Urine

I. Physical properties of urine:

A. Volume:

1. Normally: 800 -2000 ml / day.

2. Polyuria is the urine excretion of more than 2000 ml/day. It is caused by:

a) Physiological polyuria as in high fluid intake (water, tea), and high protein diet (the end product of protein metabolism is urea which causes osmotic diuresis).

b) Pathological polyuria as in diabetes mellitus (glucose causes osmotic diuresis) and in diabetes insipidus due to lack of antidiuretic hormone. (Note: diabetes means increased urine volume).

c) Oliguria and anuria: Even under condition of severe water restriction, an individual usually excretes at last 500 ml urine/day. Oliguria is the excretion of less than 500 ml/ day. Anuria is the excretion of less than 125 ml / day. They may be caused by:

1) Physiological oliguria as in low fluid intake and at hot weather due to excessive sweating.

2) Pathological oliguria or anuria as in urinary obstruction (by stones or tumor), excessive vomiting and diarrhea or due to shock and hemorrhage.

B. Odor:

1. Fresh urine has an aromatic odor.

2. On standing, for any length of time, urine gets the odor of ammonia due to decomposition of urea by bacteria and release of ammonia.

3. Some diets and medicine may change urine odor.

C. Color:

1. Normally, urine is pale or amber yellow.

2. Dilute urine is pale yellow, while concentrated urine appears almost deep orange.

3. The color of urine is due to 2 pigments; urochrome and urobilin.

4. Variations of urine color may result from many metabolic products, drugs and foods.

a) Red or red brown color due to hematuria.

b) Yellow-brown or green-brown due to jaundice.

D.Aspect (appearance):

1. Normally, freshly voided urine is transparent.

2. Turbid urine may be associated with the presence of abnormal constituents e.g. pus (pyuria), red cells (hematuria), chyle (chyluria) and crystals (calcium phosphate or urate).

E. Specific gravity (urine relative mass density):

1. Specific gravity (SG), of any liquid is its density compared with the density of distilled water, which has a density of 1,000. (Liquid density / water density).

2. Normally, the specific gravity of urine collected over 24-hours ranges 1015-1025.

3. The higher the urine specific gravity, is the more the dissolved solids in urine e.g. urea, uric acid, sugar.

4. Urine specific gravity indicates the concentrating power of the kidney.

5. Variations of specific gravity:

a) Decreased in cases of dilute urine as in diabetes insipidus.

b) Increased in cases of concentrated urine as in diabetes mellitus.

F. Urine pH:

1.  Normally, urine pH is acidic (about 6).

2. Acidity of urine results from conversion of basic phosphate (Na₂HPO₃) into acid phosphate (NaH₂PO₃) in distal convoluted tubules of the kidney.

3. After meals, urine pH becomes less acidic. This is due to the formation of gastric HCl is associated with absorption of more bicarbonate. The later is then excreted in urine making it alkaline. This process is called alkaline tide.

4. Low urine pH (below 6): may be associated with:

a) High protein diet.

b) Metabolic and respiratory acidosis.

c) Urinary tract infection by a type of bacteria called: E.coli.

5. High urine pH (above 6): may be associated with:

a) High citrus fruits and vegetables.

b) Administration of some alkalies as sodium bicarbonate.

c) Potassium depletion, as it leads to alkalosis.

G.Deposits (sediments):

1. Normally, urine contains no visible deposits.

2. Upon centrifugation, one or more of the following deposits may appear by using microscope:

a) Pus cells which are dead leucocytes (pyuria): It indicates urinary tract infection.

b) Red cells (hematuria).

c) Epithelial cells: Squamous epithelium is normally present in female urine. They are derived while urine passing female genital tract. Columnar or transitional epithelium are derived from kidney, ureter or bladder due to a variety of causes e.g. infection.

d) Parasites and ova: e.g. bilharzial ova.

e) Casts: These are cylindrical structures formed from mucoproteins in the distal convoluted tubules. After formation, they become loose and go down the tubules into the urine. They indicate chronic glomerulonephritis.

f) Crystals: as urate, oxalate, and phosphate crystals.

II.Normal constituents of urine:

Organic materials	Inorganic materials
Urea, Ammonia, Creatinine Creatine, Uric acid, Amino acids, Proteins, Sugars Others	Sodium (Na+), Potassium (K+), Chloride (CI-) Bicarbonate (HCO3-), Phosphate, Sulfate

A. Nonprotein nitrogenous compounds

1. Urea:

a) It is end product of protein metabolism. It is the main

solute in urine.

b) Normally it ranges 20-40 g/day.

c) It is formed in the liver, and excreted by the kidney.

d) It constitutes about 85% of the total urinary nitrogen.

2. Ammonia:

 a) Normally it is about 0.7 g/day.

b) Ammonia in urine is derived from deamination of amino acids mainly glutamine:

c) Formation of ammonia by the kidney is increased in acidosis as in diabetes mellitus. In alkalosis, ammonia is almost absent in urine.

3. Creatinine and creatine:

a) Normally creatinine excretion is about 1.4 g/day, while creatine excretion ranges 0-0.2 g/day.

b) Creatinine (anhydrous creatine) is the end product of creatine metabolism.

c) Creatinine excretion depends on muscle bulk of the individual and not on diet.

4. Uric acid:

a) It is end product of purine metabolism.

 b) Normally it is about 0.5 g/day.

c) Uric acid is either derived exogenously from diet or endogenously from breakdown of tissue nucleoproteins in liver.

d) Uric acid is acidic because it contains 3 enol groups (C-OH) that can give (H⁺) ions.

e) Uric acid solution is alkaline in reaction. This is because uric acid is slightly soluble in water but highly soluble in alkalis. So, the alkaline reaction of uric acid is due to the alkali in which uric acid is dissolved and not uric acid itself.

f) Uric acid excretion is increased in leukemia, severe liver disease and gout.

g) Allanation is a substance derived from partial oxidation of uric acid in birds. Human urine contains very small amount of allanation.

