Lactation and its control

Question 1

Discuss the composition of colostrum

Answer 1

• More fats, proteins, minerals, vitamins
• Lactose conc= lower
• IgG, IgM, IgA = provides newborn with immunoprotection

Question 2

Describe the composition of regular milk

Answer 2

-Most fat, protein, carbohydrate and water

Question 3

What is the main contributor to osmolatirty in milk?

Answer 3

Lactose

Question 4

What stimulates the laying down of fat in late pregnancy and what is the purpose?

Answer 4

-Progesterone, to prepare for the demands of lactation

Question 5

How do the compounds enter the milk?

Answer 5

• 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

Question 6

Describe synthesis of lipids in the mammary gland

Answer 6

• TG made from FA in chylomicrons and LDL in blood

- In non ruminants glucose, in ruminants= acetate or B-hydroxybutyrate

Question 7

What cells are present in milk?

Answer 7

• Contains leukocytes and dislodged mammary epithelial cells

- During inflammation number of cells increases- due to neutrophil invasion

Question 8

Why does a low cell count in milk increase risk of E.coli?

Answer 8

-Too low conc of leukocytes

Question 9

What can be used as a parameter of milk quality?

Answer 9

-Cell density

Question 10

What cycles does the mammary gland undergo?

Answer 10

• Mammogenesis
• Lactogenesis
• Weaning
• Involution

Question 11

What does growth hormone and steroids stimulate the growth of?

Answer 11

Duct growth (branching)

Question 12

Which cells produce placental lactogen?

Answer 12

-Binucleate cells of the placenta

Sows use relaxin instead of placental lactogen

Question 13

What does the fall in P4 do?

Answer 13

-Removes inhibition on myometrial cells and the inhibition of prolactin on mammary gland-> so lactogenesis begins

Question 14

Discuss arachidonic acid and P4 and E2

Answer 14

• P4 induces storage of arachidonic acid 4 during pregnancy

- E2 induces convertion of arachidonic acid to PGF2a

Question 15

What causes the onset of lactogenesis?

Answer 15

• 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.

Question 16

Which hormones affect galactopoeisis?

Answer 16

• Prolactin
• Oestrogen
• Progesterone
• Cortisol

Question 17

The density of prolactin receptors if regulated by?…

Answer 17

-Thyroid/ adrenal/ ovarian hormones

Question 18

What does prolactin regulate the production of?

Answer 18

-Alpha lactalbumin

Question 19

What competes with prolactin?

Answer 19

-P4 hence the inhibition

Question 20

Which two molecules bind to form lactose synthase?

Answer 20

Galactosyltranferase and alpha lactabulin

Question 21

What molecule controls lactogenesis?

Answer 21

Alpha lactalbulim

Question 22

What is the effect of P4 and prolactin on lactose?

Answer 22

• P4 inhibits synthesis of alpha lactalbumin hence INHIBITS lactose
• Prolactin stimulates synthesis of alpha lactabulin hence STIMULATES lactose

Question 23

What does the secretion/ release of milk depend on?

Answer 23

• Secretion= prolactin

- Release= oxytocin

Question 24

In ruminants what can substitute for prolactin?

Answer 24

-Growth hormone

Question 25

What is FIL?

Answer 25

• Feedback inhibitor of lactation
• Build up of milk in alveoli increases concentrations of FIL which inhibits formation of secretory vesicles in the Golgi.

Question 26

Describe the milk ejaculation reflex (milk let down)

Answer 26

• Neuro endocrine reflex

- Oxytocin binds to surface of the myoepithelial cells in the alveoli stimulating them to release milk

Question 27

Why is it good that oxytocin release is stimulated by stretching of the cervix?

Answer 27

Because means that milk is let down during parturition so neonate can suckle straight away

Question 28

What effects does oxytocin have on milk let down?

Answer 28

• Stimulates myoepithelial cells so pressure is increased in alveoli
• Reduces resistance in the excretory ducts
• Reduces resistance in the teat canal

Question 29

List all the roles of oxytocin

Answer 29

• Social bonding
• Maternal bonding
• Milk let down
• Contraction of myometrium
• Part of feedback for luteolysis

Question 30

List the hormones that regulate metabolic changes during lactation

Answer 30

• Prolactin
• Growth hormone
• Insulin

Question 31

How does lactation act as a natural contraceptive?

Answer 31

-Reduces concentration of GnRH as suckling causes opioid production which blocks GnRH secretion thus preventing ovulation.