Lactation

Question 1

How many steps are there in milk secretion and what are they?

Answer 1

5

1. merocrine secretion
2. apocrine secretion
3. apical transport
4. transcytosis
5. paracellular pathway

Question 2

Describe merocrine secretion

Answer 2

Protein, lactose, minerals and other components of the aqueous phase of milk is contained in golgi-derived secretory vesicles which secrete the components out of the apical cell-surface via merocrine secretion

Question 3

Describe the 3rd step of milk secretion

Answer 3

apical transport

ions, water and glucose move directly across the apical membrane of the cell

most of the minerals (mg, ca, po3) exit the cell via secretory vesicles.

The cell can be permeable to some substances. There are mineral transporters (e.g na/k transporters) on the apical and basal surfaces which help regulate the milk content.

e.g keep K conc high in
milk content .since ECF has high NA and low K

Question 4

Describe the 4th step of milk secretion

Answer 4

transcytosis

some proteins are transported from blood into milk through the secretory cells by the process of transcytosis.
Immunoglobulins and hormones/growth factors all enter milk via this process.

Question 5

Describe the 5th step of milk secretion

Answer 5

paracellular pathway

allows the passage of substances between epithelial cells. This pathway only opens during pregnancy, involution, and in inflammatory states such as mastitis

Question 6

Describe the 2nd step of milk secretion

Answer 6

apocrine secretion (milk fat secretion via the milk fat globule)

large lipid droplets bulge out of the apical membrane and eventually become enveloped by the apical membrane of the cell.

milk ejection process is important to get rid of the fat from the cell

sometimes parts of the cytoplasm are released out of the cell along with fat droplets= in milk

Question 7

Define the milk ejection reflex

Answer 7

The removal of milk from alveolar lumen which requires 2 actions:

1. generation of negative pressure at the sinuses by suckling of the offspring on the teat
2. generation of positive pressure at the alveoli by the contraction of myoepithelial cells

Question 8

the active compression of the alveoli is controlled by

Answer 8

the milk ejection reflex

Question 9

Describe the sensory receptors of milk ejection

Answer 9

teats have pressure-sensitive nerve receptors in the dermis. Mechanical stimulation of the teats activates these receptors. Tactile stimuli are transformed into nerve impulses.

Question 10

describe the afferent pathway of milk ejection

LAQ

Answer 10

The nerve impulses travel via the spinothalamic nerve tract to the hypothalamus. The nerves converge on the paraventricular and supraoptic nuclei in the hypothalamus.

Neurons in these hypothalamic nuclei synthesise the oxytocin precursor and package it into vesicles. The oxytocin-containing vesicles are transported from the cell body in the hypothalamus, down the axons to the neuron endings in the post pituitary. (hypothalamo-neurohypophysial tract).

Nerve impulses from the teat, stimukate oxytocin-containing neurons in the post pituitary causing the release of oxytocin.

Question 11

A cluster of nerve cells in the brain is often called

Answer 11

a nucleus

Question 12

Define what the hypothalamo-neurohypophysial tract is

Answer 12

the tract from the cell body of the hypothalamus, down the axons to the neuron endings in the posterior pituitary

Question 13

Describe the efferent pathway of milk ejection

Answer 13

the release of oxytocin into the blood where it is transferred to the mammary gland

Question 14

What is the process of the effectors in milk ejection

Answer 14

The effectors are the receptors for oxytocin on the myoepithelial cells. The binding of oxytocin causes the myoepithelial cells to contract, increasing the intra-lumenal (intra-mammary) pressure and ejection of milk from the alveolar lumen. Timing of oxytocin release relative to milk removal is important as oxytocin has a very short half-life.

Question 15

___ acts as the primer for fatty acid synthesis, thereafter ___ adds carbons to the growing FA chain

Answer 15

acetyl-coA acts as the primer for the fatty acid synthesis, thereafter malonyl-coA adds 2 carbons to the growing

Question 16

How is malonyl-CoA (c3) produced in the fatty acid synthesis pathway?

Answer 16

acetyl-CoA (c2) + CO2 + ATP=> Malonyl-COA (c3)

enzyme used here is actyl-CoA carboxylase

Question 17

How is palmitate produced in the fatty acid synthesis pathway?

