lactation

Question 1

stages of mammary development

Answer 1

mammogenesis = mammary epithelial cell (MEC) proliferation

• stimulated by estrogen (+ GH + IGF-1)
• ductal elongation
• throughout puberty
• fluctuation of progesterone influences alveolar development

lactogensis = ductal development & differentiation of MEC into alveolar cells capable of synthesizing & secreting milk

• initiation of lactation
• late pregnancy milk production
• during pregnancy
• inititated by rising estrogen, prolactin, GH, & placental lactogen

galactopoiesis = lactation
* parturition ➔ weaning
* stimulus = emptying of milk & sucking

involution = apoptosis of MEC & regression of mammary gland

Question 2

who lactates

Answer 2

animals in the class mammalia that have fur & mammary glands

• mammals make milk
• monotrema = egg-laying mammals (e.g. platapus)
• marsupials = pouched animals (e.g. kangaroos, koalas, opossums)
• eutherians have a placenta (e.g. cows, horses, humans – majority)

Question 3

milk components & composition

Answer 3

components

• mostly water
• protein (casein & whey) ➔ only found in milk, unique to mammary glands
• fat (triglycerides)
• carbohydrate (lactate) ➔ unique to mammary glands

composition

• varies between species
• colostrum = diff composition than mature milk (higher protein content & maternal antibodies)
• can change based on
  
  • breed
  • stage of lactation (e.g. colostrum vs milk, early, mid, or late)
  • type of feed
  • parity of dam = low many litters (unit of age)
  • age of young

Question 4

mammary gland

Answer 4

• makes & transfers food from parent to offspring
• exocrine gland ➔ designed for synthesis & secretion
  
  • exocrine = ducts (eg ducts salivary & sudoriferous (sweat) glands)
  • range from skin-surface milk patch (monotremes) to defined glands & teats
• milk is synthesized in specialized cells arranged in alveoli then secreted outside body by duct system

Question 5

mammary gland anatomy

Answer 5

• same internal structures, diff external appearance
• # of glands varies w/ species:
  • cow = 4 glands + 4 teats
  • sheep & goats = 2 glands + 2 teats
  • mare = 4 glands + 2 teats
  • sows = 6-20 glands each w/ 1 teat
• glands in ungulates in posterior portion
• glands in humans & primates in anterior portion
• glands in litter-bearing in both anterior & posterior

Question 6

udder anatomy

Answer 6

• each gland w/in udder is separated ➔ acts as own entity
  
  • multiple glands & teats to protect against
    
    • defect/damage
    • infx
  • redundancy & safety precautions
• udder suspensory/support system: set of ligaments & connective tissue keep udder close to body wall
  
  • udder = very very heavy ➔ more milk emptied = more made & filled in
  • not being full/heavy all the time
  • w/out suspension system cow develops pendulous = swinging ➔ ↑ chance of damage & infx
  • median suspensory ligament: 2 parallel sheets of elastic material runs the length of udder = main support ➔ allows expansion
  • lateral suspensory ligament: inflexible fibrous ligaments from pelvis form swing around udder ➔ strong support (more rigid)
  • skin = protection + little bit of support
• made of 2 types of tissue
  
  1. secretory tissue: synthesizing & secreting milk: mammary epithelial cells (MEC) make & secrete milk ➔ main workforce
  2. connective tissue
     
     • fibrous tissue - collagen
     • fatty tissue - adipose
• supramammary lymph node = 2º lymphoid organ ➔ immune surveillance & initiate response
• parenchyma (glandular tissue) = functional part of secretory tissue
• gland cistern & teat cistern = milk storage
• furstenberg’s rosette = mucosal folding that folds over the streak canal as barrier ➔ protection from bacteria/infx
• streak canal = channel where milk exits ➔ circular sphincter muscles hold canal shut
• alveolus = smallest functional unit of secretory tissue
  
  • mammary epithelial cells (MEC) in single layer lining lumen (central cavity)
  • lactose = osmoregulator ➔ draws water in
  • myoepithelial cells = muscular-like cell ➔ contracts when oxytocin is present (+ capillary BV surround each alveolus)
  • squeezing spherical structure forces milk out