Endocrine Glands 3191. Amines. These are hormones derived from the amino
acids tyrosine and tryptophan. They include the hormones
secreted by the adrenal medulla, thyroid, and pineal glands.
2. Polypeptides and proteins. Proteins are large polypeptides,
so the distinction between the two categories is somewhat
arbitrary. Antidiuretic hormone is a polypeptide with nine
amino acids ( table 11.2 ), too small to accurately be called a
protein. If a polypeptide chain is larger than about 100 amino
acids, such as growth hormone with 191 amino acids, it can
be called a protein. Insulin blurs the two categories, because
it is composed of two polypeptide chains derived from a sin-
gle, larger molecule (see chapter 3, fig. 3.23).
3. Glycoproteins. These molecules consist of a protein bound
to one or more carbohydrate groups. Examples are follicle-
stimulating hormone (FSH) and luteinizing hormone (LH).
4. Steroids. Steroid hormones are derived from cholesterol
after an enzyme cleaves off the side chain attached to the
five-carbon “D” ring ( fig. 11.2 ). Steroid hormones include
testosterone, estradiol, progesterone, and cortisol.
In terms of their actions in target cells, hormone mol-
ecules can be divided into those that are polar, and therefore
water-soluble, and those that are nonpolar, and thus insoluble
in water. (For a discussion of water solubility, see chapter 2In ovariesIn adrenalsIntestesCholesterolPregnenolone Progesterone
Secreted by
corpus luteum
of ovariesCortisol (hydrocortisone)Adrenal
cortexCorpus
luteumOvaryFollicles
Ovary in ovarySecreted by adrenal cortexSecreted by
follicles of ovariesEstradiol-17βAndrostenedione TestosteroneTestis
Seminiferous
tubulesInterstitial
Spermatic (Leydig) cells
cordSecreted by Leydig
cells of testesHO
HO
HOHOOHOHOHOCH 2 OH
COCH 3
CCH 3
CO OOO OOBACDFigure 11.2
Simplified biosynthetic
pathways for steroid
hormones. Notice that progesterone (a hormone
secreted by the corpus luteum of the ovaries) is a
common precursor of all other steroid hormones and that
testosterone (the major androgen secreted by the Leydig
cells of the testes) is a precursor of estradiol-17 b , the
major estrogen secreted by the follicles of the ovaries.Hormone Structure Gland Primary Effects
Antidiuretic
hormone9 amino
acidsPosterior
pituitaryWater retention and
vasoconstriction
Oxytocin 9 amino
acidsPosterior
pituitaryUterine and mam-
mary contraction
Insulin 21 and 30
amino acids
(double
chain)Beta cells
in islets of
LangerhansCellular glucose up-
take, lipogenesis,
and glycogenesisGlucagon 29 amino
acidsAlpha cells
in islets of
LangerhansHydrolysis of stored
glycogen and fatACTH 39 amino
acidsAnterior
pituitaryStimulation of
adrenal cortex
Parathyroid
hormone84 amino
acidsParathyroid Increase in blood
Ca^21 concentration
FSH, LH,
TSHGlyco-
proteinsAnterior
pituitaryStimulation of
growth, develop-
ment, and secre-
tory activity of
target glandsTable 11.2 | Examples of Polypeptide and
Glycoprotein Hormones