HUMAN BIOLOGY

134 Chapter 7

A B

Major Cardiovascular disorders

(Figure 7.19). Calcium deposits may enter the plaque and

harden both it and the vessel wall.

Sometimes abnormal blood clots form at the site of a

plaque. If a clot sticks to the plaque, it is called a thrombus.

If it floats off into the bloodstream it becomes an embolus.

A thrombus can grow big enough to completely block an

artery. An embolus may dangerously clog a smaller vessel

in the heart, lungs, or elsewhere.

Surgery may be the only answer for a severely blocked

coronary artery. In a coronary bypass, a section of a large ves-

sel taken from the chest is stitched to the aorta and to the

coronary artery below the affected region (Figure 7.20).

In laser angioplasty, laser beams vaporize the plaques.

In balloon angioplasty, a small balloon is inflated inside a

blocked artery to flatten a plaque so there is more room

in the artery. A small wire cylinder called a stent may be

inserted to help keep the artery open (Figure 7.20).

“Plaque-busting” drugs called statins are widely used

to lower blood LDL levels. Statins block a process in the

liver that produces cholesterol for use in normal cell activi-

ties. As a result, the liver makes use of LDLs it removes

from blood.

Disease, an injury, or an inborn defect can weaken an

artery so that part of its wall balloons outward. This pouch-

like weak spot is called an aneurysm (ann-yoo-rizm).

Aneurysms can develop in various parts of the cardiovascu-

lar system, including the aorta and vessels in the brain and

abdomen. If an aneurysm bursts, it can cause serious and

even fatal blood loss. A minor aneurysm may not present

any immediate worry, but in the brain, especially, an aneu-

rysm is potentially so dangerous that it requires immediate

medical treatment.

heart damage can lead to heart attack

and heart failure

A heart attack—medically, a myocardial infarction (MI)—is

damage to or death of heart muscle due to reduced blood

flow to the affected region. Usually the attack happens

The leading cause of death in the United States isn’t cancer

or car accidents, it’s cardiovascular disease (CVD). We can’t

do much about risk factors such as getting older or having

a family history of heart trouble. But we often do have con-

trol over risk factors such as smoking, high levels of blood

lipids such as cholesterol and trans fats, obesity, a lack of

exercise, and hypertension.

arteries can clog, stiffen, or weaken

In arteriosclerosis—hardening of the arteries—arteries

become thicker and stiffen. In atherosclerosis, however,

the condition gets worse as cholesterol and other lipids

build up in the artery wall.

Having too many lipids in the blood greatly increases

the risk of atherosclerosis. This lipid overload may be due to

a variety of factors, including your personal genetics (fam-

ily history) and a diet high in cholesterol and trans fat. In

the blood, proteins called LDLs (low-density lipoproteins)

bind cholesterol and other fats and carry them to body

cells. Proteins called HDLs (high-density lipoproteins) also

pick up cholesterol in the blood, but they carry it to the

liver where it is processed. Eventually it moves into the

intestine and is excreted in feces. Because HDLs help

remove excess cholesterol from the body, they are often

termed “good cholesterol.”

Surplus LDLs in the blood increases the atherosclerosis

risk. This is why LDLs are called “bad cholesterol.”

Blood tests measure the relative amounts of HDLs and

LDLs in a person’s blood in milligrams (mg). A total of

200 mg or less per milliliter of blood is considered acceptable

(for most people), but experts agree that LDLs should make

up only about one-third of this total, or about 70 to 80 mg.

When LDLs infiltrate artery walls, cholesterol builds up

there. Defensive cells called macrophages (“big eaters”) also

move into the wall and begin to remove LDLs by the process

of phagocytosis described in Section 3.11. Next, inflam-

mation sets in and a fibrous net forms over a growing,

artery-clogging mass called an atherosclerotic plaque

Figure 7.19 Plaques and blood clots may clog arteries. A A normal artery. B An artery

narrowed by a plaque and clogged further by a blood clot. (A: © Ed Reschke; B: Biophoto Associates/

Science Source)

7. 8

atherosclerotic

plaque

blood clot

sticking to

plaque

narrowed

lumen

wall of artery

unobstructed

lumen of

normal artery

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