DISORDERS OF BLOOD FLOW AND BLOOD PRESSURE

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Yofesi Isaac ObonyoNursing Science Student

LEARNING OBJECTIVES

• Discuss at least three major properties of endothelial cells and their associated functions/factors.

• List the five types of lipoproteins and state their function in terms of lipid transport and development of atherosclerosis.

• Describe the role of low-density lipoprotein receptors in removal of cholesterol from the blood.

• Cite the criteria for diagnosis of hypercholesterolemia.

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LEARNING OBJECTIVES

• List the vessels most commonly affected by atherosclerosis and describe the vessel changes that occur.

• Describe possible mechanisms involved in the development of atherosclerosis.

• List risk factors for atherosclerosis.

• Describe the role of inflammation in the development of atherosclerosis and how it can be assessed clinically.

• State the signs and symptoms of acute arterial occlusion.

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LEARNING OBJECTIVES

• Describe the pathology associated with the vasculitidesand relate it to four disease conditions associated with vasculitis.

• Compare the manifestations of ischemia associated with peripheral arterial disease, Raynaudphenomenon, and thromboangiitis obliterans.

• Distinguish between the pathology and manifestations of aortic aneurysms and dissection of the aorta.

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ARTERY STRUCTURE

Tunica intima: Endothelium

Tunica media: smooth muscle

Tunic adventitia: collagen and elastic fibers

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QUESTION

Which vessel layer can expand to accommodate pressure changes?

a. Tunica intima

b. Tunica media

c. Tunica adventitia

d. Tunica externa

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ANSWER

b. Tunica media

The tunica media is composed of smooth muscle, which can stretch/expand to accommodate changes 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

or vasoconstriction• Creates growth factors that can stimulate

smooth muscle • Forms a smooth lining of the blood vessels

that resists clot formation• Creates compounds to promote clot

formation in 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 factors that promote plaque formation

• Plaques block the arteries

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LIPOPROTEINS

• The more protein, the higher the density

• The more lipid, the lower the density

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QUESTION

Tell whether the following statement is true or false:

LDL is considered to be “good” cholesterol.

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ANSWER

False

LDL (low density lipoproteins) has more lipids and less protein—it’s the “bad” cholesterol. HDL (high density) has more protein and less fat—it’s considered “good” cholesterol.

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LIPID TRANSPORT IN THE BODY

• Dietary lipids absorbed as chylomicrons

• Adipose and muscle cells take up lipids from chylomicrons

• Chylomicron remnants are intermediate-density lipoproteins

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LIPID TRANSPORT IN THE BODY

• IDLs become low-density lipoproteins (“bad cholesterol”)

• These can deliver fat to the liver and by other tissues

• LDL receptors are necessary for the liver to take them up

• Some LDLs are taken up by scavenger cells like macrophages

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FATTY STREAKS AND ATHEROSCLEROTIC PLAQUES

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ATHEROSCLEROSIS

• Atherosclerosis develops because scavenger cells encounter 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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SCENARIO

A man has several genetic defects in his lipoprotein receptors…

• His liver lacks LDL receptors

• His muscle cells lack receptors for the apoproteins on chylomicrons

• His scavenger cells have extra LDL receptors

Question:

• Why might he develop atherosclerosis?7/1/2014 18

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 key organs.

d. All of the above constitute immediate threats.

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Answer

c. Clots may break loose and block blood flow to key organs.

If a clot breaks loose, becoming an embolus, it may lodge in a blood vessel to the brain, heart, or lungs. When blood flow is significantly decreased or blocked altogether, the result is tissue death—in the examples 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 is sitting down• The pain occurs when she is walking to

church on Sundays• The skin on her left leg is shinier than on the

right legQuestion:• What could have caused all this? How?

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ANEURYSMS

• Wall of artery weakens and stretches

• Risk of rupture and hemorrhage

• Risk of clot formation

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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

• α2 agonists

• Calcium channel blockers7/1/2014 25