water minerals metabolism & kidney function

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  • 1. WATER-MINERAL METABOLISM

2. Reabsorbtion. Lenght of renal tubules is about 100 km. So, all important for our organism are reabsorbed during passing these tubules. Epitelium of renal tubules reabsorb per day 179 L of water, 1 kg of NaCl, 500 g of NaHCO3, 250 g of glucose, 100 g of free amino acids.All substances can be divided into 3 group:1. Actively reabsorbed substances.2. Substances, which are reabsorbed in a little amount.3. Non-reabsorbed substances.To the first group belong Na+, Cl-, Mg2+, Ca2+, H2O, glucose and other monosaccharides, amino acids, inorganic phosphates, hydrocarbonates, low-weight proteins, etc.Na+ reabsorbed by active transport to the epitelium cell, then into the extracellular matrix. Cl- and HCO3- following Na+ according to the electroneutrality principle, water according to the osmotic gradient. From extracellular matrix substances go to the blood vessels. Mg2+ and Ca2+ are reabsorbed with help of special transport ATPases. Glucose and amino acids use the energy of Na+ gradient and special carriers. Proteins are reabsorbed by endocytosis.Urea and uric acid are little reabsorbable substances.Creatinin, mannitol, inulin and some other substances are non- reabsorbable.Some substances (K+, ammonia and other) are secreted into 3. Peculiarities of biochemical processes inkidney.Kidney have a very high level of metabolicprocesses. They use about 10 % of all O2, whichused in organism. During 24 hours throughkidney pass 700-900 L of blood. The main fuel forkidney are carbohydrates. Glycolysis, ketolysis,aerobic oxidation and phophorillation are veryintensive in kidney. A lot of ATP formed in result.Kidney have plenty of different enzymes: LDH (1, 2,3, 5), AsAT, AlAT. Specific for kidney is alanineamino peptidase, 3rd isoform. 4. Organic compounds of urine.Proteins. Healthy people excretes 30 mg of proteins per day. Asa rule these are low weight proteins.Urea. This is main part of organic compounds in urine. Ureanitrogen is about 80-90 % of all urine nitrogen. 20-35 g of ureais excreted per day in normal conditions.Uric acid. Approximately 0,6-1,0 g of uric acid is excreted perday in form of different salts (urates), mainly in form of sodiumsalt. Its amount depends from food.Creatinin and creatin. Near 1-2 g of creatinin is excreted perday, what depended from weight of muscles. This is theconstant for each person. Men excrete 18-32 mg of creatininper 1 kg of body weight per day, women 10-25 mg. Creatininis non-reabsorbable substance, so this test used for evaluatingof renal filtration.Amino acids. Per day healthy person excretes 2-3 g of aminoacids (free amino acids and different low weight moleculepeptides). Also products of amino acids metabolism can befound in the urine.Couple substances. Hypuric acid (benzoyl glycine) is excreted inamount 0,6-1,5 g per day. This index increases after eating alot of berries and fruits, and in case of proteins decay in theintestines. 5. Indican (potassium salt of indoxylsulfuric acid). Per day excrition of indican isabout 10-25 g. Increasing of indicans level in urine is due to inrtensification ofdecay proteins in the intestines and chronic diseases, which are accompanied byintensive decopmosition of proteins (tuberculosis, for example).Organic acids. Formic, acetic, butyric, -oxybutyric, acetoacetic and some otherorganic 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 andsome products of vitamines metabolism. These data can be used for evaluating ofsupplying our organism by vitamines.Hormones. Hormones and their derivates are always present in urine. Their amountdepends from functional state of endocrinal glands and liver. There is a very wideused test determination of 17-ketosteroids in urine. For healthy man this index is15-25 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 byroutine methods of investigations.Glucose. In normal conditions present in so little amount that cannot be found byroutine methods of investigations.Galactose. Present in the newborns urine, when digestion of milk or transformation ofglalactose into glucose in the liver are violated.Fructose. It is present in urine very seldom, after eating a lot of fruits, berries andhoney. In all other cases it indicates about livers disorders, diabetes mellitus.Pentoses. Pentoses are excreted after eating a lot of fruits, fruit juices, in case ofdiabetes mellitus and steroid diabetes, some intoxications.Ketone bodies. In normal conditions urine contains 20-50 mg of ketone bodies andthis amount cannot be found by routine methods of clinical investigations.Porphyrines. Urine of healthy people contains a few I type porphyrines (up to 300mkg per day). 