Reproductive cycle, Pregnancy and labor

Reproductive cycle, Pregnancy and labor


At the end of this
lecture, student will be able to

• Discuss the process of oogenesis in ovaries

• Describe the major events of each phase of the
reproductive cycle

• Correlate the events of uterine cycle with the events of
the ovarian cycle

• Prepare a labelled diagram of the major hormonal changes
that occur during the uterine and ovarian cycles

• Describe the functions of various hormones involved in

• Explain the events associated with the three stages of

• Describe the structural and functional changes which occur
in mother during pregnancy

• Explain on sex differentiation


• Oogenesis

• Reproductive cycle

• Hormonal changes during reproductive cycle

 • Preganacy, Hormones,
Structural and functional changes in mother

• Labor – Stages

• Sex determination


• Formation of gametes in the ovaries

• Begins in females before they are even born

During early fetal
development, primordial germ cell in


Differentiate into oogonia (diploid, 2n)


Produce millions of
germ cells

â                                           â

Germ cells degene(Process
Atresia)            Develop into larger cells(Primary oocytes)

• At birth 200,000 – 2,000,000 primary oocytes in each ovary

• About 40,000 at puberty

• Around 400 will mature and ovulate


It encompasses the ovarian and uterine cycles

Ovarian cycle

– Series of events in the ovaries that occur during and
after the maturation of an oocyte

– Develop a secondary oocyte

Uterine (menstrual)

– Concurrent series of changes in the endometrium of uterus

– Prepare the endometrium each month to receive a fertilized

Phases of
the Female Reproductive Cycle

• Encompasses 4 phases

– The menstrual phase

– The preovulatory phase

– Ovulation

– The postovulatory phase

• Cycle typically ranges from 24 to 35 days

• The pre ovulatory phase is more variable in length than
the other phases


• Also called menstruation or menses

• lasts for roughly the first 5 days of the cycle

Events in the ovaries

• FSH, several primordial follicles develop into primary,
secondary follicles

Events in the uterus

• Stratum functionalis of the endometrium is shed

• Discharges blood, tissue fluid, mucus, and epithelial

• Declining levels of progesterone and estrogens à stimulate release of
prostaglandins à
uterine spiral arterioles constrict. (Cells they supply become oxygen-deprived
and start to die)


• Time between the end of menstruation and ovulation

• This phase is more variable in length than the other

• It lasts from days 6 to 13 in a 28-day cycle

Events in the ovaries

• A single secondary follicle will outgrow & become
dominant follicle

• Dominant secondary follicle becomes the mature (graafian)

• Continue to enlarge and produce estrogen

• With reference to the ovarian cycle,

The menstrual + preovulatory = follicular phase, as ovarian
follicles are growing and developing

Events in the uterus

• Estrogens liberated into the blood by growing ovarian

• Stimulate the repair of the endometrium

• Cells of the stratum basalis undergo mitosis, produce a
new stratum functionalis

• Endometrium thickens, straight endometrial glands develop

• Arterioles coil and lengthen, penetrate the stratum

• Also termed the proliferative phase because the
endometrium is proliferating


• Rupture of the mature (graafian) follicle, Release of the
secondary oocyte into the pelvic cavity

• Occurs on day 14 in a 28-day cycle

• Secondary oocyte remains surrounded by its zona pellucida
and corona radiata

• Brought about by a surge of LH

High levels of estrogens exert a positive feedback effect (green
arrows) on the hypothalamus and anterior pituitary, thereby increasing
secretion of GnRH and LH

• Signs and symptoms include

– Increased basal body temperature

– Clear, stretchy cervical mucus

– Changes in the uterine cervix

– Abdominal pain


• Time between ovulation and onset of the next menses

• Most constant part of the female reproductive cycle

• It lasts for 14 days in a 28-day cycle, from day 15 to day

Events in one ovary

• The mature follicle collapses

• A blood clot forms from minor bleeding of the ruptured
follicle, the follicle becomes the corpus hemorrhagicum

• Theca interna cells mix with the granulosa cells,
transforms into corpus luteum cells under the influence of LH

• Corpus luteum secretes progesterone, estrogen, relaxin,
& inhibin

• The luteal cells also absorb the blood clot

• Also called the luteal phase

• If the oocyte is
not fertilized,

– Corpus luteum has a lifespan of only 2 weeks

– Secretory activity declines

– Degenerates into a corpus albicans

– Levels of progesterone, estrogens, and inhibin decrease

– Release of GnRH, FSH, and LH raise

– Follicular growth resumes, a new ovarian cycle begins

• If the secondary
oocyte is fertilized and begins to divide

– Corpus luteum persists past its normal 2-week lifespan.

– “Rescued” from degeneration by human chorionic
gonadotropin (hCG)

– Produced by the chorion of the embryo, 8 days after

– LH, hCG stimulates the secretory activity of the corpus

• Presence of hCG in maternal blood or urine – indicator of
pregnancy hormone detected by home pregnancy tests

Events in the uterus

• Progesterone and estrogens from corpus luteum promote

– Growth, coiling of the endometrial glands

– Vascularization of the superficial endometrium

– Endometrium thickens in readiness for implantation

• Endometrial glands secrete glycogen

• Also called the secretory phase of the uterine cycle

• If fertilization
and implantation do not occur

– Corpus luteum degenerates

– Discharge of the endometrium

– Initiation of another reproductive cycle

Female reproductive

Summary of hormonal interactions in the ovarian and uterine cycles

its maintenance and parturition

• Corpus luteum can only survive for about 2 weeks in the
absence of a pregnancy

• Corpus luteum will survive for the first 6-10 weeks of a

• Secrete progesterone

• Progesterone secretion is required for the maintenance of
a pregancy

• After implantation, embryo secretes hCG

• Placenta also secretes increasing amounts of estrogen
(mainly estriol)

