Excretory Products and Their Elimination
| 279
MÏÇTÜRÏTÏØÑ
Gradual filling of urinary bladder causes stretching. As a result, stretch
receptors on its wall send impulses to CNS. (AIPMT 2009) The CNS passes
on motor messages . It causes the contraction of smooth muscles of the
bladder and simultaneous relaxation of the urethral sphincter . It results
in micturition (release of urine).
The neural mechanism causing micturition is called micturition reflex.
An adult human excretes 1 to 1.5 litres of urine (25-30gm urea) per day
Urine is a light yellow coloured watery fluid , slightly acidic (pH 6.0) and
has a characteristic odour.
(NEET 2015)
Various conditions can affect the characteristics of urine.
Analysis of urine helps in clinical diagnosis of many metabolic disorders
and malfunctioning of the kidney.
E.g. Glycosuria (presence of glucose) and Ketonuria (presence of ketone
bodies) in urine indicates diabetes mellitus..
RØLË ØF LÜÑGS, LÏVËR & SKÏÑ ÏÑ ËXÇRËTÏØÑ
LUNGS:
Remove 18 litres /
day(200 ml/minute) of
CO2 and water.
LIVER :
Secretes bile containing
bilirubin, biliverdin, cholesterol,
degraded steroid hormones,
vitamins and drugs. Most of
them pass out along with
digestive wastes.
SKIN (Sweat glands & sebaceous glands):
Sweat contains water, NaCl, small amounts of urea, lactic acid,
etc. Primary function of sweat is to give a cooling effect on body
surface. It also helps in removal of some of the wastes mentioned
below. Sebaceous glands eliminate sterols, hydrocarbons, waxes
etc. through sebum. Sebum provides a protective oily covering for
the skin. Saliva eliminates small amounts of nitrogenous wastes.
RËGÜLÅTÏØÑ ØF THË KÏDÑËÝ FÜÑÇTÏØÑ
It is done by hormonal feedback mechanisms involving the hypothalamus,
JGA and the heart.
Changes in blood volume, body fluid volume and ionic concentration
activate osmoreceptors in the body