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Repro Bio 3 > Mammary gland > Flashcards

Mammary gland Flashcards

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Biology 101 flashcards
1
Q

monotremes

A
  • prototherians: platypus, echidna)
  • lay eggs, very altricial young
  • do not have nipples –> mammary glands discharge directly onto specialized area of skin (areola) from where the young suck or lick it up
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2
Q

marsupials

A
  • metatheria
  • short gestation period (length of luteal phase of estrous cycle)
  • young born at an immature, almost embryonic stage
  • following birth, they climb to pouch, attach to nipple (swells, fixed to it)
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3
Q

eutherians

A
  • true placental mammals
  • neonatal development varies from altricial to precocious but are all dependent on milk for earl y part of post-uterine life
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4
Q

number of mammary glands

A

varies from 2 (1 pair) in humans, sheep, goats up to 18 (9 pairs) in the sow

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5
Q

positioning of mammary glands

A
  • thorax (primates, elephants, bats)
  • abdominal (whales)
  • inguinal (cow, goat, sheep)
  • along ventral thorax/abdomen/inguinal region (sow, rat, rabbit)
  • almost dorsal (coypu)
  • determined during embryonic development
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6
Q

shape of mammary glands

A
  • ranges from flattened sheets, flat but circular, prominent, dependent
  • all females except monotremes have nipples/teats
  • absent in males in some species
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7
Q

2 basic tissue types

A
  • parenchyma (secretory)

- supporting tissue (stroma)

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8
Q

structure of milk secreting tissue

A
  • similar across species
  • basic structure = alveolus
  • sack lined by single layer of secretory epithelial cells, outside is myoepithelial layer, then basement membrane, then capillaries
  • secretion through capillary milk duct
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9
Q

alveoli arrangement

A
  • arranged in groups called lobules
  • individual capillary milk ducts empty into intralobular ducts
  • enter progressively larger ducts
  • each lobule surrounded by CT
  • groups of lobules = lobes
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10
Q

how are differences in mammary glands manifested

A

in anatomy and arrangement of duct system

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11
Q

ducts in dogs and humans

A

12-20 major ducts have openings on each nipple

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12
Q

ducts in cow, goat, sheep

A
  • major ducts empty into a large gland cistern, which is continuous with the teat cistern
  • this is drained via the single streak canal
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13
Q

ducts in mare and sow

A
  • 2 glad systems, with relatively small glands, are drained into a single teat
  • teat has 2 openings or streak canals (one for each gland system)
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14
Q

galactophores

A

ducts discharging at the nipple (or skin in monotremes)

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15
Q

what is outside glandular tissue

A
  • stroma (mix of CT and fat cells) –> mammary fat pad

- supporting tissue for parenchymal development

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16
Q

cow supporting mammary gland structures

A
  • udder divided into L and R halves by median suspensory ligament (elastin and collagen)
  • elastin predominates –> shock absorber
  • lateral suspensory ligaments, lamellar plates
  • skin is infection barrier
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17
Q

embryonic mammary development

A
  • mammary glands derived from embryonic ectoderm
  • development begins as bilateral linear thickening of ectoderm
  • become discontinuous to finish as mammary buds (grow into underlying mesoderm)
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18
Q

fetal development - primary cord

A
  • after mammary bud attains spherical shape
  • groups of cells proliferate out of the sphere and form cords of cells that elongate deeper into dermal tissue to form primary cord
  • number of primary cords that grow out of each bud determine the number of ducts that will open onto the nipple
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19
Q

fetal development - secondary cords

A
  • once primary cord attains certain size, distal end branches to form 2 or more secondary buds
  • these elongate into cords that eventually form large milk ducts
  • ruminants: they discharge into gland cistern
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20
Q

fetal development - canalization of the cords

A
  • when cords elongating, also increase in diameter
  • result is cells in center of cord get farther away from nutrient source and die
  • cords become hollow and form mammary ducts
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21
Q

fetal development - supporting tissue

A
  • CT supporting structures for mammary gland

- heifer: growth of 4 glands and fat pads, median suspensory ligament, 4 distinct quarters

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22
Q

what is development of mammary gland controlled by

A

factors from the local mesenchyme

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23
Q

what happens when you remove mammary mesenchyme

A

no formation of the mammary gland

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24
Q

development of mammary fat pad

A
  • early in development: layer of adipose tissue cells surround mammary bud
  • adequately formed fat pad is necessary for successful progression of mammary growth
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25
Q

ovarian factors in mammary gland development

A

no requirement for ovarian factors (steroid hormones) in the development of the mammary glands during fetal life

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26
Q

testosterone in male rat fetuses

A

influence of testosterone in male fetuses causes the primary mammary cord to lose its attachment to the surface epithelium during later fetal life –> male mice/rats have no nipples (same with horses, beavers)

