Physiology Of Lactation Flashcards
The mammary gland develops _________ and duct development becomes accelerated under the influence of _______ _______ after puberty
Pre-puberty
Steroid hormones (such as oestradiol and progesterone)
What is the acceleration of the mammary gland growth due to steroid hormones called?
Allometric growth (faster than normal body growth) and
During pregnancy we see accelerated duct development, but only when during pregnancy will we start seeing lobulo-alveolar development?
Second half of pregnancy
What are lobulo alveoli?
-found where
-function
-Small lobules which proliferate at the ends of duct branches in mammary gland
-secrete and store milk
(Image on anki)
Alveoli formation is stimulated by which pregnancy hormones?
Progesterone
Prolactin
Placental lactogens
Further duct development is stimulated by…
Oestradiol
Growth hormone
Cortisol
Alveolar secretly activity is suppressed by which hormone?
Progesterone
What occurs in the lobulo-alveolar during its development?
Serum like excretions start to form & become visible in the alveoli, but are then re-absorbed
Are alveoli able to overcome progesterone suppression
Yes- even though it inhibits formation of milk, its unable to prevent fluid secretions
Describe what occurs in process of Lactogenesis I
➢Alveolar secretions become apparent in the last weeks before parturition
➢extracellular fluid-like secretions change to a milk-like, pre-colostrum composition
➢Secretions are re-absorbed due to ‘leaky’ junctions between epithelial cells
Describe what occurs in Lactogenesis II
-After parturition Colostrum like secretions in alveoli now begin to change to normal milk
-Alveolar secretions can no longer be re-absorbed due to epithelial tight junctions
-Milk accumulates in the alveolar lumen and flows into the ducts and cistern
The removal of progesterone before parturition allows
the onset of active lactation (lactogenesis 2)
Lactogenesis 2 is directly stimulated by what?
a rise in circulating prolactin
Describe the describe the regulation of the onset of lactation in dairy cows
onset of lactation leads to a very rapid increase in yield in the first 5 days, then slows down and becomes a more linear increase until peak lactation
Composition of milk
Lactose
Caseins & whey proteins (lactoferrin, a- lactalbumin, b-lactoglobulin)
Fats
Steroid hormones
Ions: Ca, P, Mg
IgG (colostrum)
Did you know that milk is an…
Emulsion! =two unmixable liquids, which needs to be homogenised
What % fat content of milk is found in offspring with large exposed surface area. What is this % for?
Milk is 50%
to counteract the immense heat loss
List the fat content of milk % in these species:
Marine mammals
Sheep’s, pigs, dogs, cats
Cows
Mares
30-50
7-10
3.5-5.5
1.6
What changes does milk composition undergo during lactation
Begins with; Colostrum secreted at the onset of lactation is very rich in immunoglobulins, proteins and lipids
There is a % drop in each one to an average apart from lactose, which increase in levels
Name the 2 neuroendocrine reflexes involved in milk ejection and milk formation
The neuro-endocrine milk let-down
The neuro-endocrine milk production
The neuroendocrine milk let-down = ejection reflex leads to…
The nearoendocrine milk production = formation reflex leads to…
- Oxytocin release
- Prolactin release
What is the Neurological part of the neuroendocrine reflex
mechanical stimulation of the udder base or the teats during e.g. cleaning, stripping, brushing, massaging, sucking or baby bumps it herself
What is the endocrinological part of the reflex?
release of the posterior pituitary hormone oxytocin
—> milk ejection
release of the anterior pituitary hormone prolactin
—> milk formation
Describe the process of neuroendocrine reflex leading to milk let-down
- Mechano-receptors convey neurological stimulus to the spinal cord up spinal thalamo-tract and to the thalamus & hypothalamus in the brain
- 2 nuclei in brain are activated
- This leads to stimulation of 2 hormones from posterior pituitary; oxytocin and ADH
- Oxytocin goes into circulation and binds to oxytocin receptors found on myoepithelial cells (smooth muscle cells that surround the alveoli)
(These receptors are all already induced as were induced in pregnancy via oestradiol rise) - Smooth muscle contractions are activated which leads to milk flow out of alveolus
- Going back to hormone release, ADH (anti diuretic hormone) which travels to kidney and conserves sodium there- this conserves water in the body
Oxytocin is released in…
Short pulses
Describe the process of neuroendocrine reflex leading to milk formation
- Mechano-receptors stimulation-> ends up at thalamus & hypothalamus
- Hypothalamus leads to releasing factor modulation which modifies synthesis of prolactin leading to its release
- Hypothalamus also down-regulates dopamine (since dopamine suppresses/negatively regulates prolactin synthesis so must be inhibited) to allow prolactin release
- Prolactin goes into circulation, stimulates epithelial cells to produce al the components of milk
- Milk is formed
Which of the 2 neuroendocrine reflexes can be conditioned and how? give example
Milk let down reflex-> can be conditioned positively or negatively. Eg stress—> causes cow to suppress milk by affecting oxytocin release
Adrenaline—> reduces mechanoreceptor and myoepithelial cell stimulation-> deuces espouse to oxytocin and therefore suppression of milk let down
Can milk formation reflex be conditioned?
Nope!
True or false, all metabolic hormones are involved in the onset and maintenance of lactation
TRUE\
Lactation stimulated or regulated by:
Prolactin, GH, Thyroxin, Insulin, Cortisol, PTH, Calcitonin, Vit. D
What occurs at the end of lactation?
Involution
what is involution?
When drying off/ weaning occurs, his leads to lack of milk removal
Tissue atrophy occurs
(Within a week of weaning, lobular alveoli disappear, duct system remains)
__________ inhibits lactation
Gestation
Which hormones regulate gestation (and therefore enhancing involuation)?
Prl, PL, GH, Cortisol, E-17b, Progesterone
Over the last few decades milk yield has doubled and tripled in dairy cows due to…
Genetic selection
How else can we increase milk yield?
-increasing frequency of milking (e.g. AMS=robotic milking)
-use of bST
What is FIL
Feedback inhibitor of lactation; peptide secreted into milk at milk formation stage; suppresses milk synthesis if there is no demand for it
What is bST
-used for what
Bovine somatotropin- used to increase milk yield; shifts nutrients towards udder/mammary gland, therefore providing nutrient supply for milk formation
BST increases milk yield by how much?
-is it still used?
15-20%
-banned in many countries due to welfare concern
