1. Physiology of milk secretion
presenter:
Karma Choki

2. Introduction
• The defining characteristic of the class
Mammalian is the ability to produce milk, an
externally secreted fluid designed specifically
to nourish the young
• The provision of milk frees the mother from
the necessity of providing a specialized
environment for rearing of the young

3. Cont……
• It allows birth to occur at a relatively early
stage of development and provides a time of
intense maternal interaction with the
newborn during early behavioral development
• In addition the nutritional reserves of the
mother may be able to sustain the suckling
through a period of famine

4. Biochemistry of human milk
• Human milk is a unique, species-specific,
complex nutritive fluid with immunologic and
growth promoting properties
• It evolves to meet the changing needs of the
baby during growth and maturation
• Breast milk is the most appropriate source of
nutrition up to the age of 6 months

5. LACTATION
• The cyclical process of milk synthesis and secretion is termed
lactation
• Lactation occurs with the help of 2 hormones, prolactin and
oxytocin
• During the second stage of lactogenesis, the breast becomes
capable of milk production but for the ongoing synthesis and
secretion of human milk, the mammary gland must receive
hormonal signals
• These signals are produced by direct response to stimulation
of the nipple and areola (mammae), are then relayed to the
central nervous system

6. The stages of lactation
1. Mammogenesis: Mammary (breast) growth occurs.
The size and weight of the breast increases
2. Lactogenesis
 Stage 1 (late pregnancy): Alveolar cells are
differentiated from secretary cells
 Stage 2 (day 2 or 3 to day 8 after birth): The tight
junction in the alveolar cell closes. Copious milk
secretion begins. Breasts are full and warm.
Endocrine control switches to autocrine (supply-
demand) control

7. 3. Galactopoiesis (later than 9 days after birth to
beginning of involution): Established
secretion is maintained. Autocrine system
control continues
4. Involution (average 40 days after last
breastfeeding): Regular supplementation is
added. Milk secretion decreases from the
buildup of inhibiting peptides

8. Prolactin
• It is a polypeptide hormone synthesized by
lactotrophic cells in the anterior pituitary
• Prolactin is necessary for the secretion of milk by the
cells of the alveoli and its level of prolactin in the
blood increases markedly during pregnancy
• It stimulates the growth and development of the
mammary tissue, in preparation for the production of
milk
• However, milk is not secreted then, because
progesterone and oestrogen, the hormones of
pregnancy, block this action of prolactin
• After delivery, levels of progesterone and oestrogen
fall rapidly, prolactin is no longer blocked, and milk
secretion begins

9. Prolactin reflex

10. • More prolactin is produced at night, so breastfeeding
at night is especially helpful for keeping up the milk
supply
• Prolactin seems to make a mother feel relaxed and
sleepy, so she usually rests well even if she breastfeeds
at night
• Suckling affects the release of other pituitary
hormones, including gonadotrophin releasing hormone
(GnRH), follicle stimulating hormone, and luteinising
hormone, which results in suppression of ovulation
and menstruation
• Frequent breastfeeding can help to delay a new
pregnancy hence, breastfeeding at night is important
to ensure this effect

11. Oxytocin
 Hormone involved in the milk ejection or letdown reflex
 The suckling infant stimulates the touch receptors that are
densely located around the nipple and areola
 This creates afferent impulses that stimulate the posterior
pituitary gland and it releases oxytocin
 Oxytocin causes the contraction of the myoepithelial cells
that line the ducts of the breast which then expel milk from
alveoli into ducts and subareolar sinuses that empty through
a nipple pore

12. Oxytocin reflex

13. • The oxytocin reflex is also sometimes called the
“letdown reflex” or the “milk ejection reflex”
• Oxytocin is produced more quickly than prolactin
• It makes the milk that is already in the breast
flow for the current feed, and helps the baby to
get the milk easily
• Oxytocin starts working when a mother expects a
feed as well as when the baby is suckling
• The reflex becomes conditioned to the mother's
sensations and feelings, such as touching,
smelling or seeing her baby, or hearing her baby
cry, or thinking lovingly about him or her

14. Cont…..
• If a mother is in severe pain or emotionally upset, the
oxytocin reflex may become inhibited, and her milk
may suddenly stop flowing well
• If she receives support, is helped to feel comfortable
and lets the baby continue to breastfeed, the milk will
flow again
• It is important to understand the oxytocin reflex,
because it explains why the mother and baby should
be kept together and why they should have skin-to-skin
contact
• Oxytocin makes a mother's uterus contract after
delivery and helps to reduce bleeding
• The contractions can cause severe uterine pain when a
baby suckles during the first few days

15. COLOSTRUM
Definition:
• It is the first milk secretion of the
breast during pregnancy and the
first 2-3 days following delivery
which contains a great quantity of
proteins and calories in addition to
antibodies and lymphocytes
• It is a serous fluid, yellow in color
and alkaline in nature with higher
specific gravity

16. • Foremilk: is the milk
(typically lower in fat)
available at the
beginning of a feeding
• Hindmilk: is milk at the
end of a feeding, which
has a higher fat content
than the foremilk at that
feeding

17. Colostrum is composed of:
• High protein
• Low carbohydrate
• High minerals esp. Na, Cl
• Antibody- Secretory IgA (High)
Importance of Colostrum:
• It is more nutritious
• It provides protection against infection due to
presence of antibodies ( IgA)
• It has got laxative action due to the presence of
large fat globules

18. Ingredients that make up breast
milk:
• Protein: Protein is responsible for the body's
metabolism and the growth and development of
body cells and tissues
• Carbohydrates: Carbohydrates are responsible
for energy and calories and is important for brain
growth and development. The main carbohydrate
in human milk is lactose (having about twice as
much as cow's milk).
• Fats: Fats (or lipids) are essential for energy and
calories, development of the brain, nerves and
blood vessels

19. • Minerals: Minerals present in breast milk include
calcium, phosphorus and magnesium. These are
important for bone growth and muscle
functioning.
• Vitamins: Water soluble vitamins B and C are
concentrated more in the fore milk (or the milk at
the beginning of a feed) and fat soluble vitamins
such as A, D E and K are more concentrated in the
hind milk (or towards the end of the feed).
• Enzymes: There are 3 enzymes present in breast
milk. They include lysozyme (an ant-bacterial
enzyme), lipase (which aids fat digestion) and
amylase (which digests carbohydrates).

20. • Hormones: The hormones present in breast milk
include prolactin, prostaglandins, insulin, thyroid
stimulating hormone, thyroxine and growth hormone.
These aid the baby's growth and development and are
not present in formula milk
• Anti-infective agents: There are many anti-infective
agents present in breast milk including leucocytes that
are capable of surrounding and destroying bacteria and
immunoglobulin's from the mother's immunity (called
IgA, IgG, IgM and IgD).
• Anti-allergenic agents: Babies who are exclusively
breastfed for the first 6 months of their life have less
chance of developing food allergies, skin disorders
(such as eczema) and allergic breathing disorders, (such
as asthma).

21. References
• PEAKER, M. (2001). The aqueous phase of
milk: ion and water transport. Symposia of
the Zoological Society of London 41, 113-
134.
• SEELIG, L. L.,JR. & BEER, A. E. (2003).
Transepithelial migration of leukocytes in
the mammary gland of lactating rats.
Biol.Reprod. 22, 1157-1163.