Chapter Summary

I. KIDNEY

A. Capsule

The capsule is composed of dense, irregular collagenous connective tissue. Occasional fibroblasts and blood vessels may be seen.

B. Cortex

The cortex consists of parts of nephrons and collecting tubules arranged in cortical labyrinths and medullary rays. Additionally, blood vessels and associated connective tissue (renal interstitium) are also present.

1. Cortical Labyrinth

The cortical labyrinth is composed of renal corpuscles and cross sections of proximal convoluted tubules, distal convoluted tubules, and the macula densa region of distal tubules. Renal corpuscles consist of mesangial cells, parietal (simple squamous) and visceral (modiÞed to podocytes) layers of Bowman’s capsule, and an associated capillary bed, the glomerulus, as well as the intervening Bowman’s space, which receives the ultraÞltrate. The afferent and efferent glomerular arterioles supply and drain the glomerulus, respectively, at its vascular pole.

Bowman’s space is drained at the urinary pole into the proximal convoluted tubule, composed of eosinophilic simple cuboidal epithelium with a brush border.The distal convoluted tubule proÞles are fewer in number and may be recognized by the pale cuboidal epithelial cells. The macula densa region of the distal tubule is associated with the juxtaglomerular (modiÞed smooth muscle) cells of the afferent (and sometimes efferent) glomerular arterioles.

2. Medullary Rays

Medullary rays are continuations of medullary tissue extending into the cortex. They are composed mostly of collecting tubules, pars recta of proximal tubules, ascending thick limbs of Henle’s loop, and blood vessels.

C. Medulla

The medulla is composed of renal pyramids that are bordered by cortical columns. The renal pyramids consist of collecting tubules whose simple cuboidal epithelium displays (1) clearly deÞned lateral cell membranes; (2) thick descending limbs of Henle’s loop, whose cells resemble those of the proximal tubule; (3) thin limbs of Henle’s loop, resembling capillaries but containing no blood; and

(4) ascending thick limbs of Henle’s loop, whose cells are similar to those of the distal tubule. Additionally, numerous blood vessels, the vasa recta, are also present, as well as slight connective tissue elements, the renal interstitium. The apex of the renal pyramid is the renal papilla, whose perforated tip is the area cribrosa, where the large collecting ducts (of Bellini) open to deliver the urine into the minor calyx.

D. Pelvis

The renal pelvis, drained by the minor and major calyces, constitutes the beginning of the main excretory duct of the kidney. The transitional epithelium of the minor calyx is reßected onto the renal papilla. The calyces are lined by transitional epithelium. The subepithelial connective tissue of both is loosely arranged and abuts the muscularis, composed of inner longitudinal and outer circular layers of smooth muscle. An adventitia of loose connective tissue surrounds the muscularis.

II. EXTRARENAL PASSAGES

A. Ureter

The ureter possesses a stellate-shaped lumen that is lined by transitional epithelium. The subepithelial connective tissue (sometimes said to be subdivided into lamina propria and submucosa) is composed of a Þbroelastic connective tissue. The muscularis is again composed of inner longitudinal and outer circular layers of smooth muscle, although in its lower portion near the bladder a third, outermost longitudinal layer of smooth muscle is present. The muscularis is surrounded by a Þbroelastic adventitia.

B. Bladder

The urinary bladder resembles the ureter except that it is a much larger structure and does not possess a stellate lumen, although the mucosa of the empty bladder is thrown into folds. The lamina propria is Þbroelastic in character and may contain occasional mucous glands at the internal oriÞce of the urethra. The muscularis is composed of three indeÞnite layers of smooth muscle: inner longitudinal, middle circular, and outer longitudinal.The circular muscle coat forms the internal sphincter at the neck of the bladder. An adventitia or serosa surrounds the bladder. The urethra is described in Chapter 17, ÒFemale Reproductive System,Ó and Chapter 18, ÒMale Reproductive System.Ó

CHAPTER OUTLINE

Graphics

Graphic 17-1 Female Reproductive System p. 414 Graphic 17-2 Placenta and Hormonal Cycle p. 415

Tables

Plates