Hormones

Overview of cells

Exocrine glands can be classified either by how they secrete their products (merocrine, apocrine, holocrine) or by the nature of the secretion itself (serous, mucous). This question categorizes the lacrimal gland by its watery, enzyme-rich secretion.

Classification by Product Type

Serous

• Characteristics: Produces a thin, watery fluid that is rich in proteins, antibodies, and enzymes (such as lysozyme).
• Lacrimal Gland Connection: The lacrimal gland secretes tears, which are almost entirely water, electrolytes, and protective antimicrobial proteins (lysozyme). This makes it a textbook example of a purely serous gland. Other examples include the parotid salivary gland and the exocrine pancreas.

Mucous

• Characteristics: Produces a thick, viscous, slimy secretion rich in glycoproteins called mucins.
• Function: Acts primarily as a lubricant and protective barrier. Examples include sublingual glands, goblet cells, and mucous glands of the respiratory tract.

Classification by Secretion Mechanism

If the question had instead focused on the cellular mechanism of secretion, the lacrimal gland would technically also be classified as a merocrine gland. Here is how those three mechanisms break down:

• Merocrine (Eccrine): The cell releases its product via standard exocytosis through the cell membrane. The secretory cell remains completely intact and undamaged.
  • Note: The lacrimal gland utilizes this mechanism to release its serous fluid.
• Apocrine: The secretory product accumulates at the apical tip of the cell. That entire top portion of the cell pinches off along with the secretion. The cell then repairs itself.
  • Examples: Mammary glands and axillary sweat glands.
• Holocrine: The entire secretory cell fills up with the product, matures, and then completely ruptures/dies to release its contents.
  • Example: Sebaceous (oil) glands of the skin.