Mammary System Flashcards
What type of organ is the mammary gland?
A reproductive organ
What is successful lactation required for?
Reproductive performance
What are monotremes?
Egg-laying mammals
What are marsupials?
Pouched mammals
What are placental mammals?
Most mammals and all domestic species
What does it mean to say that the mammary gland is dynamic?
It will not fully develop if it is not necessary
When will the mammary gland develop?
Pregnancy
When is the greatest amount of mammary growth?
First gestation
What are the main components of milk?
Water, protein, fat, carbohydrates, vitamins, and minerals
What proteins are found in milk?
Casein and whey
What fats are found in milk?
Mainly triglycerides
What carbohydrates are found in milk?
Mainly lactose
What vitamins are found in milk?
Fat and water soluble vitamins
What minerals are found in milk?
Iodine, calcium, phosphorus, and more
What do different environments affect?
Milk composition (more fat/water/etc.)
What is the structure of the bovine udder?
Large and heavy and can weigh more than 100lbs
Has 4 teats, 1 per gland
What is the relation between the milk from each gland in a cow?
It does not mix
What is the medial suspensory ligament?
The main support structure
Where is the medial suspensory ligament attached?
The abdominal wall
What is the medial suspensory ligament made of and why?
It’s made of elastic tissue because it needs flexibility and less tension
What are the four individual glands of the cow called?
Separate quarters
How do the quarters relate to each other?
They are mostly independent
What are the three main parts of each bovine gland?
Teat, annular ring, gland cistern
What are the parts of the teat?
Apex, teat canal, Furstenberg’s rosette, teat cistern
What is the functional/secretory unit of the mammary gland?
Alveolus
What are the four parts of the alveolus?
Secretory/luminal epithelial cells, myoepithelial cells, ductal epithelial cells, and arterioles, capillaries, and venules
What lines the alveoli and how does it vary?
Simple epithelium that varies from columnar to cuboidal in height
What happens to the ducts of the alveolus?
The small initial ducts converge to form larger ducts, which converge to form larger ducts
What do the alveolar ducts terminate in?
A large, single basin called the lactiferous sinus
What is the lactiferous sinus divided into?
The gland cistern and the teat cistern
What marks the difference between the gland cistern and teat cistern
The annular ring, which contains a vein and some smooth muscle
What does the wall of the empty cistern have and what happens when the cistern is full of milk?
It contains overlapping longitudinal and circular folds that go away when the cistern is full
The wall also contains diverticula/pockets
What connects the teat cistern with the external teat?
A narrow opening at the end called the teat canal, streak canal, or papillary duct
What does the teat canal open at?
Ostium papillae
What surrounds the distal end of the teat canal?
A sphincter of smooth muscle fibers
What is the udder supported by?
Dense system of fibroelastic ligaments called the suspensory apparatus
What are the supportive elments of the suspensory apparatus?
Two medial laminae
Why are the medial laminae able to be easily separated?
They are only connected by loose areolar connective tissue with almost no blood vessels or nerves passing through them
Where are the medial laminae the thickest?
Close to the body wall
Where are the medial laminae the thinnest and why?
Near the intermammary groove because as they descend, the medial laminae give off sheets of connective tissue that interdigitate into the udder
What part of the suspensory apparatus is composed of dense, white, fibrous connective tissue?
Lateral laminae
How do the lateral laminae compare to the medial laminae?
They are less elastic than the medial laminae because the medial laminae are made mostly of elastic connective tissue
What part of each mammary gland do the lateral laminae pass around?
The lateral side of each half of the mammary gland, meeting at the medial laminae’s both cranial and caudal ends
Where are the lateral laminae thickest and thinnest and why?
It is thickest closest to the body wall and gets thinner as it progresses ventrally because it gives off sheets of connective tissue into the gland
How many litres of blood flow is needed for every litre of milk produced?
At least 500
What percent of cardiac output is devoted to the mammary glands?
~10%
Where does mammary blood supply originate from?
Caudal aorta
What is the path for blood flow to the mammary glands?
Caudal aorta -> external iliac artery -> external pudic/pudendal artery -> Cranial and caudal mammary arteries
Where do the caudal mammary arteries take nutrients?
To the rear of the mammary glands
What is characteristic of the mammary arteries?
Thick walled with no valves
What do the main veins that drain the udder form and where is it attached?
Venous circle/circle of venous that is attached to the abdominal wall
What does the circle of venous allow?
Blood mixing
What are two alternative routes the blood can take to return to the heart?
Inguinal canal/external pudic vein
Subcutaneous abdominal vein/milk vein
What do the nerves in the udder have no direct contact with?
Alveolar cells
What are the three major functions of the afferent neurons in the mammary glands?
They cause milk ejection
They cause neurohormonal reflex
They cause oxytocin release
What does oxytocin release do in the mammary glands?
It causes contraction of the alveoli, which causes milk ejection
What is typical typical nervous function is not present in the mammary gland efferent neurons?
There is no parasympathetic activity in the mammary glands
What neurons cause sympathetic activity in the mammary glands?
Efferent neurons
What does sympathetic activity in the mammary glands result in?
Vasoconstriction, which decreases the amount of nutrients reaching the mammary glands
What hormone causes vasoconstriction in the mammary glands?
Adrenaline/epinephrine
What glands and organs are important for hormone release?
Pituitary gland, thyroid gland, adrenal gland, ovaries, and pancreas
What hormone does the thyroid gland secrete and what is its function?
