Medicine

PHYSICAL-CHEMICAL PROPERTIES AND CHEMICAL COMPOSITION OF NORMAL URINE

Physical-chemical properties and chemical composition of normal urine. Pathological components of urine

 

 

Peculiarities of biochemical processes in kidney.

Kidney have a very high level of metabolic processes. They use about 10 % of all O2, which used in organism. During 24 hours through kidney pass 700-900 L of blood. The main fuel for kidney are carbohydrates. Glycolysis, ketolysis, aerobic oxidation and phophorillation are very intensive in kidney. A lot of ATP formed in result.

Metabolism of proteins also present in kidney in high level. Especially, glutamine deaminase is very active and a lot of free ammonia formed. In kidney take place the first reaction of creatin synthesis.

Kidney have plenty of different enzymes: LDG (1, 2, 3, 5), AsAT, AlAT. Specific for kidney is alanine amino peptidase, 3rd isoform.

Utilization of glucose in cortex and medulla is differ one from another. Dominative type of glycolysis in cortex is aerobic way and CO2 formed in result. In medulla dominative type is anaerobic and glucose converted to lactate.

Two sources contribute to the renal ammonia: blood ammonia (is about one-third of excreted ammonia), and ammonia formed in the kidney. The predominant source for ammonia production within the kidney is glutamine, the most abundant amino acid in plasma, but  a small amount may originate from the metabolism of other amino acids such as asparagine, alanine, and histidine. Ammonia is secreted into the tubular lumen throughout the entire length of the nephron. Secretion occurs both during normal acid-base balance and in chronic acidosis.Metabolic acidosis is accompanied by an adaptive increase in renal ammonia production with a corresponding increase in urinary ammonium excretion.

Kidney cortix like liver appear to be unique in that it possess the enzymatic potential for both glucose synthesis from noncarbohydrate precursors (gluconeogenesis) and glucose degradation via the glycolytic pathway. Gluconeogenesis is important when the dietary supply of glucose does not satisfy the metabolic demands. Under these conditions, glucose is required by the central nervous system, the red blood cells, and possibly other tissues which cannot obtain all their energy requirements from fatty acids or ketone body oxidation. Also, gluconeogenesis may be important in the removal of excessive quantities of glucose precursors from the blood (lactate acid after severe exercise for example). Although the biosynthetic pathways are similar, there are several important differences in the factors which regulate gluconeogenesis in the two organs. 1) The liver utilizes predominately pyruvate, lactate and alanine. The kidney cortex utilizes pyruvate, lactate, citrate, α-ketoglutarate, glycine and glutamine. 2) Hydrogen ion activity has little effect upon hepatic gluconeogenesis, but it has marked effects upon renal gluconeogenesis. Thus, when intracellular fluid pH is reduced (metabolic acidosis, respiratory acidosis or potassium depletion), the rates of gluconeogenesis in slices of renal cortex are markedly increased. The ability of the kidney to convert certain organic acids to glucose, a neutral substance, is an example of a nonexcretory mechanism in the kidney for pH regulation.

 

Regulation of urine formation.

Na-uretic hormone (produced in heart) decrease reabsorbtion of Na+, and quantity of urine increased.

Aldosteron and some other hormones (vasopressin, renin, angiotensin II) increase Na-reabsorbtion and decrease quantity of urine.

 

Role of kidney in acid-base balance regulation.

Kidney have some mechanisms for maintaining acid-base balance. Na+ reabsorbtion and H+ secretion play very important role.

1. Primary urine has a lot of Na2HPO4 (in dissociated form). When Na+ reabsorbed, H+ secreted into urine and NaH2PO4 formed.

2. Formation of hydrocarbonates. Inside renal cells carboanhydrase forms from CO2 and H2O H2CO3, which dissociated to H+ and HCO3-. H+ excreted from cell into urine (antiport with Na+) and leaded with urine. Na+ connect with HCO3-, NaHCO3 formed and go to the blood, thereupon acidity decreased.

3. Formation of free ammonia. NH3 used for formation of NH4+ (H+ ion associted), and different acid metabolites excreted as ammonia salts.

 

Role of kidney in water balance regulation.

Excessive entrance of water leads to dilution of extracellular fluid. Decreasing of osmolality inhibits secretion of antidiuretic hormone. Walls of collective tubules stay non-penetrated to water and dilutive urine formed.

If volume of blood circulation increases, circulation in kidney increases also and hyperosmotic medium of kidney medulla removed. Some substances in these conditions return into blood. So, excess of water carried with urine and a lot of soluble substances are reabsorbed into blood. After water loading stopped, hyperosmolality in kidney medulla returns for previous stage during some days.

 

Physical and chemical characteristics of urine.

Urine amount (diures) in healthy people is 1000-2000 ml per day. Day-time diures is in 3-4 times more than night-time.

