Lactation Part 1 & 2 Flashcards
The __ consists of a single layer of epithelial cells surrounding the lumen.
Alveolus
Alveolus?
Basic component of secretory tissue
Sac-like structure where milk is synthesized
___ is surrounded by arterioles and venules.
Alveolus
Each cubic inch of udder tissue may contain approximately ___ alveoli.
1 million
T/F: the lumen that the alveolus surrounds secretes milk.
False: single layer of epithelial cells secrete milk on alveolus
Function of myoepithelial cells?
Specialized muscle cells surrounding alveolus
Needs oxytocin-induced contraction for milk ejection
Groups of alveoli empty into a duct forming a unit called a __, which ultimately empty into the ___.
Lobule
Gland cistern
Several lobules create a ___.
Lobe
What do ducts provide?
Storage area for milk and a means for transporting it outside mammary glands.
How are myoepithelial cells arranged?
In a longitudinal pattern
Ducts are lined by two layers of ___.
Epithelium
Difference between cow and goat udder?
Goat: one large gland cistern per teat and one streak canal per teat and only 2 teats
Mare mammary anatomy?
2 teats with 2 mammary glands per teat
Sow mammary anatomy?
10-14 teats with 2 glands/teat
Dog and cat mammary anatomy?
5-6 ducts per teat
Primate and elephant mammary anatomy?
8-10 ducts per nipple per teat
Human mammary anatomy?
10-20 openings/nipple and 20-40 mammary glands
Ducts terminate in nipple; no gland cistern
Areola?
In humans, circular pigmented area located in center of breast
Canalization of mammary gland arises from what?
Ectoderm (outer part of ICM)
Where cells begin to thicken to form the mammary bud?
Mammary line (mammary ridge)
Mammary development occurs at __ days.
32 days
The ___ lengthens and branches out to form channels-canals duct system.
Secondary bud
The postnatal changes in this stage have no secretory activity but do have teats an openings.
At birth
The postnatal changes in this stage have isometric growth and allometric growth with no secretory activity
Birth to puberty
Isometric growth?
Same rate as other tissues
Allometric growth?
Disproportionately faster growth
At this stage in postnatal changes the mammary glands grow in size, there is more fat ad connective tissue, branching and rebranching of ducts, and no secretory activity.
Puberty
At this stage in postnatal changes there is rapid growth, branching and rebranching of ducts with alveoli forming on the end of branches, and no secretory activity.
Early pregnancy
At this stage in postnatal changes, there is secretory activity due to hormonal changes and reduced progesterone and increased estrogen
End of pregnancy
At this stage in postnatal changes, there is exponential cell growth, 65% more DNA, and more prolactin, GH, and cortisol
Early lactation
At this stage in postnatal changes cell numbers decrease.
Declining lactation
At this stage in postnatal changes there is mammary gland involution via pressure atrophy
Dry period
What is the composition of milk adapted to?
The nutritional requirements of the neonate
What is the majority of milk composed of?
Water 88%
What are the four factors that influence milk composition?
1) species of mammal
2) breed of mammal
3) stage of lactation
4) disease state of mammary gland
What does colostrum contain?
Total solids, minerals (Ca, P), decreased lactose, immunoglobulins
Why is the passive transfer of immunity to young an essential process?
Provides protection during early life when it’s own immune system is being established…following ingestion immunoglobulins in colostrum move from gut lumen across intestinal barrier into blood
___ absorption in the gut decreases with time especially after gut is stimulated.
Antibody
Milk given without colostrum will stimulate gut closure for absorption of __.
Immunoglobulins
___ are as high in the calf as the dam within a few hours.
Immunoglobulins
When is a calf’s immune system functional?
1-2 months postpartum
Function of RER?
Synthesis of Proteins
Function of SER?
Synthesis of Fat
Function of Golgi?
Packaging of proteins
Lactose production
What components diffuse from blood and move through (transcellular) or between (paracellular) epithelial cells into alveolar lumen without alteration by cells?
Serum albumin, immunoglobulins, vitamins, minerals, and water
Which components are synthesized by mammary secretory cells from blood precursors?
Fat, most proteins, lactose
___ draws in water for alveolar milk synthesis-secretion.
Lactose
Milk and blood are ___.
Isoismotic
AA form ___.
Caseins
Glucose forms ___.
Lactose
Acetate and butyrate and FA make ___.
Triglycerides, short chain FA, long chain FA
Which milk protein comprises 80% of milk?
Casein
Which protein gives milk it’s white/opaque appearance?
Casein
What is the function of casein?
Source of AA, Ca, P
Which protein is characterized by low solubility at pH 4.5?
Casein
What is the major CHO in milk?
Lactose
Which protein is a disaccharide composed of a galactose molecule joined with a glucose molecule?
Lactose
Which protein is synthesized in the Golgi?
Lactose
Lactose is synthesized by what enzyme? Composed of why two proteins?
Lactose synthetase
Galactosyl transferase
a-lactalbumin
What are the major milk minerals?
Ca, P, K, Cl, Mg, Na
What are the minor milk proteins?
Cu, I, Mn, Zn, Fe
Which milk minerals are needed for bone formation and teeth?
Ca, P
Which mineral is complexes with casein?
Ca
Three minerals bound to proteins?
Ca, Fe, Zn
Three minerals associated with lactose and movement of water into and out of the mammary gland?
