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Urination (Micturition)
Micturition is the act of emptying the bladder or passing the urine. Control over urination is twofold. There is an internal sphincter which is controlled by the autonomic nervous system and has no voluntary control. It is normally in a state of contraction and relaxes when accumulation of urine in the bladder makes voiding necessary. An additional external urethral sphincter permits voluntary control over urination and the voiding reflex can be consciously suppressed. In the very young children, urination is a completely reflex action. Normally in an adult, the presence of about 300 ml. of urine in the bladder will stimulate a desire to urinate, which is primarily a reflex act but the reflex stimulation can be inhibited and urine will continue to accumulate. When the contents reaches a volume of about 700 ml, the average person will have difficulty in controlling the reflex Emotional stress may prevent the bladder to relax after urination and stimulate an urge to urinate.
Failure of the kidneys can lead to a severe toxic condition called uremia or urine in blood, Toxic wastes build up in the blood and tissues and ultimately poison the body. An artificial kidney utilizing the principle of dialysis can be used to prolong patient's life. Two to three treatments a week are required and each treatment takes five to twelve hours. Home dialysis units are now available.
Besides cleaning and filtering the blood, kidneys encourage production of red blood cells. They regulate the proportion of sodium and potassium salts, water and other substances in the blood. A little too much or a shade too little of any of them can be fatal they control vital water balance. It also keeps blood neither too acidic nor too alkaline.
Thus, kidneys are very discriminating processing plants, carefully regulating our sea of internal fluids. Survival of the whole body relies on the delicate balancing processes of these two organs, no bigger than the size of a clench:d fist.
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