Urinalysis

Urinalysis - basic concepts

Kidney, as excretory organ, excreted metabolites, in particular, nitrogenous end products of protein and other analytes. Furthermore, as an endocrine organ, the kidneys participate in the metabolism of the renin-angiotensin and the kinin-kallikrein system, the glucose metabolism, produce erythropoietin, prostaglandin, vitamin D.

Urine is the end product of renal activity. The formation and excretion of urine by the kidneys is carried by glomerular filtration and diffusion, tubular reabsorption and secretion. The functional activity of the kidneys leads to the maintenance of acid-base balance and regulation of electrolyte and water balance of the body, the regulation of the osmotic state of the blood and tissues, contributes to maintaining homeostasis.

Urine contains water, metabolites, electrolytes, trace elements, hormones, vitamins, exfoliated cells and tubules urinary tract mucosa, leukocytes, salts mucus.

Structural-functional unit of kidney is nephron, which consists of a glomerulus and tubule. The glomerular filtrate (primary urine) contains all low molecular weight non-protein part of blood plasma, in the same concentration as in plasma. Primary urine specific gravity - 1,010; pH - 7.4; viscosity - 1.02. Primary urine contains proteins with molecular mass less than 70 kDa. Their number varies from 30-50 up to 70-80 mg per day.

In the renal tubule occurs reabsorption and substances secretion due to activity of renal tubular epithelium. Reabsorption of substances from the primary urine, and secretion by renal epithelium into the lumen of the tubules substances from capillaries near-tubular or formed in tubular epithelium, leads to the formation of the final urine.

Proximal tubule cells mainly provide the preservation of most of the substances, filtered at the glomerulus. They reabsorbed protein, amino acids, glucose, vitamins, various electrolytes and about 80% water. About the proximal tubule is judged by the transport of glucose.

Loop of Henle (thin segment of the tubule) acts as a counter-duplicating systems: two adjacent tubules in which the fluid flows in the opposite direction, ensuring the processes of concentration and dilution of urine.

The distal tubules and collecting ducts carry the stability of acid-base status, regulate the constancy of the water balance and electrolyte composition of the internal environment of the body, providing a certain blood concentration of ions - K, Na, Ca, Mg, Cl, HPO4 and others. The maintenance of acid-base status also depends on the ability of renal epithelial cells to secrete substances (H-ions as a result of acidogenesis and ammonia due to the renal ammonium synthesis), which replaces Na, keeping alkaline valence to the body, and as the basis used for removal of acid valences.

Osmotic dilution of urine and its concentration allows to make a conclusion about the state of the distal segment of the nephron and collecting ducts.

Collecting tubes are a continuation of the distal tubule. Ending in papillae, collecting tube opens into the renal calyx. From there, the urine flows through the ureters into the bladder. The structure of the walls of the renal calyx, pelvis, ureters, bladder, excretory ducts of the prostate and urethra are similar. Their mucosa is lined with transitional epithelium. Stratified squamous epithelium lined the urethra, vagina, external genitals of the woman and the distal (outer) part of the urethra men.

In normal urine sediment can be found a small number of squamous cells and isolated cells of transitional epithelium. Increasing the number of transitional epithelial cells and the appearance of the renal epithelium is characteristic of kidney and urinary tract diseases.

The basis of kidney disease is damage of glomerular membrane or tubular epithelial by inflammatory, infectious, toxic, or other processes, or genetically determined defect, causing a impaired structure and function.

There are kidney disease, mainly affecting the glomeruli (acute and chronic glomerulonephritis, nephro-angiosclerosis, nephrosis) and with a primary lesion of the renal tubules (acute and chronic pyelonephritis, acute and chronic renal insufficiency of any etiology).