Urinary System
Learning Objectives:
Describe the structure of the renal cortex vs. medulla and correlate it with functions of both
Describe the structure of each segment of the nephron
Describe the morphology of the juxtaglomerular apparatus and explain its function during regulation of the circulatory and renal systems
Distinguish collecting tubules from nephron tubules
Explain the circulation of the kidney
Describe the microstructure of the ureter, urinary bladder, and urethra and correlate it with the function and location in the body
Describe the microstructure of the medulla and cortex of the adrenal gland and correlate each with its origin and function
No Slide:
Draw a schematic representation of the passage of urine from the kidneys to the urethra. What happens in each part of the kidney?
Iowa Virtual Slidebox: Kidney (256); Kidney (236)
Examine this slide with your naked eye or at minimum zoom. How can you distinguish between the cortex and the medulla at first glance?
The cortex is slightly more darkly-staining than the medulla, and contains more circular structures (convoluted tubules and glomeruli) while the medulla contains only “straight” structures.
Examine the junction between cortex and medulla. This junction is irregular. The cortex is subdivided into alternating regions: 1) the cortical labyrinth consisting of glomeruli and convoluted tubules and 2) the medullary rays consisting primarily of radially directed straight segments of the loop of Henle and collecting tubules.
What are the different regions/components of a nephron? Draw them below.
Your drawing should include the renal corpuscle, proximal tubule (with convoluted and straight parts), the loop of Henle (with thin descending, thick ascending, and thick ascending limbs), the distal tubule (with convoluted and straight parts, and end with a connecting tubule.
Within the renal corpuscle identify the vascular capillary tuft called the glomerulus. Search for a renal corpuscle in which you can identify the vascular pole. What happens here? What lies opposite of the vascular pole?
The vascular pole is where afferent arteries enter the renal corpuscle and efferent arteries exit. The urinary pole lies on the opposite side.
What is the capsule of the glomerulus called? This structure has a visceral and parietal layer. The parietal layer is continuous with which other structure?
Bowman’s Capusle/Renal capsule. The squamous cells of the parietal layer become more cuboidal at the urinary pole, where they are continuous with the proximal convoluted tubule.
The proximal convoluted tubules surround glomeruli and are abundant. What type of epithelium do they have? How would you describe how it stains?
They have a simple cuboidal to low columnar epithelium. They have a lumen that is “fuzzy” and cells are larger, resulting in fewer nuclei visible in each section.
What is the juxtaglomerular apparatus? What two types of cells comprise it? What enzyme doses its cells release?
The juxtaglomerular apparatus is a part of the distal tubule that contacts the vascular pole of a glomerulus. IT is comprised of macula densa cells (part of the distal tubule) and of juxtaglomerular cells, which are modified smooth muscle cells mostly on the afferent afteriole. These cells secrete renin.
The distal convoluted tubules of a nephron are in close contact with the macula densa. What type of epithelium do they have? How would you describe how it stains? Contrast this with the staining of the proximal tubules.
DCTs have a cuboidal epithelium. These cells stain very similar to the proximal tubule, but are smaller, resulting in more nuclei present in each cross section, and also have no brush border, so their lumen is more clearly defined.
Iowa Virtual Slidebox Kidney (224) (222)
Move on to the medullary rays of the kidney. Identify the collecting tubules. How can you differentiate these cells from those of the distal convoluted tubule?
Collecting duct cells (Principal cells) are more lightly staining. Additionally collecting ducts also have intercalated cells, which bulge into the lumen of the collecting duct and stain more darkly.
Iowa virtual slidebox: Kidney (236)
Examine the cortical labyrinth and rays as described previously. Be certain that you understand the blood supply of the renal corpuscle, the convoluted tubules, and the loop of Henle, and the functional significance of these. Consult your textbook and its illustrations.
Your description should include the branches of the renal artery that contribute to the glomerulus, and then continue on to discuss the vasa recta and peritubular capillaries.
The ureter connects the renal pelvis to the bladder. Observe these sections at low power first to see if you can make out four distinct layers. What are these? (There may also be sublayers of, e.g., muscularis!)
From the lumen out:
Epithelium (Transitional or urothelium)
Connective tissue layer (lamina propria)
Muscularis (with inner longitudinal and outer circular layers) – note that near the urinary bladder, you might see an additional outer longitudinal layer.
Adventitia (sometimes you’ll also observe a serosa, e.g., Iowa Ureter 257
Iowa Virtual Slidebox: bladder 375
What are the layers of the urinary bladder? How do they compare with those of the ureter?
The urinary bladder has, from the lumen out:
Transitional epithelium
Submucosa (absent in the ureters!)
Muscular layers (VERY loosely arranged into 3 layers, but more like interlacing bundles)
Adventitia
Iowa Virtual Slidebox: Bladder (258) Urinary bladder (229)
What type of epithelium exists in the bladder? What is special about this type of eptithelium?
Note: Begin by observing this epithelium in 258, but then move on to see less pristine examples in the other bladder and ureter slides.
Urothelium/Transitional epithelium with umbrella cells. The cells that bulge into the lumen are called “dome” cells or “umbrella” cells, and become flattened when the bladder is distended.
Optional: Sometimes dome cells are binucleate. Cruise along and see if you can find a binucleate dome cell
Iowa Virtual Slidebox: Bladder (230)
This bladder has been processed in such a way as to preserve it in its distended state. Observe the differences between the apical layer of cells in this preparation vs. the other examples of transitional epithelium.
Iowa Virtual Slidebox: Urethra (male) 231
Observe here that urethra passes through the corpus spongiosum of the penis. This erectile body is filled with vascular channels and covered by a connective tissue layer called the tunica albuginea.
Turn your attention to the epithelial lining of the penile urethra and try to find patches of stratified columnar epithelium and stratified squamous epithelium. Both are present throughout most of the urethra’s length, but stratified squamous becomes more common distally.
Iowa Virtual Slidebox: Urethra (female) 376
The female urethra transitions from transitional epithelium to a stratified squamous epithelium. In addition to a venous plexus that surrounds the urethra, the female urethra is also surrounded by smooth and skeletal muscle.