Normal colour of urine is yellow (like hay or amber), what is due to presence of urochrom (derivate of urobilin or urobilinogen). Some another colour substances are uroerythrin (derivate of melanine), uroporphyrines, rybophlavine and other. Colour depends from urine concentration.

Urine is transparent. This characteristic depends from amount of different salts (oxalates, urates, phosphates), amount of present epitelium cells and leucocytes.

Density of urine depends from concentration of soluble substances. Borders of variation are from 1002 to 1035 g/l. Near 60-65 g of hard substances are excreted with urine per day.

In normal conditions urine has acid or weak acid reaction (pH=5,3-6,8). This depends from presence of NaH2PO4 and KH2PO4.

Fresh urine has a specific smell, which is due to presence of flying acids. But a lot of microorganisms, which are present in urine, split urea and free ammonia formed.

 

Organic compounds of urine.

Proteins. Healthy people excretes 30 mg of proteins per day. As a rule these are low weight proteins.

Urea. This is main part of organic compounds in urine. Urea nitrogen is about 80-90 % of all urine nitrogen. 20-35 g of urea is excreted per day in normal conditions.

Uric acid. Approximately 0,6-1,0 g of uric acid is excreted per day in form of different salts (urates), mainly in form of sodium salt. Its amount depends from food.

Creatinin and creatin. Near 1-2 g of creatinin is excreted per day, what depended from weight of muscles. This is the constant for each person. Men excrete 18-32 mg of creatinin per 1 kg of body weight per day, women – 10-25 mg. Creatinin is non-reabsorbable substance, so this test used for evaluating of renal filtration.

Amino acids. Per day healthy person excretes 2-3 g of amino acids (free amino acids and different low weight molecule peptides). Also products of amino acids metabolism can be found in the urine.

Couple substances. Hypuric acid (benzoyl glycine) is excreted in amount 0,6-1,5 g per day. This index increases after eating a lot of berries and fruits, and in case of protein’s decay in the intestines.

Indican (potassium salt of indoxylsulfuric acid). Per day excrition of indican is about 10-25 g. Increasing of indican’s level in urine is due to inrtensification of decay proteins in the intestines and chronic diseases, which are accompanied by intensive decopmosition of proteins (tuberculosis, for example).

Organic acids. Formic, acetic, butyric, β-oxybutyric, acetoacetic and some other organic acids are present in urine in a little amount.

Vitamines. Almost all vitamines can be excreted via kidney, especially, water-soluble. Approximately 20-30 mg of vit C, 0.1-0.3 mg of vit B1, 0.5-0.8 mg of vit B2 and some products of vitamine’s metabolism. These data can be used for evaluating of supplying our organism by vitamines.

Hormones. Hormones and their derivates are always present in urine. Their amount depends from functional state of endocrinal glands and liver. There is a very wide used test – determination of 17-ketosteroids in urine. For healthy man this index is 15-25 g per day.

Urobilin. Present in a little amount, gives to urine yellow colour.

Bilirubin. In normal conditions present in so little amount that cannot be found by routine methods of investigations.

Glucose. In normal conditions present in so little amount that cannot be found by routine methods of investigations.

Galactose. Present in the newborn’s urine, when digestion of milk or transformation of glalactose into glucose in the liver are violated.

Fructose. It is present in urine very seldom, after eating a lot of fruits, berries and honey. In all other cases it indicates about liver’s disorders, diabetes mellitus.

Pentoses. Pentoses are excreted after eating a lot of fruits, fruit juices, in case of diabetes mellitus and steroid diabetes, some intoxications.

Ketone bodies. In normal conditions urine contains 20-50 mg of ketone bodies and this amount cannot be found by routine methods of clinical investigations.

Porphyrines. Urine of healthy people contains a few I type porphyrines (up to 300 mkg per day).

 

Inorganic compounds of urine.

Urine of healthy people contains 15-25 g of inorganic compounds.

NaCl. Per day near 8-16 g of NaCl excreted with urine. This amount depends from amount of NaCl in food.

Potassium. Twenty-four hours urine contains 2-5 g of K, which depends of amount of plants in the food.

Different drugs can change excretion of Na and K. For example, salicylates and cortikosteroids keep Na and amplify excretion of K.

Calcium. Twenty-four hours urine contains 0.1-0.3 g, which depends from content of calcium in the blood.

Magnesium. Content of magnesium in urine is 0.03-0.18 g. So little amount of calcium and magnesium in urine can be explained by bad water solubility of their salts.

Iron. Amount of iron in urine is about 1 mg per day.

Phosphorus. In urine are present one-substituted phosphates of potassium and sodium. Their amount depends from blood pH. In case of acidosis two-substituted phosphates (Na2HPO4) react with H+ and one-substituted phosphates (NaH2PO4) formed. In case of alkalosis one-substituted phosphates react with bases and two-substituted phosphates formed. So, in both cases amount of phosphates in urine increases.

