Micturition or Urination
Micturition or Urination
The process in which the urinary bladder becomes empty is called Micturition or Urination. It is called urination in simple language. About 150 to 180 liters water is filtered through the glomeruli in a day. Only 1.5 liters water is excreted from the body and rest of water viz about 99 percent water is reabsorbed.
The urine keeps on coming into the urinary bladder from the kidneys through the ureters. The capacity of urinary bladder is about 600 to 800 ml but the urinary bladder is filled complete rarely. Contracted waves produced in the muscular layer of ureter keep on supplying urine into the urinary bladder from the renal pelvis in the form of drizzles at the regular interval of 10 to 20 seconds. When 300 ml urine gathers in the urinary bladders, sensitive receptors of pelvic nerve get stimulated because of extending the walls of urinary bladder. When these stretch receptors supply impulses in the sacral region of spinal cord where parasympathetic neurons get stimulated and impulses of nerves reach to the brain stem and cerebral cortex because of which a person feels the desire of urination. As the number of sensitive impulses and repetition, the motor impulses loosen the contraction of detrusor muscle and internal contracted muscle in the form of reflex action and the internal hole of urethral tract gets opened but looseness of the external contracted muscle viz opening of urethral depends on the will. As the contracted muscles become loose, the urinary bladder starts to become empty and the urine is excreted outside. In this process, there is a pressure on the diaphragm by checking breath and contraction of abdominal walls and because of which the urinary bladder become empty. As the urination gets complete, powerful contraction originate in the external contracted muscle and muscles of pelvis region. The excretion of urine from the urethra is because of gravitational power in women but the expulsion of last drops of urine in men is because of voluntary contractions of bulbocavernosus muscle.
Higher centers of the brain in children do not get developed so this is the reason that they have no control on the tissues of voluntary muscles of external contracted viz opening of external urethra is not voluntary. Urination is governed by the spinal reflex action which starts when the urinary bladder gets enlarged because of filling urine. Parasympathetic neurons contract to the urinary bladder and the fibers of voluntary muscle of external contracted become loose consequently the urine comes out itself. As the child grows, the brain of the child becomes developed and the control on the brain starts to increase on the voluntary muscles fibers and then the process of urination become voluntary.