5. Amino acids:

a) Normally it ranges 150-200 mg/day.

6. Other nonprotein nitrogenous compounds: excreted in urine include hippuric acid, indican, purines and coproporphyrins.

B. Proteins: proteins as such are excreted in urine In very small amounts (less than 30 mg/liter).

C.Sugars: 50 % of people excrete 2-3 mg/dl after heavy meal.

D. Other organic constituents: include ascorbic acid, ketone bodies, oxalic acid, phenols as well as some hormones, vitamins and enzymes.

E. Inorganic constituents: as Na⁺, K⁺, CI^-, HCO₃^- phosphate and sulfate.

III.Abnormal constituents of urine:

A. Sugars:

1. Glucose: Normally less than 0.1 gram glucose is excreted per day. Causes of glycosuria (excessive excretion of glucose)

2. Fructose: (fructosuria), galactose (galactosuria) and pentose (pentosuria):

3. Lactose (lactosuria): presence of lactose in urine, it may occur in mothers during pregnancy, lactation and the weaning period.

B. Proteins (proteinuria):

1. Normal urine contains very little amount of proteins (less than 30 mg/liter). These are:

a) Albumin and globulins (30 %).

b) Mucoproteins of renal origin called: Tamm Horsfall

mucoprotein (70%).

 2. Microalbuminuria is the excretion of proteins (30-200 mg/liter). It indicates early affection of kidney as in diabetes mellitus. It cannot be detected by ordinary methods and needs special techniques for its detection.

3. Proteinuria: It is the presence of protein in urine (more than 200 mg/liter). It is characteristic of all acute and chronic kidney diseases:

a) Most excreted proteins are albumin (albuminuria) due to its low molecular weight and higher plasma concentration compared with globulins.

b) Proteinuria (albuminuria) may be classified into:

1) Prerenal proteinuria: as in heart failure due to renal venous congestion.

2) Renal proteinuria: due to kidney affection (glomerular) as in glomerulonephritis, or tubular as in pyelonephritis).

3) Postrenal proteinuria: due to lower urinary tract affection as inflammation or tumor of urinary bladder.

4)  Other proteins in urine:

a) Bence Jones protein:

It is an abnormal type of globulins (light chains of immunoglobulins), present in urine of patients suffering from multiple myeloma (malignant plasma cells). It is precipitated at 50°-60°C, dissolved at 100°C and re-precipitated on cooling.

b) Hemoglobin (hemoglobinuria):

It indicates intravascular hemolysis as in malaria and hemolytic anemia.

c) Myoglobin (myoglobinuria): It indicates massive muscle damage as in burns and severe electric shock.

c. Ketone bodies (ketonuria):

1. Normally, less than 18 mg of ketone bodies are excreted per day.

2. Ketonuria is the presence of ketone bodies in the urine in abnormal concentrations.

3. Ketonuria may occur associated with ketosis in any condition where carbohydrate utilization is impaired e.g. starvation, carbohydrate poor diet and diabetes mellitus.

D. Bilirubin:

1. The presence of bilirubin in the urine occurs in obstructive jaundice and in some stages of toxic jaundice.

2. It gives the urine a dark greenish brown color.

E. Blood (hematuria):

1. It is the presence of blood or intact red cells in urine.

2. It is caused by urinary bilharziasis, glomerulonephritis, and traumatic or malignant diseases.

F. Porphyrins:

1. Normally, trace of coproporphyrins is excreted in urine per day.

2. The presence of excess amount of coproporphyrins or uroporphyrins in urine occurs in patients suffering from porphyrias.

IV. Urinary stones (calculi):

A. Over 10% of adult males suffer from urinary stones at least once in a life.

B. Urinary stones are almost always composed of substances normally excreted in the urine. These substances for unknown causes are supersaturated, precipitated and form crystals. The crystals are then bound together by a binding substance forming stone.

C. Urinary stones may be classified into:

1. Simple stone: consisted only of a single constituent.

2. Mixed stone: consisted of two or more constituents.

D. Chemical composition of urinary calculi:

The most common substances enter in stone formation are:

1. Calcium oxalate.

2. Calcium phosphate.

3. Calcium carbonate.

4. Magnesium ammonium phosphate (triple phosphate).

5. Less commonly stones are formed of:

a) Uric acid: 4-10% .

b) Cystine stone: less than 1%.

c) Xanthine stone: very rare.

E. Causes of urinary calculi:

There are many factors that may predispose to the formation of calculi:

1. Change in urine pH: as in infection of urinary tract, this makes the urine alkaline due to the action of bacteria on urea. Alkalinity causes precipitation of crystals and stone formation.

2. Disturbance in vitamins:

a) Excess vitamin D (= hypervitaminosis D): leads to the absorption of excess calcium and causes calcium stone formation.

b) Excess vitamin C (=L-Ascorbic acid): L-ascorbic acid can be converted in human to oxalate, which may lead to the formation of calcium oxalate stones.

c) Deficiency of vitamin A: leads to roughness of the lining epithelium of the urinary tract. This leads to precipitation of crystals and stone formation.

3. Disturbance in hormones: as in hyperparathyroidism. It leads to hypercalcuria and formation of calcium stones.

4. Excess excretion of uric acid: as in gout. This leads to formation of uric acid stones.

5. Excess excretion of cystine: as in cystinuria. This leads to formation of cystine stones.

6. Excess mucoproteins in urine: Mucoproteins act as the cement substance that binds the excreted salts to form stone.

Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com