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Lactation Flashcards

1
Q

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

A

5

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

Describe merocrine secretion

A

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

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3
Q

Describe the 3rd step of milk secretion

A

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

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4
Q

Describe the 4th step of milk secretion

A

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.

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5
Q

Describe the 5th step of milk secretion

A

paracellular pathway

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

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6
Q

Describe the 2nd step of milk secretion

A

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

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7
Q

Define the milk ejection reflex

A

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
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8
Q

the active compression of the alveoli is controlled by

A

the milk ejection reflex

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9
Q

Describe the sensory receptors of milk ejection

A

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

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10
Q

describe the afferent pathway of milk ejection

LAQ

A

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.

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11
Q

A cluster of nerve cells in the brain is often called

A

a nucleus

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12
Q

Define what the hypothalamo-neurohypophysial tract is

A

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

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13
Q

Describe the efferent pathway of milk ejection

A

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

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14
Q

What is the process of the effectors in milk ejection

A

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.

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15
Q

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

A

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

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16
Q

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

A

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

enzyme used here is actyl-CoA carboxylase

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17
Q

How is palmitate produced in the fatty acid synthesis pathway?

A

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

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18
Q

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

A

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

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19
Q

_____is a secondary control mechanism in protein synthesis

A

translation is a secondary control mechanism in protein synthesis

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20
Q

There are _ types of milk proteins

A

There are 8 types of milk proteins

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21
Q

The amount of milk proteins produced depends on ?

A

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

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22
Q

translation is regulated as

A

lactation progresses

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23
Q

What does the shut down of lactation mean for protein synthesis

A

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.

24
Q

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

A

post-translational modifications (3)

  1. Proteolysis
  2. Glycosylation
  3. Phosphorylation
25
Q

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

A

post-translational modifications/ protein modification (3)

  1. Proteolysis
  2. Glycosylation
  3. Phosphorylation
26
Q

Describe the post-translational modifications

A
  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

27
Q

Describe proteolysis

A

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

28
Q

Describe Glycoslysation

A

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.

29
Q

Describe phosphorylation

A

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

30
Q

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

A

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

31
Q

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

A

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

32
Q

What are the key nutrients for milk synthesis in ruminants

A

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

33
Q

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

A

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

34
Q

What are the key nutrients for milk synthesis in ruminants

A

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)

35
Q

What is glucose used for in non-ruminants and ruminants

A

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

ruminants= lactose, and some amino acids

36
Q

How do non-ruminants get their nutrients

A

non-ruminants

glucose=from diet (absorbed from gut)

aa/dietary protein= from muscle (gut absorption and tissue mobilisation)

fatty acids = from diet, from adipose

37
Q

How do ruminants get their nutrients

A

ruminants

glucose = from propionate/lactate

acetate and beta-hydroxybutyrate,
propionate-lactate = from rumen fermentation

fatty acids = from diet or adipose

38
Q

___ of the diet of dairy cows is protein to _____

A

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

39
Q

excess protein downside?

A

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

40
Q

what happens if ruminants are fed a lot of starch?

A

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

41
Q

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

A

k-casein

42
Q

What are kinases?

A

kinases are enzymes that will phosphorylate proteins with ATP that vary in specificity

Kinases are membrane-bound in the sER and golgi.

43
Q

what are caesins?

A

caseis are the phosphoproteins and contain multiple sites for phosphorylation.

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

44
Q

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

A

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

45
Q

Milk production is characterised as?

A

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

46
Q

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

A

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
  5. nutrient utilisation within the gland
  6. milk-secretion and removal
47
Q

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

A

There are 5 tissue types in which metabolic adaptations are induced during lactation

  1. mammary gland
  2. adipose
  3. liver
  4. gut
  5. muscle
48
Q

How is the mammary gland affected during induced lactation?

A

There is a surge in demand for nutrients in mammary gland

49
Q

How is adipose tissue affected during induced lactation?

A

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

50
Q

How is the liver affected during induced lactation?

A

increased gluconeogenesis to provide more glucose

51
Q

How is the gut affected during induced lactation?

A

increased absorption of calcium and phosphate

52
Q

How are the muscle tissues affected during induced lactation?

A

=decreased muscle protein synthesis

53
Q

____ is where milk is made

A

Alveoli

54
Q

Describe the flow of milk from the alveoli to the infant

A

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

55
Q

What are the main milk secretion processes?

A

There are 2 main milk secretion processes

  1. cellular secretion - getting milk out of cells
  2. milk ejection - getting milk out of the gland
56
Q

.

A

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

. (6 decks)

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