LActation and control Flashcards
Describe colostrum
Secretion formed during first 24hr after parturition
Contains more proteins, fat, minerals and vits than normal milk
Lower lactose concentration
Supplies neonate with immunoprotection
What proteins are found in milk?
caseins
lactalbumin
lactoglobulin
immunoglobulins
What cells are found in milk?
leukocytes and dislodged mammary epithelial cells
neutrophils if inflammation present
What is diapedesis?
passage of cells through intact cell wall
Describe what causes the lactation curve
More sucking => more milk
neonates grow, wean and suckle less => less milk
What is the effect of litter size on milk production
higher number of offspring => higher milk production
Describe the synthesis of milk
Alveolar epithelium:
- high number of mitochondria
- mitochondria synthesis fatty acids and non-essential AAs
- RER synthesised secretory proteins
- SER synthesis phospholipids an triglycerides
Describe the entry of compounds into milk
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
How are lipids synthesised in the mammary gland?
Triglycerides made from:
- FAs in chylomicrons and LDL in the blood
- glucose (non-ruminants)
- acetate and B-hydroxybutyrate (ruminants)
What is rheostasis?
Maintenance of different metabolic state than what is ‘normal’ e.g., during lactation
Explain the changes to metabolism during lactation
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
Describe the hormonal control of lactation during pregnancy
Describe the hormonal switches at parturition leading to lactation
What is the initiation of milk secretion?
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
What are the hormones that affect galactopoiesis?
prolactin - regulates production of a-lactalbumin
oestrogen
progesterone - competes with prolactin
cortisol - growth and differentiation of golgi apparatus (where lactose is synthesised)
Describe the control of lactogenesis by a-lactalbumin
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
What is galactopoiesis?
maintaining lactation
What factors maintain milk supply?
regular suckling
prolactin (secretion)
oxytocin (release)
What factors reduce milk secretion?
lack of suckling => reduced prolactin release
Accumulation of milk in alveoli increases conc of feedback inhibitor of lactation
Explain how suckling maintains lactation
Suckling stimulates paraventricular nucleus => reduced dopamine => stops inhibition of prolactin release from anterior pit gland
What does the milk ejection reflex require?
sensory and neural activation
oxytocin release
contraction of alveoli and ducts
Mechanical transfer of milk
Describe the role of oxytocin in milk let down
Cause contraction of myoepithelial cells to squeeze milk out of alveoli into ducts
Oestrogen induces myoepithelial cells to express oxytocin receptors
Describe the process of mammary gland involution
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
Explain lactational anoestrus
Suckling induced opioid production => blocks GnRH secretion preventing ovulation
What is embryonic diapause/delayed implanatation?
extension of the period between blastocyst development and implantation
Adaptive mechanism so young are born at same time each year
Why does lactation cause delayed implantation?
reduces metabolic stress on animal of lactating and supporting pregnancy at same time
What conditions affect lactation?
pseudopregnancy
Galactosis - congestion of gland combined with oedema and inflammation
Agalactia - lack or reduced milk production
Mastitis
Describe the effect of mastitis on lactation
Grade 1 - inflammation changes milk quality
Grade 2 - infection destroys glandular tissues
Grade 3 - toxins absorbed causing systemic upset
