Arrange in order lobes lobules with cluster of acini lactiferous duct lactiferous sinus
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Here is the correct anatomical order, arranged from the largest structural unit down to the smallest, following the path milk takes from production to the nipple:
Breast Structural Hierarchy (Largest → Smallest / Production → Exit)
| Order | Structure | Description |
|---|---|---|
| 1 | Lobe | The breast has 15-20 lobes of glandular tissue, separated by connective tissue and adipose tissue |
| 2 | Lobule | Each lobe contains 20-40 lobules (also called terminal duct lobular units, TDLUs) |
| 3 | Cluster of acini | Each lobule is composed of 10-100 acini (alveoli) - the actual milk-secreting units |
| 4 | Lactiferous duct | Small ductules from the acini drain into lactiferous ducts; each lobe ends in one major lactiferous duct (2-4 mm diameter) |
| 5 | Lactiferous sinus | Each lactiferous duct dilates into a lactiferous sinus (ampulla) just beneath the nipple-areolar complex, acting as a small reservoir |
Then → Nipple opening (the duct constricts again to a 0.4-0.7 mm orifice at the nipple surface)
Memory aid (large to small):
Lobes → Lobules → Acini → Lactiferous duct → Lactiferous sinus → Nipple "Lovely Ladies Always Love Licking Nipples" (mnemonic)
Key point:
The lactiferous sinus comes after the lactiferous duct in the flow direction (acini → duct → sinus → nipple), but structurally the sinus is a dilation of the duct located subareolarly. Some texts list the sinus before the duct opening at the nipple, but in terms of milk flow: acini produce milk → drain into ducts → collect in sinuses → exit at nipple.
- Sabiston Textbook of Surgery, 28th ed.: "There are 15 to 20 lobes, each ending with a lactiferous duct...Each of these major ducts has a dilated portion (lactiferous sinus) below the NAC and progressively branches and ultimately ends in the terminal ductules or acini."
- Mulholland & Greenfield's Surgery, 7th ed.: "Each lobe is composed of 20 to 40 lobules, which are themselves composed of 10 to 100 alveoli. Each lobe ends in a lactiferous duct that dilates into lactiferous sinuses, which then open through constricted orifices into the nipple."
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