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Ch. 82 Pregnancy and Lactation By Natasha McDougal and Jordan Shellmire
Pregnancy
Fertilization and Implantation Sperm are transported through the vagina to the ampulla of
the fallopian tubes
Sperm must penetrate the corona radiata and the zona
pellucida to reach the ovum
Ovum are in the secondary oocyte stage but once sperm
enters the ovum divides and forms the mature ovum and
polar body (which is expelled)
Developing blastocyst enters the uterus and implants in 1-3
days
Trophoblast cells on the blastocyst cause implantation
Trophoblast cells and other adjacent cells form the placenta and
various membranes of pregnancy
Nutrition of the Embryo Decidual Cells
Pre-fertilization the body of the uterus contains decidua-like
cells
Decidual cells develop following fertilization through glycogen
and lipid accumulation
Trophoblast cells on the implanted blastocyst digest these
decidual cells as a form of nutrition until placental diffusion
can begin
Nutrition of the Embryo
Placenta
Fetal gut in supplying nutrients
Fetal lung in exchanging O2 and CO2
The fetal kidney in regulating fluid volumes and disposing of
waste metabolites
Endocrine gland synthesizing many steroids and protein
hormones that affect both maternal and fetal metabolism
Clicker Question For the first 10 weeks of gestation the fetus gets its nutrition
from:
a. Decidual cells
b. The placenta
c. The mother’s blood
Hormonal Factors in Pregnancy Human Chorionic Gonadotropin
Causes persistence of the Corpus Luteum
Prevents menstruation
Produced by trophoblast cells
Causes production of testosterone in male fetus
Estrogen
Enlargement of uterus
Enlargement of breasts
Relaxes pelvic ligaments
Progesterone
Decreases uterine contractility
Causes development of decidual cells
Hormonal Factors in Pregnancy Human Chorionic Somatomammotropin
Secreted at 5 weeks gestation
May promote growth
Decreases glucose usage by the mother
Other hormonal factors
Pituitary secretion
Corticosteroid secretion
Thyroid gland secretion
Parathyroid gland secretion
Relaxin
Changes During Pregnancy Weight Gain
Most women have increased appetite
Typical weight gain is 25-35 pounds
Metabolism
Increased thyroxine levels (secreted via the placenta) and
adrenocortical hormones
BMR increases by 15% in the latter half of pregnancy
Nutrition
Mother’s body stores protein, calcium, and phosphates for the last
months of pregnancy
Increased insulin secretion after 3rd month of pregnancy
Decreased insulin sensitivity
No changes to glucagon sensitivity
Changes During Pregnancy Circulatory System
30-40% increase
in cardiac
output
30% increase in
blood volume
Kidney Function
Increased sodium
and water
retention
Amniotic Fluid Generally between 500 and 1000 milliliters
Water is replaced every 3 hours
Electrolytes Sodium and Potassium are replaced every 15
hours
A large portion of amniotic fluid is derived from renal
excretion from the fetus
Pre-eclampsia Multisystem disorder specific to human pregnancy
Characterized by maternal hypertension, proteinuria, and generalized edema
It is a disease of the placenta
Failure of trophoblast invasion
Supply of both nutrients and oxygen to the placenta is disturbed
Affects 7-13% of pregnancies in the US
Cause is unknown
Thought to be related to limited blood supply to uterine arteries
causing ischemia
Clicker Question Changes during pregnancy include all of the following except:
a. Blood flow decreases
b. Metabolism increases
c. Respiration increases
d. Amniotic Fluid develops
Parturition: Progressive Hormonal Changes
Progesterone prevents expulsion of the fetus
Estrogens increase uterine contractility
The change in the estrogen to progesterone ratio helps to
increase contractility of the uterus
Oxytocin causes contraction of the uterus
Fetal adrenal glands secrete cortisol and prostaglandins
Parturition: Progressive Mechanical Changes Stretch of uterine musculature
Stretch of the cervix
A positive feedback
mechanism
Braxton Hicks contractions
Lactation
Development of the Breasts Begins at puberty due to
estrogen stimulation and
increases during
pregnancy, due to
estrogen, progesterone
and prolactin
Estrogens stimulate growth
of the breasts’ mammary
glands plus the
deposition of fat to give
the breasts mass
Development of the Breasts During pregnancy large quantities of estrogens are secreted
by the placenta
cause the ductal system of the breasts to grow and branch
Final development of the breasts into milk secreting organs
requires progesterone
Once the ductal system has developed, progesterone
simultaneously with estrogen causes additional growth of
breast lobules
Prolactin Lactation is initiated by precipitous drop in estrogen and
progesterone after delivery
Prolactin- promotes milk secretion
Secreted by anterior pituitary, starting from 5th wk of pregnancy
until birth, then cycles
1st milk = colostrum -- same proteins and lactose as milk, but
no fat
Prolactin surges each time mother nurses baby due to nerve
impulses from nipples to hypothalamus
Without nursing stimulation, there is no prolactin surge, and loss
of milk production
Prolactin When not nursing,
hypothalamus
produces prolactin
inhibitory hormone
Lactation inhibits
FSH, LH and thus
lactation interferes
with reproductive
function
Ejection Milk is secreted continuously into the alveoli of the breasts,
but does not flow easily from the alveoli into the ductal
system
Milk must be ejected from the alveoli into the ducts.
Caused by a combined neurogenic and hormonal reflex
At first suckling baby receives no milk for the first 30 seconds
Sensory impulses are transmitted through somatic nerves from
the nipples to the spinal cord and then to the hypothalamus,
where they cause oxytocin and prolactin secretion
Oxytocin is carried in the blood to the breasts, where it causes
myoepithelial cells to contract expressing milk from the alveoli
into the ducts at a pressure of +10 to 20 mm Hg
Baby’s suckling becomes effective in removing the milk
Ejection This is called milk ejection or milk let-down
Suckling can cause milk to flow from both breasts.
Milk Composition Human Milk (%)
Water 88.5
Fat 3.3
Lactose 6.8
Casein 0.9
Lactalbumin and other 0.4
proteins
Ash (calcium/other) 0.2
Cow’s Milk (%)
Water 87.0
Fat 3.5
Lactose 4.8
Casein 2.7
Lactalbumin and other 0.7
proteins
Ash 0.7