14.07 Identify Parts of a Nephron in Images

When examining diagrams, photomicrographs, or electron micrographs of kidney sections, use the following tips to help identify key nephron structures and blood vessels.

Key Structures to Identify

1. Glomerulus:
   • Found in the cortex, it is a small, dense capillary network.
   • Surrounded by Bowman’s capsule, it will often appear as a cluster of small circular spaces in section views.
2. Bowman’s Capsule (Renal Capsule):
   • Surrounds the glomerulus in the cortex.
   • Look for a thin, cup-like structure around the glomerulus, appearing as a circular or oval shape in cross-sections.
3. Proximal Convoluted Tubule (PCT):
   • Located in the cortex, close to the glomerulus.
   • Identifying Feature: Microvilli on the luminal surface, giving it a fuzzy or dense appearance in micrographs.
   • Cuboidal epithelial cells in the PCT are packed with mitochondria, though mitochondria may not always be visible in all images.
     
     
4. Loop of Henle:
   • Extends from the cortex into the medulla.
   • Has distinct segments:
     • Thin Segment: Thinner, less densely packed cells, often visible in the descending limb.
     • Thick Segment: Thicker with cuboidal cells, often found in the ascending limb.
5. Distal Convoluted Tubule (DCT):
   • Located in the cortex, near the collecting ducts.
   • Distinguishing Feature: Absence of microvilli, giving it a clearer lumen than the proximal tubule.
6. Collecting Duct:
   • Runs through the medulla.
   • Larger diameter than other tubules, often with clearly defined cell borders and no microvilli.
   • Appears pale or clear, surrounded by thick walls compared to nearby nephrons.

Tips for Differentiating Between the Cortex and Medulla

• Cortex:
  • Contains the glomeruli and Bowman’s capsules.
  • Look for the proximal convoluted tubules, identifiable by their microvilli. Only the cortex has microvilli-rich proximal tubules.
• Medulla:
  • Contains loops of Henle and collecting ducts.
  • Proximal convoluted tubules and glomeruli are absent, which is a quick way to determine if you are in the medulla.

Histological Characteristics to Note

Collecting Ducts:

• Wide, with visible cell borders and a larger lumen.

Microvilli Presence:

• Only proximal convoluted tubules have microvilli on their inner surface, which helps increase surface area for reabsorption.

Cell Density and Thickness:

• Thick Segment of the Loop of Henle: Larger cuboidal cells, compared to the thin segment.
• Thin Segment of the Loop of Henle: Narrower lumen, lined with squamous cells.