Development of the Breasts
The breasts begin to develop at puberty. This
development is stimulated by the estrogens of the
monthly female sexual cycle;
Estrogens stimulate growth of the breasts’
mammary glands plus the deposition of fat to give
the breasts mass.
In addition, far greater growth occurs during the
high estrogen state of pregnancy, and only then
does the glandular tissue become completely
developed for the production of milk.
Growth of the Ductal System
All through pregnancy, the large quantities of
estrogens secreted by the placenta cause the ductal
system of the breasts to grow and branch.
Simultaneously, the stroma of the breasts increases in
quantity, and large quantities of fat are laid down in
Also important for growth of the ductal system are at
least four other hormones: growth hormone,
prolactin, the adrenal glucocorticoids, and insulin.
Each of these is known to play a role in protein
Development of the LobuleAlveolar System
Final development of the breasts into milk secreting
organs requires progesterone.
progesterone—acting synergistically with estrogen,
causes additional growth of the breast lobules, with
growing of alveoli and development of secretory
characteristics in the cells of the alveoli.
These changes are analogous to the secretory effects
of progesterone on the endometrium of the uterus
during the latter half of the female menstrual cycle.
Phases Of Lactation
• Preparation of breast for milk secretion –
• Synthesis & secretion of milk –
• Expulsion of milk – galactokinesis
• Maintenance of lactation - galactopoesis
Initiation of Lactation
Prolactin hormone is secreted by the mother’s
anterior pituitary gland, and its concentration in her
blood rises steadily from the 5th week of pregnancy
until birth of the baby, at which time it has risen to 10
to 20 times the normal nonpregnant level.
In addition, the placenta secretes large quantities of
hCS, which probably has lactogenic properties, thus
supporting the prolactin from the mother’s pituitary
The fluid secreted during the last few days before and
the first few days after parturition is called colostrum;
it contains essentially the same concentrations of
proteins and lactose as milk, but it has almost no fat.
Initiation of Lactation
Immediately after the baby is born, the sudden loss of
both estrogen and progesterone secretion from the
placenta allows the lactogenic effect of prolactin from
the mother’s pituitary gland to assume its natural milk
promoting role, and over the next 1 to 7 days, the
breasts begin to secrete copious quantities of milk
instead of colostrum.
growth hormone, cortisol, parathyroid hormone, and
These hormones are necessary to provide the amino
acids, fatty acids, glucose, and calcium required for
Initiation of Lactation
After birth of the baby, the basal level of prolactin secretion
returns to the nonpregnant level over the next few weeks.
Each time the mother nurses her baby, nervous signals from the
nipples to the hypothalamus cause a 10- to 20-fold surge in
prolactin secretion that lasts for about 1 hour.
If this prolactin surge is absent or blocked as a result of
hypothalamic or pituitary damage or if nursing does not continue,
the breasts lose their ability to produce milk within 1 week or so.
Milk production can continue for several years if the child
continues to suckle, although the rate of milk formation normally
decreases considerably after 7 to 9 months.
The hypothalamus mainly stimulates production of all the other
hormones, but it mainly inhibits prolactin production. Consequently,
damage to the hypothalamus or blockage of the hypothalamic
hypophysial portal system often increases prolactin secretion.
prolactin inhibitory hormone
It is almost certainly the same as the catecholamine dopamine, which is
known to be secreted by the arcuate nuclei of the hypothalamus and can
decrease prolactin secretion as much as 10-fold.
L-Dopa decreases prolactin secretion by increasing the formation of
dopamine, and bromocriptine and other dopamine agonists inhibit
secretion because they stimulate dopamine receptors. Chlorpromazine
and related drugs that block dopamine receptors increase prolactin
In most nursing mothers, the ovarian cycle and ovulation
stop until a few weeks after cessation of nursing.
The reason seems to be that the same nervous signals from
the breasts to the hypothalamus that cause prolactin
secretion during suckling—either because of the nervous
signals themselves or because of a subsequent effect of
increased prolactin — inhibit secretion of GnRH by the
hypothalamus & so FSH, LH from ant. pituitary.
After several months of lactation, in some mothers,
especially in those who nurse their babies only some of the
time, the pituitary begins to secrete sufficient gonadotropic
hormones to restore the monthly sexual cycle, even though
Ejection (or “Let-Down”) Process
Milk is secreted continuously into the alveoli of the breasts, but milk does
not flow easily from the alveoli into the ductal system and, therefore,
does not continually leak from the breast nipples.
When the baby suckles, it receives virtually no milk for the first half
minute. Sensory impulses - somatic nerves from the nipples - spinal cord –
hypothalamus - oxytocin .
The oxytocin via blood to the breasts, where it causes myoepithelial cells
to contract, thereby expressing the milk from the alveoli into the ducts.
So, within 30 seconds to 1 minute after a baby begins to suckle, milk
begins to flow. This process is called milk ejection or milk let-down –
opposite breast also
Fondling of the baby by the mother or hearing the baby crying often gives
enough of an emotional signal to the hypothalamus to cause milk ejection
– inhibition by psychogenic stimuli
More lactose, less protein, less ash
At the height of lactation in the human mother, 1.5 liters of milk
may be formed each day (and even more if the mother has twins).
about 50 grams of fat enter the milk each day, and about 100 grams
of lactose, which must be derived by conversion from the mother’s
Also, 2 to 3 grams of calcium phosphate may be lost each day;
multiple types of antibodies and other anti-infectious agents are
secreted in milk along with the nutrients.
neutrophils and macrophages - Escherichia coli bacteria, which
often cause lethal diarrhea in newborns.
