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MAMMARY GLAND AND LACTATION
LEARNING OBJECTIVE
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At the end of lecture student should be able to know,
Anatomy of mammary gland,
Physiology of mammary gland,
Lactation reflex,
Hormonal effect.
MAMMARY GLAND
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An organ in mammals that produces milk to feed young offspring.
It is an exocrine gland that is an enlarged and modified sweat gland.
Breasts start developing between the ages of 9-14
years for most women.
When hormonal changes associated with puberty
begin to occur.
The mammary glands, or milk producing areas, lie
between the pectoralis major muscle and the skin.
The glands that make milk in the breast are arranged
into rounded areas called lobules.
MAMMARY GLAND
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15-20 of these lobules exists per breast.
Besides glands, the breast contains fatty tissue, ducts
that carry milk to the nipple, and small amounts of muscle that open and close the
nipple.
ANATOMY
ANATOMY
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Skin
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Fatty Tissue
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Fascia (superficial and deep) – This a type of tissue that is found between
muscles and different tissue layers in the body. It helps hold tissues together.
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Coopers ligament –
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This the body’s own natural bra. This ligament helps hold the breast up and
keeps it from sagging
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Acini – The “sacklike” end of the channel that carries milk. The surrounding
glandular, or milk producing tissue dumps milk into these small areas before it is
carried away in the ducts.
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Areola – Another term for nipple.
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Main Duct – The milk from the 15-20 lobules all collects
into this duct.
Glandular tissue – The part of the breast that produces
the milk.
Retromammary Space – An area below the breast
tissue, but still above the muscle.
Pectoralis (Major and Minor) – The muscles lying
directly beneath the breast.
Axilla – Another term for armpit.
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Ribs
MAMMARY GLAND PHYSIOLOGY
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Milk is produced in the alveolus.
The alveolus is made up of gland cells around a central
duct.
The milk is produced by the gland cells.
Surrounding the gland cells are the myoepithelial cells
which contract to cause milk ejection into the milk duct.
The milk then travels down the lactiferous ducts.
Milk is stored largely in the alveoli with little storage in the ducts between breastfeedings.
Mothers continue to make milk between feedings and they make
more milk during feedings
When an infant breastfeeds, the infant draws the nipple and the
areola into their mouth.
The mother's nipple elongates to about twice its normal length.
The nipple height is compressed between the tongue and the
palate.
Milk is ejected about 0.03 seconds after maximum nipple
elongation
PHYSIOLOGY
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Lactation is used for the breast milk production or formation in mothers after the birth of
baby.
Lactation starts following delivery or birth of baby, the
preparation of effective lactation starts during
pregnancy
STAGES OF LACTATION
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The lactation can be divided into four stages to understand its proper physiology.
Preparation of Breasts or Mammogenesis
Synthesis and secretion of milk from breast alveloi or Lactogenesis
Ejection of milk outside the breast or Galactokinesis
Maintenance of lactation or Galactopoiesis
Mammogenesis Or Preparation Of Breasts For Breast Milk Production:
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Pregnancy is associated with a remarkable growth in the size of breast.
The enhanced size of breast in pregnancy is due to the growth of ducts and
lobuloalveolar (ducts and segments) systems in breast.
An intact nerve supply is not essential for the growth of mammary glands during
pregnancy.
Estrogen, Adrenal steroids and Growth hormone affect the ducts during this phase.
Progesterone, Estrogen, Prolactin, Adrenal steroids and Growth hormone affect the
lobuloalveolar segment of the breast in this phase of breast milk production.
Lactogenesis For Breast Milk Production
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Some secretory activity is evident in the form of Colostrum or early milk during
pregnancy or just after child birth.
This secretory activity is accelerated following birth of baby.
This early form of milk is essential and very good for the health of the baby.
Secretory activity refers to secretion of milk in the milk producing unit of breast or in
alveoli.
Actual milk secretion starts actually on 3rd or 4th day after the birth of baby.
Around this time breasts become engorged, tense, tender and feel warm.
Despite the high prolactin level during pregnancy, milk secretion is kept in abeyance.
Perhaps the steroids Estrogen and Progesterone that are circulating in the blood of
pregnant lady make the breast tissue unresponsive to prolactin presence.
When the circulating Estrogen and Progesterone are withdrawn from the blood after the
birth of baby, Prolactin begins its milk secretory activity in previously fully developed and
prepared breasts.
This secretory activity is enhanced directly and indirectly by Growth hormone, Thyroxine,
Glucocorticoids and Insulin.
Nursing effort is not essential for secretion of milk.
Galactokinesis or Ejection Of Milk For Breast Milk Production:
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Discharge of milk from the mammary glands of breast depends upon the suction exerted
by the baby during suckling. Contractile mechanism also helps by expressing the milk
from alveoli into the ducts.
During suckling, a conditioned nervous reflex is set up. The impulses start from the
nipples to Supraoptic nucleus in brain and thence along the hypothalamo-pituitary axis to
posterior pituitary. It appears to be so complicated and essentially when the love of baby
is there, all this is simply a loving privilege of Moms!