Function of
progesterone during pregnancy

• Inhibits the contractions of the uterine myometrium

• Helps to keep the embryo/fetus in the uterus

• Maintains the uterine endometrium in a secretory, nutrient
rich state to support the developing embryo/fetus

Function of estrogen
during pregnancy

• Maintains the secondary sexual characteristics of the

• Stimulate mammary gland growth in preparation for

• Contractions of the myometrium at the time of birth

Human chorionic
gonadotropin (hCG)

• Secreted by chorion in to blood

• Stimulates the corpus luteum to continue production of
progesterone and estrogens

• Placenta is fully established, the secretion of hCG is
greatly reduced


• Hormone produced first by the corpus luteum of the ovary
and later by the placenta

• Increases the flexibility of the pubic symphysis

• Helps dilate the uterine cervix during labor

Human chorionic
somatomammotropin (hCS)

• Also known as human placental lactogen (hPL)

• Rate of secretion of hCS increases in proportion to
placental mass

• Help prepare the mammary glands for lactation

• Enhance maternal growth by increasing protein synthesis

• Regulate certain aspects of metabolism in both mother and

Hormones during pregnancy

Changes during

• Near the end of the third month of pregnancy, the uterus
occupies most of the pelvic cavity

• Fetus continues to grow

• End of a full-term pregnancy, the uterus fills nearly the
entire abdominal cavity

• Pregnancy-induced physiological changes also occur,

• Weight gain due to the fetus, amniotic fluid, the
placenta, uterine enlargement, and increased total body water

• Increased storage of proteins, triglycerides, and minerals

• Breast enlargement in preparation for lactation

• Lower back pain due to lordosis (hollow back)

• The maternal blood volume increases by over 30%

• Respiratory activity increases by about 20%

• Increased urine output

• Constipation

• Pregnancy amenorrhea


Process by which
the fetus is expelled from the uterus
through the vagina, also referred to
as giving birth

• True labor

Dilation of the

– Expulsion of the fetus

– Delivery of the placenta

• False labor

Pain in abdomen
at irregular intervals

– No cervical dilation

• Control of labor contractions during parturition occurs
via a positive feedback cycle

True labor can be
divided into three stages

1.   Stage of dilation

• Time from the onset of labor to the complete dilation of
the cervix

• Lasts 6–12 hours

• Regular contractions of the uterus

• Usually a rupturing of the amniotic sac, and complete
dilation (to 10 cm) of the cervix

2. Stage of expulsion

• The time (10 minutes to several hours) from complete
cervical dilation to delivery of the baby

3. Placental stage

• The time (5–30 minutes or more) after delivery until the
placenta or “afterbirth” is expelled by powerful uterine contractions

• Constrict blood vessels that were torn during delivery,
reducing the likelihood of hemorrhage

• Labor lasts longer with first babies, about 14 h

• After delivery of the baby, maternal reproductive organs
and physiology return to the prepregnancy state (Puerperium, about 6 weeks)

• Tissue catabolises, the uterus undergoes a remarkable
reduction in size, Involution

• For 2–4 weeks after delivery, women have a uterine
discharge called lochia

• Consists initially of blood and later of serous fluid
derived from the placenta


• There are 46 human chromosomes (of 23 different pairs) in
a normal somatic cell

Karyotype- An
entire set of chromosomes arranged in decreasing order of size and according to
the position of the centromere

• 22 pairs are called autosomes- homologous chromosomes look
alike and have the same appearance in both males and females

Human karyotype showing autosomes and sex chromosomes

• Two members of the 23rd pair are the sex chromosomes

• They look different in males and females

In females, the
pair consists of two chromosomes called X

In males, X
chromosome + Y chromosome (smaller)

• Y chromosome has only 231 genes

• Spermatocyte undergoes meiosis, gives rise to

– Two sperm that contain an X chromosome

– Two sperm that contain a Y chromosome.

• Oocytes have no Y chromosomes, produce only X-containing

• If the secondary
oocyte is fertilized by an X-bearing sperm
, the offspring normally is female (XX).

Fertilization by a
Y-bearing sperm produces a male (XY)

• Individual’s sex is determined by the father’s chromosomes

• Sex is determined at the time of fertilization by the
presence or absence of a Y chromosome in the sperm


• Oogenesis is the formation of gametes in the ovaries

• Female reproductive cycle comprises of uterine and ovarian

• Function of the ovarian cycle is to develop a secondary

• Function of the uterine (menstrual) cycle is to prepare
the endometrium each month to receive a fertilized egg

• Uterine and ovarian cycles are controlled by GnRH from the

• If fertilization and implantation do not occur, the corpus
luteum degenerates

• If fertilization and implantation do occur, the corpus
luteum is maintained by hCG

• Pregnancy is maintained by human chorionic gonadotropin
(hCG), estrogens, and progesterone

• During pregnancy, several anatomical and physiological
changes occur in the mother

• During pregnancy, some joints become less stable, and
certain physical activities are more difficult to execute

• Labor is the process by which the fetus is expelled from
the uterus through the vagina to the outside

• Oxytocin stimulates uterine contractions via a positive
feedback cycle

• Each somatic cell has 46 chromosomes—22 pairs of autosomes
and 1 pair of sex chromosomes

• In females, the sex chromosomes are two X chromosomes

• In males, they are one X chromosome and a much smaller Y