Physiology Of Lactation

Question 1

The mammary gland develops _________ and duct development becomes accelerated under the influence of _______ _______ after puberty

Answer 1

Pre-puberty
Steroid hormones (such as oestradiol and progesterone)

Question 2

What is the acceleration of the mammary gland growth due to steroid hormones called?

Answer 2

Allometric growth (faster than normal body growth) and

Question 3

During pregnancy we see accelerated duct development, but only when during pregnancy will we start seeing lobulo-alveolar development?

Answer 3

Second half of pregnancy

Question 4

What are lobulo alveoli?
-found where
-function

Answer 4

-Small lobules which proliferate at the ends of duct branches in mammary gland
-secrete and store milk

(Image on anki)

Question 5

Alveoli formation is stimulated by which pregnancy hormones?

Answer 5

Progesterone
Prolactin
Placental lactogens

Question 6

Further duct development is stimulated by…

Answer 6

Oestradiol
Growth hormone
Cortisol

Question 7

Alveolar secretly activity is suppressed by which hormone?

Answer 7

Progesterone

Question 8

What occurs in the lobulo-alveolar during its development?

Answer 8

Serum like excretions start to form & become visible in the alveoli, but are then re-absorbed

Question 9

Are alveoli able to overcome progesterone suppression

Answer 9

Yes- even though it inhibits formation of milk, its unable to prevent fluid secretions

Question 10

Describe what occurs in process of Lactogenesis I

Answer 10

➢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

Question 11

Describe what occurs in Lactogenesis II

Answer 11

-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

Question 12

The removal of progesterone before parturition allows

Answer 12

the onset of active lactation (lactogenesis 2)

Question 13

Lactogenesis 2 is directly stimulated by what?

Answer 13

a rise in circulating prolactin

Question 14

Describe the describe the regulation of the onset of lactation in dairy cows

Answer 14

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

Question 15

Composition of milk

Answer 15

Lactose
Caseins & whey proteins (lactoferrin, a- lactalbumin, b-lactoglobulin)
Fats
Steroid hormones
Ions: Ca, P, Mg
IgG (colostrum)

Question 16

Did you know that milk is an…

Answer 16

Emulsion! =two unmixable liquids, which needs to be homogenised

Question 17

What % fat content of milk is found in offspring with large exposed surface area. What is this % for?

Answer 17

Milk is 50%

to counteract the immense heat loss

Question 18

List the fat content of milk % in these species:
Marine mammals
Sheep’s, pigs, dogs, cats
Cows
Mares

Answer 18

30-50
7-10
3.5-5.5
1.6

Question 19

What changes does milk composition undergo during lactation

Answer 19

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

Question 20

Name the 2 neuroendocrine reflexes involved in milk ejection and milk formation

Answer 20

The neuro-endocrine milk let-down
The neuro-endocrine milk production

Question 21

The neuroendocrine milk let-down = ejection reflex leads to…

The nearoendocrine milk production = formation reflex leads to…

Answer 21

1. Oxytocin release
2. Prolactin release

Question 22

What is the Neurological part of the neuroendocrine reflex

Answer 22

mechanical stimulation of the udder base or the teats during e.g. cleaning, stripping, brushing, massaging, sucking or baby bumps it herself

Question 23

What is the endocrinological part of the reflex?

Answer 23

release of the posterior pituitary hormone oxytocin
—> milk ejection

release of the anterior pituitary hormone prolactin
—> milk formation

Question 24

Describe the process of neuroendocrine reflex leading to milk let-down

Answer 24

1. Mechano-receptors convey neurological stimulus to the spinal cord up spinal thalamo-tract and to the thalamus & hypothalamus in the brain
2. 2 nuclei in brain are activated
3. This leads to stimulation of 2 hormones from posterior pituitary; oxytocin and ADH
4. 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)
5. Smooth muscle contractions are activated which leads to milk flow out of alveolus
6. Going back to hormone release, ADH (anti diuretic hormone) which travels to kidney and conserves sodium there- this conserves water in the body

Question 25

Oxytocin is released in…

Answer 25

Short pulses

Question 26

Describe the process of neuroendocrine reflex leading to milk formation

Answer 26

1. Mechano-receptors stimulation-> ends up at thalamus & hypothalamus
2. Hypothalamus leads to releasing factor modulation which modifies synthesis of prolactin leading to its release
3. Hypothalamus also down-regulates dopamine (since dopamine suppresses/negatively regulates prolactin synthesis so must be inhibited) to allow prolactin release
4. Prolactin goes into circulation, stimulates epithelial cells to produce al the components of milk
5. Milk is formed

Question 27

Which of the 2 neuroendocrine reflexes can be conditioned and how? give example

Answer 27

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

Question 28

Can milk formation reflex be conditioned?

Answer 28

Nope!

Question 29

True or false, all metabolic hormones are involved in the onset and maintenance of lactation

Answer 29

TRUE\

Question 30

Lactation stimulated or regulated by:

Answer 30

Prolactin, GH, Thyroxin, Insulin, Cortisol, PTH, Calcitonin, Vit. D

Question 31

What occurs at the end of lactation?

Answer 31

Involution

Question 32

what is involution?

Answer 32

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)

Question 33

__________ inhibits lactation

Answer 33

Gestation

Question 34

Which hormones regulate gestation (and therefore enhancing involuation)?

Answer 34

Prl, PL, GH, Cortisol, E-17b, Progesterone

Question 35

Over the last few decades milk yield has doubled and tripled in dairy cows due to…

Answer 35

Genetic selection

Question 36

How else can we increase milk yield?

Answer 36

-increasing frequency of milking (e.g. AMS=robotic milking)
-use of bST

Question 37

What is FIL

Answer 37

Feedback inhibitor of lactation; peptide secreted into milk at milk formation stage; suppresses milk synthesis if there is no demand for it

Question 38

What is bST
-used for what

Answer 38

Bovine somatotropin- used to increase milk yield; shifts nutrients towards udder/mammary gland, therefore providing nutrient supply for milk formation

Question 39

BST increases milk yield by how much?
-is it still used?

Answer 39

15-20%
-banned in many countries due to welfare concern