6. Regulation of urine formation.Na-uretic hormone (produced in heart) decreasereabsorbtion of Na+, and quantity of urineincreased.Aldosteron and some other hormones (vasopressin,renin, angiotensin II) increase Na-reabsorbtionand decrease quantity of urine.Role of kidney in acid-base balance regulation.Kidney have some mechanisms for maintainingacid-base balance. Na+ reabsorbtion and H+secretion play very important role.1. Primary urine has a lot of Na2HPO4 (in dissociatedform). When Na+ reabsorbed, H+ secreted intourine and NaH2PO4 formed. 7. 2. Formation of hydrocarbonates. Insiderenal cells carboanhydrase forms from CO2and 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 formedand go to the blood, thereupon aciditydecreased.3. Formation of free ammonia. NH3 used forformation of NH4+ (H+ ion associted), anddifferent acid metabolites excreted asammonia salts. 8. 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. 9. Melting point of water 0 oC; boiling point 100 oC.Water plays an important role in the thermal regulation ofliving organisms. Waters high heat capacity coupled with thehigh water content found in most organisms (between 50%and 95%, depending on species) contributes to themaintenance of an organisms internal temperature.Water is a remarkable solvent. Waters ability to dissolve alarge variety of ionic and polar substances is determined by itsdipolar structure and its capacity to form hydrogen bonds.Salts such as sodium chloride (NaCI) are held together byionic (or electrostatic) forces. They dissolve easily in waterbecause dipolar water molecules are attracted to the Na+ andCl- ions.Organic molecules with ionizable groups and many neutralorganic molecules with polar functional groups also dissolve inwater. Their solubility is due primarily to the hydrogen bondingcapacity of water. Nonpolar compounds are not soluble inwater. Because they lack polar functional groups, suchmolecules cannot form hydrogen bonds. 10. The state and distribution of water in the organism. There are two water compartments in the body:- Intracellular water- Extracellular water Extracellular fluid is divided into:- interstitial fluid- Plasma Biological role of water:Water is an essential constituent of cell structures and provides the media in which the chemical reactions of the body takes place and substance are transported. It has a high specific heat for which, it can absorb or gives off heat without any appreciable change in temperature. It has a very high latent heat. Thus, it provides a mechanism for the regulation of heat loss by sensible or insensible perspiration on the skin surface.The fluidity of blood is because of water. 11. Distribution of water in an adult man, weighing 70 kg Body weightVolume (l) Compartment (%)Total 60 42ICF 40 28ECF 20 14Interstitial fluid1510,5 Plasma53,5 12. Water balance. Endogenous water.Water intake.Water is supplied to the body by exogenous and endogenoussources.Exogenous water: water intake is highly variable which mayrange from 0,5-5 liters. Ingestion of water is mainlycontrolled by a thirst centre located in the hypothalamus.Endogenous water: the metabolic water produced within thebody is the endogenous water. This water (300-350ml/day) is derived from the oxidation of foodstuffs. It isestimated that 1g each of carbohydrate, protein and fat,respectively, yield 0,6 ml, 0,4 ml and 1,1 ml of water.Water output.Water losses from the body are variable. There are fourdistinct routes for the elimination of water from the body:urine, skin, lungs and feces. 13. Regulation of Water Metabolism Antidiuretic hormone or Vasopressin which has got the property toenhance water reabsorption2. Hypothalamus known as a thirst centre. Besides this,osmoconcentration of plasma also stimulates supraoptic andparaventricular nuclei3. Adrenal Cortex. Aldosterone has controll excretion of sodium andpotassium by the kidneys4. Rennin-Angiotensin system. Angiotensin II stimulates the synthesisand secretion of aldosterone and the release of vasopressin, andthereby increases renal absorption of Na+ and H2O.5. Prostaglandins. They may also increase urinary loss of water byinhibiting the antidiuretic effect of vasopressin and by increasing theurinary sodium.6. Solutes. Osmotic effect of Na+ helps to retain water in extracellularfluids. Eleva

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