Na, Cl, K
T/F: the mammary gland synthesizes vitamins but not minerals.
F: synthesizes minerals not vitamins
Where are vitamins in milk absorbed?
From Blood
Which vitamins does milk contain?
All B-vitamins, fat soluble vitamins (A, D, E)
How are fat soluble vitamins increased in milk?
By increasing vitamin content I blood supply to mammary gland
Vit D function?
Bone growth, Ca absorption in intestine, milk fortified
Vit E function?
Antioxidant, protects lipids, low in milk
What are a few other substances in milk other than vitamins, minerals, and proteins?
Cellular metabolites, cells (leukocytes, epithelial cells), viruses, bacteria
Which disease can be passed from mother to offspring via milk?
AIDS
Reproductive function of mammary glands?
Nourishment of the neonate = survival of the species
The duct and alveolar framework is constructed during this stage of mammary development.
Puberty
Exponential lobulo-alveolar growth occurs during this stage of mammary development.
Pregnancy
In puberty, estrogen stimulates ___ growth.
Duct
In pregnancy, estrogen stimulates ___ growth.
Duct
In puberty, progesterone stimulates __ growth.
Alveolar
In pregnancy, progesterone stimulates ___ growth.
Lobulo-alveolar growth
In puberty, what two hormones play a secondary role?
Prolactin
GH
In pregnancy, what three hormones play a secondary role?
Insulin, thyroid hormone, ACTH-corticosteroids
In pregnancy, what three hormones have synergistic effects with steroids?
Placental lactogen, prolactin, GH
Lactogenesis?
Initiation of milk secretion
What are the two stages of lactogenesis?
1) cytological and enzymatic differentiation of mammary epithelial cells
2) copious secretion of all milk components
Lipid and protein granules formed in epithelial cells accumulate in the ___.
Alveolar lumen
When does lactogenesis occur on cows? Humans and rats?
Cows: ten days before parturition
Humans and rats: at parturition
At parturition, progesterone levels need to be ___, glucocorticoids need to be ___, and prolactin needs to be ___.
Decreased
Increased
Increased
Which hormone is the key negative regulator of lactogenesis?
Progesterone
___ progesterone inhibits lactose production which is key for milk secretion.
High
Of the two proteins that make up the enzyme that synthesizes lactose, which one does progesterone inhibit?
a-lactalbumin
What will injections of progesterone at parturition prevent and inhibit?
Prevents a-lactalbumin synthesis inhibiting lactose synthesis
Hypophysectomy?
Removal of pituitary gland
If you remove a goat’s pituitary gland and inject it with prolactin, what will occur?
Milk yield will be restored and prolactin will increase prior to parturition
Which hormone will increase the rate of casein and a-lactalbumin synthesis in rabbit and bovine mammary explants?
Prolactin
Which hormones induce differentiation of RER and Golgi?
Glucocorticoids
Function of adrenalectomy?
Blocks casein and casein mRNA synthesis
Because these two hormones bind to the same receptor they are competing with each other.
Progesterone and glucocorticoids
When nearing parturition, progesterone levels __ and glucocorticoid levels ___.
Decrease
Increase
Lactation?
Combination of milk secretion and milk removal
Milk secretion?
Synthesis of milk by epithelial cells and passage from cytoplasm into alveolar lumen
Milk removal?
Ejection of milk from the alveolar lumen and removal of milk from ducts ad cisterns
Involution?
Regression of mammary gland
Failure to remove milk results in involution via a(n) ___ in intramammary pressure causing a(n) ___ in synthesis.
Increase
Decrease
In which week does milk yield reach a maximum before gradually decreasing?
6-8 weeks
T/F: After the 5th month of gestation, non-pregnant cows decline more rapidly in milk yield than pregnant cows.
F: opposite
Adrenals maintain ___.
Metabolism
Adrenalectomy decreases milk production in goats and rats. What can you inject them with to restore milk production?
Glucocorticoids
If you inject a non-pregnant animal with this hormone, you can stimulate 60-70% of anticipated milk yield.
Progesterone
Milk in the udder must be forced from alveoli and small milk ducts by activation of ___.
Neuroendocrine reflex (milk letdown, milk ejection)
Neuroendocrine reflex?
Stimulus associated with nursing activates the nervous system in the teats. Nerve impulses travel to spinal cord to paraventricular nuclei in hypothalamus causing the terminal portion of nerve cells located in the posterior pituitary to release oxytocin. Oxytocin released from PP travels to heart, transported to all parts of the body by arterial blood. Oxytocin the enters the mammary gland by the arterial blood and binds with OTR on myoepithelial cells causing alveolar contractions resulting in milk ejection.
When do myometrial contractions occur?
20-60 seconds after stimulation
Why is it important to remove milk rapidly during the period when oxytocin is causing contractions of myoepithelial cells?
Because oxytocin has a half-life of 1-2 minutes effective for 6-8 minutes
Why must cows be happy when milked?
Any external unpleasant event at milking causes the release of epinephrine from the adrenal medulla into the blood. With vasoconstriction, the blood supply to the udder is decreased ad prevent oxytocin from activating myoepithelial cells.
Gradual involution?
Begins after peak lactation
Subtle changes in milk yield and composition
Initiated involution?
Occurs after cessation of milking
Pronounced changes in milk yield and composition
Essentially opposite of changes that occur during lactogenesis