Sulfur. Amount of sulfur in twenty-four hours urine is 2-3 g per day (in form of SO42-).

Ammonia. Ammonia is excreted in ammonium sulfates and couple substances. Ammonium salts make up 3-6 % of all nitrogen in urine. Their amount depends from character of food and blood pH.

 

Pathological components of urine, which are due to different metabolic disorders in organism.

Glucosuria. Occurs in two cases – when level of glucose in blood more than kidney threshold (8-10 mmol/l), so called extrarenal glucosuria (diabetes mellitus), and when the kidney cannot reabsorb even normal quantity of glucose, so called renal glucosuria (kidney insufficiency).

Ketonuria. Due to some diseases and pathological conditions (diabetes mellitus, starwation, severe heart weakness, when amount of fat in the food more than amount of carbohydrates) level of ketone bodies increases in a big amount (up to 20-50 g per day). This is the index of deep metabolic disorders, especially in carbohydrates metabolism.

Bilirubinuria. It occures in case of hepatic parenhimatous inflammatory processes or in case of obstruction of gall bladder ductus. Urine has a colour as dark bear. After some times it stays yellow-green (bilirubin oxydized to biliverdin).

Urobilinuria. Increasing of amount of urobilin is due to haemolytic or parenhimatous hepatitis, when decomposition of mesobilinogen in liver is depressed.

Creatinuria. Amount of creatin in urine increases due to different pathological processes in muscles like myopathy and myodistrophy, starvation, hypovitaminosis E, radiation sickness, hyperthyreosis. Also this is present in small children and in women after delivery.

Indicanuria. Increasing of indican’s level in urine is due to intensification of decay proteins in the intestines, weaken of intestine peristaltic (atony, constipation), and chronic diseases, which are accompanied by intensive decopmosition of proteins (tuberculosis, for example).

Phenylketonuria. Innate deficiency of phenylalanine hydroxilase in liver makes transformation of phenylalalnine in tyrosine impossible. Amount of phenylalanine in our organism increases more than 10 times and this amino acid utilized by another pathway with phenylbutyric and phenylacetate formation. These substances cannot be utilized and heaped up in blood and tissue. Growth of brain is stopped. With urine a lot of phenylbutyric and phenylacetate excreted. Fresh urine with FeCl3 gives olive-green colour. This test is wide spread in maternity homes, because special diet can prevent problems with child health.

 

Causes of changes of normal components’ content in urine.

Urea. Decreasing of urea in urine is due to deficiency of protein in diet, disorders of liver functions (especially, liver cyrrhosis, phosphorus intoxication), acidosis (ammonia used for neutralization of acids), inflammatory or destructive processes in kidney (nephritis, when urea is not excreted and uremia appeared). Increasing of urea in urine is due to excess of proteins in diet, and different diseases, which are accompanied by intensive proteins’ decomposition (diabetes mellitus, malignant tumors, infectious diseases with fever).

Creatinin. Amount of creatinin in urine decreases in case of disorders of glomerular filtration (amount in blood increases in the same time). Increasing of creatinin in urine is due to intensive muscle work, intensive proteins’ decomposition, excess of creatinin in diet (meat).

Amino acids. Increasing of amino acids’ level take place in case of intensive decomposition of tissues’ proteins (trauma, burns, radiation sickness etc.). Also it indicates about liver function’s disorders, especially about depressing of proteins and urea formation.

Uric acids. Decreasing of uric acid in urine is present, when diet has mainly a carbohydrates without purines. Meat, caviar, gland tissues, where a lot of nucleoproteins are present, can be cause of increasing level of uric acid in urine. Leucoses, gout, burnes, radiation sickness, usage of aspirin and corticosteroids also can be causes of hyperuricuria.

Enzymes. Different enzymes can be present in urine according to disorders of organs’ functions and these dates can be used for precise topic diagnostic.

Inorganic compounds. Concentration of inorganic compounds depends from their amount in diet (particularly for sodium, potassium), from character of diet (plants contains a lot of potassium, and level of this ion in urine increases when diet consists of plants mainly; meat and other proteins can be cause of increasing of ammonia salts in urine), from blood pH (in case of alkalosis or acidosis level of  phosphates in urine increases), from some diseases and physiological stages (during pregnancy and in case of parathyroid glands hypofunction level of calcium in urine decreases).

General nitrogen. General nitrogen – it’s a sum of all compounds which contains nitrogen. Near 80-90 % of general nitrogen belongs to urea. Another parts – uric acid, creatinin and amino acids. So, level of general nitrogen depends from level of these substances.

 

Indeces of renal functions disorders.

