Wk.11 Lactation Flashcards
The mammary gland
Are modified sweat glands which produce milk (lactation) to support neonatal development
- Mammary glands develop in both sexes, but only female mammary glands are
functional
- Hormones produced during late gestation are essential for final development
Mammary gland structure - macroscopic
Develop:
- Evenly spaces along mammary ridge (companion animals & pigs)
- Consolidated in udder (4 teets = quarters, 2 teets = halfs)
What is benefit of having multiple mammary glands
Specifically if only have 1 offspring.
- Evolutionary backup (i.e. if one gland is not functional)
- Production capacity of milk is higher (each gland operates independently)àallows for
more frequent feeding (i.e. use next gland)
Mammary gland structure - macroscopic
Each gland consists of: Parenchyma (secretory tissue)
- Lobes containing multiple lobules
- Branching alveoli within lobules
Duct system
- Small ducts draining from lobules
- Large ducts draining from lobes
- Gland cistern (large reservoir – stores milk)
Teat/nipple
- Teat cistern (small reservoir)
- Teat canal
Mammary glands also have lots of connective tissue and fatty deposits
Mammary gland structure – macroscopic TEAT
The teat itself has a relatively sophisticated opening:
- Smooth muscle sphincter
- Teat canal (aka streak canal) w/ significant waxy,
keratin secretion
- Fursentberg’s rosette (mucosal folds)
These features defend the mammary gland against invading pathogens
Different canal systems for different species
Some species have multiple canals per teat Generally one teat = one gland
Mammary gland support - ligaments
Skin
- Minor role in support Median suspensory ligament
- Separates right and left halves
- Connects udder to abdominal wall
- Elastic tissue – responds to weight of
udder
Lateral suspensory ligament
- Surrounds the outer wall of udder
- Attached to prepubic and subpubic
tendons
- inflexible
Mammary gland support - vasculature
Entry = external pudendal a.
Exit = external pudendal v and subcutaneous abdominal (Milk) v
* milk vein VERY obvious
Mammary gland structure - microscopic
The secretory tissue is made of alveoli (sac like structures) Alveoli contain
- secretory epithelial cells (alveolar cells)
- myoepithelial cells (similar to SM)
- many small capillaries
The placenta has multiple endocrine functions, including promoting development of the dam’s mammary glands
Which placental hormone is involved in mammary development?
Answer: D, Lactogen
Not C (prolactin) comes from pituitary not placenta
Mammary gland development
Mammals are born with rudimentary mammary glands (lactiferous ducts), which further develop during puberty and pregnancy
Hormones drive this development:
- E2 (i.e. during puberty) = branching of ducts
- P4 = initial alveoli formation (during puberty) but inhibits lactogenesis (post puberty). i.e. 2 roles.
- Prolactin (pituitary) and placental lactogen = peak in late gestation, promote alveolar dev and lactogenesis.
Each subsequent lactation causes some more additional growth in secretory tissue.
Prolactin synthesis regulated by E2.
Remember E2 low during pregnancy, but right
at end of gestation it peaks… that late peaks
brings increase in prolactin
Progesterone inhibits lactogenesis. During pregnancy P4 is high, the P4 drop before parturition helps cause lactogenesis.
Milk synthesis
Milk synthesis (lactation) requires both raw inputs and synthesis of products:
- From blood (water, minerals, vitamins, some fats, antibodies)
- Synthesised by alveolar epithelial cells (milk proteins – casein, why, some fats, lactose
What about things that aren’t supposed to be in milk?
If a product doesn’t have drug residue data, you use the standard withholding period = 35 days for milk
Milk letdown
After milk is secreted, it must be ejected to a suckling neonate or milking machine – this process is milk letdown
There is no direct innervation of the alveoli, because myoepithelial cells are not smooth muscles, its because they have receptors to oxytocin, and this is what they respond to when they contract, rather than a direct nerve impulse
Mammary gland involution
Milk production will peak in the first few weeks after parturition and then slowly taper off, due to weaning
Pressure atrophy
- If no milk is being removed from mammary glandàbuild up of pressureàdecrease alveolar functionàdecreased milk production
*Increased secretory tissue will increase milk in subsequent lactations?? * Can extend lactation if continue to take milk out
Mammary Issues
