What is the function of the teat canal aka streak canal in the mammary gland & where is it?
The streak canal/teat canal keeps milk in/bacteria out of udder. It is the canal immediately proximal to the teat sphincter.
What is the teat cistern?
Teat duct with capacity of 30-45 mL; separted from teat canal by Furstenberg’s rosette
What is the gland cistern?
Collecting duct for mammary ducts, capacity up to 400 mL; separated from teat cistern by cricoid fold aka cisternal ringfold; from here branch the mammary milk ducts.
What is the stroma in the mammary gland?
Connective tissue of mammary gland that acts as support system.
What is the parenchyma of the mammary gland?
Glandular, secretory tissue.
What are the alveoli of the mammary gland?
Secreting epithelial cells called alveolar cells; each surrounded by capillary network and myoepithelial cell, which contracts to eject milk into lobule.
What is the function of the duct system of the mammary gland?
Storage & transport of milk; lined by two layers of epithelium; myoepithelium arranged longitudinally; shorten to increase diameter to facilitate milk flow
What are the lobules and lobes of the mammary gland?
Clusters of alveolar tissue supported by stroma;
alveoli → lobules → lobes
What is a galactophore?
Receives milk from lobe, empties into gland cistern.
What separates the mammary gland into four quarters?
Median, lateral and intermammary ligaments. The lateral side produces ~60% of milk, median ~40%.
Median suspensory ligament - separates R & L halves of udder; connects udder to abdominal wall; made of lamellae, elastic tissue that stretches
Lateral suspeonsory ligament - inflexible; surrounds outer wall of udder; attached to prepubic & subpubic tendons
Intermammary groove - formed where lateral suspensory ligament & median suspensory ligament meet
How many gallons of blood need to pass through the udder to make one gallon of milk?
Which arteries supply blood to the udder?
External pudendal arteries
cranial mammary artery.
How does blood exit the udder?
External pudendal veins
Subcutaneous abdominal veins
When does mammogenesis begin and where?
Week 7-8 of gestation -
primary & secondary ducts develop from paired mammary ridges on ventral surface of developing embryo
What are the hormones involved in mammogenesis?
- major influence at puberty, when primary & secondary ducts grow & divide, + ↑ in lobuloalveolar units
- aids devt of stromal tissue
- deposition of fat
- inhibits secretion of milk
- promotes development of lobules & alveoli
- ↑ alveolar-cell proliferation, enlargement → secretory
- inhibits milk secretion (only w/ stim. from PRL)
- IGF-1, cortisol, PRL & relaxin aid in lobuloalveolar growth
- IGF-1, cortisol & relax in aid in ductal growth
When does mammogenesis end?
- receptors for E2 & P4
- in cow, P4 elevated thru gestation, E2
during 2nd half
- E2 & P4 elevated → geometric cell multiplication → lobuloalveolar growth
- 1st half: ductal growth & alveolar formation
- 2nd half: mostly lobuloalveolar growth w/ continuing ductal growth, due to influence of progesterone
Lactogenesis is the onset of milk secretion. When does it begin and where?
- secretory activity accelerates
- colostrum produced
Days 2/3 - 8 postpartum
- copious milk production - milk vol. ↑ rapidly from 36-96 hours postpartum, then levels off
What are the hormones involved in lactogenesis?
Triggered following expulsion of placenta by ↓ P4 & E2 & continued PRL (uninhibited release from ant. pituitary)
Prolactin - (PRL):
- ↑ by oxytocin, ↓ by dopamine (PIH)
- suckling response inhibits PIH; levels rise & fall in proportion to frequency, intensity & duration of nipple & suckling stim
- falls ~50% in first week postpartum in breastfeeding women
- if no breastfeeding, PRL returns non-pregnancy levels by Day 7 postpartum
- JAK-stat signalling cascade important in milk
When does lactogenesis end?
If milk is not regularly suckled, pressure atrophy - pressure from increasing milk volume applied to alveolar cells inhibits lactation.
What is galactopoeisis?
Maintenance of lactation.
Requires removal of milk from breast.
How does galactopoesis begin?
What hormones are involved in galactopoeisis?
Suckling → Thyroid Stimulating Hormone (TSH), Growth Hormone (IGF-1) & ACTH influence general metabolism
PRL - stimulates milk synthesis
What does milk ejection refer to, and when does it begin?
Expulsion of milk from alveoli
Which hormones are involved in milk ejection?
Milk Ejection Reflex (+ feedback):
Suckling → Oxytocin (post. pit)
- causes myoepithelia to contract → stored milk pushed down into ducts thru collecting sinuses → nipple pores/teats
What is involution?
Termination of milk secretion & mammary gland regression
When does involution begin?
Cow: Within 7 days of drying off
Mammary epithelial cells de-differentiate during dry period; aging cells lost by apoptosis & replaced by division of remaining cells
Rodents: Defoliation; mammary epithelial cells fall of basement membrane; requires more extensive regeneration at start of next lactation
When does involution end?
When mammary epithelial cells return to normal size & shape.
What is the composition of milk? What affects the composition, and how does it differ between species and breeds?
Milk composition & volume produced are very variable between & within species.
In general, milk is comprised of fat, protein, lactose & ash. It also contains immunoglobulins from the mother, and growth hormone.