ANATOMY AND PHYSIOLOGY - Mammary Glands and Lactation

Question 1

Describe the development of the rudimentary duct system of the mammary glands

Answer 1

The rudimentary duct system develops during embryonic development from the proliferation of the epidermis of the thoracic to inguinal regions of the mammary ridge followed by the invagination of the tissue into the underlying mesoderm

Question 2

What is the name of the mammary duct system that the neonate is born with?

Answer 2

Mammary anlagen

Question 3

Describe the pattern of pre-pubertal growth of the mammary duct system

Answer 3

The mammary duct system undergoes isometric growth until reaching a period of allometric growth just before puberty where the duct system develops at a faster rate than the rest of the organism

Question 4

Describe the pattern of peri-pubertal growth of the mammary duct system

Answer 4

The mammary duct system undergoes accelerated growth during the peri-pubertal period due to the influence of steroid hormones (oestrodiol and progesterone)

Question 5

What are supernumerary teats?

Answer 5

Supernumerary teats are residual, non-functional teats left over from embryonic development

Question 6

How many pairs of mammary glands does the bitch typically have?

Answer 6

The bitch typically has five pairs of mammary glands (cranial thoracic, caudal thoracic, cranial abdominal, caudal abdominal and inguinal pairs)

Question 7

In smaller dog breeds, sometimes there are only four pairs of mammary glands. Which pair will typically not develop?

Answer 7

Cranial thoracic mammary glands

Question 8

How many pairs of mammary glands does the queen typically have?

Answer 8

The queen typically has four pairs of mammary glands (caudal thoracic, cranial abdominal, caudal abdominal and inguinal pairs)

Question 9

What is an udder?

Answer 9

Consolidated, pendulous mass consisting of one or two pairs of mammary glands located at the inguinal region

Question 10

How many pairs of mammary glands are found within the equine udder?

Answer 10

The equine udder consists of one pair of inguinal mammary glands

Question 11

How many pairs of mammary glands are found within the porcine ‘udder’?

Answer 11

The porcine udder consists of six to seven pairs of mammary glands running from the thoracic to the inguinal region

Question 12

How many pairs of mammary glands are found within the udder of small ruminants (ewe and goat)?

Answer 12

The small ruminant udder consists of one pair of inguinal mammary glands

Question 13

How many pairs of mammary glands are found within the bovine udder?

Answer 13

The cow udder consists of two pairs of inguinal mammary glands

Question 14

(T/F) A fully lactating bovine udder can extend all the way from the vulva to the umbilicus

Answer 14

TRUE

Question 15

What is the name of the structure that divides the the left and right rows of mammae in the bovine udder?

Answer 15

Inter-mammary groove

Question 16

Where are supernumerary teats usually seen on the bovine udder?

Answer 16

Supernumerary teats are usually seen on the hindquarters of the bovine udder

Question 17

What is the function of the suspensory apparatus of the udder?

Answer 17

The suspensory apparatus supports the weight of the lactating udder

Question 18

What are the components which make up the suspensory apparatus?

Answer 18

Paired medial ligaments
Lateral ligaments

Question 19

What structure are the medial ligaments derived from?

Answer 19

Tunica flava

Question 20

What structure are the lateral ligaments derived from?

Answer 20

Aperneurotic tendon of the external abdominal oblique muscle

Question 21

Which structures extend from the medial and lateral ligaments into the glandular parenchyma?

Answer 21

Secondary laminae extend into the glandular parenchyma

Question 22

Which of the components of the suspensory apparatus is elastic in nature?

Answer 22

Medial ligaments

Question 23

Which of the components of the suspensory apparatus is collagenous in nature?

Answer 23

Lateral ligaments

Question 24

What are the structures found within the parenchyma of the mammary glands?

Answer 24

The lobes containing smaller structures known as lobules are located within the parenchyma of the mammary glands

Question 25

What is contained within the lobules of the mammary gland?

Answer 25

The lobules contain the alveoli and the associated ductiles

Question 26

What are the two cells found within the alveoli of the mammary glands?

Answer 26

Alveolar cells Myoepithelial cells

Question 27

What is the function of the alveolar cells?

Answer 27

The alveolar cells are milk producing cells

Question 28

What is the function of the myoepithelial cells?

Answer 28

The myoepithelial cells surround the alveoli and contract to eject the milk from the lumen of the alveoli into the lactiferous ducts

Question 29

Where are all of the main components of milk derived from?

Answer 29

The main components of milk are derived from components of blood

Question 30

What are the lactiferous ducts?

Answer 30

The lactiferous ducts are large ducts which convey milk from the alveoli to the lactiferous sinus

Question 31

What is the function of the lactiferous sinus?

Answer 31

The lactiferous sinus is a milk storage cavity

Question 32

Which two areas make up the lactiferous sinus?

Answer 32

Gland sinus Teat sinus

Question 33

What is the teat canal/papillary duct?

Answer 33

The teat canal/papillary duct is the canal running from the teat sinus to the teat ostium

Question 34

Why is the mucosal surface of the teat canal/papillary duct highly folded with stratified squamous epithelium?

Answer 34

To help seal the duct between milking/suckling to prevent infection

Question 35

What is the function of the teat sphincter?

Answer 35

The teat sphincter contracts to seal off the duct between milking/suckling to prevent infection

Question 36

How long does it take the teat sphincter to fully close?

