Essentials of Anatomy and Physiology

HCl NaHCO 3 →NaCl H 2 CO 3
What has happened here? Hydrochloric acid, a
strong acid that would greatly lower pH, has reacted
with sodium bicarbonate. The products of this reac-
tion are NaCl, a salt that has no effect on pH, and
H 2 CO 3 , a weak acid that lowers pH only slightly. This
prevents a drastic change in the pH of the extracellu-
lar fluid.
If a strong base, such as sodium hydroxide, is added
to the extracellular fluid, this reaction will occur:

NaOH H 2 CO 3 →H 2 O NaHCO 3
Sodium hydroxide, a strong base that would greatly
raise pH, has reacted with carbonic acid. The products
of this reaction are water, which has no effect on pH,
and sodium bicarbonate, a weak base that raises pH
only slightly. Again, this prevents a drastic change in
the pH of the extracellular fluid.
In the body, such reactions take place in less than a
second whenever acids or bases are formed that would
greatly change pH. Because of the body’s tendency to
become more acidic, the need to correct acidosis is
more frequent. With respect to the bicarbonate buffer
system, this means that more NaHCO 3 than H 2 CO 3 is

needed. For this reason, the usual ratio of these

buffers is 20:1 (NaHCO 3 :H 2 CO 3 ).

ORGANIC COMPOUNDS

OF IMPORTANCE

Organic compounds all contain covalently bonded

carbon and hydrogen atoms and perhaps other ele-

ments as well. In the human body there are four major

groups of organic compounds: carbohydrates, lipids,

proteins, and nucleic acids.

CARBOHYDRATES

A primary function of carbohydratesis to serve as

sources of energy in cell respiration. All carbohydrates

contain carbon, hydrogen, and oxygen and are classi-

fied as monosaccharides, disaccharides, oligosaccha-

rides, and polysaccharides. Saccharidemeans sugar, and

the prefix indicates how many are present.

Monosaccharides, or single-sugar compounds,

are the simplest sugars. Glucose is a hexose, or six-

carbon, sugar with the formula C 6 H 12 O 6 (Fig. 2–6).

Fructose and galactose also have the same formula,

Some Basic Chemistry 33

Figure 2–6. Carbohydrates. (A) Glucose, depicting its structural formula. (B) A disac-

charide such as sucrose. (C) Cellulose, a polysaccharide. (D) Starch, a polysaccharide.

(E) Glycogen, a polysaccharide. Each hexagon represents a hexose sugar such as glucose.

QUESTION:What is the chemical formula of glucose?

H

C

OH

CH 2 OH

C

H

OH

C

H

H

C

OH

H

C

OH

A Glucose

E Glycogen

B Disaccharide

C Cellulose

D Starch

o