Mammary gland development

Question 1

Define Mammogenesis

Answer 1

Mammogenesis: Mammary growth at puberty or during pregnancy.

Question 2

Define Lactogenesis

Answer 2

Lactogenesis: Initiation of milk secretion at parturition – production of colostrum.

Question 3

Define Galactopoiesis

Answer 3

Galactopoiesis: Continued milk secretion during lactation.

Question 4

Where do mammary glands develop?

Answer 4

They arise along two lateral lines on the ventral surface of the developing fetus called mammary ridges. The mammary ridges extend from the axillary region to the inguinal region.

Question 5

How do mammary glands develop?

Answer 5

Mammary glands are glands that originate from the epidermis, they are thickened epidermal tissue that develops into a primary mammary bud. This bud then branches and grows deeper into the dermis and becomes a secondary mammary bud.
These then canalise and become lactiferous ducts

Question 6

Each alveolus is surrounded by ……………

Answer 6

Myoepithelial cells surround each alveolus and the ducts.

Contraction of myoepithelial cells propels the milk out of the alveoli into the ducts

Question 7

What are the lobules?

Answer 7

Groups of alveoli form the lobules (~200 alveoli surrounded by connective tissue) and groups of lobules form lobes

Question 8

Dog teats:
How many?
How many canals per teat?
Position?

Answer 8

Approx 10
8-22
Abdominal

Question 9

Cat teats:
How many?
How many canals per teat?
Position?

Answer 9

8 teats
4-8 canals
Abdominal

Question 10

Sow teats:
How many?
How many canals per teat?
Position?

Answer 10

8-18 teats
2 canals
Abdominal

Question 11

Cow teats:
How many?
How many canals per teat?
Position?

Answer 11

4 teats
1 canal
Inguinal

Question 12

Mare teats:
How many?
How many canals per teat?
Position?

Answer 12

2 teats
1 canal
Inguinal

Question 13

How are marsupial mammary gland different?

Answer 13

Mammary glands within the pouch.

Young form a direct seal around the teat.

Question 14

How are monotremes mammary gland different?

Answer 14

Mammary tissue is essentially a band of sweat glands.

No teats – the milk runs out along the hair shafts.

Question 15

Describe the suspensory ligaments of the mammary glands

Answer 15

1. Medial suspensory ligament arising from the symphyseal tendon (attaches the prepubic tendon to the pubic symphysis). Mainly yellow elastic connective tissue.
2. Lateral suspensory ligaments running from the symphyseal 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 16

Which ligament is responsible for lateral deviation of the teats in the older cow?

Answer 16

Medial suspensory ligament

Question 17

What is the blood supply to thoracic mammary glands?

Answer 17

Mammary arteries are branches of thoracic and pectoral aa

Question 18

What is the blood supply to abdominal mammary glands?

Answer 18

Branches of the cranial and caudal superficial epigastric aa.

Question 19

What is the blood supply to Inguinal mammary glands?

Answer 19

Mammary aa. are branches of the external pudendal a.

Question 20

What is the blood supply to the mammary glands of cats and dogs?

Answer 20

Anterior glands: lateral and internal thoracic, cranial superficial epigastric aa.
Caudal glands: caudal superficial epigastric aa. (from external pudendal)

Question 21

What is the lymph supply to the mammary glands (not cow)?

Answer 21

Cranial glands lead to axillary, and accessory axillary
Caudal glands lead to superficial inguinal (mammary) nodes
Note that lymph from middle glands drains either caudally or cranially, not a mixture.

Question 22

What is the venous drainage of the cow udder?

Answer 22

Venous drainage is via:
The external pudendal veins into the ext. iliacs then cau.v.cava.
The superficial epigastric veins (a.k.a milk veins) then to the internal thoracic v, then the cranial vena cava.
The perineal veins into the internal pud.v. then the caudal vena cava.

Question 23

What is the lymphatic drainage of the cow udder?

Answer 23

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

These are the superficial inguinal. L.n. of other species.

Question 24

Describe the innervation of the cows udder

Answer 24

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 in cattle (1st, 2nd lumbar, inguinal and perineal)

No parasympathetic innervation
Myoepithelial cells are not innervated

Question 25

How is mammary gland growth mediated

Answer 25

It is endocrine mediated, and complete development and ability to secrete milk does not occur until puberty.

Question 26

Is growth of the mammary glands linear?

Answer 26

Birth to puberty: isometric growth (like any other tissue).

After puberty: allometric growth

Question 27

What is the effect of oestrus cycle on the mammary gland?

Answer 27

During oestrous or menstrual cycles ducts begin to branch under the effect of oestrogen, whereas more alveoli are formed under the influence of progesterone

Question 28

What stimulates complete and rapid growth of the mammary gland?

Answer 28

Complete and rapid growth of ducts occurs in the presence of prolactin and growth hormone (increase at puberty).

During pregnancy: terminal alveoli grow into lobules. Prolactin, adrenal cortical hormones and placental lactogen (relaxin from CL in pigs) allow the synthesis of milk.

Question 29

How is the secretion of milk inhibited?

Answer 29

As the need for milk as sole nutrient begins to decrease pressure builds up in the gland.
Cells become less functional (pressure atrophy) until they 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.