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 bud Where’s it going?

Primary sprout

Days 80-100)

Secondary sprout (days 100-130)

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 mammalswith 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 20XGROWTH

RATE!!

Rodent

4 weeks old

Rodent

4 weeks old

BIRTH TO PUBERTYExtensive duct development

into fat pad / tissue

Fat pad is ESSENTIAL!!

BIRTH TO PUBERTY

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 growthand branching

PUBERTY TO CONCEPTION

PUBERTY TO CONCEPTION

PUBERTY TO CONCEPTION

PREGNANCY

Hamster - 94%Mouse - 78%Sheep - 78%Rabbit - 66%Rat - 60%

PREGNANCY

RodentDay 9

PREGNANCY

RodentDay 16

PREGNANCY

PREGNANCY

PARTURITION - CALVING

PARTURITION - CALVING

PARTURITION - CALVING

PARTURITION - CALVING

PARTURITION - CALVING

PARTURITION - CALVING

PARTURITION - CALVING

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

INVOLUTION

INVOLUTION

ALVEOLUS

ALVEOLUS

ALVEOLUS