In general, the size or secretions of many endocrine
glands diminish as the body ages (Figure 9.21 ). Hormonal
changes include diminished output by endocrine glands,
diminished sensitivity of target
tissues
to
hormonal
stimulation, and increased secretions of some glands as
a consequence of failed negative-feedback loops within
the endocrine system. For example, the cessation of se-
cretions of estrogen and progesterone from the ovaries
causes one of the most dramatic changes in the female
endocrine system—menopause (see Chapter 16). Also,
insufficient dietary calcium leads to elevated PTH secre-
tion and diminished secretions of calcitonin and calcitriol;
these events lead to osteoporosis, weakening of bone and
increased occurrences of bone fractures (see Chapter 5).
1.
How
does aging affect the ovaries in women?
Adrenal glands
- The adrenal
cortex tissues become more
fibrous with age, so the
secretions of cortisol and
aldosterone diminish, which
impairs the body’s ability to
respond to stress and to
regulate the mineral
composition of the blood. For
example, lack of aldosterone
causes the kidney to excrete
sodium.
Kidneys
- Calcitriol secretion diminishes.
Estrogen and progesterone
secretions diminish greatly,
which causes ovulation and
the menstrual cycle to stop
(menopause).
The
testes
continue to produce
sperm and secrete testosterone as
men age, but the secretions of
testosterone diminish. Large
decreases in testosterone
production do not occur until well
into old age. The decrease in
testosterone reduces sex drive and
can lead to increased body fat.
Pancreas
- Insulin secretion and insulin sensitivity of the target
tissues diminishes with age, which affects changes in blood
glucose; increases occur faster and the return to normal glucose
levels occurs more slowly.
Parathyroid glands
- Increase
PTH secretion due to insufficient
calcium in the diet. Elevated levels
of PTH cause increased bone
resorption by osteoclasts, which
leads to weakening of the bones
and susceptibility to fractures
(osteoporosis).
Aging Alters the Endocrine System 279
previous page 314 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online next page 316 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online Home Toggle text on/off