Lecture 24- Mammary Gland and Lactation

Question 1

Mammary Gland

Answer 1

evolved 200 million years ago
distinguished mammals from other animals
secretes milk for the nourishment and survival of newborn

highly evolved and complex epidermal gland

• branched tubule-alveolar structure with apocrine mode of secretion
• diverse cell composition

Question 2

Parenchyma

Answer 2

derived from ectoderm
glandular or secretory portion of the gland
epithelial cells, alveoli, ducts, and cisterns
embedded in the storm

Question 3

Stroma

Answer 3

derived from mesoderm
cellular: adipose tissue, blood vessels, nerves, myoepithelial cells, fibroblasts, immune cells
Acellular: supportive connective tissue, extracellular matrix and collagen

Question 4

Parenchyma Tissue Structure of Dairy Cows

Answer 4

Alveolus- secretory basic unit of the gland lined by secretory epithelial cells

Ducts- drainage of milk from alveoli

Lobules- group of adjacent lobules drained by a common duct and encased in connective tissue septum

lobes- group of adjacent lobules drained by a common duct and encased in connective tissue septum

gland cistern- storage ~ 400mL
teat cistern- storage ~ 40mL

streak canal and sphincter muscle
- holds milk inside and bacteria outside the udder

Question 5

Secretory Pathways of Alveolar cell from lactating mammary gland

Answer 5

these pathways operate in parallel to transform precursors derived from the blood or interstitial fluid into milk constituents

exocytosis –> lipid –> apical transport –> transcytosis –> paracellular pathway

Question 6

Mammary Epithelium

Answer 6

lined by epithelial cells that synthesize and secrete milk
alveoli: small bulb- shaped structure with hollow centre or lumen that collects milk components and water

surrounded by:

• network of capillaries- supply precursors and deliver hormones
• myoepithelial cells- induce milk ejection by contraction when stimulated by oxytocin
• basement membrane- selective transfer of molecules
• interstice

terminal ducts provide a way out for the milk produced

• lined by two layers of epithelium
• myoepithelial cells arranged longitudinally

Question 7

Neural Regulation of Milk Letdown

Answer 7

autonomic nervous system: maintains homeostasis

• parasympathetic: normal activity
• sympathetic: fight/ flight response
  - inhibit milk letdown
  - vasoconstriction
• somatic nervous system: respond to external stimuli
  
  • stimulus
    
    • touch: calf suckling, udder wipe
    • sound: milking machine, music
      - visual: something different
  • response
    
    • oxytocin release
    • muscle contraction- myoepithelial cells of the alveoli
    • milk ejection

Question 8

Colostrum

Answer 8

first milk removed after calving
high concentration of immunoglobulins
important for passive transfer of immunity
failure in passive transfer results in greater mortality and morbidity and reduced performance

Question 9

Mammogenesis

Answer 9

is the process of structural gland development
- pre and post natal
most development occurs in late pregnancy

Question 10

Lactogenesis

Answer 10

is the process of milk synthesis and secretion

- few weeks prior and after parturition

Question 11

Milk secretion

Answer 11

is the synthesis/ secretion by epithelial cells to alveolar lumen

Question 12

milk removal

Answer 12

is the passive removal from the cistern and the ejection of milk from the alveolar lumen