## Core Concept
Holocrine glands are a type of exocrine gland that secrete their products by releasing entire cells. This process involves the disintegration of the glandular cells to release their product. Holocrine glands are typically found in the skin and are involved in various functions, including lubrication and protection.

## Why the Correct Answer is Right
The correct answer, **D. Sebaceous glands**, is right because sebaceous glands are a classic example of holocrine glands. They produce sebum, an oily substance that helps to lubricate and protect the skin and hair. The process of sebum production involves the accumulation of lipids in the cytoplasm of sebaceous gland cells, which eventually rupture to release sebum into the ducts.

## Why Each Wrong Option is Incorrect
* **Option A:** Salivary glands are primarily merocrine glands, which secrete their products through exocytosis without losing part of the cell. Therefore, they do not fit the definition of holocrine glands.
* **Option B:** Sweat glands (eccrine glands) are also merocrine glands, releasing their secretions through exocytosis without cell damage or loss.
* **Option C:** Mammary glands are considered apocrine glands during lactation, as they release a portion of the cell along with the secretory product. However, they are not holocrine glands.

## Clinical Pearl / High-Yield Fact
A key point to remember is that holocrine glands, like sebaceous glands, are involved in the production of sebum, which plays a crucial role in skin health. Disorders of sebaceous glands, such as acne, are common and can be related to overproduction of sebum.

## Correct Answer: D. Sebaceous glands