend to form clots or emboli



Unstable Plaques

Have thin fibrous caps

Plaque can rupture and cause a clot to form

May completely block the artery

The clot may break free and become an embolus



Question

What immediate threat do unstable plaques present?

a. Clot formation will increase pressure in the vessel.

b. Plaque may lead to angina (chest pain).

c. Clots may break loose and block blood flow to keyorgans.

d. All of the above constitute immediate threats.



Answer

c. Clots may break loose and block blood flow to keyorgans.

Rationale:If a clot breaks loose, becoming an embolus, itmay lodge in a blood vessel to the brain, heart, orlungs. When blood flow is significantly decreased orblocked altogether, the result is tissue deathin theexamples here, stroke, heart attack, or pulmonary

embolus. The other choices represent more long-term/chronic problems.



Scenario

A woman complains of pain in her left leg.

Her foot is cool and pale

She reports that it is often red and warm when she issitting down

The pain occurs when she is walking to church on Sundays

The skin on her left leg is shinier than on her right leg

Question: What could have caused all this? How?



Aneurysms

Wall of arteryweakens and

stretches

Risk of ruptureand hemorrhage

Risk of clotformation


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Discussion

How would each of the following affect blood pressure?

Vasodilation

Decreased stretching of baroreceptors

Hypoxemia

Inhibiting angiotensin-converting enzyme

Beta blockers Alpha-2 agonists

Calcium-channel blockers

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LEC 17 Blood Flow & Pressure