The Menstrual Cycle
&
Pregnancy
HONORS ANATOMY &
PHYSIOLOGY
THE REPRODUCTIVE SYSTEM
PART 3
Female Reproductive Cycle
 2 parts:
Ovarian Cycle
1.
1.
series of events in ovaries occurring during &
after maturation of oocyte
2. Uterine (Endometrial) Cycle
1.
2.
concurrent with ovarian cycle
series of changes in endometrium to repare it
for implantation of fertilized egg
Hormonal Regulation
 Hypothalamus secretes GnRH (gonadotropin-
releasing hormone) that controls both the ovarian &
uterine cycles
 GnRH stimulates release of FSH & LH from anterior
pituitary
Effects on Ovaries
FSH
 initiates follicle growth
 stimulates:
follicles to release E
 granulosa cells to
turn androgens  E

LH
 stimulates :
 further development of
follicles
 release of E from
follicles
 release of androgens
from theca cells
 @ midcycle LH surge
triggers ovulation
 corpus luteum  E, P,
relaxin, inhibin
Estrogens
 3 of 6 different estrogens are present in significant
amts:
1. ß estradiol
2. Estrone
3. Estrial


most abundant in non-pregnant female
made from cholesterol in ovaries
Functions of Estrogens
promote development &maintenance of female
reproductive structures, 2◦ sex characteristics
2. increase protein anabolism working synergistically
with hGH
3. lowers cholesterol (1 reason females <50 yo have
lower risk of CAD)
4. moderate levels inhibit release of GnRH, FSH, LH
(negative feedback loop)
1.
Progesterone
 secreted by corpus luteum
 with E prepares endometrium for implantation &
breasts for lactation
Relaxin
 produced by corpus luteum
 inhibits contractions of myometrium
 during pregnancy, placenta secretes more relaxin…@
end of pregnancy it increases flexibility of pubic
symphysis & may help dilate cx
Inhibin
 secreted by granulosa cells of growing follicles & by
corpus luteum after ovulation
 action: inhibits secretion of FSH & to lesser extent
LH
Hormones of the Menstrual Cycle
Phases of the Menstrual Cycle
Menstrual Phase
2. Preovulatory Phase
1.


in ovaries called follicular phase
in uterus: proliferative phase
3. Ovulation
4. Postovulatory Phase


in ovaries called luteal phase
in uterus: secretory phase
Menstrual Phase
 aka menstruation, menses
 ~1st 5 d of cycle (d 1 of flow = day 1 of cycle)
 Ovaries:
 FSH causes several primordial follicles to
develop  1◦ follicles  2◦ follicles
 Uterus:
 declining E & P levels  prostaglandins 
constriction of uterine spiral arterioles  O
deprived tissue  death & shedding 50 – 150 mL
of blood, tissue fluid, mucus, epithelial cells
(entire stratum functionalis sloughs off)
Preovulatory Phase
 time between end of menses  ovulation
 most variable length in time (reason cycles vary in
length)
 Ovaries:
follicles secrete E & inhibin  d 16
 one 2◦ follicle in 1 of the 2 ovaries becomes the
dominant follicle (secretes more E & inhibin 
decreases FSH)
 dominant follicle (Graafian) enlarges until
ovulation:~2cm

Preovulatory Phase (Proliferative)
 Uterus:
E stimulates repair of endometrium producing
new stratum functionalis
 new endometrial glands form
 endometrium thickens from ~4 to 10 mm

Ovulation
 d 14 in 28 d cycle
 2◦ oocyte surrounded by zona pellucida & corona
radiata
 higher levels of E @ end of preovulatory phase have
+ effect on cells that secrete LH & GnRH: their
increase leads to ovulation
 OTC test for LH surge used to predict ovulation
Mittleschmerz
 pain noted @ time of ovulation
 caused by small amt of blood that leaks into pelvic
cavity from ruptured follicle
Postovulatory Phase (Luteal)
 time between ovulation & onset of next menses
 Most constant part of cycle = 14 days (d15 – 28)
 Ovary:
 under influence of LH, granulosa cells
transformed  corpus luteum cellswhich secrete
E, P, relaxin, inhibin
 if oocyte not fertilized: corpus luteum lasts 2 wks
 corpus albicans
 + fertilization: corpus luteum persists until
“rescued” by hCG (human chorionic
gonadotropin) which is made by chorion of
embryo @ ~ 8d after fertilization
Postovulatory Phase (Secretory)
 Uterus:
P & E made by corpus luteum promote: growth &
coiling of endometrial glands
 vascularization of superficial endometrium
 thickening of endometrium (12 – 18 mm)
 these changes peak 1 wk after ovulation
 if no fertilization levels of P & E decline which
eventually causes menstruation

Homeostatic Imbalances
 Dysmenorrhea

painful menses
 Amenorrhea
absence of menses
 #1 reason = pregnancy

 Endometriosis
disorder in which endometrium grows outside
uterus
 +/- painful
 can cause infertility due to scarring

Embryonic Period
 Fertilization:
Nuclei from sperm merges with nuclei from 2◦
oocyte forming a diploid nucleus
 Fallopian tube normal site of fertilization w/in 12
-24 hrs after ovulation
 sperm can remain viable up to 48 hrs after
deposition in vagina

Fertilization
 sperm must penetrate 2 layers:
corona radiata
1.

