Mammary gland and lactogenesis

Question 1

Define mammogenesis?

Answer 1

— Mammary growth at puberty or during pregnancy.

Question 2

Define lactogenesis?

Answer 2

— Initiation of milk secretion at parturition — production of colostrum.

Question 3

Define galactopoiesis?

Answer 3

— Continued milk secretion during lactation.

Question 4

Where do mammary glands originate from?

Answer 4

. Mammary glands are glands that originate from the
epidermis.
. They arise along two lateral lines on the ventral
surface of the developing fetus.
. These lines are called mammary ridges.
. Mammary ridges extend from the axillary region
to the inguinal region.
. Number and position of glands depend on the
species.

Question 5

What is the anatomy of the mammary gland?

Answer 5

Glandular tissue with secretory epithelial cells and excretory ducts.

Excretory ducts empty into the gland cistern.

Epithelial cells surround a spherical lumen: alveolus (also called alveolar cells).

Myoepithelial cells surround each alveolus and the ducts.

Contraction of rnyoepithelial cells propels the milk out of the alveoli

Groups of aveoli form lobules

Groups of lobules form the the lobes

Question 6

Which animals have two canals per teat?

Answer 6

Camel.

Question 7

Which animals have 1 canal/cistern per teat?

Answer 7

Cow, ewe and goat.

Question 8

Which animals have 2-3 ducts per teat?

Answer 8

Mare and sow.

Question 9

Which animals have 5-6 ducts per teat?

Answer 9

Bitch and queen.

Question 10

Which animals have 8-10 ducts per teat?

Answer 10

Primates and elephants.

Question 11

How are monotremes (platypus) different with regards to milk secretion?

Answer 11

— Mammary tissue is essentially a band of sweat
glands.
— No teats — the milk runs out along the hair
shafts.

Question 12

How is the udder suspended in ruminants?

Answer 12

The ruminant mammary gland (udder) is
supported by a strong suspensory ligament,
divided into two parts:
1. Medial suspensory ligament arising from
the symphyseal tendon (attaches the prepubic
tendon to the pubic symphysis). Mainly connective tissue.
2. Lateral suspensory ligaments running from
the symphseal tendon and the external crus
of the inguinal ring, assisted by the medial
femoral fascia, and then runs ventrally over the
lateral aspect of the udder. Inelastic connective
tissue.

Question 13

Thoracic glands are supplied by what vasculature?

Answer 13

mammary arteries are branches of thoracic and pectoral aa.

Question 14

Abdominal glands are supplied by what vasculature?

Answer 14

Branches of the cranial and caudal superficial epigastric aa.

Question 15

Inguinal glands are supplied by

Answer 15

Mammary aa. which are branches of the external pudendal a.

Question 16

Why is lymphatic drainage important to consider when removing a mammary tumour?

Answer 16

Lymphatic drainage of dogs, it drains either caudally or cranially respective to area but the middle glands go each way and we don’t know which way it is this
very important when removing mammary tumours as need to consider the lymph drainage.

Question 17

What is venous and lymphatic drainage of the bovine mammary gland?

Answer 17

Venous drainage is via:
— The external pudendal veins into the ext. iliacs then caudal vena cava.
— The superficial epigastric veins (aka milk veins) then to the internal thoracic vein, then the cranial vena cava.
— The perineal veins into the internal pudendal vein
then the caudal vena cava.

Lymphatic drainage arises in lobules, not in alveoli. It leaves gland via mammary lymph nodes (upper rear of udder in cattle).

Question 18

What is the innervation of the bovine mammary gland?

Answer 18

No parasympathetic innervation.

Four spinal nerves supply them 1st and 2nd lumbar, inguinal and perineal.

Question 19

What is isometric growth and allometric growth?

Answer 19

Isometric growth means that all the body parts grow at approximately the same rate and the adult proportions are not significantly different from those of the
juvenile.

Allometric growth. the increase in size of different organs or parts of an organism at various rates.

Question 20

How does mammary gland involution occur?

Answer 20

As the need for milk as sole nutrient begins to
decrease pressure builds up in the gland.
Cells become less functional (pressure atrophy).
Cells become atrophic and die by apoptosis.
Immune cells (lymphocytes and macrophages)
invade the tissue (they participate in the production
of IgG for the next lactation).
Cells will remain non functional until next
pregnancy.

