## **Core Concept**
The cortical collecting duct (CCD) is a part of the nephron in the kidney, playing a crucial role in electrolyte and water balance. It is composed of specific types of cells that facilitate its function.

## **Why the Correct Answer is Right**
The cortical collecting duct contains two main types of cells: **principal cells (or P cells)** and **intercalated cells (or I cells)**. Principal cells are involved in the transport of sodium, potassium, and water, expressing ENaC (epithelial sodium channel) and the potassium channel ROMK. Intercalated cells, on the other hand, are involved in acid-base balance, expressing H+-ATPase.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the cell types found in the cortical collecting duct.
- **Option B:** This option is incorrect as it likely includes cell types not specific to the CCD or omits one of the correct types.
- **Option C:** This option might include cell types relevant to other parts of the nephron or include incorrect cell types for the CCD.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the cortical collecting duct's function is critical in regulating potassium levels, blood pressure, and acid-base balance. The **principal cells** are key in this regulation through their action on sodium and potassium.

## **Correct Answer:** D. Principal cells and intercalated cells.