This document summarizes the female menstrual cycle and processes of fertilization and implantation. It describes the hormonal interactions between the hypothalamus, pituitary gland, ovaries and uterus that regulate the monthly menstrual cycle. It explains follicular development, ovulation, formation of the corpus luteum, and the endometrial changes regulated by estrogen and progesterone in preparation for potential implantation. The processes of fertilization, cleavage, morula and blastocyst formation are outlined. Implantation of the blastocyst in the uterine wall typically occurs 6-7 days post fertilization.

1. MENESTRUAL CYCLE
FERTILIZATION
IMPLANTATION

2. • Monthly menstruation is an obvious
marker that the various levels of
interaction between
-hypothalamus,
- pituitary,
- ovary &
-uterus are functional.

4. Endocrine cycle
Ovarian cycle
Endometrial cycle

6. GnRH…………………..Hypothalamus
Gonadotropins………..Pitutary
-FSH
-LH
Steroids…………………Ovary
-Estrogen
-Progestrone

7.  GnRH -Gonadotropin Releasing Hormone
 controlling factor for gonadotropin secretion
 synthesized by neurosecretory cells in the
hypothalamus
 carried by hypophysial portal system to anterior
lobe of pitutary
 Unique among releasing hormones b/se
1. simultaneously regulates the secretion of 2
hormones (FSH & LH)
2. must be secreted in pulsatile fashion to be
effective

9. Gonadotropins (FSH and LH)
-produced by the anterior pituitary
gonadotroph cells
-responsible for ovarian follicular stimulation
-FSH, LH, TSH, hCG all share identical α
subunits and differ only in the structure of
their β subunits

10.  The structural similarity between FSH, LH, and TSH.
The α subunits are identical and the β subunits differ.

11. Follicle Stimulating Hormone (FSH)
-stimulates development of ovarian
follicles
-stimulates production of estrogen by
follicular cells
Luetinizing Hormone (LH)
-trigger for ovulation ( release of
secondary oocyte)
-stimulates follicular cells & corpus
luteum to produce progesterone

13.  regulated at both endocrine and paracrine
levels
 Phases of ovarian cycle
-Follicular (pre ovulatory)
phase,
-Ovulation, and
-Luteal (post ovulatory) phase

14.  Oocytes in the ovary
- 7 million present during fetal life ,
- 2 million present at birth ,
- 400,000 present at the onset of
puberty, &
 >99.9 % of follicles undergo atresia
through a process of apoptosis
 Only 400 follicles are normally released
during female reproductive life

15. Development of ovarian follicle
characterized by;
-growth & differentiation of primary oocyte
-proliferation of follicular cells
-formation of zona pellucida
-dev’t of theca folliculi

16. Occurs around mid cycle
Triggered by a surge in LH production
Mechanism of ovulation………..

17.  After ovulation the walls of ovarian follicle & theca folliculi
develop in to glandular structure, corpus luteum, under LH
influence
 Corpus Luteum;
-secrets progesterone & some estrogen
-prepare endometrium for implantation
 Fate of corpus Luteum;
1) If the oocyte is fertilized
-enlarges to form corpus luteum of pregnancy
-placenta takes over function by around 8-10 wks
2) If no fertilization occurred
-involutes & degenerates 10-12 days after ovulation
-subsequently transformed in to white scar tissue in the
ovary….corpus albicans

19.  The functional layer of the endometrium is sloughed off
& discarded with the menestrual flow
 Origin of menstrual blood
-arterial bleeding greater than venous
 Mechanism of mensus….
rupture of arteriole of a coiled artery
hematoma formation
Superficial endometrium distends & ruptures
Fissures develop in adjacent functionalis layer
Blood & tissue fragments sloughed

20. Coincides with growth of ovarian follicles
Controlled by estrogen
2 to 3 fold increase in the thickness of
endometrium
Phase of repair & proliferation
Glands increase in number & length
Spiral arteries elongate
Length of cycle may vary among women

21.  Coincides with luteal phase of ovary
 Progesterone dependant
 Glandular epithelium secrete a glycogen rich
material
 Glands become wide, tortuous and saccular
 Endometrium thickens
 Spiral arteries become increasingly coiled
 Direct arteriovenous anastomosis are
prominent features
 Length of cycle usually fixed ( 14 days)

22. 1) If fertilization does not occur;
-the corpus luteum degenerates
-estrogen & progesterone levels fall &
the secretory endometrium enters an
ischemic phase
-menestruation occurs.

23. 2) If fertilization occurs;
-Decidualization (transformation of
secretory endometrium to decidua)
 DECIDUA
-a specialized, highly modified
endometrium of pregnancy
-a function of hemochorial placentation
 Types of decidua
1. Decidua basalis
2. Decidua capsularis
3. Decidua parietalis

24.  Duration of flow
1-8 days (5 on average)
 Frequency / cycle length
21-36 days (28 on average)
 Amount of blood flow
10-80ml (50 on average)
 Character of blood
Dark, non-clotting blood
 Degree of discomfort
No dysmenorrhea

25. CERVIX
VAGINA
BREASTS

27.  The union of egg & sperm
 Sequence of coordinated events
1. Passage of sperm through corona radiata
2. Penetration of the zona pellucida
3. Fusion of plasma membranes of the oocyte
& sperm
4. Completion of the second meiotic division of
oocyte & formation of female pronucleus
5. Formation of the male pronucleus
6. Fusion of pronuclei into a single diploid
aggregation of chromosomes…….the ootid
becomes a zygote

29. 10 microns (0.01mm)
(0.05 to 0.1 microns)
(0.5 to 1.5 microns)
(5 microns)
(5 to 8 microns)
(60 microns)
VIRUS
BACTERIA
RBC
LYMPHOCYTE
SPERM
SIZE COMPARISONS
100 microns
OVUM

30. SPERM NUCLEUS
EGG NUCLEUS
DIPLOID NUCLEUS
(syngamy - syn = together;
gamy = gametes)
FERTILIZATION ZYGTOTE ( = yoke)

31. Usual site is the ampulla of the fallopian
tubes
Results when intercourse occurs during
the 2 days preceding or on the day of
ovulation
Restores the normal diploid number of
chromosomes
Determines chromosomal sex of the
embryo

32.  Zygote
- a diploid cell with 46 chromosomes
-undergoes cleavage into blastomeres
 Morula..a solid mulberry-like ball of
cells
 The morula enters the uterine cavity
about 3 days after fertilization
 Gradual accumulation of fluid b/n the cells
of the morula ……..early blastocyst

40. The Blastocyst
1. Earliest stages of blastocyst;
-wall consists of single layer of ectoderm
2.As early as 4-5 days after fertilization;
-58 cell blastula differentiatesinto
5 embryo producing cells(inner cell
mass)
53 cells to form trophoblasts

41.  Takes place 6 or 7days after fertilization
 Divided in to 3 phases
1) APPOSITION
-initial adhesion of the blastocyst to the
uterine wall
2) ADHESION
-increased physical contact b/n the blastocyst &
uterine epithelium, &
3) INVASION
-penetration & invasion of syncytiotrophoblasts &
cytotrophoblasts in to the endometrium , inner
third of the myometrium & , uterine vasculature.

42.  Succesful implantation requires receptive
endometrium
 Uterine receptivity is limited to days 20-24 of
the cycle
 Implantation most commonly occurs on the
upper posterior uterine wall
 At the time of interaction with the
endometrium, the blastocyst is composed of
100-250 cells.
 By the 10th day the blastocyst becomes totally
encased with in endometrium

44. Hmmm…! Life is a journey!