O

Vitamin B12 (cyanocobalamin)

Figure 18.14

Vitamin Bi2, which has the most complex molecular structure of the vitamins, contains cobalt (Co).

When the gastric glands of some individuals fail to secrete adequate amounts of intrinsic factor, cyanocobalamin is poorly absorbed. This leads to pernicious anemia, in which abnormally large red blood cells called macrocytes are produced when bone marrow cells do not divide properly because of defective DNA synthesis.

7. Folacin, or folic acid. Folacin is a yellow crystalline compound that exists in several forms. It is easily oxidized in an acid environment and is destroyed by heat in alkaline solutions; consequently, this vitamin may be lost in foods that are stored or cooked.

Folacin is readily absorbed from the digestive tract and is stored in the liver, where it is converted to a physiologically active substance called folinic acid. Folinic acid functions as a coenzyme that is necessary for the metabolism of certain amino acids and for the synthesis of DNA. It also acts with cyanocobalamin in promoting production of normal red blood cells.

Good sources of folacin include liver, leafy green vegetables, whole-grain cereals, and legumes. A

Vitamin C (ascorbic acid)

Glucose (a monosaccharide)

Vitamin C (ascorbic acid)

Glucose (a monosaccharide)

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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