Page 14 - LN- EXCRETION

Alcohol inhibits the release of ADH and caffeine interferes with ADH action and sodium
reabsorption. Thus, both of these artificially dilute the urine and are called diuretics.
Urination is a reflex response in babies, but is controlled consciously in older children and
adults.
Urine
An adult man normally passes about 1-1.5 L of urine per day.
Composition Urine normally contains, water 95%, salts 2%, urea 2.6%, uric acid 0.3%, traces
of creatinine, creatine, ammonia, etc.
Colour Pale yellow, due to pigment urochrome produced by the breakdown of haemoglobin.
pH Ranges from 4.5-8.2, average pH 6.0 (i.e., slightly acidic).
Odour Unpleasant, if allowed to stand imparts strong smell like, ammonia.
Note:
Least concentration of urea is found in renal vein because urea is excreted through urine
formed in kidney. On an average, 25-30 g of urea is excreted out per day. Highest
concentration of urine is found in hepatic vein because urea is synthesised in liver.
Analysis of urine helps in clinical diagnosis of many metabolic disorders as well as
malfunctioning of the kidney.
For example, presence of glucose (glycosuria) and ketone bodies (ketonuria) in urine are
indicative of diabetes mellitus and presence of protein, blood and pus in the urine is called
proteinuria, haematuria and pyuria respectively.
Role of Other Organs in Excretion
Other than the kidneys, there are some accessory excretory organs also that help in the
elimination of excretory wastes.
These are described as follows
1. Lungs
Carbon dioxide and water are the waste products formed in respiration. Lungs remove the
CO 2 and some water as vapour in the expired air. About 18 L of CO 2 per hour and 400 mL of
water per day are eliminated by human lungs.
2. Liver
It changes the decomposed haemoglobin of the worn-out red blood corpuscles into bile
pigments, i.e., bilirubin and biliverdin. These pigments passes into the alimentary canal with
the bile for elimination in the faeces. The liver also excretes cholesterol, steroid hormones,
certain vitamins and drugs via bile.
Liver deaminates the excess and unwanted amino acids, producing ammonia, which is
quickly combined with CO 2 to form urea in urea cycle or Ornithine cycle, which is further
removed by the kidneys.
3. Skin
The sweat and sebaceous glands in the skin can eliminate certain substances through their
secretions.
(i) Sweat Glands The secretion of sweat glands (sweat) is an aqueous fluid containing NaCl,
lactic acid, small amounts of urea, amino acids and glucose. Control of sweat lost is an
example of homeostasis control, for regulating the body temperature (i.e., to facilitate a
cooling effect on the body surface).
(ii) Sebaceous Glands Sebum from sebaceous glands eliminates sterols, fatty acids, waxes
and hydrocarbons. This secretion is mainly meant for protective oily covering of the skin.
4. Intestine
Epithelial cells of colon excrete excess salts of calcium, magnesium and iron along with