Balanced diet – easily digestible
Protection against infection
Sterile – inexpensive
Right temperature – rare chances of allergy
Amenorrhea – birth control
Involution of uterus – oxytocin
Protection against breast engorgement & so infection
Protection against obesity, cancer
Emotional bonding with baby
Circulatory – heart – 4th week – 65/min – 140/min
Blood (RBC): 3rd week – yolk sac, 6th week – liver,
3rd month – spleen, afterwards – bone marrow
RS – no respiration – no air - inhibition of
respiration during the later months of fetal life
prevents filling of the lungs with fluid and debris
from the meconium
CNS: spinal cord, brain stem reflex – 4th month,
cerebral cortex last month, even after birth
GIT: 4th month – ingestion & absorption of amniotic
fluid – meconium formed
KIDNEY: 2nd trimester, 70 – 80 % of amniotic fluid is
urine – oligohydramnios
Metabolism: glucose for energy – converted to fat, Ca,
phosphorus accumulation in last 4 weeks – rapid
weight gain due to ossification, after 4th month – X ray
Iron: 3rd week iron in Hb, iron store in liver, Vitamins
Onset of Breathing – the child ordinarily begins to
breathe within seconds and has a normal respiratory
rhythm within less than 1 minute after birth.
Asphyxia – sensory from cooling of skin
Danger of hypoxia –
(1) Compression of the umbilical cord;
(2) Premature separation of the placenta;
(3) Excessive contraction of the uterus, which can cut
off the mother’s blood flow to the placenta;
(4) Excessive anesthesia of the mother
(5) Head trauma or prolonged delivery
Onset of Breathing
Can tolerate hypoxia for 10 minutes – adult only 4 minutes
Expansion of the Lungs
At birth, the walls of the alveoli are at first collapsed because
of the surface tension of the viscid fluid that fills them. More
than 25 mm Hg of negative inspiratory pressure in the lungs
is usually required to oppose the effects of this surface
tension and to open the alveoli for the first time.
But once the alveoli do open, further respiration can be
effected with relatively weak respiratory movements.
the first inspirations of the normal neonate are extremely
powerful, usually capable of creating as much as 60 mm Hg
negative pressure in the Intrapleural space.
First, loss of the tremendous blood flow through the placenta, which
approximately doubles the SVR at birth.
This increases the aortic pressure as well as the pressures in the left ventricle
and left atrium.
Second, the PVR greatly decreases as a result of expansion of the lungs. In the
unexpanded fetal lungs, the blood vessels are compressed because of the
small volume of the lungs. Immediately on expansion, these vessels are no
longer compressed and the resistance to blood flow decreases.
Also, in fetal life, the hypoxia of the lungs causes considerable tonic
vasoconstriction of the lung blood vessels, but vasodilation takes place when
ventilation of the lungs eliminates the hypoxia.
All these changes together reduces the pulmonary arterial pressure, right
ventricular pressure, and right atrial pressure.
Closure of the Foramen Ovale
The low right atrial pressure and the high left atrial pressure
cause blood now to attempt to flow backward through the
foramen ovale; that is, from the left atrium into the right atrium.
The small valve that lies over the foramen ovale on the left side
of the atrial septum closes over this opening, thereby preventing
further flow through the foramen ovale.
In 2/3rd of all people, the valve becomes adherent over the
foramen ovale within a few months to a few years and forms a
But even if permanent closure does not occur, the left atrial
pressure throughout life normally remains 2 to 4 mm Hg greater
than the right atrial pressure, and the backpressure keeps the
Closure of the Ductus Arteriosus
↑ SVR elevates the aortic pressure while ↓ PVR reduces the pulmonary
arterial pressure. So, after birth, blood begins to flow backward from the
aorta into the pulmonary artery through the ductus arteriosus.
After only a few hours, the muscle wall of the ductus arteriosus constricts
markedly, and within 1 to 8 days - functional closure of the ductus
Then, during the next 1 to 4 months, the ductus arteriosus ordinarily
becomes anatomically occluded by growth of fibrous tissue into its
The degree of contraction of the smooth muscle in the ductus wall is highly
related to availability of oxygen.
In one of several thousand infants – PDA. The failure of closure result from
excessive ductus dilation caused by vasodilating prostaglandins in the
ductus wall – indomethacin role
Closure of the Ductus Venosus
In fetal life, the portal blood from the fetus’s abdomen joins
the blood from the umbilical vein, and these together pass
by way of the ductus venosus directly into the vena cava
bypassing the liver.
Immediately after birth, blood flow through the umbilical
vein ceases, but most of the portal blood still flows through
the ductus venosus, with only a small amount passing
through the channels of the liver.
Within 1 to 3 hours the muscle wall of the ductus venosus
contracts strongly and closes this path of flow. As a
consequence, the portal venous pressure rises from near 0
to 6 to 10 mm Hg, which is enough to force portal venous
blood flow through the liver sinuses.
Glucose – immature liver – first 2 to 3 days – fluid imbalance
– weight loss
RS: TV 16 ml x RR 40 = RMV 640 ml / min, FRC more due to ↑
BV: 300 + 75
CO: 500 ml / min
BP: 70/50 – 90/60 – 110/70
hyperbilirubinemia - jaundice
Blood: Erythroblastosis Fetalis
Kidney: Acidosis, dehydration, overhydration
Liver: hypoproteinemic edema, low coagulation factors
Hypothermia - ↑ BMR, BSA more as compared to
Vitamin D – rickets, iron deficiency, Vitamin C – scurvy
Allergy due to newly developing immunity
Diabetic mother – large babies – RDS
RDS – chyne stroke breathing – Oxygen
therapy – danger of blindness – retrolental
Instable body temperature – role of