Chapter 9 • Urinary System
ChapterSummary
•The kidney has 3 major regions: the hilum, cortex, and medulla.
-The hilum is the point of entrance and exit forthe renal vessels and ureter. The upper expanded portion of the ureter is called the renal pelvis, and divides into 2 or 3 major calyces and several minor calyces.
-The cortex has several renal columns that penetrate the entire depth of the kidney.
-The medulla forms a series of pyramids that direct the urinary stream into a minor calyx.
•The uriniferous tubule is composed of the nephron and collecting tubule.
-The nephron contains the glomerulus (a tuft of capillaries interposed between an afferent and efferentarteriole). Plasma filtration occurs here. Bowman's capsule has an inner visceral and outer parietal layer. The space between is the urinary space. The visceral layer is composed of podocytes resting on a basal lamina, which is fused with the capillary endothelium. The parietal layer is composed of simple squamous epithelium that is continuous with the proximal tubule epithelial lining. The proximal convoluted tubule is the longest and most convoluted segment ofthe nephron. Most of the glomerular filtrate is reabsorbed here. The loop ofHenle extends into the medulla and has a thick
and thin segment. It helps to create an osmotic gradient important for concentration ofthe tubular filtrate. The distal convoluted tubule reabsorbs sodium and chloride from the tubular filtrate.
-The collecting tubules have a range of cells from cuboidal to columnar. Water removal and urine concentration occur here with the help ofthe antidiuretic hormone. The blood supply is via renal artery and vein.
•The vasa rectae supply the medulla. They play an important role in maintaining the osmotic gradient. The juxtaglomerular apparatus OGA) is composed ofjuxtaglomerular cells, which are myoepithelial cells in the afferent arteriole. They secrete renin. The JGA also contains Polkissen cells (function unknown), located between afferent and efferent arterioles, and the macula densa. Macula densa cells are located in the wall ofthe distal tubule, located near the afferent arteriole. They sense sodium concentration in tubular fluid.
