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urinary system
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urinary system anatomy
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Urinary SystemThe major function of this system is the elimination of excess water, salts, and waste products.
Above 170 bpm, your thinking is reduced to the primitive fight or flight response. Running (or
charging) is at its peak performance. The vast majority of people also tend to lose control of
their bladder and bowels at this stage because even those functions consume resources that
the body prefers to save for fighting or running.
Although renal function declines substantially with age, it usually remains sufficient for
removing bodily wastes. Nevertheless, reduced renal function decreases the elderly person's
ability to respond to various physiological and pathological stresses. In general, aging is
associated with an increased incidence of kidney problems. There is a decline in the number of
nephrons by about 30-40% between ages 25 and 85. Nephrons are the basic functional units of
the kidneys and are made up of a renal corpuscle and renal tubules. There is also a reduction in
filtration rate due to cumulative damage to the system and to reduction in blood flow to the
kidneys.
Urine is formed by the kidneys through three processes: filtration, reabsorption and secretion.
The ultimate source of urine is blood, and a large amount of blood is transported to the kidneys
for filtration by way of the renal arteries. Renal blood flow progressively decreases from 1200
mL/minute at age 30 to 40 years to 600 mL/minute at age 80. A decrease in the glomerular
filtration rate, or the rate at which blood is forced through and filtered by the renal corpuscle in
the kidneys, is the most important functional defect caused by aging.
, Since the kidneys receive up to 25% of the resting cardiac output through the renal arteries, a
large portion of total blood volume is filtered through the renal corpuscle each day. At this rate,
it wouldn’t take long to totally deplete the body’s entire blood volume. Since this is obviously
not a common problem, the body must have some way to recover a majority of that filtered
blood. The process that returns necessary items from the filtrate back into the blood is called
reabsorption.
Reabsorption is responsible for returning 99% of filtrate back to the circulatory system.
Reduced nephron sensitivity which occurs with age, however, results in less reabsorption of
water, so urination becomes more frequent while daily fluid requirements increase. At the
same time, there is usually a loss of thirst which compounds the problem. The muscles that
help regulate the release of urine become weaker which leads to problems with incontinence
and often involves slow leakage of urine. This is usually a more common problem in women. In
males, urinary retention might develop due to chronic inflammation of the prostate gland.
Swelling of the gland prevents the flow of urine as it puts pressure on the urethra.
Maintaining Water-Salt Balance
It is the job of the kidneys to maintain the water-salt balance of the blood. They also maintain
blood volume as well as blood pressure. Simple examples of ways that this balance can be
changed include ingestion of water, dehydration, blood loss and salt ingestion.
Reabsorption of water
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