The kidney weight remains stable from maturity until 40 years of age and then progressively decreases so that at age 80, the renal mass is only 70% of the adult.
The genito-urinary system consists of the urinary tract and the genitals and sexual organs. The urinary tract is further divided into upper and lower urinary tract.
Upper Urinary Tract: Kidney and Ureters
Glomerular Filtration Rate (GFR)
The blood is filtered by the kidney through a process called glomerular filtration to form urine. The GFR declines with aging. There is however high degree of individual variability. Decreased GFR usually represents some underlying kidney disease.
After age of 40, GFR decreases by 0.8 to 1 ml/min/year on an average.
Usually kidney function derangements due to some other medical conditions are accompanied by raised serum creatinine. However, the decreased GFR of old age is generally not accompanied by raised serum creatinine.
Renal Blood Flow (RBF)
On an average the decline in blood flow to the kidney is at the rate of about 10% per decade from about 600ml/min in a young adult to 300ml/min at 80yrs of age. The blood supply to the inner kidney (medulla and pelvis) is relatively intact and it is generally the outer kidney (cortex) that suffers infarcts. This also explains the reduced GFR since most of the glomeruli are placed in the cortex. The renal blood vessels become rigid like most other blood vessels of the body as the person ages and their response to intrinsic dilators also fails. The efficiency of renin angiotensin system (an important mechanism of controlling the blood pressure) also gets blunted.
The kidney tubules perform the vital function of handling the balance of acid and base load, thus effectively cleansing the blood while maintaining the normal fluid and electrolyte balance. The tubular function definitely declines over age. The kidney fails to keep a perfect balance of fluid and electrolytes as the person ages.
In general the aged kidney is granular in appearance with modest decrease in the tissue volume. A notable change in the size of the kidney due to loss of nephrons, which are the basic structural units of kidney.
Kidney disease and hypertension are closely related and more so in old age. They are both the cause and effect. High blood pressure is dangerous to the kidney and chronic kidney disease is associated with sustained hypertension that does not respond well to medication. Even in the absence of high blood pressure there are notable changes in the kidney during old age.
Medication with a number of nephro-toxic drugs over a period of time also causes marked decline in kidney function. The most commonly implicated drugs are the NSAIDs (non-steroidal anti inflammatory drugs), a class of pain killers. Unfortunately, pain management is an essential requirement in old age and many of these drugs are available as over the counter drugs, which can be dispensed without a prescription.
Lower Urinary Tract: Bladder and Urethra
The function of the lower urinary tract is to isolate the upper urinary tract from the external environment and thus protect the kidneys from ascending infections. The bladder stores urine after it is formed and allows for periodic release. The disorders are of two types in old age. Either there is reflux of urine into the upper urinary tract causing persistent urinary tract infections or there is a trouble in emptying (retention/incontinence).
Urinary tract infections
The urethra is short in females and comparatively very long in male. The urethral opening in the female is also very close to the anal opening and the vaginal opening, two potential sources of infection even in healthy adult. The bladder is therefore much more protected in the male from external infections than in females. In old age, however, the resistance is reduced to quite an extent making urinary tract infection a very common entity in elderly, more so in females.
The bladder function (voiding of urine) declines as a person ages due decline in the muscle mass as well as the nervous tissue.
All these changes lead to storage of urine for prolonged periods of time and gradual sagging of the urinary bladder. Gradually the tone of the bladder decreases to such an extent that it is unable to hold the urine for as long as required and this leads to incontinence. With declining bladder function, it is neither able to evacuate completely nor fast enough, leading to a sense of incomplete voiding and a poor stream.
Changes specific in females
Age related changes of the lower urinary tract become more common in females especially after middle age when menopause sets in. The estrogen in the female, which is responsible for the innate immunity decreases after menopause leading to frequent urinary tract infections.
The prostate gland in the male grows under the influence of testosterone throughout life. The prostate encircles the urethra and its growth causes constriction of the urethra gradually over years. There are no symptoms in the earlier years and by the 7th or 8th decade there is poor stream and sometimes even retention of urine.
Genitals and Sexual Function
The genitals undergo atrophy with age and the sex drive (libido) reduces with age. Fertility drops in general in both sexes.
Women have significantly reduced libido in old age and the decline is quite marked from the menopausal days. After menopause and the subsequent vulvo-vaginal atrophy, sex can be uncomfortable in females, which in turn has an adverse affect on the libido.
Women are infertile after menopause whereas men are technically fertile till their terminal days. However, elderly men do very notably complain of erectile dysfunction and premature or sometimes retrograde ejaculation.
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