T3, which increases metabolic rate to meet the metabolic demands of lactation
What hormone does the adrenal gland secrete and what is its function?
Cortisol, which “turns lactation on”
What hormones do the ovaries secrete and what are their function?
Progesterone and estradiol, which help with mammary development
What hormone does the pancreas secrete?
Insulin
Why is the hypophysis/pituitary gland important?
It activates the other glands that secrete hormones
What part of the pituitary gland releases the hormones that activate other glands and organs?
Adeno Hypophysis
What part of the pituitary gland releases oxytocin?
Neurohypophysis
What hormones are released from the adenohypophysis?
Prolactin, Thyroid stimulating hormone (TSH), LH, FSH, Somatotropin, Adrenocorticotropic hormone (ACTH)
What is hypophysectomy?
Destruction of the pituitary gland
What happens is hypophysectomy occurs?
No hormones are released and lactation doesn’t occur
What is galactopoiesis?
The enhancing/continued production of lactation
What hormone assists with galactopoiesis?
Growth hormone (rbST)
What type of hormone is oxytocin?
Peptide hormone
Where is oxytocin produced?
Hypothalamus
Where is oxytocin released from?
Neurohypophysis
What is oxytocin responsible for?
Milk ejection
What can cause oxytocin release?
Sights and sounds related to milking
What cells are responsible for milk secretion and what do they specifically do?
Epithelial cells lining the alveoli. They synthesize and release lipids, proteins, and lactose for milk
What happens to the epithelial cells when the alveoli are filled with milk?
They shrink, become low-cuboidal epithelium, and have relatively low secretory activity
After milk is released, what happens to the epithelium cells lining the alveoli?
They increase their secretory activity and begin to fill the alveoli again
What describes the shape of the epithelial cells lining the alveoli during the milk secretion process?
They start columnar and gradually reduce to cuboidal as the alveoli fill with milk
What is lactogenesis?
The establishment of milk secretion
What function does estrogen have in lactogenesis?
Promotes the growth of the ductile system
What function does progesterone have in lactogenesis?
It acts with estrogen to promote the growth and anatomical development of the secretory alveoli
What is prolactin’s role in lactogenesis?
Helps with anatomical and functional development of secretory epithelium to promote milk secretion
When is increased prolactin needed?
Near parturition so lactogenesis and milk secretion can adequately occur
What can stop milk let-down?
Epinephrine/adrenaline
Where is epinephrine released from and what can cause it to be released?
It’s released from the adrenal medulla and can be triggered by rough handling, loud noises, and rough milking
What are three effects that epinephrine release can have?
1.) Blocks oxytocin release from the pituitary gland
2.) Reduces mammary blood flow by slowing the smooth muscle contractions
3.) Blocks oxytocin receptors on epithelial cells
What does proper teat stimulation result in?
Oxytocin release (ejections are increased, not production)
Increased circulating oxytocin concentration
Increased myoepithelial cell contraction
Enhanced milk harvest
Decreased milking time
What can milking/nursing empty?
Only the cisterns and largest ducts of the udder
What forces milk from the alveoli to the cisterns?
Contraction of the myoepithelial cells surrounding the alveoli
When do the myoepithelial cells surrounding the alveoli contract?
When exposed to oxytocin
What does the neuroendocrine reflex do?
Releases oxytocin from the neurohypophysis
What stimuli is included in the afferent side of the neuroendocrine reflex?
Visual and auditory stimuli and sensory nerves from the mammary glands, particularly the nipples/teats
What is the usual stimulus for the milk ejection reflex?
Suckling on the teats
What are ways the milk ejection reflex can be stimulated/inhibited?
It can be trained to be stimulated just by barn sounds, the sight of the suckling young etc.
And it can be inhibited by disturbances like a dog barking
What do stressful stimuli do to the milk ejection reflex?
Increase activity of the sympathetic nervous system, which inhibits the milk ejection reflex by reducing oxytocin release, by reducing blood flow, and by counteracting the effects of oxytocin on myoepithelium cells
How much milk may remain in a gland after milking?
Up to 25%
What does colostrum contain?
A high concentration of immunoglobulins produced by the immune system of the dam
What concentrates immunoglobulin in the colostrum?
Selective transport by the epithelial cells lining the alveoli
Why are immunoglobulins needed by the neonate?
To provide immune protection against infectious agents in the environment until the offspring’s immune system is fully functional
Why is colsotrum consumption especially important in farm animals?
There is limited transfer of immunoglobulins from the dam to the fetus through the placenta
What is the primary immunoglobulin that must be consumed by neonates?
IgG
What does IgA do?
Neutralizes pathogens and endotoxins
Most neonates are born with limited amounts of body fat and get their energy from what?
Milk proteins and lipids in colostrum
What does colostrum have a relatively low concentration of and what does this make it?
It has a low concentration of lactose, which makes it a good source of energy
What does most species’ colostrum have a high concentration of?
Vitamin A, Vitamin D, and Iron
Why does colostrum have a relatively low amount of lactose?
It is produced relatively early before birth and progesterone, which is released until right before birth, inhibits production of lactose, so lactose isn’t able to be made and put into the colostrum
What is closure?
When changes occur 24 hours after a neonate’s birth that prevent it from absorbing intact IgG from the gastrointestinal tract to the blood. After this point, immunoglobulins are digested similarly to other proteins colostrum is relatively useless
