epithelial cell differentiation

what are the milk producing cells arranged into?

spheres called alveoli

what are clusters of alveoli called?

lobules

what do lobules drain into?

ducts

what supports alveoli structurally & nutritionally?

stroma → vasculature + connective tissues

when do milk producing functional units develop?

only during pregnancy

what is the basic glandular unit?

alveolus (acini in some texts)

what lines the alveolus?

a single layer of mammary epithelial cells that secrete milk

what is the function of duct-lining cells?

a cluster of alveoli and their associated ducts

what is a lobule?

a cluster of alveoli and their associated ducts

define parenchyma

function cells of an organ (carry out specialized functions)

what are the parenchymal cells of the mammary gland?

epithelial cells (alveoli + ducts) and myoepithelial cells

what embryonic layer does parenchyma derive from?

ectoderm

define stroma

supporting cells and tissues of an organ

what are the main stromal cells in immature mammary glands?

adipocytes, vasculature, fibroblasts

what are the main stromal cells in lactating glands?

vasculature, fibroblasts, some adipocytes

what embryonic layer does the stroma derive from?

mesoderm

what is the function of myoepithelial cells?

they contract to squeeze alveoli and push milk into ducts

where are myoepithelial cells located?

surrounding alveoli and ducts, just beneath the basement membrane

what 3 processes are required for successful lactation?

1.proliferation of mammary epithelial cells

2.structural differentiation of mammary epithelial cells

3.biochemical activation for milk synthesis & secretion

what are the two phases of mammary development leading to lactation?

mammogenesis and lactogenesis

what does the cell membrane consist of?

phospholipid bilayer

what is the role of the mitochondria?

energy production

what is the role of the nucleus?

genome storage and transcription

function of rough ER?

protein and fatty acid synthesis

function of golgi bodies?

packaging secretory products

what do secretory vesicles contain?

packaged aqueous and protein components

what do lipid droplets contain?

packaged lipid components

what happens during mammogenesis?

increase in number of mammary epithelial cells; alveoli form along ducts

what is the state of mammary epithelial cells in virgin animals?

primarily duct cells, non-functional

what is lactogenesis?

biochemical and structural changes in late gestation that activate cells for milk production

describe epithelial cells before/early lactogenesis

-short cells

-large nucleus → ~50% of volume

-straight apical membrane

-few organelles

-may contain large lipid droplets

describe epithelial cells after lactogenesis

-taller cells

-basal nucleus → ~20% of volume

-lacy apical membrane

-abundant organelles

-apical secretory vesicles

-smaller lipid droplets

what happens to the lumen during differentiation?

increases in volume and fills with milk components

what structural changes occur in mammary epithelial cells?

-cells lengthen

-nucleus shifts to basal side

-secretory vesicles & lipid droplets move apically

-increased lumen space

what cellular composition changes occur?

higher density of ribosomes, golgi, mitochondria, vesicles, ER

what characterizes alveoli during late pregnancy?

-high protein concentration in lumen

-large lipid droplets

-squat epithelial cells

what characterizes alveoli during early lactation?

-larger lumen

-smaller lipid droplets

-more secretory vesicles

-expanded epithelial cells

what happens to alveoli right after milking?

-lumen appears oblong

-fills and rounds as milk accumulates

what connects mammary epithelial cells?

intercellular adhesion proteins

function of adhesion proteins?

prevent stromal fluid from entering lumen & milk components from leaking into stroma

what are tight junctions?

highly permeable junctions near the apical surface of epithelial cells

state of tight junctions prepartum vs postpartum?

-prepartum → leaky

-postpartum → strong and impermeable

when can tight junctions become leaky again?

during mastitis, inflammation, or involution

what is the basement membrane?

-anchors epithelial cells to connective tissue

-provides nutrients

-removes waste via interstitial fluid

what is the basement membrane composed of?

collagen and adhesive proteins → non-cellular

what does the basement membrane separate in the fetus?

epithelium (parenchyma) from mesenchyme (stroma)

what does the basement membrane separate in adults?

mammary epithelial cells from underlying connective tissue