ANATOMY AND PHYSIOLOGY - Mammary Glands and Lactation Flashcards
Describe the development of the rudimentary duct system of the mammary glands
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
What is the name of the mammary duct system that the neonate is born with?
Mammary anlagen
Describe the pattern of pre-pubertal growth of the mammary duct system
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
Describe the pattern of peri-pubertal growth of the mammary duct system
The mammary duct system undergoes accelerated growth during the peri-pubertal period due to the influence of steroid hormones (oestrodiol and progesterone)
What are supernumerary teats?
Supernumerary teats are residual, non-functional teats left over from embryonic development
How many pairs of mammary glands does the bitch typically have?
The bitch typically has five pairs of mammary glands (cranial thoracic, caudal thoracic, cranial abdominal, caudal abdominal and inguinal pairs)
In smaller dog breeds, sometimes there are only four pairs of mammary glands. Which pair will typically not develop?
Cranial thoracic mammary glands
How many pairs of mammary glands does the queen typically have?
The queen typically has four pairs of mammary glands (caudal thoracic, cranial abdominal, caudal abdominal and inguinal pairs)
What is an udder?
Consolidated, pendulous mass consisting of one or two pairs of mammary glands located at the inguinal region
How many pairs of mammary glands are found within the equine udder?
The equine udder consists of one pair of inguinal mammary glands
How many pairs of mammary glands are found within the porcine ‘udder’?
The porcine udder consists of six to seven pairs of mammary glands running from the thoracic to the inguinal region
How many pairs of mammary glands are found within the udder of small ruminants (ewe and goat)?
The small ruminant udder consists of one pair of inguinal mammary glands
How many pairs of mammary glands are found within the bovine udder?
The cow udder consists of two pairs of inguinal mammary glands
(T/F) A fully lactating bovine udder can extend all the way from the vulva to the umbilicus
TRUE
What is the name of the structure that divides the the left and right rows of mammae in the bovine udder?
Inter-mammary groove
Where are supernumerary teats usually seen on the bovine udder?
Supernumerary teats are usually seen on the hindquarters of the bovine udder
What is the function of the suspensory apparatus of the udder?
The suspensory apparatus supports the weight of the lactating udder
What are the components which make up the suspensory apparatus?
Paired medial ligaments
Lateral ligaments
What structure are the medial ligaments derived from?
Tunica flava
What structure are the lateral ligaments derived from?
Aperneurotic tendon of the external abdominal oblique muscle
Which structures extend from the medial and lateral ligaments into the glandular parenchyma?
Secondary laminae extend into the glandular parenchyma
Which of the components of the suspensory apparatus is elastic in nature?
Medial ligaments
Which of the components of the suspensory apparatus is collagenous in nature?
Lateral ligaments
What are the structures found within the parenchyma of the mammary glands?
The lobes containing smaller structures known as lobules are located within the parenchyma of the mammary glands
What is contained within the lobules of the mammary gland?
The lobules contain the alveoli and the associated ductiles
What are the two cells found within the alveoli of the mammary glands?
Alveolar cells
Myoepithelial cells
What is the function of the alveolar cells?
The alveolar cells are milk producing cells
What is the function of the myoepithelial cells?
The myoepithelial cells surround the alveoli and contract to eject the milk from the lumen of the alveoli into the lactiferous ducts
Where are all of the main components of milk derived from?
The main components of milk are derived from components of blood
What are the lactiferous ducts?
The lactiferous ducts are large ducts which convey milk from the alveoli to the lactiferous sinus
What is the function of the lactiferous sinus?
The lactiferous sinus is a milk storage cavity
Which two areas make up the lactiferous sinus?
Gland sinus
Teat sinus
What is the teat canal/papillary duct?
The teat canal/papillary duct is the canal running from the teat sinus to the teat ostium
Why is the mucosal surface of the teat canal/papillary duct highly folded with stratified squamous epithelium?
To help seal the duct between milking/suckling to prevent infection
What is the function of the teat sphincter?
The teat sphincter contracts to seal off the duct between milking/suckling to prevent infection
How long does it take the teat sphincter to fully close?
It takes the teat sphincter approximately thirty minutes to fully close
What is the function of the Furstenberg rosette?
The Furstenburg rosette consists of lots of lymphatic tissue so carries out an immunosurveillance function
What is the functional significance of the vascular plexus present in the teat wall?
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
Which species’ have a paired branching duct system per mammary gland (two ostia)?
The mare and the sow have a paired branching duct system
Which species’ have a multiple branching duct system per mammary gland (multiple ostia)?
The bitch and the queen have a multiple branching duct system
What is the main arterial supply to the udder?
External pudendal artery
Why does the external pudendal artery have a sigmoid flexure at the level of the inguinal canal?
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.
What are the two main routes of venous drainage of the udder?
External pudendal vein caudal drainage
Subcutaneous abdominal vein (milk vein) cranial drainage
When and how is the subcutaneous abdominal vein (milk vein) formed?
The subcutaneous abdominal vein (milk vein) develops during the first pregnancy from the anastomosis of the caudal and cranial superficial epigastric veins
Why should you not use the subcutaneous abdominal vein (milk vein) for intravenous injections or blood sampling?
Because the subcutaneous abdominal vein (milk vein) is prone to hematomas
What are the main arterial supplies to the canine, feline and porcine mammary glands?
Lateral thoracic arteries
Internal thoracic arteries
External pudendal arteries
Which lymph nodes drain the udder?
The superficial inguinal lymph nodes
What can be indicated by the enlargement of the superficial inguinal lymph nodes?
Mastitis
What is the main nerve involved in the milk letdown reflex?
Genitofemoral nerve
What are the three hormones which accelerate mammary duct development and maturation during pregnancy?
Oestrodiol
Growth hormone
Cortisol
When does lobulo-alveolar formation occur?
Lobulo-alveolar formation occurs within the second half of pregnancy
Which hormone suppresses the secretory activity of the alveoli before parturition occurs?
Progesterone
What are the two stages of the initiation of milk secretion?
Lactogenesis I
Lactogenesis II
Describe what occurs during lactogenesis I
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
Describe what occurs during lactogenesis II
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
What hormone changes are essential for the onset of lactogenesis II?
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
What are the two main components of milk?
Lactose
Casein
What is the function of the casein protein in milk?
Casein binds to calcium ions
Describe the mechanism of the milk letdown neuroendocrine reflex
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
Which of the lactation reflexes (milk letdown and milk production) can be positively or negatively conditioned?
Milk letdown neuroendocrine reflex
How can stress influence the milk letdown neuroendocrine reflex?
Adrenaline release due to stress can reduce mechanoreceptor and myoepithelial cells stimulation
What is involution of lactation (‘drying off’)?
Involution of lactation is the process by which an active, lactating mammary gland atrophies and regresses into a quiescent state
List three methods that can be used to increase milk yield in the dairy industry?
Genetic selection
Increased milking frequency
Administration of Bovine somatotrophin (bST) growth hormone
How does increases the frequency of milking increase milk yield?
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
(T/F) Bovine somatotrophin (bST) growth hormone is used commonly in the dairy industry
FALSE. Bovine somatotrophin (bST) growth hormone is banned in most countries due to welfare concerns
