Biochem of lactation

Question 1

breast development/differentiation results due to what hormones?

Answer 1

prolactin, progesterone, estrogens, growth hormone, cortisol, human placental lactogen (hPL)

Question 2

what type of gland is the mammary gland?

Answer 2

it is an exocrine gland -

Question 3

what features of breast milk are nourishing to the neonate?

Answer 3

1) fats, proteins, sugar, vitamins, minerals, water
2) protection = immunoglobulins absorbed via intestinal tract

Question 4

Describe the different structures of the mammary glands pictured below

Question 5

what part of the gland actually produces milk?

Answer 5

the alveolar cells

Question 6

how is milk excreted from the alveolar cells?

Answer 6

myoepithelial cells contract when exposed to oxytocin

Question 7

how long does the WHO recommend sole breastfeeding?

Answer 7

6 months -

Question 8

what is the principle hormone responsible for lactation?

Answer 8

Prolactin

Question 9

what cells in the anterior pituitary produce prolactin in response to signals?

Answer 9

Lactotrophs

negative stimulis = under inhibiotry control by dopamine

positive stimulus = thyrotropin-releasing hormone, oestrogen, progesterone and suckling reflex

Question 10

describe the positive and negative influences on prolactin formation

Answer 10

Question 11

high prolactin levels supresses what hormones?

Answer 11

FSH and LH - generally speaking ovulation does not occur during lactation = unreliable contraceptive control

Question 12

what is hyperprolactinemia?

Answer 12

excess prolactin development associated with infertility b/c of the natural contraceptive effects of the prolactin cycle

Question 13

what are the causes of hyperprolactinemia?

Answer 13

overproduction of prolactin (i,e) pituitary adenomas - reduced dopamine levels (disinhibition)

physiological stimuli = like suckling

hormonal effects = pregnancy, oestrogen therapy or hypothyroidism

drugs = antipsychotic drugs or opiate

Question 14

what are the three changes during and after pregnancy?

Answer 14

1. mammogenesis = development of ducts and alveolar systems of the breast
2. lactogenesis - milk synthesis
3. galactogenesis - milk letdown

Question 15

what hormones are essential for mammogenesis ?

Answer 15

• prolactin - required for mammogenesis and lactogenesis, completes cellular differentiation and development of lactogenic capacity
• oestrogens - stimulate ductal development development begins at puberty
• progesterone - needed to complete mammogenesis of alveolar system
• insulin - required for multiplication of epithelial cells and development of lobulalveolar architecture

Question 16

what are the three stages of lactogenesis?

Answer 16

1- mid pregnancy to about 30 hours post birth - capacity for lactogenesis but high levels of progesterone inhibit milk secretion and supress volume

2- 30-40 hours after birth to 2/3 months post-partum - delivery of placenta- decreases progesterone, estrogen and HPL - this abrupt withdrawal of progesterone in presence of high prolactin causes increase in milk volume

3- 2/3 months post-partum onwards - established lactation, autocrne control of milk synthesis (local unlike the other), primary control mechanism is milk removal by the babies diet

*therefore as long as the breast is emptied of milk, there will be initiation of milk development - which is why lactogenesis can go on indefinitely*

Question 17

what is lactose composed of? What is the enxyme necessary for it’s synthesis?

Answer 17

lactose= glucose + galactose

• 2 glucoses required for each lactose molecule synthesized- one glucose converted to UDP- glucose- then UDP-galactose

lactose synthase enzyme is responsible for its synthesis

Question 18

what are the two components of lactose synthase?

Answer 18

catalytic component = galactosyltransferase

regulatory = alpha-lactobumin

Question 19

why does milk not come in until after the placenta is delivered?

Answer 19

b/c progesterone is still being produced when the placenta is attached - and this is inhibitory of the milk-protein gene expression in the mother

Question 20

what cells contract and allow for expulsion of milk?

Answer 20

the myoepithelial cells surrounding the alveoli

Question 21

what components of breast milk are we still trying to simulate in formula?

Answer 21

enzymes, vitamins, trace elements and growth factors - not fully understood yet

Question 22

why can’t you substitute one species mlik for another’s?

Answer 22

it could be very damaging to the kidneys of children b/c for example bovine mlik has far more electrolytes than what are contained in human breast milk

Question 23

why do we replace dairy fats in infant formula with fats of vegetable or marine origin?

Answer 23

we replace them for shelf life

Question 24

is infant formula - safe and effective?

Answer 24

it is safe - not as nutritionally packed as breast milk, but it’s used when breast milk is not available

Question 25

what are the components of human milk that is not found in formula?

Answer 25

Lactoferrin protein (for intestinal health)

• Anti-infectious oligosaccharides & glycoconjugates
• Growth factors
• Long-chain polyunsatursated fatty acids (LCPUFA)

–Docosahexaenoic acid (DHA, omega-3) and arachidonic acid (AA, omega-6)

•Fat-digesting enzyme, lipase

Components particularly important for preterm infant & infant with feeding problems

Breast milk: automatically adjusts to infant’s needs; levels adjust as baby gets older

Question 26

what are some of the beneficial effects of human milk?

Answer 26

Improved gastrointestinal function, digestion, and absorption of nutrients

• Improved cognitive and visual development
• Improved host defense with reduced rates of infection (e.g. sepsis, necrotizing enterocolitis, and urinary tract infection)
• Enhanced maternal psychological well-being and maternal-infant bonding

Question 27

what is colostrum?

Answer 27

first liquid produced - yellow and thicker milk that is very high in concentrated nutrition - low in fat and high in proteins and carbohydrates so it’s easy to digest

It has a super high concentration of antibodies especially IgA - helps to protect the lungs, throat, and intestines -

laxative effect - which helps pass the first bowel movements and prevents newborn jaundice -

Question 28

what is weaning?

Answer 28

reduction of breast milk and/or

formula to replace it with more solid food

• Introduce more solid food after first six months (WHO)
• formula-fed, between 4-6 months of age