Histology Mentor

Urinary System, Questions 95-101

95. Question - Diagram the features that are seen on a frontal slice of the human kidney including the major blood vessels.

Major calyces empty into the renal pelvis and are formed by the fusion of minor calyces. The renal sinus contains the major and minor calyces, the renal pelvis, branches of the renal artery and vein and fat.

96. Question - Diagram a nephron (uriniferous tubule) showing the locations of its components within the renal lobe. What is a renal lobule? Where does the nephron end?

A renal lobule consists of the collecting ducts and nephrons that contribute to one medullary ray. The nephron ends where it joins the collecting duct.

97. Question - Diagram the fine structure of a renal corpuscle and structures related to it.

The vascular pole is where the arterioles enter and leave and the urinary pole is where the proximal tubule begins.

98. Question - Illustrate the fine structure of each of the tubular components of the nephron.

One or two cilia have been demonstrated on many of the cells in all parts of the nephron of rat and human. They are thought to serve a sensory function.

99. Question - Very briefly explain the function of each of the components of the nephron.

Filtration occurs through the fenestrated capillaries of the glomerulus in the renal corpuscle to enter the urinary space by passing through the basement membrane and the filtration slits between the podocyte processes (pedicels). Podocytes support the capillaries and the basal lamina is the ultimate filter. Reabsorption of about 85% of the glomerular filtrate occurs in the proximal tubule along with 100% of the glucose, amino acids and other nutrients. The renal loop establishes and maintains the high osmolality of the renal pyramid. The descending thin segment equilibrates with the interstitium, the ascending segment actively pumps solutes into the interstitium but not water. The distal tubule is involved with maintaining electrolyte balance both by influencing, via the macula densa, the secretion of renin by the juxtaglomerular cells in the afferent arteriole and by responding to changes in aldosterone.

100. Question - Diagram the entire length of a collecting duct indicating its locations within the renal lobe. Explain the difference in the vascular supply to the cortex and medulla.

Efferent arterioles leaving renal corpuscles that are located near the medulla (juxtamedullary nephrons) turn down into the medulla as a tassel (vasa rectae). Both descending and ascending non-fenestrated vessels are in the tassel allowing countercurrent exchange to take place. Efferent arterioles of all other renal corpuscles supply the fenestrated peritubular capillary network of the cortex.

101. Question - Identify the characteristic features of the ureter and urinary bladder. Diagram and explain the significance of the fine structure of transitional epithelium.

The ureter is a small tube with a stellate lumen. Its lamina propria is dense connective tissue without glands or muscularis mucosae. The mucosa of the urinary bladder is similar. They both are lined by transitional epithelium, also called urothelium. The surface cells of this epithelium are adapted to protect the underlying cells and to greatly increase the surface membrane when distended - see diagram.

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