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.

renal artery – почечная артерия

renal veins – почечные вены

expanded upper – расширенный верхний

minor calyces – незначительные чашечки

to supply – снабжать

arcuate arteries – дугообразные артерии

to subdivide – подразделять

numerous – многочисленный

interlobul – междолевой

to ascend – поднимать

perpendicularly – перпендикулярно

arcuate arteries – дугообразные артерии