OBJECTIVES : At the end of this laboratory you should be able to:

1. Identify the kidney, ureter, and urinary bladder microscopically.

2. Distinguish between the cortex and medulla of the kidney.

3. Identify the segments of the nephron, ie, the proximal tubule, distal tubule, and Bowman's capsule with the glomerulus and the loop of Henle.

4. Identify medullary rays, distinguishing them from other regions of the kidney cortex

5. Identify the arteries, arterioles, capillaries, and veins, relating them to the nephron and collecting ducts.

6. Identify the macula densa and understand its relationship to the glomerulus.

7. Identify the urinary and vascular poles of Bowman's capsule.

8. Correlate the light microscopy of each part of the nephron with its ultrastructure.

SLIDES FOR THIS LABORATORY : 35, 36, 37, and Supplemental Slides 111, 112.

Slide 35 Kidney.

Observe the cortex , medulla , and delicate connective tissue capsule . Note the relatively large arteries and veins between the cortex and medulla. These are the arcuate arteries and veins . Recall that arcuate arteries give rise to interlobular arteries which run through the cortex. From the interlobular arteries, the afferent arterioles branch off to supply the kidney glomeruli.

Renal corpuscles (glomerulus + Bowman's capsule) as well as the proximal and distal convoluted tubules are found in the cortex. One can distinguish proximal convoluted tubules from distal convoluted tubules by these characteristics:

1) Staining - proximal tubules are more eosinophilic than the distal.

2) Nuclei - proximal tubule cells have more heterochromatic nuclei than those of distal tubule cells; and there are more nuclei per unit area in the distal tubule than there are in the proximal tubule.

3) Cytoplasm - the distal tubule cells appear with less cytoplasm.

4) Microvillus "brush" border - in the proximal convoluted tubules the “brush” border has sloughed and can be seen in the lumen; thus, the lumen appears partially filled.

Observe the medullary rays and identify collecting tubules within the rays. Identify the vascular and urinary poles of the renal corpuscles. Also observe the parietal layer of Bowman's capsule , the urinary space , and podocytes . Find the macula densa of the distal convoluted tubule.

Carefully study the medullary region and note the vasa recta , thin and thick limbs of the loop of Henle , and collecting ducts . Collecting ducts in the medulla are distinguished by the clarity with which the borders of adjacent lining cells stand out.

Supplemental Slide 111 Kidney.

In this slide, the tubules are better preserved. The proximal tubule nuclei are smaller and stain more intensely than those of the distal tubules .

Slide 36 Ureter.

Observe the transitional epithelium . Examine the layers of smooth muscle . Inner longitudinal and outer circular layers are distinguishable in this slide. Note the lamina propria . The obvious spaces in this layer are artifact caused by excessive shrinkage and extraction of ground substance.

Supplemental Slide 112 Ureter.

This is a special preparation in which a more stretched ureter is placed next to a more contracted one. Note the morphology of the transitional epithelium in the distended and partially relaxed states and compare both of these with the nearly fully contracted ureter in Slide 36.

Slide 37 Urinary Bladder.

Note the mucosa , submucosa , muscularis , and the serosa or peritoneal surface of the bladder. Observe the inner longitudinal, middle circular and outer longitudinal bands of smooth muscle in the muscularis. Examine the transitional epithelium with its characteristic dome shaped surface cells. Observe any nerves or autonomic ganglion cells in the bladder wall.