American Medical Association Family Medical Guide - American Medical Association [316]
Capillaries are tiny, thin-walled blood vessels that form a network (see below) between the smallest arteries (arterioles) and the smallest veins (venules). They carry blood to the cells and remove waste products. Nutrients and oxygen in the blood pass through the tiny spaces in the thin capillary walls into tissues; wastes such as carbon dioxide are taken up in the blood and carried to organs that break them down and eliminate them.
Valves in the veins
The veins contain one-way valves that open to allow used, oxygen-depleted blood to be pumped back to the heart, and close to keep blood from flowing backward. When you are physically active, your muscles contract and squeeze your veins, the valves open, and blood is pumped back toward your heart.
Atherosclerosis
Atherosclerosis is the buildup of hardened fatty deposits called plaque inside arteries. A buildup of plaque can reduce or block the flow of blood to tissues supplied by an artery.
How plaque causes blood clots to form
A buildup of plaque in an artery can cause blood clots to form. Cracks develop in the roughened surface of plaque (top). The body reacts as though the cracks are an injury and forms blood clots to seal them and promote healing (center). If a clot grows large enough (bottom), it can block blood flow in the artery and cause a heart attack or stroke.
A large plaque deposit causes turbulence in the bloodstream, which may cause blood clots to form. Plaque also is prone to cracking. Your body may react as though the cracks are an injury and form blood clots around them. If a clot grows large enough or breaks loose, or if a small bit of plaque breaks loose, it can block blood flow in the artery, causing a heart attack or stroke.
If atherosclerosis reduces or blocks blood flow in arteries elsewhere in the body, tissues receiving blood from these arteries can be damaged or destroyed. For example, if an artery in the brain is blocked, a stroke results. Blocked blood flow in an arm or leg can lead to gangrene (tissue death). Reduced blood flow to the kidneys can result in kidney failure.
Heart Disease
Heart disease is the No. 1 killer of American men and women. The disease kills more women each year than all cancers combined and 10 times more women than breast cancer. A woman’s risk increases sharply after menopause. Doctors call heart disease a lifestyle disease because it generally results from things we do to ourselves, such as getting too little exercise, eating too much and too many of the wrong kinds of foods (those high in fat and calories and low in nutrients) and too few of the right kinds of foods (those rich in antioxidants and fiber), and weighing more than we should. People who smoke increase their risk even more. Doctors believe that nearly all cases of heart disease could be eliminated if people adopted lifestyle measures such as exercising regularly, eating a nutritious diet, quitting smoking, and staying at a healthy weight.
Risk Factors
A number of factors can increase your risk of heart disease. Although you cannot control risk factors such as age, gender, race, and family health history, you can control other risk factors by following a healthy lifestyle. Because heart disease often does not cause symptoms, especially in the early stages, many people who died of heart disease were not aware that they had it. The following factors can increase your risk of heart disease:
• Age Your chances of developing heart disease increase with age. In men, the risk increases at age 45; in women, the risk increases at age 55.
• Gender Men are generally at greater risk of developing heart disease than women up to age 55; a woman’s