356 Chapter 11
D. The gonads secrete sex steroid hormones.
1. Leydig cells in the interstitial tissue of the testes secrete
testosterone and other androgens.
2. Granulosa cells of the ovarian follicles secrete estrogen.
3. The corpus luteum of the ovaries secretes progesterone,
as well as estrogen.
E. The placenta secretes estrogen, progesterone, and a variety
of polypeptide and protein hormones that have actions
similar to some anterior pituitary hormones.11.7 Paracrine and Autocrine Regulation 349
A. Autocrine regulators are produced and act within the
same tissue of an organ, whereas paracrine regulators are
produced within one tissue and regulate a different tissue
of the same organ. Both types are local regulators—they
do not travel in the blood.
B. Prostaglandins are special twenty-carbon-long fatty acids pro-
duced by many different organs. They usually have regulatory
functions within the organ in which they are produced.- Glucagon raises blood glucose by stimulating the
breakdown of liver glycogen. It also promotes lipolysis
and the formation of ketone bodies. - The secretion of insulin is stimulated by a rise in blood
glucose following meals. The secretion of glucagon is
stimulated by a fall in blood glucose during periods of
fasting.
B. The pineal gland, located on the roof of the third ventricle of
the brain, secretes melatonin. - Melatonin secretion is regulated by the suprachiasmatic
nucleus of the hypothalamus, which is the major center
for the control of circadian rhythms. - Melatonin secretion is highest at night, and this
hormone has a sleep-promoting effect. In many species,
it also has an antigonadotropic effect and may play a
role in timing the onset of puberty in humans, although
this is as yet unproven.
C. The gastrointestinal tract secretes a number of hormones that
help regulate digestive functions.
Test Your Knowledge
- Which of these statements about hypothalamic-releasing
hormones is true?
a. They are secreted into capillaries in the median eminence.
b. They are transported by portal veins to the anterior
pituitary.
c. They stimulate the secretion of specific hormones from
the anterior pituitary.
d. All of these are true. - The hormone primarily responsible for setting the basal
metabolic rate and for promoting the maturation of the brain is
a. cortisol. c. TSH.
b. ACTH. d. thyroxine. - Which of these statements about the adrenal cortex is true?
a. It is not innervated by nerve fibers.
b. It secretes some androgens.
c. The zona glomerulosa secretes aldosterone.
d. The zona fasciculata is stimulated by ACTH.
e. All of these are true.- Which of these statements about the hormone insulin is
true?
a. It is secreted by alpha cells in the islets of Langerhans.
b. It is secreted in response to a rise in blood glucose.
c. It stimulates the production of glycogen and fat.
d. Both a and b are true.
e. Both b and c are true.
Match the hormone with the primary agent that stimulates its
secretion.
- Epinephrine a. TSH
- Thyroxine b. ACTH
Review Activities
- Corticosteroids c. Growth hormone
- ACTH d. Sympathetic nerves
e. CRH - Steroid hormones are secreted by
a. the adrenal cortex.
b. the gonads.
c. the thyroid.
d. both a and b.
e. both b and c. - The secretion of which of these hormones would be
increased in a person with endemic goiter?
a. TSH c. Triiodothyronine
b. Thyroxine d. All of these - Which of these hormones uses cAMP as a second
messenger?
a. Testosterone
b. Cortisol
c. Insulin
d. Epinephrine - Which of these terms best describes the interactions of
insulin and glucagon?
a. Synergistic c. Antagonistic
b. Permissive d. Cooperative - Which of these correctly describes the role of inositol
triphosphate in hormone action?
a. It activates adenylate cyclase.
b. It stimulates the release of Ca^2 1 from the endoplasmic
reticulum.
c. It activates protein kinase.
d. All of these.