The term polyuria implies an increased volume of urine

Causes:

(i) when the ingestion of fluids is increased.

(ii) Foods – contain varying amount of water and water is produced by oxidation of food staffs (“metabolic water”). Salty and spicy foods and beverages like beer have diuretic influence. Coffee and tea also have this property.

(iii) In diabetes insipidus – absence of ADH.

(iv) In diabetes mellitus – high concentration of sugar increases the os.pr. and impedes reabsorption of water from tubules.

(v) In chronic renal diseases – when the tubules are unable to concentrate. Increased flow of urine at night is frequently one of the earliest symptoms of chronic renal diseases and called as nocturia. It is defined as passage of volume of over 500 ml of urine having sp.gr. below < 1.018 during a 12-hour night period (6 PM to 6AM). Note: polyuria that occurs in early stages of chronic glomerulonephritis is thought to be a compensatory mechanism for the smaller number of healthy functioning renal unit.

(vi) In certain hysterical conditions associated with an increased fluid intake.

(b) Oligouria

The term oligouria implies to a decreased urinary output. A cessation of urine output is called as anuria.

Causes of oligouria:

(i) when the intake of fluid is restricted.

(ii) Loss of excessive fluid through extra-renal channels, f.e. excessive sweating, diarrhoea, vomiting, gastric and intestinal suctions.

(iii) In febrile conditions with less intake of fluid.

(iv) Reduction of blood supply to the kidneys as in haemorrhage, dehydration and oligaemic shock.

(v) In renal diseases, f.e. acute glomerulonephritis, tubular nephrosis due to incompatible blood transfusion, sulphonamide anuria, crush syndrome and poisoning by heavy metals.

(vi) Bilateral obstruction to the ureters.

(vii) Reflex causes induced by renal stones or an operation on the kidney or bladder.

(viii) Addison’s disease (in adrenal insufficiency).

II. Colour

The colour of normal urine is amber yellow. The principal pigment is urochrome (stercobilin), which is yellow. This is a compound formed in cleavage of hemoglobin. Small amounts of uroerythrin, coproporphyrin and uroporphyrin are usually present. Uroerythrin is red, which is possibly derived from melanins. Uroporphyrin and coproporphyrins are brownish-red Fe-free pigments arising from heme synthesis.

1. urine becomes colorless in polyuria; if due to the sp.gr. is high (1.025-1.060).

2. in oligouria, with concentrated urine the color is darkbrown.

3. Riboflavin and one of its metabolic products, uroflavin may be present and gives a greenish fluorescence to the urine.

4. Abnormally, excessive amounts of some of the normal pigments notably coproporphyrin and uroporphyrins may be excreted.

5. Among the chromogens that are not normal is homogentisic acid which occurs in inborn error of metabolism known as alkaptouria. Note:in this condition, when passed, urine is of normal colour but assumes a smoky or blackish hue on standing. The darkening begins in top, from exposure to atmospheric O2 and travels downwards.

6. The color may also be changed due to the appearance of free hemoglobin in haemoglobinuria, or due to bile pigments or due to melanins.

7. Foreign pigments are occasionally found after their administration.

8. Porphyrinuria occurs in porphyria, a hereditary disorder of heme metabolism.

9. Simple porphyrinuria seen in toxic and disease conditions and lead poisoning and chronic liver diseases.