乳腺发育

乳腺发育（mammogenesis）又称乳房发育（breast development），主要是在出生后，在青春期时，女性乳腺中会形成小管及分支，这建立了从乳头开始，类似树的网络^[1]。

在发育时，乳腺上皮细胞持续的产生，由少见的上皮细胞维护，配成了乳腺祖^{[来源请求]}（mammary progenitor），一般认为这是由组织中残留的干细胞所衍生^{[来源请求]}。

胚胎时的乳腺发育

胚胎的乳腺发育可以分为一系列不同的阶段。第一阶段约在10.5胚胎日（E10.5），乳腺会出现在上肢和下肢之间，在中线两侧一边一个。第二阶段约在11.5胚胎日（E11.5），乳腺上的基盘会形成，最后会形成乳头。第二阶段约在12.5胚胎日（E12.5），基盘内的细胞会退缩到间充质内，这是乳腺的基质^[2]。

胚胎时在体内已有干细胞，在胚胎发育过程中其数量会持续增加^[3]。

出生后的乳腺发育

婴儿在出生后，乳腺管延伸到乳腺脂肪垫，约自出生后四周开始，乳腺管会显著成长，而且会往淋巴结生长。乳腺管的末端芽是乳腺管末端的高度增生结构，也会在此阶段大幅的扩大及增生。此阶段的特征就是末端芽的出现，约到七至八周为止。

青春期的乳腺

青春期时乳腺管已进入乳腺脂肪垫的末端，此时末端芽比较不会增生，体积也会缩小。会由主乳腺管再形成分支乳腺管，并且充满整个乳腺脂肪垫。乳腺管的成熟会在性成熟时减缓，而且会因着动情周期的影响，乳腺会有定期增生后再复原的周期变化^[4]。

怀孕

怀孕时的乳腺系统会快速增生，而且会在分支乳腺管形成乳腺泡，可以制造母乳。

哺乳

生产后，乳腺中乳腺泡的细胞会分泌母乳，称为哺乳。乳腺泡附近肌上皮细胞的收缩使母乳进入乳腺管中，再借由婴儿的吸吮而进入乳头。

退化

在婴儿断奶后，哺乳停止，乳腺会渐渐复原。其过程是可控制的乳腺上皮细胞凋亡，乳腺会回到怀孕前的状态。

雌激素受体

乳腺的发育是由乳腺中的雌激素受体（英语：estrogen receptor alpha）、孕酮受体、催乳素受体活化所产生^[5]。雌二醇、[孕酮]]及催乳素活化乳腺中的受体，开始乳腺的成长^[5]。有些植物性雌激素（英语：phytoestrogen）（例如8-prenylnaringenin）也会活化受体，刺激乳腺的发育^[6]乳腺的雌激素受体是由GATA-3转录因子所控制^[7]^[8]。