granulosa cells that surround 2◦ oocyte
2. zona pellucida

clear glycoprotein layer between corona radiata
& oocyte’s plasma membrane
Fertilization
 ZP3: 1 of glycoproteins acts as sperm receptor
 acrosomal reaction: occurs when ZP3 binds to
specific membrane protein on sperm head plasma
membrane  release of contents of acrosome
Acrosomal Reaction
 acrosomal enzymes digest a path thru zona pellucida
 lashing flagella of sperm pushes it forward
 several sperm bind to ZP3 molecules but only 1st
sperm to penetrate zona pellucida & reach plasma
membrane of oocyte “wins”
 once diploid nucleus formed its called a zygote
Cleavage of the Zygote
 rapid M phase but no growth
 1st division begins ~24 hrs after fertilization taking 6




hrs to complete, following divisions take less time
~2 d after fertilization = 4 cells
~ 3 d after = 16 cells
cells get progressively smaller, & are called
blastomeres
morula (mulberry) solid sphere of cells, still
surrounded by zona pellucida & still about size of
original zygote
Blastocyst Formation
 ~ end of 4th d: # of cells in morula increase as it is
still moving thru fallopian tube  enter uterine
cavity on d 4-5
 glycoprotein secretions fromendometrial glands
enter morula providing nourishment
 @ ~ 32 cell size, fluid enters morula & collects
between blastomeres forming fluid-filled cavity =
blastocyst cavity (up to ~100 cells) & now called a
blastocyst or blastula (still ~ same size as original
zygote)
Blastocyst Forms Layers
 2 distinct structures form:
Inner cell mass
1.

eventually becomes embryo
2. Trophoblast


ultimately forms fetal portion of placenta
5th d: blastocyst digests hole thru zona pellucida
& squeezes out
Implantation
 attachment of blastocyst to endometrium
 after implantation endometrium becomes modified
& is called decidua
Trophoblast
 develops into 2 layers (both part of chorion):
Syncytiotrophoblast
2. Cytotrophoblast
1.
hCG is Produced
 hCG: human chorionic gonadotropin
 Produced by trophoblast starting on d 6
 hCG causes endometrium to grow & proliferate
 hCGprevents the menstrual cycle from occuring
 reason female misses her menses when she is
pregnant
Inner Cell Mass
 differentiates into a bilaminar disc
Hypoblast
2. Epiblast
1.
Amnion
 thin protective membrane
 develops from cytotrophoblast
Gastrulation
 @ end of cleavage stage, cells making up the blastula





move
surface proteins help cells recognize each other &
help sort cells
3 layers of gastrula formed: called the 3 germ layers
Endoderm
Mesoderm
Ectoderm
Extraembryonic Membranes
 develop from the germ layers but are NOT part of the
embryo (lost at birth)
 lie outside embryo & provide protection &
nourishment
 4 components:
1. chorion
2. amnion
3. allantois
4. yolk sac
Placentation
 formation of the placenta
 site of exchange of nutrients & wastes between the
mother & fetus
 also functions as protective barrier & produces
several hormones to maintain pregnancy (hCG)
Week 2
 implantation continues until complete emersion into
endometrium
Weeks 3 - 4
 development of nervous system & cardiovascular
system evident
Weeks 5 - 8
 embryo will develop all structure that an adult has by
end of week 8
Embryo/ Fetus
Embryonic Period
Fetal Period
 1st thru 8th wk
 begins @ 9th wk & goes
 characterized by
until birth @ 38 wks
(from fertilization)
 characterized by
growth & development
of structures formed in
embryonic period
development of
structures (organs)
Maternal Changes in Pregnancy
 uterus nearly fills abdominal cavity
 GI tract compressed may cause heartburn,
constipation
 pressure on bladder causes frequency & urgency
 compression of inferior vena cava may cause varicose
veins, &/or edema in legs
 compression on renal vessels may cause elevated BP
(renal hypertension)
Maternal Hormone Changes During Pregnancy
 pregnancy maintained by hCG, E, & P
 relaxin increases flexibility of pubic symphysis
 hCS (human chorionic somatomammotropin)
contributes to:
 breast development
 protein anabolism
 catabolism of glucose & fatty acids
Labor
 process by which fetus is expelled from uterus
 true labor involves dilation & thinning of cx
 false labor may have painful contractions but there
are no cervical changes
Positive Feedback Loop
Adjustments Infant Makes at Birth
 Infant’s respiratory & cardiovascular systems
undergo changes to enable them to become selfsupporting
Maternal Breast Changes
 hormonal changes, increased blood flow, & changes
in breast tissue cause breast to feel heavy, swollen, or
sore
 breast tenderness commonly starts w/in 4 wks
 areolas enlarge & darken
 Colostrum the yellowish1st milk your baby gets may
leak out any time after 3rd mo
 contains Ig A antibodies, protein, fatsoluble vitamins, minerals
 replaced by milk after 2 – 4 days baby
nursing
Breastfeeding is Best
Lactation Hormones
Prolactin
 made in anterior
pituitary
 release controlled by
dopamine
 action: activates
mammary glands to
make milk
 several minutes of baby
nursing stimulates
release
Oxytocin
 made in hypothalamus
& stored in posterior
pituitary
 baby nursing
stimulates its release
 action: milk let down