MAMMOGENESIS DEVELOPMENT OF THE MAMMARY GLAND Fetal period Prepubertal Postpubertal Pregnancy Lactation Dry off or involution
MAMMOGENESIS Development of the mammary gland Parenchymal tissue: epithelial structures - alveoli - ducts Stromal Tissue: Supporting Tissues - cellular: fibroblasts, endothelial, WBC - non-cellular: collagen, connective tissue, fat pad or tissue
SKIN GLAND *skin = derived from; *gland = secreting organ holocrine secretion - sebaceous gland - lipid - sac structure - cell disintegrates/ secreted eccrine secretion - sweat gland - tubular structure - no loss of cells
SKIN GLAND apocrine/ merocrine secretion - mammary gland - compound tubular / sacular structure - some loss of cell components / H2O and salts
FETAL DEVELOPMENT Three distinguishable layers of cells Ectoderm: (outer layer) - skin / nervous system Mesoderm: (middle) - muscle / blood endoderm: (inner) - alimentary canal
MAMMARY BAND ectoderm thickening (day 30) MAMMARY STREAK
MAMMARY LINE ectoderm thickening (day 35) MAMMARY CREST
MAMMARY HILLOCK ectoderm thickening / pushing into mesoderm MAMMARY BUD Mesoderm pushes out teat formation Cow: day 43.” “. ***** Human: day 49
Ectoderm pushing in Development of primary sprout Mesoderm pushing out - teat formation - skin invaginates in ** keratin**
Rodent Mammary budWhere’s it going?
Primary sprout Days )
Secondary sprout (days ) Primary sprout : apoptosis / canalization * occurs from inside gland to streak canal
Rodent newborn Connective tissue and fat in most species
Primary sprout What about humans / other mammals with multiple exit ducts? Secondary buds EpithelialCords(lactiferousducts)
AT BIRTH Teats are well developed - mastitis Male gland similar to female ( < developed) No secretory / glandular parts yet! Non secretory tissue ( blood / lymph / connective) is well formed.
PREPUBERTAL isometric growth: same rate as body Fat pad* / connective tissue* / duct network **** essential**** (no secretory tissue!) allometric growth: faster than body ** fat deposition BUT 20X GROWTHRATE!!
Rodent 4 weeks old
Rodent 4 weeks old
BIRTH TO PUBERTY Extensive duct development into fat pad / tissue Fat pad is ESSENTIAL!!
BIRTH TO PUBERTY
How many layers thick? 1, 2, 5, ?
PUBERTY TO CONCEPTION Considerable ductal growth / branching associated with estrus cycles TDLU : terminal ductule lobular unit No secretory tissue / alveolus!!! Acyclic vs. cyclic animals? Acyclic: extended estrus in absence of copulation (rabbit): lots of ducts/ few alveoli Cyclic: estrus cycles, bursts of ductal development around proestrus/ estrus
PUBERTY TO CONCEPTION Extensive duct growth and branching
PUBERTY TO CONCEPTION
PREGNANCY Hamster - 94% Mouse - 78% Sheep - 78% Rabbit - 66% Rat - 60%
PREGNANCY Rodent Day 9
PREGNANCY Rodent Day 16
PREGNANCY
PARTURITION - CALVING
A. Fully differentiated alveolar epithelial cells characterized by presence of numerous vacuoles (V), rounded basally positioned nuclei (N), abundant cytoplasm, and frequent occurrence of large apically located lipid droplets (F); alveolar lumen is L. B. Intermediately differentiated alveolar epithelial cells showing fewer cellular vacuoles, more irregularly shaped nuclei, and greater nuclear to cytoplasmic ratio. C. Undifferentiated alveolar epithelial cells displaying relative absence of cellular vacuoles, highly irregularly shaped nuclei, a mixture of large and small lipid droplets, and very large nuclear to cytoplasmic ratio, (X4,000).
INVOLUTION
ALVEOLUS