Holocrine Glands: Sebaceous Glands as Prototypical Example

Holocrine (hypocrine) secretion = cell accumulates product → ruptures → releases cellular debris + product.

Mechanism

1. Basal cells proliferate → differentiate → migrate centrally.
2. Cytoplasm fills with lipid droplets (sebum).
3. Nucleus pyknotic → membrane disintegrates → whole cell secreted.
4. New cells replace.

Sebaceous Glands

• Attached to hair follicles (except Meibomian, Fordyce).
• Androgen-regulated (testosterone → DHT via 5α-reductase).
• Sebum: Triglycerides, wax esters, squalene, cholesterol. Lubricates, waterproofs, antimicrobial.

Other Holocrine Glands

• Meibomian (tarsal) — eyelid lipid layer.
• Zeis/Moll (eyelash) — modified sebaceous/sweat.

Contrast

• Merocrine (eccrine): Exocytosis (sweat, salivary, pancreas).
• Apocrine: Apical bleb pinched off (axillary, genital, mammary).