HUMAN BIOLOGY

sections 15.5, 15.6 Growth hor-
mone (GH) influences growth throughout
the body, but effects are most obvious in
bones and skeletal muscles.
Thyroid hormone affects overall
metabolism, growth, and development. The
thyroid also makes calcitonin, which helps
lower blood levels of calcium and phosphate. Parathyroid
hormone is the main regulator of blood calcium levels.

sections 15.7, 15.8 The adrenal
cortex makes two kinds of steroid hormones,
the glucocorticoids and mineralo corticoids.
Cortisol and other glucocorticoids raise
the blood level of glucose and reduce
inflammation. Mineralocorticoids adjust
levels of minerals such as potassium and
sodium in body fluids.
The adrenal medulla releases epinephrine and nor-
epine phrine. Their hormonelike effects include the regulation
of blood pressure and the metabolism of carbohydrates. (Some
neurons also release them as neurotransmitters.)

sections 15.9, 15.10 Blood levels of
glucose are regulated by insulin and gluca-
gon, which are secreted in the pancreatic
islets by beta and alpha cells, respectively.
Insulin stimulates muscle and adipose cells
to take up glucose, while glucagon stimulates
glucose-releasing reactions in muscle and the
liver. Negative feedback governs both processes. Somatostatin
released by islet delta cells can inhibit the release of insulin,
glucagon, and some other hormones.
In blood sugar disorders, a lack of insulin or cells’ inability
to respond to it unbalances blood glucose levels.

section 15.11 The gonads produce sex
hormones. A female’s ovaries mainly make
estrogens and progesterone and a male’s
testes mainly make testosterone. The pineal
gland in the brain produces melatonin in
response to light/dark cycles. Melatonin
influences sleep/wake cycles as part of an
internal biological clock.
The thymus makes hormones that help T cells mature. The
heart secretes ANP, which helps regulate blood pressure. The
GI tract secretes several hormones that function in digestion.

review Questions

1. Distinguish among hormones, neurotransmitters, local
   signaling molecules, and pheromones.


2. A hormone molecule binds to a receptor on a cell membrane.
   It doesn’t enter the cell; rather, the binding activates a second
   messenger inside the cell that triggers an amplified response
   to the hormonal signal. Is the signaling molecule a steroid or
   a nonsteroid hormone?
   3. Which hormones produced in the posterior and anterior lobes
   of the pituitary gland have the targets indicated? Below, fill in
   the blanks using the abbreviations noted in Section 15.3.

the endOCrIne system 303

anterior

growth- lobe

promoting

effects

on most

cells

adrenal

cortex thyroid gonads

mammary

glands

tubules in

kidneys

mammary glands

in breasts

smooth muscle

in uterus

posterior

lobe

© Cengage Learning

4. Name the main endocrine glands and state where each is
   located in the body.


5. Give two examples of feedback control of hormone activity.

seLF-Quiz Answers in Appendix VI

1. are molecules released from a signaling cell that
   have effects on target cells.
   a. Hormones d. Pheromones
   b. Neurotransmitters e. a and b
   c. Local signaling molecules f. all of the above


2. Hormones are produced by.
   a. endocrine glands and cells d. a and b
   b. some neurons e. a and c
   c. exocrine cells f. a, b, and c


3. ADH and oxytocin are hypothalamic hormones secreted
   from the pituitary’s lobe.
   a. anterior c. primary
   b. posterior d. secondary

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