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mammary glands and lactation, milk components + more about milk, cellular…
mammary glands and lactation
internal anatomy
streak canal
keep milk in
keeps bacteria out
teat cistern
duct in teat
30-45mL
separated from streak canal by
rosette
(folds of tissue)
gland cistern
separaed from teat cistern by
crocoid fold
holds up to 400mL
collecting area for mammary ducts
stroma
fibroblasts, adipocytes, plasma cells, blood vessels
parenchyma
gladular, secreting tissue/funtional unit of the mammary gland
alveoli
: secreting epithelial cells
small bulb, hollow centr
lined with secretory cells
surrounded by network of capillaries and myoepithelial cells (for contractions)
lobule
groups of alveoli emptying into a duct
lobe
group of lobules
ducts of lobe empty into
galatophore
-->
gland cistern
mammary gland suspension
skin
minor role
median suspensory ligament
separates left and right halves of udder
connects udder to abdominal wall by
lamellae
elastic --> responds to weight of milk
lateral suspensory ligament
inflexible
surrounds outer wall of udder
attachment: prepubic, subpubic tendons
intermammary groove
where lateral and median suspensory ligament meets
circulation
1:400 gallon milk:blood ratio
mammary arteries
cranial mammary artery, caudal mammary artery
entry of blood to udder
2 external pudic arteries
, one for each half
venous outflow
external pudic veins
drains from here when laid down
subcutaneous abdominal veins
also called the milk vein
drains when stood up
stages in mammary gland development
mammogenesis
development of mammary tissue
lactogenesis
onset of milk secretion
late pregnancy/after parturition
galactopoesis
maintenance of lactation
milk ejection
expulsion of the milk from alveoli
involution
termination of milk secretion, mammary gland regression
mammogenesis
7-8 week of gestation
primary, secondary ducts develop
BMP4 + BMPR1A to MSX2
--> inhibits hair follicle formation
PTHLH
signals from epithelium to mesenchyme to increase BMPR1A expression
endocrine factors:
ant pit, adrenal, pancreas, vescular follicle, corpus luteum
lactogenesis
onset of milk secretion
second half of pregnancy --> production of
colotrum
lactogenesis 1
secretion of milk during later pregnancy
lactogenesis 2
occurs after birth
copius milk secretion --> abruptly levels off
galactopoiesis
maintainence of milk supply
requires removal of milk from breast
supply-demand response
steroids and lactation
oestrogen
development of stromal tissue
growth of extensive ductal system
deposition of fat in breasts
inhibits secretion of milk
progesterone
development of lobules and alveoli
alveolus
: proliferate, enlarge, secretory
inhibits secretion of milk
prolactin
milk production
signals through JAK/Stat --> proliferation of lobu-alveolar system
release inhibited by
dopamine
suckling inhibits
dopamine release
rises and falls in prop to freq, intensity, duration of nipple stimulation
lactogenesis
triggered by the explulsion of placenta -->
fall in progesterone and estrogen levels, continued presence of prolactin
other regulatory factors
growth hormone
from ant pit
works with E2 to develop mammary gland ducts
insuline-like growth factor IGF-1
produced by liver
primary mediator of GH
glucocoritcoids and ACTH
maintains tight junctions in
breast parenchyma
(produces milk) --> prevents inflammation/
mastitis
milk ejection reflex
causes alveoli to release milk
suckling --> msg up nerve pathways -->
paraventricular, supraoptic nuclei
-->
hypothalamus
-->
oxytocin
(from hypothalamus) --> alveolar myoepithelia contracts --> stored milk ejected
involution
cow
mammary epithelial de-differentiates
day7: non secretory
ageing cells: apoptosis
rodents
defoliation
next lactation: more extensive regeneration
changes in mammary gland during life
max capacity reached at 3rd
capacity starts to regress 6-7th parturition
milk components + more about milk
amino acids
specific transport system
proteins
formed in rER
transferred from the rER to golgi apparatus --> secretory vesicles
casein
secreted as a micelle
glucose to lactose
glucose enters basolateral membrane
enters golgi and converted to lactose
milk fat precursors to milk fat
milk fat triglycerides
synthesised in sER, forms small droplets
lipid droplets fuse together, moves towards apical membrane, drop out of cell
stages of milk content
1. colostrum
day 1-3
creamy yellow
proteins, immunoglobin, minerals, vitamins
2. transitional milk
2-4 days
breast milk wuith some colostrum
3. mature milk
7+ days
90% water
10% carbs, proteins, fats
factors affecting milk production
breed/genotype
nutrition, energy level in diet
health/disease
interval since last milk withdrawal
litter size
age
stage of lactation
cellular mechanisms for milk synthesis & secretion
exocytosis
golgi derived vesicles
most components
lipid synthesis and secretion
bulge against and eventually released bound by membrane
packed in Golgi
fatty acids, glycerol
transmembrane secretion
ions and water
transcytosis
for small molecules
eg. immunoglobins, hormones, albumin
paracellular pathway
direct transfer between tissue
if bacteria invades --> mastitis