Official reprint from UpToDate®
www.uptodate.com ©2017 UpToDate, Inc. and/or its affiliates. All Rights Reserved.

Physiology of lactation

Richard J Schanler, MD
Debra C Potak, RN, BSN, IBCLC
Section Editor
Steven A Abrams, MD
Deputy Editor
Alison G Hoppin, MD


The breast undergoes dramatic changes in size, shape, and function in association with puberty, pregnancy, and lactation. These changes are critical to successful breastfeeding.

The physiology of lactation is reviewed here. The stages of breast development and breast anatomy are discussed elsewhere. (See "Breast development and morphology".)


The breast is composed of a stroma consisting of fat and connective tissue that supports a tubuloalveolar parenchyma (figure 1) [1]. The normal breast tissue of adult women contains three types of lobules, known as types 1, 2, and 3. Formation of type 1 lobules (Lob 1) begins with puberty (picture 1). The changing levels of estrogen and progesterone during menstrual cycles stimulate Lob 1 to sprout new alveolar buds and evolve to more mature structures called type 2 and type 3 lobules (Lob 2 and 3) (picture 2 and picture 3 and picture 4). After puberty is completed, further maturation of the breast does not occur except during pregnancy. (See "Breast development and morphology".)

Pregnancy — The alveolar development and maturation of the epithelium that occurs in response to the hormonal changes of pregnancy is known as stage II mammogenesis [1]. Progesterone plays an important role in stimulating alveolar development during this phase [2,3].

The maximum branching capability of the breast is expressed during this period. The secretory acinus that is formed represents a terminal outgrowth that marks the full extent of glandular differentiation.

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:

Subscribers log in here

Literature review current through: Oct 2017. | This topic last updated: Jun 23, 2016.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2017 UpToDate, Inc.
  1. Neville MC. Anatomy and physiology of lactation. Pediatr Clin North Am 2001; 48:13.
  2. Plath A, Einspanier R, Peters F, et al. Expression of transforming growth factors alpha and beta-1 messenger RNA in the bovine mammary gland during different stages of development and lactation. J Endocrinol 1997; 155:501.
  3. Neville MC, McFadden TB, Forsyth I. Hormonal regulation of mammary differentiation and milk secretion. J Mammary Gland Biol Neoplasia 2002; 7:49.
  4. Russo J, Russo IH. The Mammary Gland, Neville MC, Daniel CW (Eds), Plenum Press, New York 1987. p.67.
  5. Dewey KG, Nommsen-Rivers LA, Heinig MJ, Cohen RJ. Risk factors for suboptimal infant breastfeeding behavior, delayed onset of lactation, and excess neonatal weight loss. Pediatrics 2003; 112:607.
  6. Neville MC, Morton J, Umemura S. Lactogenesis. The transition from pregnancy to lactation. Pediatr Clin North Am 2001; 48:35.
  7. Anderson AM. Disruption of lactogenesis by retained placental fragments. J Hum Lact 2001; 17:142.
  8. Lawrence, RA, Lawrence, RM. Breastfeeding, a guide for the medical profession, Mosby, Philadelphia, 2005. p. 966.
  9. Nguyen DA, Neville MC. Tight junction regulation in the mammary gland. J Mammary Gland Biol Neoplasia 1998; 3:233.
  10. Butte NF, Villalpando S, Wong WW, et al. Human milk intake and growth faltering of rural Mesoamerindian infants. Am J Clin Nutr 1992; 55:1109.
  11. Howie PW, McNeilly AS, McArdle T, et al. The relationship between suckling-induced prolactin response and lactogenesis. J Clin Endocrinol Metab 1980; 50:670.
  12. Johnston JM, Amico JA. A prospective longitudinal study of the release of oxytocin and prolactin in response to infant suckling in long term lactation. J Clin Endocrinol Metab 1986; 62:653.
  13. Wilde CJ, Addey CV, Bryson JM, et al. Autocrine regulation of milk secretion. Biochem Soc Symp 1998; 63:81.
  14. Peaker M, Wilde CJ. Feedback control of milk secretion from milk. J Mammary Gland Biol Neoplasia 1996; 1:307.
  15. Ramsay DT, Kent JC, Owens RA, Hartmann PE. Ultrasound imaging of milk ejection in the breast of lactating women. Pediatrics 2004; 113:361.
  16. Sobhy SI, Mohame NA. The effect of early initiation of breast feeding on the amount of vaginal blood loss during the fourth stage of labor. J Egypt Public Health Assoc 2004; 79:1.
  17. Insel TR, Young L, Wang Z. Central oxytocin and reproductive behaviours. Rev Reprod 1997; 2:28.
  18. Insel TR, Gingrich BS, Young LJ. Oxytocin: who needs it? Prog Brain Res 2001; 133:59.