Page 652 - Fundamentals of anatomy physiology

Spotlight Figure 18–2
Structural Classification of Hormones

HORMONES

The hormones of the body can be divided into three groups
on the basis of their chemical structure.

Amino Acid Derivatives Peptide Hormones Lipid Derivatives

Amino acid derivatives are small molecules Peptide hormones are chains of amino There are two classes of lipid derivatives:
that are structurally related to amino acids, acids. Most peptide hormones are eicosanoids, derived from arachidonic
the building blocks of proteins. synthesized as prohormones—inactive acid, a 20-carbon fatty acid; and steroid
molecules that are converted to active hormones, derived from cholesterol.
Derivatives of Tyrosine hormones before or after they are secreted.
Eicosanoids
Glycoproteins
Thyroid Hormones Eicosanoids O COOH
These proteins are more than 200 (Ī-kō-sa-noydz) CH3
I I HH O amino acids long and have carbohy- are important OH
HO O C CC drate side chains. The glycoproteins paracrine fac- OH
include thyroid-stimulating hormone tors that coor-
I I H NH2 OH (TSH), luteinizing hormone (LH), and Prostaglandin E
follicle-stimulating hormone (FSH)
Thyroxine (T4) from the anterior lobe of the pituitary dinate cellular activities and affect
gland, as well as several hormones
produced in other organs. enzymatic processes (such as blood

clotting) in extracellular fluids. Some

Catecholamines eicosanoids, such as leukotrienes

(lu-kō-TRĪ-ēns), have secondary roles as

OH H H hormones. A second group of

HO C CN eicosanoids—prostaglandins—are
HO
CH3 Short Polypeptides/ involved primarily in coordinating local
Small Proteins
HH cellular activities. In some tissues,
This group of peptide hormones
Epinephrine is large and diverse. It includes prostaglandins are converted to
hormones that range from short
chain polypeptides, such as thromboxanes (throm-BOX-ānz)
antidiuretic hormone (ADH) and
oxytocin (OXT) (each 9 amino acids and prostacyclins (pros-ta-SĪ-
long), to small proteins, such as
insulin (51 amino acids), growth klinz), which also have strong
hormone (GH; 191 amino acids), and
prolactin (PRL; 198 amino acids). This paracrine effects.
group includes all the hormones
secreted by the hypothalamus, heart, Aspirin suppresses the
thymus, digestive tract, pancreas, and production of prostaglandins.
posterior lobe of the pituitary gland,
Sources of tyrosine as well as several hormones Steroid Hormones
include meat, dairy, and fish. produced in other organs.

Derivative of Tryptophan Steroid hormones OH
are released by the

Melatonin H H reproductive organs

H3C H C N C CH3 (androgens by the HO
O H CHO testes in males, Estrogen
estrogens and

progesterone by the

N Structure of ovaries in females), by the cortex of
H insulin
Chain B the adrenal glands (corticosteroids),

and by the kidneys (calcitriol). Because

circulating steroid hormones are

Turkey is a well-known bound to specific transport proteins in
source of tryptophan. Other sources
include chocolate, oats, bananas, dried Chain A the plasma, they remain in circulation
dates, milk, cottage cheese, and peanuts.
longer than do secreted peptide

hormones.

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