Memmler's Structure and Function of the Human Body by Unknown

Author:Unknown
Language: eng
Format: epub
Publisher: Jones & Bartlett Learning, LLC
Published: 2019-10-03T22:00:00+00:00

BOX 14-1 Clinical Perspectives

Lipoproteins: What’s the Big DL?

Although cholesterol has received a lot of bad press in recent years, it is a necessary substance in the body. It is found in bile salts needed for digestion of fats, in hormones, and in the cell’s plasma membrane. However, high levels of cholesterol in the blood have been associated with atherosclerosis (hardening of the arteries) and heart disease.

It now appears that the total amount of blood cholesterol is not as important as the form in which it occurs. Cholesterol is transported in the blood in combination with other lipids and with protein, forming compounds called lipoproteins. These compounds are distinguished by their relative density. High-density lipoprotein (HDL) is composed of a high proportion of protein and relatively little cholesterol. HDLs remove cholesterol from the tissues, including the arterial walls, and carry it back to the liver for reuse or disposal. In contrast, low-density lipoprotein (LDL) contains less protein and a higher proportion of cholesterol. LDLs carry cholesterol from the liver to the tissues, making it available for membrane or hormone synthesis. However, excess LDLs can deposit cholesterol along the lining of arterial walls. Thus, high levels of HDLs (60 mg/dL and above) indicate efficient removal of arterial plaques, whereas high levels of LDLs (130 mg/dL and above) suggest that arteries will become clogged.

Diet is an important factor in regulating lipoprotein levels. Saturated fatty acids (found primarily in animal fats) raise LDL levels, while unsaturated fatty acids (found in most vegetable oils) lower LDL levels and stimulate cholesterol excretion. Thus, a diet lower in saturated fat and higher in unsaturated fat may reduce the risk of atherosclerosis and heart disease. Other factors that affect lipoprotein levels include cigarette smoking, caffeine, and stress, which raise LDL levels, and exercise, which lowers LDL levels.

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