Encyclopedia of Health and Medicine

A
aging, urinary system changes that occur with
At birth the structures of the urinary system are
fully developed and function under the automatic
control of the NERVOUS SYSTEM. The newborn’s KID-
NEYS filter BLOOD and make URINE. The BLADDER collects
the urine and, when it fills to a point that
triggers the micturition REFLEX, it empties to drain
urine via the URETHRA to outside the body. Voluntary
control over URINATION develops between
three and five years of age, the rite of passage
from babyhood to childhood. The urinary system
typically then functions at a steady level for
decades, unless disease alters its structures
(notably the KIDNEYS).
Changes in the Kidneys and Bladder
Beginning around age 40 the number, size, and
efficiency of nephrons, the filtering units of the
kidneys, begins to diminish. At birth each kidney
contains a million or more nephrons. By age 70
the kidneys have lost about 30 percent of the
nephrons they contained at birth. They are
smaller overall in size and take longer to filter the
blood that flows through them. They may allow
more water to enter the urine and keep more
electrolytes in the blood circulation. The imbalance,
even when slight, often affects BLOOD PRES-
SURE and other vital functions and increases the
risk for DEHYDRATION.
Other changes in the body often affect the kidneys
as well as other structures of the urinary system.
With aging fibrous tissue throughout the
body begins to lose elasticity, becoming more rigid.
This reduced FLEXIBILITY can harden and narrow
the blood vessels that supply the kidneys, slowing
blood flow into the kidneys and through the
nephrons. It also diminishes the bladder’s ability
to distend (expand), decreasing bladder capacity.
175
Age-related changes in NERVE and BRAIN function
also slow the micturition REFLEX, allowing the
bladder to become more full before triggering the
urge to urinate. These changes can result in URI-
NARY URGENCY and URINARY FREQUENCY.
The Effects of Other Changes
and Health Conditions
Age-related changes in the reproductive system—
MENOPAUSE in women and BENIGN PROSTATIC HYPER-
PLASIA (BPH) in men—affect the urinary system as
well. The normal and usually harmless enlargement
with aging of the PROSTATE GLAND in men can
constrict the urethra, interfering with the flow of
urine during urination. Relaxation of the pelvic
structures that accompanies the decline of the levels
of ESTROGENS in women who are past
menopause affects the woman’s ability to control
the flow of urine, allowing problems such as stress
incontinence (urine leakage with coughing, sneezing,
or laughing). As well, stretching and tearing
of the pelvic muscles and ligaments that may have
occurred during PREGNANCY and CHILDBIRTH may
weaken these structures, allowing the bladder to
sag and pressure the VAGINA (CYSTOCELE).
HYPERTENSION (high blood pressure) and DIA-
BETES, two conditions that become increasingly
common with advancing age, are particularly hazardous
to the kidneys and between them account
for about 80 percent of RENAL FAILURE (acute and
chronic) and END-STAGE RENAL DISEASE (ESRD). Early
and appropriate treatment for these conditions
can significantly slow their actions on the kidneys,
highlighting the importance of routine health
screening for them. The risks for BLADDER CANCER,
RENAL CANCER, NEPHROPATHY, NEPHROLITHIASIS (kidney
stones), and UROLITHIASIS
increase with age.
(bladder stones) also