Mammary glands

In general Milk producing organs The number and location of the glands varys widely between mammals

Development overview

Development Evolved over 300 million years ago Most likely from sweat glands Embryonic, pubertal and reproductive stages

Embryonic MG development The embryonic mammary mesenchyme provides inductive signals -> mammary epithelial cell differentiation Wnt signaling (Outside -> receptor -> inside cell) -> signals to regulate dorsal/ventral patterning of the placodes -> Pairs of symmetrically localized placodes (1)

Embryonic MG development TBX3 identified as an important factor, found in both human and mice (Wnt signaling) BMP4 antagonizes Tbx3 (vice versa) Add fibroblast growth factors (FGF) -> placement and pattern of placodes

Embronic MG development

Embronic MG development

Embronic MG development Formation of ductal lumen (Branching) Generation of nipple structure (modifications of the skin, suppression of hair...) PTHLH budding -> branching (g-protein), nipple formation

Pubertal development Even at birth, the gland is able to produce milk Puberty -> Fast growth -> filling of the fat pad Terminal end buds penetrate the fat pad -> cap cells of TEB differentiate into myoepithelial cells = outer layer of tubular ductal bilayer around the inner luminal cells

Cell differentation

Function of the parts Myoepithelial cells contract to push milk out Milk comes through lactiferous duct and out through nipple pores Areolae Areolae glands Lipoid fluid (moisture) Traget for the baby Fat supports all the structures Suspensory ligamens hold brests on place

Lactation Mammary gland undergoes many changes Gland maturation & alveologenesis Regulated by progesterone and prolactin (PRL) Transformations Ductal branching Proliferating epithelial cells  alveloar buds  alveoli, milk secreting lobules http://upload.wikimedia.org/wikipedia/commons/9/91/Breastfeeding%28milkfinal%29.png

Lactation Baby suckles Mechano receptor neurons stimulated Message to hypothalamus Stimulates oxytocin production Oxytosin stimulates myoepithelial cells Inhibits dopamine Dopamine inhibits prolactin

Prolactin Oxytocin Secreted by anterior pituitary Three intramolecular disulphide bonds Oxytocin Stored in posterior pituitary gland It has many functions in sexual reproduction

Other hormonal effects Progesterone Steroid hormone Many function For ex. In menstrual cycle & pregnancy Induces alveoloar maturation together with prolactin Growth hormone Estrogen ACTH

References http://upload.wikimedia.org/wikipedia/commons/6/64/Illu_breast_anatomy.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/9/97/Piglets1.jpg/800px-Piglets1.jpg http://link.springer.com/article/10.1023%2FA%3A1018708704335#page-1 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3404495/