Answer 17

Acetyl-CoA (c2) + CO2 + ATP=> malonyl-CoA (c3)

Acetyl-CoA (c2) + 7Malonyl CoA (7xc3) + 14NADPH => palmitate (c16) + 7CO2 + 14NADPH + 8CoA

exy used in 1st step= acetyl-coa carboxylase

ezy used in the last step= fatty acid synthetase

Question 18

___ is the key control for the type of protein and how much protein synthesized

Answer 18

mRNA is the key control for the type of protein and how much protein synthesised

Question 19

_____is a secondary control mechanism in protein synthesis

Answer 19

translation is a secondary control mechanism in protein synthesis

Question 20

There are _ types of milk proteins

Answer 20

There are 8 types of milk proteins

Question 21

The amount of milk proteins produced depends on ?

Answer 21

The amount of milk proteins produced depends on how much mRNA is produced for each of those proteins.

separate mRNA templates for individual caesin proteins, whey proteins, alpha-lactabulin, beta-lactaglobulin

Question 22

translation is regulated as

Answer 22

lactation progresses

Question 23

What does the shut down of lactation mean for protein synthesis

Answer 23

Therfore, the shut down of lactation means that transcription of the proteins are lost therfeore there is no need for mRNA and transcription will stop.

Question 24

How many post-translational modifications are there and what are they?

Answer 24

post-translational modifications (3)

1. Proteolysis
2. Glycosylation
3. Phosphorylation

Question 25

How many post-translational modifications are there and what are they?

Answer 25

post-translational modifications/ protein modification (3) 1. Proteolysis 2. Glycosylation 3. Phosphorylation

Question 26

Describe the post-translational modifications

Answer 26

1. Proteolysis (intracellular) =removal of certain sequences 2. Glycosylation =addition of carbohydrate chains e.g k-casein 3. phosphorylation =alpha and beta caseins all occur in golgi

Question 27

Describe proteolysis

Answer 27

One of the 3 post-translational modifications =removes signal peptide sequences within the rER =this occurs as the protein is being synthesised and aka co-translational modification = peptide sequences of around 10-20aas at the front end of the N-terminus of the protein

Question 28

Describe Glycoslysation

Answer 28

1 of 3 post-translational modifications occurs in the rER and golgi apparatus =after the protein has formed, adds carbohydrate chains e.g kappa casein =glycosytransferases are responsible for adding sugars to aas (Asp, Ser, Thr) k-casein is the major glycosylated milk-specific protein synthesized by the epithelial cells, It is very heterogeneously glycosylated.

Question 29

Describe phosphorylation

Answer 29

1 of 3 post-translational modifications =occurs after the completion of the polypeptide chain. =can occur at Ser, Thr, Glu, Asp, His, Lys, and Tyr. many enzymes will phosphorylate proteins with ATP, but they differ in specificity (kinases) alpha and beta caseins have a lot of phosphorylation sites which allow the transport of calcium into milk = the phosphorylation aids formation and stabilization of the casein micelle by complexing calcium. occurs in the golgi

Question 30

What happens to immature proteins once they have been translated from RNA?

Answer 30

Immature protein goes into the lumen of the ER and then goes into the golgi where it undergoes the post-translational modifications

Question 31

What are the key nutrients for milk synthesis in non-ruminants

Answer 31

non-ruminants Glucose = use for lactose, fat and amino acids protein/amino acids = can be converted to glucose acetate and alpha-hydroxybutyrate = milk fat and energy propionate/lactate = converted to glucose fatty acids = milk fat

Question 32

What are the key nutrients for milk synthesis in ruminants

Answer 32

Ruminants glucose = used for lactose and glycerol aas/protein =converted to glucose acetate and beta=hydroxybutyrate = milk fat and energy propionate/lactate = converted to glucose fatty acids = converted to milk fat

Question 33

What are the key nutrients for milk synthesis in non-ruminants

Answer 33

non-ruminants Glucose = use for lactose, glycerol, fatty acids and amino acids = provides precursor aas for protein synthesis protein/amino acids = can be converted to glucose =gut absorption and some tissue mobilisation acetate and alpha-hydroxybutyrate = milk fat and energy propionate/lactate = converted to glucose fatty acids = milk fat

