Urine

What is urine? Urine is a liquid waste product of the body secreted by the kidneys by a process of filtration from blood and excreted through the urethra.

Composition Urine is a transparent solution that can range from colorless to amber but is usually a pale yellow. It is normally odorless but can acquire strong odors due to bacterial action. Urine is an aqueous solution of metabolic wastes such as urea, dissolved salts, and organic compounds. Most noticeably, ammonia is produced by breakdown of urea, a major component of urine.

Hazards Urea is toxic and can be irritating to skin and eyes. High concentrations in the blood can cause damage to organs of the body. Low concentrations of urea such as in urine are not dangerous.

Characteristics The typical bright yellow colour of urine is caused by the pigment urochrome as well as the degradation products of bilirubin and urobilin.

Unusual coloration Yellowing/light Orange may be caused by removal of excess vitamin B from the bloodstream. Bloody urine is termed hematuria, potentially a sign of a bladder infection. Dark orange to brown urine can be a symptom of jaundice or Gilbert's syndrome. Black or dark-colored urine is referred to as melanuria and may be caused by a melanoma. Reddish or brown urine may be caused by porphyria. Dark yellow urine is usually indicative of dehydration.

Turbidity Turbid urine may be a symptom of a bacterial infection. and can also be due to crystallization of salts such as calcium phosphate.

PH The pH of urine can normally vary between 4.5 and 8.   The pH of urine can normally vary between 4.5 and 8. Strongly acidic or alkaline urine may be symptomatic of disease.

Volume The amount of urine produced depends on numerous factors including : state of hydration, activities, environmental factors, size, and health. In adult humans the average production is about 1 - 2 L per day. Polyuria is a condition of excessive production of urine (> 2.5 L/day), in contrast to oliguria where < 400 mL are produced per day, or anuria with a production of < 100 mL per day.

Density or specific gravity Normal urine density or specific gravity values vary between 1.003-1.035 (g.cm-3) , and any deviations may or may not be associated with urinary disorders.

Substances found in normal urine Urine is aprox. 95% water. The other components of normal urine are the solutes that are dissolved in the water component of the urine.

Organic molecules These are electrically neutral and can be relatively large (compared with the 'simpler' ions - below).These include: Urea Creatinine Others

Urea Urea is an organic (i.e. carbon-based) compound whose chemical formula is: CON2H4 or (NH2)2CO. It is also known as carbamide. Urea is derived from ammonia and produced by the deamination of amino acids. The amount of urea in urine is related to quantity of dietary protein

Creatinine Creatinine is a normal (healthy) constituent of blood. It is produced mainly as a result of the breakdown of creatine phosphate in muscle tissue. It is usually produced by the body at a fairly constant rate (which depends on the muscle mass of the body).

Uric acid Uric acid is an organic (i.e. carbon-based) compound whose chemical formula is: C5H4N4O3. Due to its insolubility, uric acid has a tendency to crystallize, and is a common part of kidney stones.

Other substances/molecules Example of other substances that may be found in small amounts in normal urine include : carbohydrates, enzymes, fatty acids, hormones, pigments, and mucins (a group of large, heavily glycosylated proteins found in the body).

Ions Are atoms or groups of atoms that have either, lost some outer electrons, hence have a positive electric charge, or have gained some outer electrons (to the atom or group of atoms), and hence have a negative electric charge. These include:

These include: Sodium (Na+) : Amount in urine varies with diet and the amount of aldosterone (a steroid hormone) in the body. Potassium (K+) : Amount in urine varies with diet and the amount of aldosterone (a steroid hormone) in the body. Chloride (Cl-) : Amount in urine varies with dietart intake (chloride is a part of common salt, NaCl). Magnesium (Mg2+) : Amount in urine varies with diet and the amount of parathyroid hormone in the body. (Parathyroid hormone increases the reabsorption of magnesium by the body, which therefore decreases the quantity of magnesium in urine.) Calcium (Ca2+) : Amount in urine varies with diet and the amount of parathyroid hormone in the body. (Parathyroid hormone increases the reabsorption of calcium by the body, which therefore decreases the quantity of calcium in urine.)

Small groups formed from a few different elements: Ammonium (NH4+) : The amount of ammonia produced by the kidneys may vary according to the pH of the blood and tissues in the body. Sulphates (SO42-) : Sulphates are derived from amino acids. The quantity of sulphates excreted in urine varies according to the quantity and type of protein in the person's diet. Phosphates (H2PO4-, HPO42-, PO43-) : Amount in urine varies with the amount of parathyroid hormone in the body - parathyroid hormone increases the quantity of phosphates in urine.

What are the abnormal constituents of urine? Abnormal urine can have: Carbohydrates Proteins ketone bodies Blood Bile salts Bile pigments Fats

CARBOHYDRATES Physiologically in pregnancy and lactation, lactose is excreted in pregnant women. Pathologically: if lactose is excreted in the urine, then this is due to lactose intolerance. Glucose could be excreted in the urine in Diabetes mellitus, renal glycosuria Fructose in essential fructosuria Galactose in galactosemia

PROTEINS: Secretion of proteins in urine is due to: 1- Increase in the permeability of the glomerular capillaries as in nephrotic syndrome 2- Damage to the capillaries membranes as in glomerulonephritis

The following proteins can be excreted in abnormal urine: Albumin Globulin Hemoglobin (protein of RBC) Myoglobin Bence Jones Proteins

Albumin and globulin are found in the urine in the condition called proteinuria, also in nephrotic syndrome and glomerular nephritis. Hemoglobin is excreted in urinay tract infections. Myoglobin is excreted due to muscular atrophy. Bence jones proteins are not usually synthesised in the body. They are produced in the condition called multiple myeloma, by plasma cells.

KETONE BODIES They are basically three chemicals : acetone acetoacetic acid beta hydroxy butaric acid All the three are the intermediates in lipid metabolism. Defect in metabolism can lead to the presence of ketone bodies in urine

Increased catabolism of fats is due to : starvation increased fat intake in diet decreased carbohydrates in the diet diabetes ketoacidosis

RBC/ HEMOGLOBIN In certain disease state such as: hemolytic anemia Urinary tract infections Renal trauma

BILE SALTS: In Jaundice BILE PIGMENTS: in obstructive jaundice