The main function of the urinary system is to excrete, which is nitrogen-containing waste product of protein metabolism. Urea is formed in liver from ammonia, which is derived from the breakdown of amino acids ( simple proteins) in the body cells. The urea is carried in the bloodstream to the kidneys.


The urinary system includes the kidneys, right and left; the ureters (renal ducts) (muscular tubes from each kidney lined with mucous membrane, which convey urine to the urinary bladder); the urinary bladder which is a hollow muscular sac; for temporary collection of urine and the urethra which is a tube through which urine is discharged from the urinary bladder and passed out of the body.

The kidneys are bean-shaped organs embedded in a cushion of adipose tissue and located behind the abdominal cavity. They consist of an outer cortex part and an inner medullar part. The kidneys can be compared with the filters because they perform the filtration of waste products from the blood. These waste products are brought to the kidneys via the renal arteries which branch into the kidneys and are rather short and thick.

The process of filtration and formation of urine takes place within the tiny tubules of the kidney. Besides, renal functions include participation in the control of: volume of blood and other fluids of the body; protein, lipid and carbohydrate metabolism; arterial pressure; erythropoesis; coagulation of blood and some тоге functions. Thus, the kidney is an organ that participates in ensuring the constancy of the main physicochemical con stants of the blood and other fluids within the body and contributes to the regulation of metabolism of various organic substances. Depending on the water balance in the organism, the kidneys produce diluted and concentrated urine. The urine тау contain many substances found in the blood plasma, as well as some compounds synthesized in the kidney itself.

The volume of urine discharge by a healthy individual тау vary widely and depends on the condition of water balance. The colour of the urine depends on the diuresis and the excretion of pigments; it changes from light yel Іон to orange. The pigments form from biliary bilirubin in the intestine where it is converted to urobilin and urochrome which are partly absorbed in the intestine and excreted by the kidneys. Some of the urinary pigments are products of haemoglobin breakdown oxidized in the kidney. Urine formed in the renal tubules passes into the renal pelvis and fills it gradually. When the filling threshold is reached, the signal of which is given by the baroreceptors the pel и muscles contract, the ureteral lumen opens and the urine flows into the urinary bladder. With the gradual increase of the volume of urine the walls of the bladder are stretched. In the initial stage of filling the tension of the walls does not change, and pressure in the bladder does not grow. When the volume of the urine reaches a definite level, tension of the smooth-muscle walls of the bladder increases sharply, the pressure of fluid in its cavity rises, and the complex reflex act of micturition occurs. Movement of urine along the urethra plays an important role in the act of micturition as it stimulates contraction of the bladder by reflex.

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