Question 21

What does colostrum contain?

Answer 21

Contains more proteins, fat, minerals and vitamins
than regular milk. However lactose concentration is
lower.
•Proteins: transfer of IgG, IgM, IgA from blood to
milk.
•Supplies the newborn with immunoprotection.
— Very important in equidae and bovidae.
— In primates and partially in dogs & cats this is also
provided by blood exchange through the placenta.

Question 22

Milk has the same osmolarity as what?

Answer 22

Blood

Question 23

Milk’s pH is?

Answer 23

6.6-6.9

Question 24

What synthesises the majority of milk components and why?

Answer 24

Epithelial cells synthesise the majority of milk components due to high number of mitochrondria.

Mitochondria: synthesis of fatty acids and non
essential amino acids.

RER: synthesis of secretory proteins (Golgi).

SER: synthesis of phospholipids and triglycerides.

Question 25

UDP-galactose + glucose in presence of lactose synthase makes?

Answer 25

Lactose + UDP

Question 26

What cells are normally found in milk?

Answer 26

Milk contains leukocytes and dislodged mammary
epithelial cells.
In healthy cows: 30,000-300,000 cells/mI.
— Too lowcount increases risk of E.coli mastitis.
. During inflammation the number of cells
increases 10-100 times:
— Due to neutrophil invasion.
. Cell density is a parameter of milk quality.

Question 27

After puberty female mammals are either?

Answer 27

Pregnant, lactating or in some form of anoestrus.

Question 28

Mammary function undergoes cycles of?

Answer 28

Mammogenesis, lactogenesis, weaning and involution.

Question 29

What does the placenta produces to induce mammary growth?

Answer 29

Placental lactogen.

Question 30

All fall in P4 near parturition does what?

Answer 30

Releases prolactin inhibition on mammary gland and lactogenesis can begin.

Question 31

What are the primary hormones affecting galactopoeisis?

Answer 31

. Prolactin
. Oestrogen
. Progesterone
. Cortisol

•Density of prolactin receptors is regulated by thyroid,
adrenal and ovarian hormones.
•Prolactin regulates the production of alpha-lactalbulmin.
•Cortisol is necessary for growth and differentiation of
golgi apparatus.
•Progesterone competes with prolactin.

Question 32

P4 induces storage of what during pregnancy?

Answer 32

Arachidonic acid

Question 33

Secretion and release of milk depend on what hormones?

Answer 33

Secretion: Prolactin
Release: Oxytocin

Question 34

Accumulation of milk in alveoli will increase concentrations of?

Answer 34

Feedback Inhibitor of Lactation.

Question 35

How is galactopoeisis maintained?

Answer 35

Suckling stimulus ->paraventricular nucleus
— Reduction in dopamine (PIF) releases inhibition on
prolactin release from adenohypophysis.
— Increased vasoactive intestinal polypeptide (VIP)
stimulates prolactin release.
Tactile stimulation of mammae maintains
prolactin production i.e. suckling and removing
milk keeps lactation going.
. Only needs 2-3x daily suckling to maintain
prolactin.
. Only tactile stimulation works

Question 36

Suckling does what to dopamine?

Answer 36

Suckling reduces dopamine production in the hypothalamus, which allows increased prolactin secretion.

Question 37

What do myoepithelial cells do and what do they react to?

Answer 37

Myoepithelial cells surround alveoli these cells function to squeeze milk out of alveoli into the ducts. They contract in response to oxytocin.

Question 38

Oxytocin has several roles. Name some?

Answer 38

• Contraction of myometrium.
• Milk ejection.
• Part of the feedback cycle for luteolysis.
• Maternal bonding.
• Social bonding.
  . Stimuli for parturition and milk let-down:
  — Stretching of cervix.
  — Suckling on teats.
  — (Also auditory cues).

Question 39

How does metabolism during lactation adjust to maintain a homeorhectic flow during lactation?

Answer 39

— Reduced fat synthesis and increased lipolysis.
— Decreased uptake of glucose in muscle and adipose
tissue-increased mammary uptake.
— Increased uptake of amino acids in the mammary gland
(breakdown of muscle protein is not sufficient).
— These changes are regulated by prolactin, growth
hormone and insulin.