Mammary Gland – Development and Gross Anatomy

Question 1

What is the significance of lactation?

Answer 1

Frees neonates from dependency on other foods, allows offspring to continue to develop outside the uterus, provides for social development and bonding, provides a natural form of contraception

Question 2

From where does the mammary gland originate?

Answer 2

Originates from the epidermis, two mammary ridges on the ventral surface of the developing embryo extend from the axillary region to the inguinal region, number and position of glands depends on the species

Question 3

What happens during pre-natal mammogenesis?

Answer 3

Mammary ridges give rise to the primary mammary bud, the primary buds push into the dermis to grow, this growth will branch into secondary mammary bud, the secondary finally bran out and canalise to form lactiferous ducts

Question 4

Describe the anatomy of the mammary gland

Answer 4

Glandular tissue with secretory epithelial cells and excretory ducts (empty into the gland cistern), epithelial cells surround a spherical lumen – alveolus (also called alveolar cells), myoepithelial cells surround the alveolus and the ducts
Groups of alveoli form the lobuli, group of lobuli form the lobes

Question 5

What properls the milk out of the ducts?

Answer 5

Contraction of myoepithelial cells, stimulated by oxytocin

Question 6

Describe the number and position of mammary glands, and the number of ducts per teat, in the common species

Answer 6

Cow – 4, inguinal, 1 duct per teat
Ewe – 2, inguinal, 1 duct per teat
Mare – 2, inguinal, 2-3 ducts per teat
Sow – 16, abdominal, 2-3 ducts per teat
Bitch – 8, abdominal, 5-6 ducts per teat
Primate – 2, thoracic, 8-10 ducts per teat

Question 7

What is the suspensory apparatus of the bovine mammary gland?

Answer 7

Supported by a medial suspensory ligament arising from the abdominal wall, and by lateral suspensory ligaments around the outside of the secretory tissue arising from the subpelvic tendon

Question 8

Describe the innervation of the bovine mammary gland

Answer 8

Somatic sensory innervation (afferent) carries impulses from tactile receptors in the skin – teats and areolae are highly sensitive
Sympathetic motor nerves (efferent) run along blood vessels (in ruminants from lumbar and sacral sympathetic chains)
Four spinal nerves involved – 1st & 2nd lumber, inguinal and perineal
No PSNS innervation, myoepithelial cells are not innervated

Question 9

Describe the vascularisation of the mammary glands

Answer 9

Thoracic glands – mammary arteries are branches of thoracic and pectoral arteries
Inguinal glands – mammary arteries are branches of the pudendal artery

Question 10

What veins are involved in the venous drainage in the bovine mammary gland?

Answer 10

External pudic vein, subcutaneous abdominal vein (milk vein) & perineal vein

Question 11

Describe the vascularisation of mammary glands in cats and dogs

Answer 11

Anterior glands – lateral, internal thoracic & superficial epigastric arteries
Caudal glands – caudal superficial epigastric (from external pudendal)

Question 12

What are the two types of mammary gland growth?

Answer 12

Isometric growth – birth to puberty
Allometric growth – after puberty, ducts begin to branch under the effects of oestrogen, more alveoli are formed under the influence of progesterone, complete and rapid growth of ducts occurs in the presence of prolactin and growth hormone

Question 13

Which hormones are responsible for the synthesis of milk?

Answer 13

Prolactin, adrenal cortical hormones & placental lactogen

Question 14

Describe the process of mammary gland involution

Answer 14

As the need for milk decreases pressure builds up in the gland, cells become less functional, cells become atrophic and die by apoptosis, immune cells (lymphocytes and macrophages) invade the tissue (produce IgG for next lactation), cells will remain non-functional until next pregnancy

Question 15

Define the following terms

Answer 15

Mammogenesis – mammary growth at puberty or during pregnancy
Lactogenesis – initiation of milk secretion at parturition, production of colostrum
Galactopoiesis – continued milk secretion during lactation

Question 16

How does colostrum differ to regular milk?

Answer 16

Contains more proteins (including IgG, IgM, IgA), fat, minerals and vitamins than regular milk, however lactose concentration is lower

Question 17

What component of milk is the main contributor to osmolarity?

Answer 17

Lactose

Question 18

Where are the various components of milk synthesised?

Answer 18

Epithelial cells synthesise the majority of milk components
Mitochondria synthesise fatty acids and non-essential amino acids
RER synthesises secretory proteins
SER synthesises phospholipids and triglycerides

Question 19

How is lactose produced?

Answer 19

UDP-galactose + glucose -> lactose + UDP (enzyme – lactose synthase)

Question 20

From what are lipids produced?

Answer 20

Triglyceride is made from fatty acids in chylomicrons and LDL in the blood, and from glucose (non-ruminants) or acetate and β-hydroxybutyrate (in ruminants)

Question 21

What are the cells in milk?

Answer 21

Milk contains leukocytes and dislodged mammary epithelial cells (in health cows – 30,000-300,000 cells/ml)