View source for Archive:Lactocyte

{{Short description|Cells that produce milk}}
{{Infobox cell
| Name        = Lactocyte 
| Image       = {{CSS image crop
|Image = A manual of human physiology, including histology and microscopical anatomy, with special reference to the requirements of practical medicine (1885) (14779254784).jpg
|bSize = 400
|cWidth = 150
|oTop = 20
|oLeft = 125
|Location = center
}}
| Caption     = 
| System      = [[Exocrine system]]
| Function = Milk secretion
| Location = [[Mammary gland]]
| Shape = Cuboidal
}}

'''Lactocytes''' are cells that synthesize and secrete milk within the mammary glands of [[lactation|lactating]] mammals.<ref>{{Cite web |title=Endosymbiont |url=https://www.endosymbiont.com/celltypes/lactocytes |access-date=2026-09-11 |website=www.endosymbiont.com}}</ref><ref name=":2">{{Cite journal |last1=Pang |first1=Wei Wei |last2=Hartmann |first2=Peter E. |date=2007-12-01 |title=Initiation of Human Lactation: Secretory Differentiation and Secretory Activation |url=https://doi.org/10.1007/s10911-007-9054-4 |journal=Journal of Mammary Gland Biology and Neoplasia |volume=12 |issue=4 |pages=211–221 |doi=10.1007/s10911-007-9054-4 |pmid=18027076 |issn=1573-7039}}</ref> In preparation of lactation, lactocytes differentiate from luminal adaptive secretory precursor (LASP) cells found in the resting mammary gland.<ref name=Gray2025>{{cite journal|vauthors=Gray GK, Carlson EG, Lev T, Marshall B, Reed AD, Sánchez-Covarrubias AP, Twigger AJ, Puig-Barbe A, Thennavan A, Omotoso A, Murrow LM|title=Defining breast epithelial cell types in the single-cell era|journal=Developmental cell|date=2025-09-08|volume=60|issue=17|pages=2218-36|doi=10.1016/j.devcel.2025.06.032|doi-access=free}}</ref>

== Terminology ==
The terminology used for mammary epithelial cells like lactocytes has been fairly inconsistent in the literature.<ref name=Gray2025/> Lactocytes have been called '''lactating mammary epithelial cells''' (lactating MECs),<ref name=Kress2010/> or just referred to as '''lactating cells'''.<ref name=Kress2010>{{cite journal|vauthors=Kress C, Ballester M, Devinoy E, Rijnkels M|title=Epigenetic modifications in 3D: nuclear organization of the differentiating mammary epithelial cell|journal=Journal of mammary gland biology and neoplasia|date=March 2010|volume=15|issue=1|pages=73-83|doi=10.1007/s10911-010-9169-x|url=https://www.researchgate.net/profile/Eve-Devinoy/publication/41417472_Epigenetic_Modifications_in_3D_Nuclear_Organization_of_the_Differentiating_Mammary_Epithelial_Cell/links/09e4151407f4314787000000/Epigenetic-Modifications-in-3D-Nuclear-Organization-of-the-Differentiating-Mammary-Epithelial-Cell.pdf}}</ref> In the case of humans, they have also been called '''breast lactating cells'''.<ref>{{cite web|url=https://www.proteinatlas.org/humanproteome/single+cell/single+cell+type/glandular+epithelial+cells#luminalcells|title=The glandular epithelial cell-specific proteome|website=Human Protein Atlas|access-date=2026-10-18}}</ref> However, some similar terms like "breast secretory cell", "luminal secretory cell", or "alveolar cell" are often confusingly used to the refer to the LASP cells (lactocyte precursors).<ref name=Gray2025/>

==Milk synthesis==

Many of these processes are still under investigation. It is thought that nutrients are transported to [[Mammary alveolus|mammary alveoli]] by transport proteins on the membranes of mammary epithelial cells. Milk proteins are synthesized in the endoplasmic reticulum and packaged into secretory vesicles, alveolar cells add nutrients such as calcium, zinc, phosphate, lactose, and citrate, and the milk is transported from the lactocyte via exocytosis. Lipids are wrapped in a [[Milk fat globule membrane|membrane and secreted as milk fat globules]]. Other transport proteins uptake nutrients from the blood and from interstitial fluid.<ref>{{Cite journal |last1=Montalbetti |first1=Nicolas |last2=Dalghi |first2=Marianela G. |last3=Albrecht |first3=Christiane |last4=Hediger |first4=Matthias A. |date=March 2014 |title=Nutrient Transport in the Mammary Gland: Calcium, Trace Minerals and Water Soluble Vitamins |url=http://link.springer.com/10.1007/s10911-014-9317-9 |journal=Journal of Mammary Gland Biology and Neoplasia |language=en |volume=19 |issue=1 |pages=73–90 |doi=10.1007/s10911-014-9317-9 |pmid=24567109 |issn=1083-3021}}</ref>

