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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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Copyright 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Artery Structure
Tunica intima:
endothelium
Tunica media: smoothmuscle
Tunica adventitia:collagen and elasticfibers
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Copyright 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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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Copyright 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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
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Lipoproteins
The more protein,the higher thedensity
The more lipid, thelower the density
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8/23Copyright 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
Tell whether the following statement is true or false.
LDL is considered to be good cholesterol.
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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.
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Lipid Transport in the Body
Dietary lipids absorbed aschylomicrons
Adipose and muscle cells take up
lipids from chylomicrons
Chylomicron remnants areintermediate-density lipoproteins
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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
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Fatty Streaks and Atherosclerotic Plaques
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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
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Atherosclerotic Plaque
CAP
CORE
MacrophagesSmooth muscle cells
Endothelial cell
Lymphocytes
Lipid-laden
macrophage(foam cell)
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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
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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?
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Stable Plaques
Have thick fibrous caps
Partially block vessels
Do not tend to form clots or emboli
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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
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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.
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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.
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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?
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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