Oxytocin is secreted from posterior pituitary which exerts several effects on the uterus
and breast. In breasts, there is contraction of the myoepithelial cells of alveoli and ducts
containing the milk.
Galactokinesis or Ejection Of Milk For Breast Milk Production:
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This is the "milk ejection" or "milk let down" reflex that forces the milk down into the
lactiferous ducts.
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From lactiferous ducts milk is expressed either by the mother by hand or sucked out by
the baby.
A sensation of rise in pressure in the breast is felt by the mother at the begining of
suckling. It is called "draught".
This effect can be produced artificially by the injection of Oxytocin hormone.
The milk ejection reflex is inhibited by several factors like pain in breasts or body, breast
engorgement, psychological upsets.
In addition this ejection reflex might be weak for several days following breast feeding
and it results in breast engorgement.
Galactopoiesis or Maintenance Of Lactation:
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The hormone Prolactin appears to be the single most important factor for maintenance
of lactation.
Sucking is also essential for maintenance of lactation. Sucking is essential for the
removal of milk from the glands in breast but also for the release of Prolactin.
Secretion of milk is a continuous process unless suppressed by congestion or emotional
disturbances.
Milk pressure reduces the rate of breast milk production.
So periodic breast feeding is necessary to relieve the pressure that in turn maintains the
secretion of milk inside the breast.
Hormonal influences
Progesterone
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progesterone inhibits lactation during pregnancy.
The fall in progesterone levels following delivery is one of the triggers for milk
production.
influences the growth in size of alveoli and lobes, high levels of progesterone inhibit
lactation before birth.
Progesterone levels drop after birth, this triggers the onset of copious milk production
Estrogens
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Estrogens are natural body substances with specific effects on the human body,
including growth and maintenance of the female reproductive system and all female sex
characteristics.
They promote growth and development of all parts of the reproductive system and
breasts; Estrogen products should never be used during pregnancy.
If used during the earlier stages of pregnancy, estrogens can seriously damage a
developing fetus.
Estrogens may reduce the flow of breast milk.
The effects of estrogens on nursing infants are not predictable
Estrogens
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stimulates the milk duct system to grow and differentiate.
Like progesterone high levels of estrogen also inhibit lactation.
estrogen levels also drop at delivery and remain low for the first several months of
breastfeeding.
It is recommended that breastfeeding mothers avoid estrogen-based birth control
methods, as a spike in estrogen levels may reduce a mother's milk supply.
Prolactin
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contributes to the increased growth and differentiation of the alveoli, also influences
differentiation of ductal structures.
High levels of prolactin during pregnancy and breastfeeding also increase insulin
resistance, increase growth factor levels (IGF-1) and modify lipid metabolism in
preparation for breastfeeding.
During lactation prolactin is the main factor maintaining tight junctions of the ductal
epithelium and regulating milk production through osmotic balance.
Growth hormone
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Structurally very similar to prolactin and contributes to its galactopoietic function.
ATCH and glucocorticoids
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ATCH and glucocorticoids have an important lactation inducing function in several
animal species.
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ACTH is thought to contribute as it is structurally similar to prolactin. Glucocorticoids play
a complex regulating role in the maintenance of tight junctions.
TSH
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a very important galactopoietic hormone, its levels are naturally increased during
pregnancy.
Oxytocin
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contracts the smooth muscle of the uterus during and after birth, and during orgasm(s).
After birth, oxytocin contracts the smooth muscle layer of band-like cells surrounding the
alveoli to squeeze the newly-produced milk into the duct system.
Oxytocin is necessary for the milk ejection reflex, or let-down to occur.
Human placental lactogen (HPL)—
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From the second month of pregnancy, the placenta releases large amounts of HPL.
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This hormone appears to be instrumental in breast, nipple, and areola growth before
birth.
Follicle stimulating hormone (FSH)
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a hormone found in humans and other animals.
It is synthesized and secreted by gonadotrophs of the anterior pituitary gland.
FSH regulates the development, growth, pubertal maturation, and reproductive
processes of the body.
Luteinizing hormone (LH)
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produced by the anterior pituitary gland.
In females, an acute rise of LH called the LH surge triggers ovulation and development
of the corpus luteum
Conditions with very low LH secretions Hyperprolactinaemia
Hyperprolactinaemia
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Is the presence of abnormally-high levels of prolactin in the blood.
Normal levels are less than 580 mIU/L for women, and less than 450 mIU/L for men.
Prolactin is a peptide hormone produced by the anterior pituitary gland primarily
associated with lactation and plays a vital role in breast development during pregnancy.
Hyperprolactinaemia may cause production and spontaneous flow of breast milk and
disruptions in the normal menstrual period in women and hypogonadism, infertility and
erectile dysfunction in men.
Hyperprolactinaemia
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Hyperprolactinaemia can be a part of normal body changes during pregnancy and
breastfeeding.
It can also be caused by diseases affecting the hypothalamus and pituitary gland.
It can also be caused by disruption of the normal regulation of prolactin levels by drugs,
medicinal herbs and heavy metals.
Hyperprolactinaemia may also be the result of disease of other organs such as the liver,
kidneys, ovaries and thyroid
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