==Structure==
{{see also|Mammary alveolus}}
[[File:Normal breast histology.png|thumb|right|Normal histology of a breast]]

The primary secreting components of the mammary gland are the [[alveoli]], which are small cavities surround by cells. In lactating mammals, a bulb-like lumen (cavity) is lined by lactocytes, which secrete milk into the lumen. The lactocytes are surrounded by a second layer of cells, called basal-myoepithelial (B-myo) cells, which function like muscle cells to squeeze milk out of the lobules (groups of alveoli) and into the milk ducts during suckling.<ref name=Gray2025/><ref name=LumenLactation>{{Cite web |title=Lactation {{!}} Anatomy and Physiology II |url=https://courses.lumenlearning.com/suny-ap2/chapter/lactation/ |access-date=2026-09-11 |website=courses.lumenlearning.com}}</ref>

==Origin and stages==

Before pregnancy, the innermost (luminal) layer of mammary ductal tissue consists of two types of [[epithelial cell]]: the ''luminal hormone sensing'' (LHS) cells and the ''luminal adaptive secretory precursor'' (LASP) cells.<ref name=Gray2025/> During pregnancy, the LHS cells receive signals from hormones (especially [[estrogen]], [[progesterone]], [[prolactin]], and [[human placental lactogen]]) and pass these signals onto nearby LASP cells, which subsequently differentiate into lactocytes.<ref name=Gray2025/>

Following secretory differentiation, pregnancy hormones suppress the lactocytes, reducing their size and function. Upon delivery of the placenta, the resulting significant drop in progesterone allows prolactin to stimulate milk synthesis and secretion in the alveoli. Initially, there are large intercellular gaps between lactocytes, allowing high transfer of maternal plasma components to enter the milk, and colostrum - the initial, immature, and highly beneficial milk - is produced. As the intercellular gaps are bridged by an apical junctional complex and the number of lactocytes increase, they begin to produce "mature" [[breast milk]].<ref name=":1">{{Cite web |last=Physiology |first=Fetal and Neonatal |date=2024-03-22 |title=Drug Transfer During Breastfeeding |url=https://clinicalpub.com/drug-transfer-during-breastfeeding/ |access-date=2026-09-11 |website=Clinical Tree |language=en-US}}</ref><ref name="ndcinstitute">{{Cite web |title=NDC {{!}} Lactogenesis: secretory differentiation and activation of the human mammary gland |url=https://ndcinstitute.au/article/d9d9a92d-471b-4c1b-80de-bdc49cc3fc5f/lactogenesis-secretory-differentiation-and-activation-of-the-human-mammary-gland |access-date=2026-09-11 |website=ndcinstitute.au}}</ref>

==Milk secretion and regulation==

Lactocytes secrete milk in a slow but mostly continuous fashion.<ref name=":2" /> However, suckling triggers a spike in the release of the hormone [[prolactin]] from the [[pituitary gland]], which stimulates the lactocytes to increase their production of milk to prepare for the next feeding.<ref name=LumenLactation/>

The mechanisms that pause milk production and control the amount of milk produced remain poorly understood. Some have hypothesized the existence of a protein (or multiple proteins), they term "feedback inhibitor of lactation", which accumulates and stops milk production. The existence and identity of this protein have yet to be definitively proven, but recently some have suggested that [[serotonin]] may be part of this.<ref>{{cite book|vauthors=Anderson SM, MacLean PS, McManaman JL, Neville MC|chapter=Lactation and its hormonal control|title=Knobil and Neill’s Physiology of reproduction|year=2015|edition=4|pages=2055-105|ISBN=9780123977694}}</ref>

As the lactocytes produce milk globules within the alveoli, intra-alveolar pressure stretches the lactocytes which prevents the cells from producing and "pinching off" fatty globule membranes, causing a reduced fat content. As the milk is removed, pressure reduces, and the fat content of the milk increases.<ref>{{Cite web |title=NDC {{!}} Limitations of the bioactive factors Feedback Inhibitor of Lactation model |url=https://ndcinstitute.au/article/781aa171-6c68-49b5-ab73-ae372fa0769b/limitations-of-the-bioactive-factors-feedback-inhibitor-of-lactation-model |access-date=2026-09-11 |website=ndcinstitute.au}}</ref>

== References ==

{{reflist}}

[[Category:Cell biology]]
[[Category:Glands]]
[[Category:Breastfeeding]]
[[Category:Breast milk]]