Answer 36

It takes the teat sphincter approximately thirty minutes to fully close

Question 37

What is the function of the Furstenberg rosette?

Answer 37

The Furstenburg rosette consists of lots of lymphatic tissue so carries out an immunosurveillance function

Question 38

What is the functional significance of the vascular plexus present in the teat wall?

Answer 38

The vascular plexus engorges in response to the correct stimulus and causes the teat to become erect, allowing the teat to be easily taken into the mouth of the neonate for suckling

Question 39

Which species' have a paired branching duct system per mammary gland (two ostia)?

Answer 39

The mare and the sow have a paired branching duct system

Question 40

Which species' have a multiple branching duct system per mammary gland (multiple ostia)?

Answer 40

The bitch and the queen have a multiple branching duct system

Question 41

What is the main arterial supply to the udder?

Answer 41

External pudendal artery

Question 42

Why does the external pudendal artery have a sigmoid flexure at the level of the inguinal canal?

Answer 42

The sigmoid flexure of the external pudendal artery allows for downward distension of the udder as it fills with milk, without stretching the blood vessels.

Question 43

What are the two main routes of venous drainage of the udder?

Answer 43

External pudendal vein *caudal drainage* Subcutaneous abdominal vein (milk vein) *cranial drainage*

Question 44

When and how is the subcutaneous abdominal vein (milk vein) formed?

Answer 44

The subcutaneous abdominal vein (milk vein) develops during the first pregnancy from the anastomosis of the caudal and cranial superficial epigastric veins

Question 45

Why should you not use the subcutaneous abdominal vein (milk vein) for intravenous injections or blood sampling?

Answer 45

Because the subcutaneous abdominal vein (milk vein) is prone to hematomas

Question 46

What are the main arterial supplies to the canine, feline and porcine mammary glands?

Answer 46

Lateral thoracic arteries Internal thoracic arteries External pudendal arteries

Question 47

Which lymph nodes drain the udder?

Answer 47

The superficial inguinal lymph nodes

Question 48

What can be indicated by the enlargement of the superficial inguinal lymph nodes?

Answer 48

Mastitis

Question 49

What is the main nerve involved in the milk letdown reflex?

Answer 49

Genitofemoral nerve

Question 50

What are the three hormones which accelerate mammary duct development and maturation during pregnancy?

Answer 50

Oestrodiol Growth hormone Cortisol

Question 51

When does lobulo-alveolar formation occur?

Answer 51

Lobulo-alveolar formation occurs within the second half of pregnancy

Question 52

Which hormone suppresses the secretory activity of the alveoli before parturition occurs?

Answer 52

Progesterone

Question 53

What are the two stages of the initiation of milk secretion?

Answer 53

Lactogenesis I Lactogenesis II

Question 54

Describe what occurs during lactogenesis I

Answer 54

When lobulo-alveolar formation occurs mid-pregnancy, the alveolar cells produce a serum like secretion which is reabsorbed due to the 'leaky junctions' of the mammary epithelium

Question 55

Describe what occurs during lactogenesis II

Answer 55

After parturition, the alveolar cells produce colostrum followed by milk. These secretions are not reabsorbed due to the development of tight junctions between the mammary epithelial cells so instead the colostrum and milk accumulate in the alveolar lumen, travel through the lactiferous ducts and into the lactiferous sinus

Question 56

What hormone changes are essential for the onset of lactogenesis II?

Answer 56

For lactogenesis II to occur, progesterone must decline to allow for the expression of prolactin receptors which allow the binding of circulating prolactin and thus the differentiation of the alveolar cells to allow milk secretion

Question 57

What are the two main components of milk?

Answer 57

Lactose Casein

Question 58

What is the function of the casein protein in milk?

Answer 58

Casein binds to calcium ions

Question 59

Describe the mechanism of the milk letdown neuroendocrine reflex

Answer 59

Mechanical stimulation of the udder base or teats stimulates oxytocin release from the posterior pituitary gland. Oxytocin binds to oxytocin receptors on the myoepithelial cells stimulating the contraction of the alveoli and thus milk letdown

Question 60

Which of the lactation reflexes (milk letdown and milk production) can be positively or negatively conditioned?

Answer 60

Milk letdown neuroendocrine reflex

Question 61

How can stress influence the milk letdown neuroendocrine reflex?

Answer 61

Adrenaline release due to stress can reduce mechanoreceptor and myoepithelial cells stimulation

Question 62

What is involution of lactation ('drying off')?

Answer 62

Involution of lactation is the process by which an active, lactating mammary gland atrophies and regresses into a quiescent state

Question 63

List three methods that can be used to increase milk yield in the dairy industry?

Answer 63

Genetic selection Increased milking frequency Administration of Bovine somatotrophin (bST) growth hormone

Question 64

How does increases the frequency of milking increase milk yield?

Answer 64

Increased milking frequency reduces the accumulation of milk which inhibits milk production due to the actions of FIL (feedback inhibitor of lactation) which suppresses milk synthesis if there is no demand

Question 65

(T/F) Bovine somatotrophin (bST) growth hormone is used commonly in the dairy industry

Answer 65

FALSE. Bovine somatotrophin (bST) growth hormone is banned in most countries due to welfare concerns