During a histology practical, a medical student observes a cross-section of the kidney and identifies the most abundant cell type in the proximal convoluted tubule (PCT). Which of the following cells is most commonly encountered?

Explanation

## Proximal Convoluted Tubule: Cellular Ultrastructure **Key Point:** The proximal convoluted tubule is lined by a single layer of cuboidal epithelial cells characterized by abundant mitochondria, extensive brush border, and high metabolic activity. These cells are the most common cell type in the PCT. ### Histological Features of PCT Epithelium | Feature | Significance | Abundance | |---------|--------------|----------| | Abundant mitochondria | ATP production for active transport | **Defining feature** | | Brush border (microvilli) | Increase surface area for reabsorption | Extensive | | Basal infoldings | Accommodate mitochondria | Prominent | | Cuboidal epithelium | Single layer, simple cuboidal | Standard architecture | | Tight junctions | Paracellular transport | Present but leaky | **High-Yield:** The proximal tubule epithelial cells are the workhorses of the nephron—they perform **65–70% of filtered glucose reabsorption, amino acid reabsorption, and water reabsorption**. The abundant mitochondria reflect this high metabolic demand for active transport. ### Mnemonic: **M.I.T.** for Proximal Tubule - **M**itochondria (abundant) - **I**ntense metabolic activity - **T**ransport (active reabsorption) ### Why Other Options Are Wrong **Principal cells** are the most abundant cell type in the **collecting duct**, not the PCT. They respond to ADH and aldosterone. **Intercalated cells** are specialized acid-base regulatory cells found in the **collecting duct** and are rare in the PCT. **Thin descending limb cells** are simple squamous epithelial cells found in the **loop of Henle**, not the PCT. They lack mitochondria and are specialized for water reabsorption. **Clinical Pearl:** Proximal tubule cells are highly vulnerable to **ischemic injury** (acute tubular necrosis) because their high metabolic demand makes them sensitive to hypoxia. This is the most common cause of acute kidney injury in hospitalized patients. [cite:Robbins Basic Pathology 10e Ch 20]