Urine Composition and Physiology

Urine Composition and Physiology

Urine is waste product in liquid form which pass out through the body by urethra.   

Composition of Urine

All the three process (Glomerular filtration, tubular re-absorption and tubular secretion), the fluid that comes out from collecting duct is called urine.

Urine volume 

Total volume of urine passed out in a day (24 hours) varies, depending upon water intake, state of physical and mental activity, environmental temperature and food intake.

Physical examination of urine 

1- Urine is a transparent.

2- Urine has a yellowish color due to the presence of urochrome, urobilin and uroerythrin pigments

Specific Gravity of Normal Urine

Specific gravity : 1.001-1.040 of urine 

ph Value Of Normal Urine

According to the American Association for Clinical Chemistry, the average value for urine pH is 6.0, but it can range from 4.5 to 8.0. Urine under 5.0 is acidic, and urine higher than 8.0 is alkaline, or basic. Different laboratories may have different ranges for "normal" pH levels.

Composition of Normal Urine

S N	Substance	Quantity excreted per day (Urine)
1	Water	1-2 liters
2	Proteins	0.1gm
3	Sodium ion	4gm
4	Chloride ion	6.3gm
5	Bicarbonate ion	0.03gm
6	Glucose	0gm
7	Urea	30gm
8	Potassium ion	2.0gm
9	Uric acid	0.8gm
10	Creatinine	1.6gm

Mechanism of Urine Formation

Nephron helps to excrete unwanted substances and also maintains the osmotic concentration of the blood plasma.

The fluid comings out from the nephron, containing unwanted components is called urine.

The following three steps are involved in urine formation :

• Glomerular filtration
• Re-absorption of solutes / tubular re-absorption
• Tubular secretion 

Glomerular Filtration

First step of urine production. Filtration of blood from glomerular capillary through glomerular capillary wall and wall of bowman’s capsule wall.

The filtration are produced in bowmen’s capsule called glomerular filtrate or ultrafiltrate.

Daily volume of glomerular filtrate in adults is 

In females – 150 liters

In male – 180 liters 

More than 99% of the glomerular filtrate back to the blood plasma via tubular re-absorption. Glomerular capillaries wall prevents the filtration of blood cells and platelets. Glomerular capillaries wall size permits all solutes in blood plasma to exit glomerular capillaries.

Average glomerular filtration rate (GFR) in adults is 

In male – 125 ml/min

In female – 105 ml/min

Tubular re-absorption: The volume of glomerular filtrate entering the proximal convoluted tubules.

Re-absorption: return of most of the filtrated water and solutes to the bloodstream.

Filtrate are reabsorbed by both active and passive process.

Solutes are reabsorbed includes water, glucose, amino acids, urea and ions such as sodium ion, potassium ion, calcium ion, chloride ion, bicarbonate ion and phosphate ion.