Okay, let's tackle this question about the endothelium of the cornea. First, I need to recall the basic anatomy of the cornea. The cornea has five layers: epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The endothelium is the innermost layer.

The question is asking which statement is true about the corneal endothelium. The options aren't provided, but the correct answer is given as option D. Wait, the user mentioned the correct answer is D but didn't list the options. Hmm, maybe I need to infer based on common facts about the corneal endothelium.

The endothelium's main function is to maintain the cornea's transparency by pumping excess fluid out of the stroma. They're hexagonal cells, and they don't regenerate once damaged. So any correct statement should relate to their function, structure, or clinical significance.

Common misconceptions might involve confusing the endothelium with the epithelium. For example, the epithelium is the outer layer, while the endothelium is the inner. Also, the endothelium has a high metabolic rate because of their active transport functions. They use the Na+/K+ ATPase pump to regulate fluid.

If the options included something about the endothelium being avascular, that's true. The cornea is avascular throughout, including the endothelium. Another point is that endothelial cell density decreases with age or injury, leading to corneal edema if too many cells are lost.

So, putting this together, the correct answer (D) might state that the corneal endothelium is a single layer of polygonal cells responsible for maintaining corneal deturgescence. The other options could be about regeneration (endothelium doesn't regenerate), being vascular (it's avascular), or having a different function like secretion instead of fluid transport.

**Core Concept**
The corneal endothelium is a single layer of specialized, non-regenerative, hexagonal cells located between the stroma and Descemet’s membrane. Its primary function is to maintain corneal transparency by actively pumping excess fluid out of the corneal stroma via Na⁺/K⁺-ATPase pumps.

**Why the Correct Answer is Right**
The corneal endothelium lacks regenerative capacity once damaged, making it critical for preventing corneal edema. These cells are avascular and do not replicate in adults, relying on adjacent cell expansion to compensate for minor losses. Their function is vital for corneal deturgescence (preventing swelling), which is essential for optical clarity.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect if it claims the endothelium can regenerate—corneal endothelial cells do not regenerate after injury.
**Option B:** Incorrect if it states the endothelium is vascular—the cornea is entirely avascular, including the endothelium.
**Option C:** Incorrect if it attributes secretion to the endothelium—the epithelium (not endothelium) secretes mucins and growth factors.

**Clinical Pearl / High-Yield Fact**
Loss of >50% of endothelial cells (via trauma, surgery, or disease) leads to corneal edema and vision loss. Endoth

✓ Correct Answer: C. It is responsible for maintaining dehydrated state of cornea