Lactation and its control Flashcards
Discuss the composition of colostrum
- More fats, proteins, minerals, vitamins
- Lactose conc= lower
- IgG, IgM, IgA = provides newborn with immunoprotection
Describe the composition of regular milk
-Most fat, protein, carbohydrate and water
What is the main contributor to osmolatirty in milk?
Lactose
What stimulates the laying down of fat in late pregnancy and what is the purpose?
-Progesterone, to prepare for the demands of lactation
How do the compounds enter the milk?
- Protein (casein) enters as granules by exocytosis
- Lactose is secreted with protein
- Lipid (triglycerides) are secreted as membrane-limited lipid droplets due to incorporation into the membrane
- Water follows lactose due to osmotic pressure
Describe synthesis of lipids in the mammary gland
- TG made from FA in chylomicrons and LDL in blood
- In non ruminants glucose, in ruminants= acetate or B-hydroxybutyrate
What cells are present in milk?
- Contains leukocytes and dislodged mammary epithelial cells
- During inflammation number of cells increases- due to neutrophil invasion
Why does a low cell count in milk increase risk of E.coli?
-Too low conc of leukocytes
What can be used as a parameter of milk quality?
-Cell density
What cycles does the mammary gland undergo?
- Mammogenesis
- Lactogenesis
- Weaning
- Involution
What does growth hormone and steroids stimulate the growth of?
Duct growth (branching)
Which cells produce placental lactogen?
-Binucleate cells of the placenta
Sows use relaxin instead of placental lactogen
What does the fall in P4 do?
-Removes inhibition on myometrial cells and the inhibition of prolactin on mammary gland-> so lactogenesis begins
Discuss arachidonic acid and P4 and E2
- P4 induces storage of arachidonic acid 4 during pregnancy
- E2 induces convertion of arachidonic acid to PGF2a
What causes the onset of lactogenesis?
- The fall in P4
- Udder size increases during pregnancy due to increased conc of E2 and placental lactogen BUT no milk produced until P4 falls.
Which hormones affect galactopoeisis?
- Prolactin
- Oestrogen
- Progesterone
- Cortisol
The density of prolactin receptors if regulated by?…
-Thyroid/ adrenal/ ovarian hormones
What does prolactin regulate the production of?
-Alpha lactalbumin
What competes with prolactin?
-P4 hence the inhibition
Which two molecules bind to form lactose synthase?
Galactosyltranferase and alpha lactabulin
What molecule controls lactogenesis?
Alpha lactalbulim
What is the effect of P4 and prolactin on lactose?
- P4 inhibits synthesis of alpha lactalbumin hence INHIBITS lactose
- Prolactin stimulates synthesis of alpha lactabulin hence STIMULATES lactose
What does the secretion/ release of milk depend on?
- Secretion= prolactin
- Release= oxytocin
In ruminants what can substitute for prolactin?
-Growth hormone
What is FIL?
- Feedback inhibitor of lactation
- Build up of milk in alveoli increases concentrations of FIL which inhibits formation of secretory vesicles in the Golgi.
Describe the milk ejaculation reflex (milk let down)
- Neuro endocrine reflex
- Oxytocin binds to surface of the myoepithelial cells in the alveoli stimulating them to release milk
Why is it good that oxytocin release is stimulated by stretching of the cervix?
Because means that milk is let down during parturition so neonate can suckle straight away
What effects does oxytocin have on milk let down?
- Stimulates myoepithelial cells so pressure is increased in alveoli
- Reduces resistance in the excretory ducts
- Reduces resistance in the teat canal
List all the roles of oxytocin
- Social bonding
- Maternal bonding
- Milk let down
- Contraction of myometrium
- Part of feedback for luteolysis
List the hormones that regulate metabolic changes during lactation
- Prolactin
- Growth hormone
- Insulin
How does lactation act as a natural contraceptive?
-Reduces concentration of GnRH as suckling causes opioid production which blocks GnRH secretion thus preventing ovulation.
