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