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27
Q

mammary development at birth

A
  • mammary gland consists of rudimentary duct system that opens at a small nipple
  • gland shows general growth at an isometric rate (same as body)
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28
Q

mammary development at puberty

A
  • several weeks before: growth of mammary gland becomes allometric (faster than general body growth)
  • due to increased secretion of ovarian hormones (estrogen) from developing follicles
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29
Q

mammary development following puberty

A
  • ultrashort cycles (mice): mostly duct growth, alveoli rarely formed
  • long cycle, full luteal (primates) and short cycle: duct development is almost full - formation of fine ductules that indicate future lobules, few alveoli
  • pseudopregnancy (bitch): duct growth accompanied by considerable lobulo-alveolar development - only seen during pregnancy in other species
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30
Q

when does full alveolar development occur in monotremes

A

in response to egg incubation

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31
Q

when does full development of mammary gland occur in eutherian mammals

A
  • only completed during pregnancy or early lactation
  • growth of gland during pregnancy fits exponential curve (growth rate inversely proportional to gestation length)
  • more lobulo-alveolar development in 2nd half of pregnancy
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32
Q

development of mammary gland in eutherian mammals during pregnancy

A
  • mammary fat pad slowly infiltrated, adipose tissue replaced by duct tissue, alveoli, lymphatic vessels, CT structures
  • alveoli arranged in lobules take over much of gland volume
  • stroma represented by thin bands of CT that divide lobules and regions of lobules into lobes
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33
Q

when do alveolar cells begin to secrete

A
  • ruminants: last third of pregnancy, alveolar lumen becomes distended
  • other species: no secretion until just before parturition
  • all species: burst of secretory activity just prior to and just after parturition
34
Q

what holds full secretory activity in check before parturition

A

high circulating progesterone levels

35
Q

what body tissue has growth and function most regulated by hormones

A

mammary gland

36
Q

what hormones does duct growth depend on

A
  • estrogen
  • adrenal steroids
  • growth hormone
37
Q

what hormones does lobulo-alveolar growth require

A
  • estrogen
  • adrenal steroids
  • growth hormone
  • progesterone
  • prolactin
38
Q

what are placental lactogens and what are they important for

A
  • prolactin-like hormones produced in placenta

- important role in mammary growth during pregnancy

39
Q

differentiation of alveolar epithelial (secretory) cells near parturition

A
  • nucleus moves to basal area, becomes rounded
  • base/lateral areas of cell filled with RER and small lipid droplets
  • apical area becomes filled with swollen golgi membrane arrays, secretory vesicles, small lipid droplets
40
Q

what happens to microscopic appearance of aveolar epithelial (secretory) cells near parturition

A
  • apical areas appear lacy/foamy

- basolateral areas darkly stained

41
Q

polarization of alveolar epithelial (secretory) cells near parturition

A
  • basal area concerned with precursor uptake and synthesis of protein, lipid
  • apical area performing posttranslational modification of proteins, packaging of these proteins/lactose ready for secretion
42
Q

general model for lactation induction at the end of parturition

A
  • increase of positive stimulators for lactation

- decline in lactogenic enzyme inhibitor

43
Q

positive stimulators for lactation

A
  • prolactin, glucocorticoids, estradiol, growth hormone +/- insulin
  • increase in mammary sensitivity to them
44
Q

lactogenic enzyme inhibitor

A

progesterone

45
Q

what does milk composition depend on

A
  • amount and type of precursors taken up by the gland

- transformation they undergo during milk synthesis

46
Q

what are major substrates extracted from the blood by mammary cells

A
  • glucose
  • amino acids
  • fatty acids
  • minerals
  • ruminants: acetate, b-hydroxybutyrate
47
Q

main precursor for fatty acid production in monogastrics v ruminants

A
  • mono: glucose

- ruminants: propionate (acetate) –> glucose used for lactose production

48
Q

what is major sugar in milk and its composition

A

lactose = glucose + galactose

49
Q

how and where is lactose synthesized

A
  • synthesized in the mammary gland from glucose supplied by bloodstream
  • cow: glucose made in liver by gluconeogenesis
50
Q

what is lactose synthesized from

A

from glucose by enzyme complex lactose synthetase (galactosyltransferase + a-lactalbumin)

51
Q

what happens when glucose and UDP-galactose enter golgi

A

form lactose and UDP under influence of lactse synthase complex

52
Q

what is golgi membrane permeable/impermeable to and why is this important

A
  • permeable to glucose/galactose (monosaccharides), impermeable to lactose (disaccharide)
  • surgar is major osmotically active component of milk, draws water into golgi vesicle –> accounts for milk volume
53
Q

what does milk protein consist of

A
  • caseins, a-lactalbumin, b-lactoglobulin, serum albumin, lactoferrin, lysozyme, immunoglobulins, NPN compounds
  • casein, a-lactalbumin, b-lactoglobulin are >90% of protein in most species ( more lactoferrin, NPN)
54
Q

what provide building blocks for milk protein synthesis

A

amino acids, NPN compounds from blood

55
Q

where are proteins made and transported to

A
  • proteins assembled on surface ribosomes of RER
  • inserted into lumen of ER
  • transported to golgi
  • micelles secreted from golgi
56
Q