参考资料

^ Sekhri, KK; Pitelka, DR; Deome, KB. Studies of mouse mammary glands. I. Cytomorphology of the normal mammary gland. J Natl Cancer Inst. Sep 1967, 39 (3): 459–90. PMID 6053715.
^ Hens, JR; Wysolmerski JJ. Key stages of mammary gland development: molecular mechanisms involved in the formation of the embryonic mammary gland. Breast Cancer Res. 10 Aug 2005, 7 (5): 220–4. PMC 1242158  . PMID 16168142. doi:10.1186/bcr1306.
^ Makarem, M; Eaves C. Stem Cells and the Developing Mammary Gland. J Mammary Gland Biol Neoplasia. Apr 2013, 18 (2): 209–19. PMID 23624881. doi:10.1007/s10911-013-9284-6.
^ Daniel, CW; Smith, GH. The mammary gland: a model for development. Journal of Mammary Gland Biology and Neoplasia. January 1999, 4 (1): 3–8. PMID 10219902. doi:10.1023/A:1018796301609.
^ ^5.0 ^5.1 Brisken; Malley. Hormone Action in the Mammary Gland. Cold Spring Harbor Perspectives in Biology (Cold Spring Harb Perspect Biol). December 2, 2010, 2 (12): a003178. PMC 2982168  . PMID 20739412. doi:10.1101/cshperspect.a003178.
^ Overk, CR; Guo, J; Chadwick, LR; Lantvit, DD; Minassi, A; Appendino, G; Chen, SN; Lankin, DC; Farnsworth, NR; Pauli, GF; Van Breemen, RB; Bolton, JL. In vivo estrogenic comparisons of Trifolium pratense (red clover) Humulus lupulus (hops), and the pure compounds isoxanthohumol and 8-prenylnaringenin.|. Chemico-biological interactions. 2008, 176 (1): 30–39. PMC 2574795  . PMID 18619951. doi:10.1016/j.cbi.2008.06.005.
^ Asselin-Labat, ML; Sutherland, KD; Barker, H; Thomas, R; Shackleton, M; Forrest, NC; Hartley, L; Robb, L; Grosveld, FG; van der Wees, J; Lindeman, GJ; Visvader, JE. Gata-3 is an essential regulator of mammary-gland morphogenesis and luminal-cell differentiation. Nature Cell Biology. Feb 2007, 9 (2): 201–9. PMID 17187062. doi:10.1038/ncb1530.
^ Kouros-Mehr, Hosein; Slorach, EM; Sternlicht, MD; Werb, Z. GATA-3 maintains the differentiation of the luminal cell fate in the mammary gland.. Cell. Dec 1, 2006, 127 (5): 1041–55. PMC 2646406  . PMID 17129787. doi:10.1016/j.cell.2006.09.048.

[1] Sekhri, KK; Pitelka, DR; Deome, KB. Studies of mouse mammary glands. I. Cytomorphology of the normal mammary gland. J Natl Cancer Inst. Sep 1967, 39 (3): 459–90. PMID 6053715.

[2] Hens, JR; Wysolmerski JJ. Key stages of mammary gland development: molecular mechanisms involved in the formation of the embryonic mammary gland. Breast Cancer Res. 10 Aug 2005, 7 (5): 220–4. PMC 1242158  . PMID 16168142. doi:10.1186/bcr1306.

[3] Makarem, M; Eaves C. Stem Cells and the Developing Mammary Gland. J Mammary Gland Biol Neoplasia. Apr 2013, 18 (2): 209–19. PMID 23624881. doi:10.1007/s10911-013-9284-6.

[4] Daniel, CW; Smith, GH. The mammary gland: a model for development. Journal of Mammary Gland Biology and Neoplasia. January 1999, 4 (1): 3–8. PMID 10219902. doi:10.1023/A:1018796301609.

[gland_activation-5] 5.0 ^5.1 Brisken; Malley. Hormone Action in the Mammary Gland. Cold Spring Harbor Perspectives in Biology (Cold Spring Harb Perspect Biol). December 2, 2010, 2 (12): a003178. PMC 2982168  . PMID 20739412. doi:10.1101/cshperspect.a003178.

[study-6] Overk, CR; Guo, J; Chadwick, LR; Lantvit, DD; Minassi, A; Appendino, G; Chen, SN; Lankin, DC; Farnsworth, NR; Pauli, GF; Van Breemen, RB; Bolton, JL. In vivo estrogenic comparisons of Trifolium pratense (red clover) Humulus lupulus (hops), and the pure compounds isoxanthohumol and 8-prenylnaringenin.|. Chemico-biological interactions. 2008, 176 (1): 30–39. PMC 2574795  . PMID 18619951. doi:10.1016/j.cbi.2008.06.005.

[7] Asselin-Labat, ML; Sutherland, KD; Barker, H; Thomas, R; Shackleton, M; Forrest, NC; Hartley, L; Robb, L; Grosveld, FG; van der Wees, J; Lindeman, GJ; Visvader, JE. Gata-3 is an essential regulator of mammary-gland morphogenesis and luminal-cell differentiation. Nature Cell Biology. Feb 2007, 9 (2): 201–9. PMID 17187062. doi:10.1038/ncb1530.

[8] Kouros-Mehr, Hosein; Slorach, EM; Sternlicht, MD; Werb, Z. GATA-3 maintains the differentiation of the luminal cell fate in the mammary gland.. Cell. Dec 1, 2006, 127 (5): 1041–55. PMC 2646406  . PMID 17129787. doi:10.1016/j.cell.2006.09.048.

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