• Janhavi Atre

Blog #1 of Series 1: Urine in normal physiology

Urine is a liquid waste product that is produced in the kidneys. Kidneys make urine by filtration of waste and water present in the blood. It is excreted in the form of urea in humans. Excess presence of urea is harmful to the body. Hence, it is passed out from the body in the form of urine.

The amount of urine excreted depends on the fluid intake. For 2 liters of fluid intake, a normal-healthy individual passes approximately 800 mL-2000 mL (approx. 1500 mL) of urine in a day. Kidney produces 30 mL urine per hour. Urinary bladder has a capacity to hold 300 mL-400 mL of urine. Although urination for 4-6 times in a day is considered as normal, the actual frequency depends on the fluid intake.

Human urine is yellowish in color and consists of water, salts, urea and other metabolic waste components. Urine consists of water and organic solutes including urea, creatinine, uric acid, and trace amounts of enzymes, carbohydrates, hormones, fatty acids, pigments, and inorganic ions: sodium (Na+), potassium (K+), chloride (Cl-), magnesium (Mg2+), calcium (Ca2+), ammonium (NH4+), sulfates (SO42-), and phosphates (e.g., PO43-).

Chemical Composition of Urine is:

· Water (H2O): 95%

· Urea: 9.3 grams/liter (g/L)

· Chloride: 1.87 g/L

· Sodium: 1.17 g/L

· Potassium: 0.750 g/L

· Creatinine: 0.670 g/L and

· Proteins, hormones & metabolites.

Table 1 enlists physical and chemical characteristics of the human urine that aid in the diagnosis of kidney diseases.

The kidneys are responsible for filtering the blood with metabolic wastes and toxins, endocrine functions, and maintaining the composition of the extracellular fluid (ECF). Urine is produced to eliminate many cellular waste products and to control the amount of water in the body. Urine volume regulation is essential for maintenance of homeostasis. Greater amount of urine will reduce the volume of water in the blood. Any abnormality in the kidneys can be diagnosed by taking into account the above-mentioned parameters. Changes in color, pH, volume, turbidity, properties are considered to be an indication of renal disturbances. Urinary parameters, thus, play a vital role in the maintenance of a healthy physiology.

Meaning/Significance of scientific terms

1. Pigment: The natural coloring substance of animal or plant tissue

2. Metabolites: The intermediate or end products of metabolism

3. Turbidity: Cloudiness or haziness of a liquid due to the presence of suspended particles. It is measure of visual clarity of the liquid (here, urine)

4. pH: A value representing acidity of alkalinity of a solution (here, urine)

5. Specific gravity: Density of a solution (here, urine) with reference to a standard liquid

6. Osmolarity: A value expressing concentration of the solution in the terms of total number of solute particles per liter of the solution

7. Urobilinogen: By-product of metabolic processes in the body

8. Leukocyte esterase: Enzyme produced by white blood cells that indicates the presence of infection

9. Bilirubin: A yellowish substance produced after breakdown of red blood cells


1. https://courses.lumenlearning.com/boundless-ap/chapter/urine/#:~:text=Urine%20is%20an%20aqueous%20solution,toxic%20ammonia%20and%20carbon%20dioxide.

2. https://opentextbc.ca/anatomyandphysiology/chapter/25-1-physical-characteristics-of-urine/

3. https://www.webmd.com/urinary-incontinence-oab/qa/what-is-urine

4. https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Book%3A_Anatomy_and_Physiology_(Boundless)/24%3A__Urinary_System/24.4%3A_Urine/24.4A%3A_Physical_Characteristics_of_Urine

About the author:

Janhavi is a graduate in Microbiology from Fergusson College, Pune and holds a post-graduate degree in Biological Sciences from NMIMS University, Mumbai. She had been a project trainee at ACTREC, Navi Mumbai and was formerly associated as Assistant Professor in Biotechnology at CKT college of ACS, Navi Mumbai. The science of cancer biology, therapeutics, nanomedicine and immunology fascinates her the most. Besides this, she loves to cook, exercise and travel.


Recent Posts

See All