what types of lipids are present in milk

A
  • 97-98% triglycerides

- remainder are mostly phospholipids

57
Q

milk fatty acids

A
  • C4 to C18
  • under C16 synthesized in mammary alveolar epithelia cells, greater than or equal to C16 derived from blood borne lipids
58
Q

what are precursors for lipid formation in ruminants, non-ruminants

A
  • ruminants: acetate, b-hydroxybutyrate, triacylglycerides

- nonruminants: glucose, triacylglycerides

59
Q

list 5 pathways for secretion of components into milk

A
  • exocytosis
  • reverse pinocytosis
  • transmembrane transport
  • transcytosis
  • paracellular transport
60
Q

exocytosis pathway for secretion of milk components

A
  • proteins, lactose, salts, non-fat components packaged into secretory vesicles in golgi
  • vesicles bud off from golgi, move to cell apex
  • membrane surrounding vesicle fuses with plasma membrane, contents released into alveolar lumen
61
Q

reverse pinocytosis pathway for secretion of milk components

A
  • lipid droplets form near ER, transported to apical membrane
  • membrane forms milk fat globule membrane –> membrane pinches off beneath it
  • globule secreted into alveolar lumen
62
Q

transmembrane transport pathway for secretion of milk components

A
  • other salts pumped into cell at base, some passively diffuse into alveolus
  • apical plasma membrane permeable to monovalent ions (Na, Cl, K), and glucose
  • impermeable to divalent cations, disaccharides
  • diffusion and pumping across basal and apical membranes
63
Q

transcytosis pathway for secretion of milk components

A
  • mechanism for proteins that are not synthesized in the alveolar epithelial cell to enter the milk (IgA, insulin, prolactin, IGF-1, albumin)
  • protein interacts with receptor at basal membrane
  • protein-receptor complex internalized, transported across cell to apical membrane where protein are released into alveolar lumen
64
Q

paracellular transport pathway for secretion of milk components

A
  • lactation: tight junctions form between adjacent mammary epithelial cells - separate interstitial spaces and alveolar lumen (close paracellular transport)
  • pregnancy: tight junctions open, large proteins can be transported this way
65
Q

in lab animals, what are the minimum requirements for continued lactation

A
  • prolactin
  • corticosteroids
  • oxytocin
66
Q

purpose of glucocorticoids in non-ruminants

A
  • regulate activity of enzymes in milk synthesis pathway by controlling their transcription rates
  • adrenalectomy causes 50% drop in milk production
67
Q

functions of prolactin in non-ruminants

A
  • maintain enzyme levels and protein synthesis
  • increases gene transcription rates and half-lives of resulting mRNAs
  • effect is enhanced by glucocorticoids
  • prevents apoptosis of mammary epithelium, maintains tight junctions
68
Q

effects of adrenalectomy on ruminant lactation

A

none or very minimal –> no requirement for glucocortioids

69
Q

what is main requirement for lactation maintenance in ruminants and what does it do

A
  • somatotropin (growth hormone)
  • maintains mammary secretory cell numbers, greater rate of milk synthesis
  • acts directly on mammary gland, increases IGF production in liver
70
Q

importance of prolactin in ruminant lactation

A
  • controversial

- role in mammary epithelial cell proliferation, function, prevention of apoptosis

71
Q

function of oxytocin in lactation maintenance

A
  • required for removal of milk from alveolus
  • mammary glands degenerate without it
  • repeated suckling/milking is necessary
72
Q

function of frequency of milk removal

A
  • increasing frequency of milk removal increases milk production
  • cows: acute and sustained effect (3 week window at beginning of lactation where you set potential)
73
Q

controls for local effects of control of milk synthesis

A
  • sustained one involves changes in genetic imprinting

- acute chages: feedback inhibitor of lactation (FIL), casein fragments, serotonin

74
Q

what is feedback inhibitor of lactation (FIL)

A
  • autocrine regulator –> inhibits same cell that secretes it
  • binds to receptor on apical plasma membrane and has immediate effects to inhibit protein/lactose secretion
75
Q

milk storage

A
  • secreted continuously, stored within the lumen of the alveolus and expansions of duct system
  • duct system large in ruminants, none in rat/rabbit, small in women
76
Q

milk passive/active ejection

A
  • milk in storage ducts available passively to suckling/milk machine
  • milk in alveoli/smaller ducts needs active ejection (majority of it)
77
Q

what is milk ejection controlled by

A

neuroendocrine reflex

78
Q

how is nipple innervated

A

intradermal sensory afferent nerves

79
Q

after nipple sensory afferent nerves synapse with nerves in spinal cord, where do they do

A

synaptic relays –> hypothalamus –> paraventricular/supraoptic nuclei (contain oxytocin producing neurons) –> posterior pituitary releases oxytocin

80
Q

purpose of oxytocin in milk ejection

A

-circulates in blood and causes contraction of myoepithelial cells –> ejects milk from alveoli into duct system

81
Q

conditioning of milk ejection reflex

A
  • may be conditioned to other stimuli (cows seeing milking parlor)
  • can be inhibited by stressful situations due to central abolition of oxytocin release

Repro Bio 3 (6 decks)

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