Introduction
Urine is a liquid by-product of metabolic waste produced by the kidneys. It is secreted by the renal tubules stored in the urinary bladder and excreted out the body through the urethra- a tube that removes urine. It maintains the homeostasis or balance of the body against changes in the environment. It often consists of toxic substances drawn from the blood that are not needed by the body and are removed from the body. The process of removal of waste products from the body is called excretion. Normal urine is pale yellow. Urinalysis is generally used for diagnostic procedures to detect any abnormality. Normal urine consists of water, urea, salts, and pigments.
What Are the Physical Features of Normal Urine?
Color
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Normal urine is pale yellow.
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Teroehrome is the color-causing pigment of urine.
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Reddish urine is due to the intake of red-colored foods such as beetroots and blackberries.
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The darker yellow color of urine suggests less water intake.
Smell
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Normal urine has a typical smell.
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The smell varies according to the food intake.
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The typical ammonia smell is due to the bacterial action on urea.
pH
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pH is the measurement of any substance's acidic or basic nature.
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Normal urine has a pH of around 6.2. However, it can range from 5.5 to 7.0
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pH seven is considered neutral, whereas a pH less than 7 is acidic, and greater than seven is alkaline.
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Urine is acidic if there is an uptake of a high protein-rich diet.
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Acidity is also increased in fever and after strenuous exercise.
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Alkaline urine is due to certain vegetables and cereals intake.
Mean Calorific Content
The mean calorific of urine is approximately one hundred kilocals per day. Calorific content is the measure of the heating power of the substance.
Volume
An adult, on average, excretes around 1000 mL to 1800 mL of urine daily. The quantity depends upon their water intake, the surrounding temperature, and diet.
Specific Gravity
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Specific gravity is a substance's density compared to another's density.
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The specific gravity of urine ranges from 1.002 to 1.037.
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It varies according to the concentration of the substances in the urine, food, water intake, and activity.
What Are the Normal Constituents of Urine?
Nitrogenous Constituents (Urea)
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Urea is the body's main by-product of protein breakdown.
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Its removal directly depends on the amount of protein ingested. It constitutes around eighty to ninety percent of the total urinary nitrogen.
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During fever or diabetes, urea excretion increases due to increased protein breakdown.
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A decrease in urea excretion is due to reduced production in some liver diseases.
Ammonia
The amino acids produce ammonia. Ammonia content increases in uncontrolled diabetes, during which kidney function is damaged.
Creatinine And Creatine
Creatinine is the waste product made by the muscles as a part of regular activity. Creatinine is formed from creatine. It is constant irrespective of the diet.
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Creatinine is excreted by children and pregnant women, and in smaller amounts in men.
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The creatinine coefficient is the ratio between the amount of creatinine removed in twenty-four hours and the body weight in kilograms.
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It is around 20 to 26 mg/kg/day in men and 14 to 22 mg/kg/day in women.
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The excretion of creatinine is reduced in many pathological conditions.
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It is decreased in hypothyroidism.
Uric Acid
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Uric acid is the substance formed when the body breaks down purines. Purines are prepared by the body and are also found in a particular food.
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It is water soluble.
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Uric acid excretion increases in conditions such as leukemia, liver diseases, and gout.
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Pure uric acid is colorless.
Amino Acids
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Amino acids are substances that form proteins.
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About 150 to 200 mg of amino acids is excreted in adult urine in 24 hours.
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An infant at birth excretes around 3 mg of amino acids per kg body weight, and up to six months, the value reaches around 1 mg per kg body weight.
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Amino acid excretion is excreted in liver disease and certain types of poisoning.
Allantoin
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It is the product of uric acid breakdown. Small quantities of allantoin are removed from urine.
Sulfates
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Sulfur in urine comes from sulfur-containing amino acids such as methionine and cysteine.
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In urine, sulfur is found in three forms:-
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Inorganic sulfur is an entirely broken-down form of sulfur.
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Conjugated or ethereal sulfur is around ten percent of the total excreted form of sulfur.
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Neutral sulfur- These are the main products of endogenous metabolism (metabolism within the organism). These do not change with diet.
Chlorides
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These are secreted as sodium chloride.
Phosphates
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The urine phosphates consist of sodium, potassium, calcium, and magnesium.
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Most phosphates come from food containing phosphates, such as meat, poultry, fish, nuts, beans, and dairy products. Phosphates from food are not entirely absorbed in the body.
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Some phosphate is also excreted in certain bone diseases like osteomalacia, diseases of the nervous system, and rickets.
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Phosphates are also secreted in conditions like hyperparathyroidism.
Oxalates
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Oxalates are usually found in lesser concentrations in urine.
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They appear as calcium oxalate crystals.
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Their concentration is increased by the intake of oxalate-rich fruits and vegetables such as spinach, peanuts, sweet potatoes, etc.
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Oxalates are excreted in large quantities In certain genetic metabolic diseases.
Minerals
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Minerals like sodium, potassium, calcium, and magnesium are found in urine.
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Sodium concentration changes with dietary intake. Potassium increases with the intake of potassium-rich foods or the breakdown of tissue.
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Calcium and magnesium are not entirely absorbed in the body, and their concentration is usually low in urine.
Enzymes
Enzymes such as amylase, pepsin, trypsin, and lipase are found in minimal concentration in urine.
Hormones And Vitamins
Sex hormones and vitamins such as B and C are found in traces in urine.
Urine Constituents In A Nutshell
Conclusion:
Normal urine is the metabolic waste product of the body. It is mostly composed of water. Other substances in normal urine are present in fewer quantities. An increase or decrease in their concentration suggests the presence of certain metabolic conditions. Urinalysis is one of the important diagnostic modalities that is carried out to check for the presence of any medical condition.
