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 myoepithelio—id cells, which are part of the juxtaglomerular apparatus. The juxtaglomerular apparatus consists of juxtaglomeru—lar 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 re—nin, which enters the bloodstream and converts the circulating polypeptide angiotensinogen into angiotensin I. An—giotensin 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.
New words
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
50. The urinary system: ureters, uretra
The calyces, renal pelves, and ureters constitute the main excretory ducts of the kidneys. The walls of these structures, in particular the renal pelvis and ureter, consist of three coats: an inner mucosa, middle muscularis, and an outer adventitia.