Reproduction -Mammary Gland

Question 1

What is the function of the teat canal aka streak canal in the mammary gland & where is it?

Answer 1

The streak canal/teat canal keeps milk in/bacteria out of udder. It is the canal immediately proximal to the teat sphincter.

Question 2

What is the teat cistern?

Answer 2

Teat duct with capacity of 30-45 mL; separted from teat canal by Furstenberg’s rosette

Question 3

What is the gland cistern?

Answer 3

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.

Question 4

What is the stroma in the mammary gland?

Answer 4

Connective tissue of mammary gland that acts as support system.

Question 5

What is the parenchyma of the mammary gland?

Answer 5

Glandular, secretory tissue.

Question 6

What are the alveoli of the mammary gland?

Answer 6

Secreting epithelial cells called alveolar cells; each surrounded by capillary network and myoepithelial cell, which contracts to eject milk into lobule.

Question 7

What is the function of the duct system of the mammary gland?

Answer 7

Storage & transport of milk; lined by two layers of epithelium; myoepithelium arranged longitudinally; shorten to increase diameter to facilitate milk flow

Question 8

What are the lobules and lobes of the mammary gland?

Answer 8

Clusters of alveolar tissue supported by stroma;

alveoli → lobules → lobes

Question 9

What is a galactophore?

Answer 9

Receives milk from lobe, empties into gland cistern.

Question 10

What separates the mammary gland into four quarters?

Answer 10

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

Question 11

How many gallons of blood need to pass through the udder to make one gallon of milk?

Answer 11

400 gallons.

Question 12

Which arteries supply blood to the udder?

Answer 12

External pudendal arteries

&

cranial mammary artery.

Question 13

How does blood exit the udder?

Answer 13

Via the:

External pudendal veins

&

Subcutaneous abdominal veins

Question 14

When does mammogenesis begin and where?

Answer 14

Week 7-8 of gestation -
primary & secondary ducts develop from paired mammary ridges on ventral surface of developing embryo

Question 15

What are the hormones involved in mammogenesis?

Answer 15

• *Oestrogen (E2)**
• 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
• *Progesterone (P4)**
• 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

Question 16

When does mammogenesis end?

Answer 16

Pregnancy only

• 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

Question 17

Lactogenesis is the onset of milk secretion. When does it begin and where?

Answer 17

• *Lactogenesis 1**
• late pregnancy*
• secretory activity accelerates
• colostrum produced
• *Lactogenesis 2**
• Days 2/3 - 8 postpartum*
• copious milk production - milk vol. ↑ rapidly from 36-96 hours postpartum, then levels off

Question 18

What are the hormones involved in lactogenesis?

Answer 18

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
  production

Question 19

When does lactogenesis end?

Answer 19

If milk is not regularly suckled, pressure atrophy - pressure from increasing milk volume applied to alveolar cells inhibits lactation.

Question 20

What is galactopoeisis?

Answer 20

Maintenance of lactation.
Requires removal of milk from breast.

Question 21

How does galactopoesis begin?

Answer 21

Post-partum suckling.

Question 22

What hormones are involved in galactopoeisis?

Answer 22

Suckling → Thyroid Stimulating Hormone (TSH), Growth Hormone (IGF-1) & ACTH influence general metabolism
PRL - stimulates milk synthesis

Question 23

What does milk ejection refer to, and when does it begin?

Answer 23

Expulsion of milk from alveoli
“let down”.

Question 24

Which hormones are involved in milk ejection?

Answer 24

Milk Ejection Reflex (+ feedback):

Suckling → Oxytocin (post. pit)
- causes myoepithelia to contract → stored milk pushed down into ducts thru collecting sinuses → nipple pores/teats

Question 25

What is involution?

Answer 25

Termination of milk secretion & mammary gland regression

Question 26

When does involution begin?

Answer 26

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

Question 27

When does involution end?

Answer 27

When mammary epithelial cells return to normal size & shape.

Question 28

What is the composition of milk? What affects the composition, and how does it differ between species and breeds?

Answer 28

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.