urinary system – мочевая система kidneys – почки bladder – мочевой пузырь excretory ducts – выделительные трубочки pronephros – первичная почка urogenital – мочеполовой
48. The urinary system: kidneys
The urinary system is the major system involved in the excretion of metabolic waste products and excess water from the body It is also important in maintaining a homeostatic balance of fluids and electrolytes. The urinary system consists of two kidneys, two ureters, the urinary bladder, and the urethra. Urine is produced by the kidneys and is then transmit ted via the ureters to the bladder for temporary storage The urethra is the final pathway that conveys urine to the exterior. This system also has an important endocrine function in the production of renin and erythropoietin, which influence blood pressure and red blood cell (RBC) formation, respec tively. Each kidney is composed of stroma and parenchyma. The stroma consists of a tough fibrous connective tissue capsule and a delicate interstitial connective tissue com posed of fibroblasts, wandering cells, collagen fibrils, and a hydrated proteoglycan extracellular matrix, which is collec tively called the renal interstitium The parenchyma consists of more than one million elaborate uriniferous tubules that represent the functional units of the kidney. The kidney contains a hilum, a cortex, and a medula. The hilum is located medially and serves entrance as the point of entrance and exit for the renal artery, renal veins, and ureter. The renal pelvis, the expanded upper, divides into two or three entrance into the kidney. These, in turn, divide into eight minor calyces. The cortex forms the outer zone of the kidney. The medulla appears as a series of medullary pyramids. Two or three pyramids may unite to form a papilla. Uriniferous tubules consist of two functionally related portions called the nephron and the collecting tubule Glomerulus is made up of several anastomotic capillary loops interposed between an afferent and an efferent arteriole. Plasma filtration occurs in the glomerulus. Bowman’s capsule consists of an inner visceral layer and an outer parietal layer. The space between these layers, the urinary space, is continuous with the renal tubule. Visceral layer is apposed to the glomerulus and closely follows the branches of the glomerular capillaries. The visceral layer is composed of a single layer of epithelial cells resting on a basal lamina, which is fused with the basal lamina of the capillary endothelium. The cells of the visceral layer, call podocytes. Cytoplasmic extensions of podocytes rest on the basal lamina. Between adjacent pedicles, a thin slit diaphragm assists in preventing large plasma proteins from escaping from the vascular system. In fact, most of the components of the glomerular filtrate are reabsorbed in the proximal tubule. Loop of Henle is a hairpin loop of the nephron that extends into the medulla and consists of thick and thin segments. The thick proximal portion of Henle’s loop, or the descending thick segment, is a direct medullary continuation of the cortical proximal convoluted tubule. The thick distal portion of the loop of Henle, the ascending thick segment, ascends to the cortex and is continuous with distal convoluted tubule. The major function of the distal tubule is to reabsorb soduim and chloride from the tubular filtrate. Collecting tubules consist of arched and straight segments.
urea – моча stroma – строма parenchyma – паренхима fibrous capsule – волокнистая капсула delicate – тонкий interstitial – промежуточный
49. The urinary system: kidney vascular sypply
Vascular supply begins with the renal artery, enters the kidney the hilum, and immediately divides into interlobar arteries The arteries supply the pelvis and capsule before passing direct between the medullary pyramids to the corticomedullary junction The interlobar arteries bend almost 90 degrees to form shoarching, arcuate arteries, which run along the corticomedullary junction. The arcuate arteries subdivide into numerous fine interlobul arteries, which ascend perpendicularly to the arcuate arteries through the cortical labyrinths to the surface of the kidney. Each interlobular artery passes midway between two adjacent medullary rays. The interlobular arteries then give off branches that become the afferent arterioles of the glomeruli. As the afferent arteriole approaches the glomerulus, some its smooth muscle cells are replaced by myoepithelioid cells, which are part of the juxtaglomerular apparatus. The juxtaglomerular apparatus consists of juxtaglomerular cells, polkissen cells, and the macula densa. Cells of the distal convoluted tubule near the afferent arteriole are taller and more slender than elsewhere in the distal tubule. The juxtaglomerular cells secrete an enzyme called renin, which enters the bloodstream and converts the circulating polypeptide angiotensinogen into angiotensin I. Angiotensin I is converted to angiotensin II, a potent vaso constrictor that stimulates aldosterone secretion from the adrenal cortex. Aldosterone increases sodium and water reabsorption in the distal portion of the nephron. Their nuclei are packed closely, so the region appear darker under the light microscope. The macula densa is thought to sense sodium concentration in the tubular fluid. Polkissen cells are located between the afferent and ef-fer ent arterioles at the vascular pole of the glomerulus, adja cent to the macula densa. Their function is unknown. Efferent glomerular arteriole divides into a second system of capillaries, the peritub-ufar plexus, which forms a dense net work of blood vessels around the tubules of the cortex. Arterial supply of the medulla is provided by the efferent arte rioles of the glomeruli near the medulla. The arterio-lae rectae and the corresponding venae rectae with their respective capillary networks comprise the vasa recta, which supplies the medulla. The endothelium of the venae rectae is fenestrated and plays an important role in maintaining the osmotic gradi ent required for concentrating urine in the kidney tubules.