Question 34

What are the key nutrients for milk synthesis in ruminants

Answer 34

Ruminants glucose = used for lactose and glycerol aas/protein =converted to glucose =protein synethesis and some glucose precursors acetate and beta=hydroxybutyrate = milk fat synthesis and energy propionate/lactate = converted to glucose, (gluconeogenesis) fatty acids/triglycerides = converted to milk fat (fat synthesis)

Question 35

What is glucose used for in non-ruminants and ruminants

Answer 35

non-ruminants = lactose, glycerol, fatty acids , amino acids =to provide precursor aas for protein synthesis ruminants= lactose, and some amino acids

Question 36

How do non-ruminants get their nutrients

Answer 36

non-ruminants glucose=from diet (absorbed from gut) aa/dietary protein= from muscle (gut absorption and tissue mobilisation) fatty acids = from diet, from adipose

Question 37

How do ruminants get their nutrients

Answer 37

ruminants glucose = from propionate/lactate acetate and beta-hydroxybutyrate, propionate-lactate = from rumen fermentation fatty acids = from diet or adipose

Question 38

___ of the diet of dairy cows is protein to _____

Answer 38

15% of the diet of dairy cows is protein to maximize milk-protein synthesis

Question 39

excess protein downside?

Answer 39

downside of dairy cows having 15-20% of protein in their diet is that the protein is converted to amonia in the rumen which is then converted by the liver to urea which is then passed out in the urine and delivered to the pasteur patch. Can then be converted to nitrate -which can then go into the waterways

Question 40

what happens if ruminants are fed a lot of starch?

Answer 40

if ruminants are fed lots of starch, some of teh starch spills over to the small intestine= therefore the animals are then able to take up starch as glucose from the smallintestine => this alleviates stress from the liver

Question 41

is the major glycosylated milk-specific protein synthesized by the epithelial cells, It is very heterogeneously glycosylated.

Answer 41

k-casein

Question 42

What are kinases?

Answer 42

kinases are enzymes that will phosphorylate proteins with ATP that vary in specificity Kinases are membrane-bound in the sER and golgi.

Question 43

what are caesins?

Answer 43

caseis are the phosphoproteins and contain multiple sites for phosphorylation. = the phosphorylation aids formation and stabilization of the casein micelle by complexing calcium.

Question 44

______aids formation and stabilization of the casein micelle by complexing ______.

Answer 44

= the phosphorylation aids formation and stabilization of the casein micelle by complexing calcium.

Question 45

Milk production is characterised as?

Answer 45

Milk production is characterised as the number of cells X (times) activity of cells

Question 46

In terms of milk production, the activity of cells is determined by

Answer 46

The activity of cells is determined by: (6) 1. nutrition intake 2. nutrition utilisation and conversion by non-mammary tissues 3. nutrient transfer to the gland 4. nutrient uptake by the gland 4. nutrient utilisation within the gland 5. milk-secretion and removal

Question 47

What are the tissue types in which metabolic adaptations are induced during lactation

Answer 47

There are 5 tissue types in which metabolic adaptations are induced during lactation 1. mammary gland 2. adipose 3. liver 4. gut 5. muscle

Question 48

How is the mammary gland affected during induced lactation?

Answer 48

There is a surge in demand for nutrients in mammary gland

Question 49

How is adipose tissue affected during induced lactation?

Answer 49

=decreased glucose uptake =increased fat mobilisation =decreased fat synthesis

Question 50

How is the liver affected during induced lactation?

Answer 50

increased gluconeogenesis to provide more glucose

Question 51

How is the gut affected during induced lactation?

Answer 51

increased absorption of calcium and phosphate

Question 52

How are the muscle tissues affected during induced lactation?

Answer 52

=decreased muscle protein synthesis

Question 53

____ is where milk is made

Answer 53

Alveoli

Question 54

Describe the flow of milk from the alveoli to the infant

Answer 54

alveoli contain about 300 individual secretory cells the alveoli collect into lobules of tissue, and th lobules are collected into lobes of tissue with ducts that drain down into the cistern of the gland- where milk is drawn out of the teat

Question 55

What are the main milk secretion processes?

Answer 55

There are 2 main milk secretion processes 1. cellular secretion - getting milk out of cells 2. milk ejection - getting milk out of the gland

Question 56

.

Answer 56

During cellular secretion, lactose is always escaping out of the cell between cells, TBCCCCC