Human Excretory System: Urine and Micturition

 Urine and micturition

urine is liquid and Consists of 96% - water, 2 % urea, 2% other substances. Other substances includes organic and inorganic Substances like Uric acid, creatinine, Hippuric acid, Na, K, Ca, Mg, Chloride etc.

About 1.5 to 2  ltrs urine is formed each day. It is transparent light yellow coloured due to pigment urochrome.

PH =6 but depends upon diet and ranges from 5 to 7.5.

specific gravity: 1.003 to 1.040

It has faint aromatic smell due to urinods. If allowed to stand, urea Changes into ammonia by bacterial action and gives strong pungent smell.

Amount of urine depends upon:

* Fluid intake: when fluid intake  is more , more urine is formed and when fluid intake is low less urine is formed.

* Environmental Condition: when temperature is high less amount of urine is formed and when temperature is low more amount of urine is formed.

* Physical activity: During more physical activity less amount of urine is formed as blood flow to Kidney is less and during less Physical activity more urine is formed.

* Intake of diuretics: Diuretics like tea, coffee, alcohol etc decreases ADH Production. thus, more urine is formed.

Micturition: also called urination. The act of voiding (passing out) urine is  called urination or micturition.

when about 300ml urine get accumulated in the bladder the urge of micturition is felt. At this time, the transitional epithelium starts to stretch and is detected by stretch receptors and the micturition reflex operates. the detrusor muscles contracts and internal urethral sphincter opens and sense of urination begins. The external urethral sphincter is voluntary and regulated by higher inhibitory Centre of brain. thus, the act of micturition Can be prolonged to some extent. parasympathetic nerves Contracts detrusor muscles and relaxes internal urethral sphincter while sympathetic nerves relaxes detrusor muscles and Contracts internal urethral sphincter.