Proteinuria. Proteinuria can be kidney and extralidney origin. Kidney proteinuria is due to damages of nephrons, when blood plasma proteins can pass through glomerular membranes. In this case albumins and globulins are present in urine. Extra kidney proteinuria is due to damages of urinary tracts and prostate.

Hematuria. This pathological component is due to damages of kidney or urinary tracts. In most cases nephrolytiasis is accompanied by hematuria. Some times hematuria is indicator of traumatical kidney damage.

Glucosuria. In most cases glucosuria is a symptom of diabetes mellitus, when level of glucose in blood more than kidney threshold (8-10 mmol/L). But sometimes glucose can be prtesent in urine even its level in blood is normal. This is so called “kidney glucosuria” which is due to disorders of glucose reabsorbtion in tubules.

Pyuria. In normal urine leucocytes are present in a very little amount. Due to different inflammatory processes of urinary tracts, urine bladder, prostate, also due to nephrolytiasis amount of leucocytes in urine increases and this situation is called “pyuria”.

Creatin. Decreasing of creatin in urine is index of kidney insufficiency.

Methods of proteins, glucose, ketone bodies, blood and bile pigments determination in urine. Clinical significance.

Proteins can be detected in urine after denaturation (during heating, because proteins under high temperature denaturated and stay visible, and after interactions with mineral acids – sedimentation with sulfosalicylic acid).

Glucose can be detected qualitatively with help of some reductive reactions (Felling’s or  Tromer’s reactions, special indicator paper “Glucotest”) and quantitatively with help of Althauzen’s method.

Ketone bodies can be detected in urine qualitatively (Legal and Herhardt tests) and quantitatively in reaction with sodium nitroprussid, acetic acid and ammonia.

Blood in the urine can be detected qualitatively by benzidin test.

Fushe, Gmelin, Rosin, Florance and Rosenbah tests are used for qualitative detection of bile pigments in urine.

Clinical significance of presence in urine different pathological components – see above.

Organic compounds of urine.

Proteins. Healthy people excretes 30 mg of proteins per day. As a rule these are low weight proteins.

Urea. This is main part of organic compounds in urine. Urea nitrogen is about 80-90 % of all urine nitrogen. 20-35 g of urea is excreted per day in normal conditions.

Uric acid. Approximately 0,6-1,0 g of uric acid is excreted per day in form of different salts (urates), mainly in form of sodium salt. Its amount depends from food.

Creatinin and creatin. Near 1-2 g of creatinin is excreted per day, what depended from weight of muscles. This is the constant for each person. Men excrete 18-32 mg of creatinin per 1 kg of body weight per day, women – 10-25 mg. Creatinin is non-reabsorbable substance, so this test used for evaluating of renal filtration.

Amino acids. Per day healthy person excretes 2-3 g of amino acids (free amino acids and different low weight molecule peptides). Also products of amino acids metabolism can be found in the urine.

Couple substances. Hypuric acid (benzoyl glycine) is excreted in amount 0,6-1,5 g per day. This index increases after eating a lot of berries and fruits, and in case of protein’s decay in the intestines.

Indican (potassium salt of indoxylsulfuric acid). Per day excrition of indican is about 10-25 g. Increasing of indican’s level in urine is due to inrtensification of decay proteins in the intestines and chronic diseases, which are accompanied by intensive decopmosition of proteins (tuberculosis, for example).

Organic acids. Formic, acetic, butyric, β-oxybutyric, acetoacetic and some other organic acids are present in urine in a little amount.

Vitamines. Almost all vitamines can be excreted via kidney, especially, water-soluble. Approximately 20-30 mg of vit C, 0.1-0.3 mg of vit B1, 0.5-0.8 mg of vit B2 and some products of vitamine’s metabolism. These data can be used for evaluating of supplying our organism by vitamines.

Hormones. Hormones and their derivates are always present in urine. Their amount depends from functional state of endocrinal glands and liver. There is a very wide used test – determination of 17-ketosteroids in urine. For healthy man this index is 15-25 g per day.

Urobilin. Present in a little amount, gives to urine yellow colour.

Bilirubin. In normal conditions present in so little amount that cannot be found by routine methods of investigations.

Glucose. In normal conditions present in so little amount that cannot be found by routine methods of investigations.

Galactose. Present in the newborn’s urine, when digestion of milk or transformation of glalactose into glucose in the liver are violated.

Fructose. It is present in urine very seldom, after eating a lot of fruits, berries and honey. In all other cases it indicates about liver’s disorders, diabetes mellitus.

Pentoses. Pentoses are excreted after eating a lot of fruits, fruit juices, in case of diabetes mellitus and steroid diabetes, some intoxications.

Ketone bodies. In normal conditions urine contains 20-50 mg of ketone bodies and this amount cannot be found by routine methods of clinical investigations.

Porphyrines. Urine of healthy people contains a few I type porphyrines (up to 300 mkg per day).