LActation and control

Question 1

Describe colostrum

Answer 1

Secretion formed during first 24hr after parturition
Contains more proteins, fat, minerals and vits than normal milk
Lower lactose concentration
Supplies neonate with immunoprotection

Question 2

What proteins are found in milk?

Answer 2

caseins
lactalbumin
lactoglobulin
immunoglobulins

Question 3

What cells are found in milk?

Answer 3

leukocytes and dislodged mammary epithelial cells
neutrophils if inflammation present

Question 4

What is diapedesis?

Answer 4

passage of cells through intact cell wall

Question 5

Describe what causes the lactation curve

Answer 5

More sucking => more milk
neonates grow, wean and suckle less => less milk

Question 6

What is the effect of litter size on milk production

Answer 6

higher number of offspring => higher milk production

Question 7

Describe the synthesis of milk

Answer 7

Alveolar epithelium:
- high number of mitochondria
- mitochondria synthesis fatty acids and non-essential AAs
- RER synthesised secretory proteins
- SER synthesis phospholipids an triglycerides

Question 8

Describe the entry of compounds into milk

Answer 8

Protein (casein) secreted in form of granules by exocytosis
Lactose secreted with protein
Lipids/tryglycerides secreted in form of membrane-limited lipid droplets by incorporation into cell membrane
Water follows lactose by osmotic pressure

Question 9

How are lipids synthesised in the mammary gland?

Answer 9

Triglycerides made from:
- FAs in chylomicrons and LDL in the blood
- glucose (non-ruminants)
- acetate and B-hydroxybutyrate (ruminants)

Question 10

What is rheostasis?

Answer 10

Maintenance of different metabolic state than what is ‘normal’ e.g., during lactation

Question 11

Explain the changes to metabolism during lactation

Answer 11

regulated by prolactin, GH and insulin:
-Reduced fat synthesis and increased lipolysis
-Decreased uptake of glucose in muscle and adipose tissue
-Increased uptake of glucose in mammary tissue
-Increased uptake of AAs in mammary glands

Question 12

Describe the hormonal control of lactation during pregnancy

Answer 12

Question 13

Describe the hormonal switches at parturition leading to lactation

Answer 13

Question 14

What is the initiation of milk secretion?

Answer 14

Increase in udder volume during pregnancy
Increased in oestrogen and placental lactogen (mimics prolactin)
Onset of milk secretion (lactogenesis) coincides with drop in circulating progesterone at parturition

Question 15

What are the hormones that affect galactopoiesis?

Answer 15

prolactin - regulates production of a-lactalbumin
oestrogen
progesterone - competes with prolactin
cortisol - growth and differentiation of golgi apparatus (where lactose is synthesised)

Question 16

Describe the control of lactogenesis by a-lactalbumin

Answer 16

Galactosyltransferase binds a-lactalbumin to become lactose synthase
Lactose synthase catalyses the production of lactose

P4 inhibits synthesis of a-lactalbumin => inhibits lactose production
Prolactin stimulates synthesis

Question 17

What is galactopoiesis?

Answer 17

maintaining lactation

Question 18

What factors maintain milk supply?

Answer 18

regular suckling
prolactin (secretion)
oxytocin (release)

Question 19

What factors reduce milk secretion?

Answer 19

lack of suckling => reduced prolactin release
Accumulation of milk in alveoli increases conc of feedback inhibitor of lactation

Question 20

Explain how suckling maintains lactation

Answer 20

Suckling stimulates paraventricular nucleus => reduced dopamine => stops inhibition of prolactin release from anterior pit gland

Question 21

What does the milk ejection reflex require?

Answer 21

sensory and neural activation
oxytocin release
contraction of alveoli and ducts
Mechanical transfer of milk

Question 22

Describe the role of oxytocin in milk let down

Answer 22

Cause contraction of myoepithelial cells to squeeze milk out of alveoli into ducts
Oestrogen induces myoepithelial cells to express oxytocin receptors

Question 23

Describe the process of mammary gland involution

Answer 23

Cessation of sucking => drop in prolactin secretion => synthesis stops
Accumulation of milk in alveoli will increase conc of feedback inhibitor of lactation (serotonin) which causes vasoconstriction
Cells become less function, become atrophic and die by apoptosis => loss of tissue mass (not to same point as pre-lactation so next lactation has greater yield)
Immune cells invade tissue

Question 24

Explain lactational anoestrus

Answer 24

Suckling induced opioid production => blocks GnRH secretion preventing ovulation

Question 25

What is embryonic diapause/delayed implanatation?

Answer 25

extension of the period between blastocyst development and implantation
Adaptive mechanism so young are born at same time each year

Question 26

Why does lactation cause delayed implantation?

Answer 26

reduces metabolic stress on animal of lactating and supporting pregnancy at same time

Question 27

What conditions affect lactation?

Answer 27

pseudopregnancy
Galactosis - congestion of gland combined with oedema and inflammation
Agalactia - lack or reduced milk production
Mastitis

Question 28

Describe the effect of mastitis on lactation

Answer 28

Grade 1 - inflammation changes milk quality
Grade 2 - infection destroys glandular tissues
Grade 3 - toxins absorbed causing systemic upset