Physiology · Reproduction, pregnancy and the fetus
Lactation !
- Regulation
- Exam priority: medium
After birth prolactin makes the breast produce milk and oxytocin squeezes it out when the baby sucks.
Updated 2026-11-01
Also called: Milk production, Milk ejection reflex
See it in 3D: Mammary gland lobes · Lactiferous ducts · Nipple · Areola · Pituitary gland
What it is
Pregnancy hormones grow the breast's ducts and alveoli, but high estrogen and progesterone block milk secretion. When the placenta is delivered those hormones fall, and prolactin can act: milk comes in over 2–4 days. Suckling then keeps prolactin high (production) and triggers oxytocin release (ejection). Regular emptying of the breast keeps supply matched to demand.
Hormone axes and feedback
Prolactin axisLesion None (normal)
Tap a box to see the hormone, or choose a lesion to see the lab pattern.
- Stimulates (+)
- Inhibits / negative feedback (−)
- Level ↑
- Level ↓
Typical values
| Parameter | Value | Note |
|---|---|---|
| Onset of copious milk | ≈2–4 days postpartum | later after cesarean or with retained placenta |
| Milk volume, established lactation | ≈750–800 mL/day | exclusive breastfeeding |
| Energy of mature milk | ≈65–70 kcal/100 mL |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Regulation
- +Suckling (nipple stimulation): Lowers dopamine → prolactin surge; triggers oxytocin release.
- +Prolactin: Milk protein, lactose and fat synthesis in alveolar cells.
- +Oxytocin: Myoepithelial contraction: milk let-down (also triggered by the baby's cry).
- −Dopamine (hypothalamus): Tonic inhibition of prolactin.
- −Estrogen and progesterone (pregnancy): Block milk secretion until the placenta is delivered.
- −Milk stasis (feedback inhibitor of lactation), stress, pain: Lower production or block let-down.
Clinical notes
- Mastitis usually comes from milk stasis with or without infection; untreated it can form a breast abscess.
- Sheehan syndrome: pituitary necrosis after severe postpartum hemorrhage; the first sign is often failure to lactate.
- A prolactinoma or dopamine-blocking drugs can cause galactorrhea and amenorrhea outside pregnancy.
Test yourself
Think of the answer, then tap the question to see it.
Prolactin is high throughout pregnancy. Why does copious milk begin only after delivery?
High placental estrogen and progesterone block prolactin's action on alveolar cells. When the placenta is delivered they fall and secretion starts within 2–4 days.
Why does exclusive breastfeeding delay the return of ovulation?
Frequent suckling keeps prolactin high, which suppresses GnRH pulses and therefore LH and FSH, so follicles do not mature.
A woman fails to breastfeed after a massive postpartum hemorrhage. What happened?
Sheehan syndrome: the enlarged pituitary of pregnancy infarcts with hypotension, so prolactin (and other anterior pituitary hormones) are lost.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Prolactin and its control by dopamine
- The posterior pituitary: ADH and oxytocin
- The placenta and pregnancy hormones
- Parturition: onset and uterine contraction
Related conditions
In Biochemistry
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 28.6 Lactation (OpenStax (Rice University), 2022); Acute Mastitis (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 83). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.