Essentials of Anatomy and Physiology

it is not as precise, it is often easier to speak of satu-
rated and unsaturated fats, indicating the predomi-
nance of one or the other type of fatty acid.
At room temperature, saturated fats are often in
solid form, while unsaturated fats are often (not
always) in liquid form. Saturated fats tend to be found
in animal foods such as beef, pork, eggs, and cheese,
but palm oil and coconut oil are also saturated.
Unsaturated fats are found in other plant oils such as
corn oil, sunflower oil, and safflower oil, but certain
fish oils are also unsaturated, and even pork contains
unsaturated fatty acids.
Unsaturated fats may be changed to saturated fats
in order to give packaged foods a more pleasing tex-
ture or taste, or to allow them to be stored longer
without refrigeration (a longer shelf life). These are
hydrogenated fats (meaning that hydrogens have been
added), also called trans fats. Trans fats contribute sig-
nificantly to atherosclerosis of arteries, that is,
abnormal cholesterol deposits in the lining that may

clog arteries, especially the coronary arteries of the

heart. (See also Box 2–3: Lipids in the Blood.)

The triglyceride forms of true fats are a storage

form for excess food, that is, they are stored energy

(potential energy). Any type of food consumed in

excess of the body’s caloric needs will be converted to

fat and stored in adipose tissue. Most adipose tissue is

subcutaneous, between the skin and muscles. Some

organs, however, such as the eyes and kidneys, are

enclosed in a layer of fat that acts as a cushion to

absorb shock.

Phospholipidsare diglycerides with a phosphate

group (PO 4 ) in the third bonding site of glycerol.

Although similar in structure to the true fats, phos-

pholipids are not stored energy but rather structural

components of cells. Lecithin is a phospholipid that is

part of our cell membranes(see Fig. 3–1; each phos-

pholipid molecule looks like a sphere with two tails;

the sphere is the glycerol and phosphate, the tails are

the two fatty acids). Another phospholipid is myelin,

Some Basic Chemistry 35

Table 2–3 CARBOHYDRATES

Name Structure Function

Monosaccharides—“Single” Sugars

Glucose

Fructose and

galactose

Deoxyribose

Ribose

Disaccharides—“Double” Sugars

Sucrose, lactose,

and maltose

Oligosaccharides—“Few” Sugars (3–20)

Polysaccharides—“Many” Sugars (Thousands)

Starches

Glycogen

Cellulose

Hexose sugar

Hexose sugar

Pentose sugar

Pentose sugar

• Most important energy source for cells


• Converted to glucose by the liver, then used for energy
  production


• Part of DNA, the genetic code in the chromosomes of cells


• Part of RNA, needed for protein synthesis within cells

Two hexose sugars • Present in food; digested to monosaccharides, which are

then used for energy production

• Form “self” antigens on cell membranes; important to
  permit the immune system to distinguish “self” from
  foreign antigens (pathogens)

Branched chains of

glucose molecules

Highly branched chains

of glucose molecules

Straight chains of

glucose molecules

• Found in plant foods; digested to monosaccharides and
  used for energy production


• Storage form for excess glucose in the liver and skeletal
  muscles


• Part of plant cell walls; provides fiber to promote peristalsis,
  especially by the colon