Biochemistry of kidneys

The role of kidneyes in regulation of water metabolism: Hypersodiumemia and serum deprivation stimulate the secretion of vasopressin. Vasopressin stimulates reabsorption of water and consequently sodium level in blood plasma is decreased. Hyposodiumemia and hypervolemia stimulate the secretion of aldosterone which stimulates reabsorption of sodium and excretion of potassium. It results in increase of osmotic pressure.

The role of kidneys in regulation of phosphorus-calcium metabolism: under influence of parathyroid hormone 1,25[OH]2vD3 is formed in kidneys. This form of vitamin D3 is named metabolic-active one and it stimulates reabsorption of calcium and phosphorus; their absorption in intestine and deposition of them in bones.

The role of kidneys in regulation of pH of blood plasma: aldosterone stimulates reabsorption of sodium and excretion of protons and potassium. In acidosis the excretion of protons is increased but excretion of bicarbonates is decreased. In alkalosis the excretion of bicarbonates is increased but excretion of protons is decreased

The role of kidneys in regulation of blood pressure: There are 2 systems responsible for regulation of blood pressure: pressory and antipressory. Renin, angiotensin, prostaglandin F2alfa belong to pressory one. Kinins, sodium-uretic factor and prostaglandins A and E belong to antipressory system.

The metabolism in kidneys: 1) metabolism of carbohydrates – kidneys carry out the glucostatic function like liver, so gluconeogenesis, glycogenogenolysis and glycogenogenesis intensively occur in kidneys. Formation of glucuronic acid occurs and kidneys carry out detoxification function in regard to some endo- and exogenic toxic products like bilirubin and some medicines. 2) metabolism of lipids – kidneys utilize lipids from blood plasma. Therefore in diseases of kidneys the level of lipids in blood plasma is increased. The reabsorption of mevalonic acid occurs in kidneys. Hence disease of kidneys destroys this function and mevalonic acid is lost through urine. It results in compensatory increased biosynthesis of cholesterol in liver. Therefore the level of cholesterol in diseases of kidneys is usually high.

1. metabolism of proteins – proteins don’t pass through kidneys in urine. Only 2% from nitrogen of urine is amino acids. So, in kidneys the cleavage of proteins occurs or molecules of proteins don’t pass in primary urine and remain in blood plasma.

Endocrine function of kidneys: in kidneys 1,25[OH]2vit.D3 and erythropoetin are formed. Eryhtropoetin stimulates erythrocytes formation in marrow.

Thus, kidneys carry out the next functions: 1) depuration (excretory one); 2) detoxification; 3) regulatory-homeostatic function; 4) metabolic function; 5) endocrine function

Normal and pathologic constituents of urine. Urine analysis – its clinical significance Composition of normal urine

A normal urine has approximately the following composition – volume/24hrs – 1500-2000ml; specific gravity – 1.015-1.025; pH=5.0-7.0

Table 14 The chemical composition of urine

Constituents	The quantity of constituent excreted with urine pro daily, in gram.
Dry rest	47-65
I. organic compounds	22-46
1) urea	20-35
2) uric acid	0.3-1.2
3) creatinine	0.5-1.8
4) hippuric acid	0.1-0.2
5) esterosulfuric acids (f.e., indican)	0.01
6) esteroglucuronic acids	Traces
7) stercobilin	Traces
8) aminoacids (2% from all nitrogen of urine)	1.0-1.3
9) organic acids without nitrogen	~ 0.5
10) vitamins, hormones	Traces
II. inorganic constituents	15-25
1) sodium	3-6.0
2) potassium	2-3.3
3) ammonium	0.6-1.3
4) calcium	0.2-0.3
5) magnesium	0.06-0.2
6) chlorides (Nacl)	3.6-9.0
7) phosphates	0.9-1.3
8) sulfates	1.8-3.0