In the Name of ALLAH, the Most Gracious, the
Most Merciful, and
Peace and Blessings be upon His Prophet
Mohamed and his conscience followers, ever!
REPRODUCTION IN HUMANS
SPERMATOGENESIS,
OOGENESIS,
CONCEPTION,
IMPLANTATION,&
INTRODUCTION TO IVF
Ahmed M. Isa, Ph.D., HCLD (ABB), REM (ACE)
Assistant Professor , Head of IVF Lab
Department of Obstetrics & Gynecology
King Khalid University Hospital
King Saud University
Sexual Reproduction in Humans
• In general, sexual reproduction is the
formation of a new individual following the
union of two gametes, one from each parent.
• In humans and the majority of eukaryotes,
plants and animals, the two gametes differ in
structure and function ("an-isogamy") and are
contributed by two different parents.
Sexual Reproduction in Humans
• These two different parents are:
1.The father or the male, who produces the
sperm, through a process called
Spermatogenesis.
2.The mother or the female, who produces
the egg, through a process called
Oogenesis.
Production of Gamets
• Spermatogenesis:
• The production of Sperms takes place in
the two Testes.
• Each testis is packed with seminiferous
tubules (laid end to end, they would
extend for more than 20 meters long)
where spermatogenesis occurs.
Male Reproductive System
or the “Semen Factory”
Seminal Fluid Components
1. Sperms: From the Epididymis. Normally, 25% of the volume.
2. Seminal Vesicle Secretion: 65-75%. amino
acids, citrate, enzymes, flavins, fructose
(energy source), phosphorylcholine,
prostaglandins (suppress female immune
system), proteins, vitamin C
Seminal Fluid Components
3. Prostate Gland Secretion: 25-30%, acid
phosphatase, citric acid, fibrinolysin,
prostate specific antigen(PSA),
proteolytic enzymes, zinc (about 135±40
µgm/ml. Zinc helps to stabilize the sperm
DNA-containing chromatin).
Seminal Fluid Components
4. Bulbo-Uretheral Glands Secretion: <1%,
galactose, mucus (increase sperm
mobility. Contributes to the cohesive jellylike texture of semen.), pre-ejaculate
(Cowper’s fluid, a lubricant), sialic acid.
Spermatogenesis:
• Steps of spermatogenesis:
• The walls of the seminiferous tubules consist
of the germinal epithelium that gives rise to
the diploid spermatogonia, which are the
precursors of the sperm.
• At puberty, Spermatogonia divide by mitosis
to either produce more spermatogonia, or
• differentiate into 1ry spermatocytes (2N).
Spermatogenesis:
• Each 1ry spermatocyte differentiates into 2
haploid secondary spermatocytes (1st Meiosis).
• Each 2ry spermatocyte differentiates into two
haploid spermatids (2nd Meiosis).
• Spermatids (4 from each 1ry spermatocyte)
develop into sperms, losing most of their
cytoplasm in the process, and developing
their long tails.
T.S. of Rat Testis (human’s is similar)
Spermatogenesis
• With 22 pairs of autosomes and an average
of two crossovers between each pair, the
variety of genetic material combinations in
the resulting sperms are very great.
• In humans, spermatogenesis from start to
end takes about 64 days before a sperm is
ready in the epididymis.
Sperm Structue:
• Sperm is a lot more than a flagellated cell.
It is consisted of:
• A head (5µm by 3µm), which has
– an acrosome on its tip, and
– a nucleus contains a haploid set of
chromosomes in a compacted state.
• A midpiece containing the mitochondria
and a single centriole.
• A tail (midpiece and tail are ~50µm long).
Diagram of an L.S. of a spermatozoan
Sperm Ultra-structure
• This electron
micrograph shows the
sperm cell of a bat.
• Note the orderly
arrangement of the
mitochondria in the
sperm mid-piece.
• In average, a normal adult man manufactures
about 100 million sperms each day.
• As they are produced, they are moved into
the epididymis where they undergo further
maturation.
• The acidic environment of the epididymis
keeps the mature sperm inactive.
• Animated Spermatogenesis:
http://wps.aw.com/bc_martini_eap_4/40/10469/2680298.cw/content/index.html
Hormones of Spermatogenesis
Testosterone:
• The Interstitial cells in each testis function
as an endocrine gland. Its principal
hormone, testosterone, is responsible for:
1. Sperm production.
2. Secondary sex characteristics of men.
• The Interstitial Cells of Leydig lie between
the seminiferous tubules.
Interstitial Cells of Leydig (7)
• LH, from the A. Pituitary
Gland, stimulates the
ICL to secrete the
Testosterone.
• Prolactin, also from the
A. Pituitary, upregulates
the LH receptor
expression on the ICL.
FSH:
• Follicle-stimulating hormone (named for its
role in females, like the LH).
• Matures the Seminiferous tubules.
• Acts directly on spermatogonia to
stimulate sperm production (aided by the
LH needed for testosterone synthesis).
Production of Gamets
Oogenesis:
• In contrast to males, the initial steps in eggs
production occur early prior to the girl’s birth.
• Diploid ovarian stem cells called oogonia,
that arise from the ovarian Germinal
Epithelium, divide by mitosis to produce
more oogonia and primary oocytes.
• The 20 weeks old female fetus already
possesses all the primary oocytes that she
will ever have; ~4-7 million eggs.
Oogenesis (Cont.):
• At birth, only 1–2 million 1ry oocytes remain,
each has begun the first meiotic division and
has stopped, at prophase I, or the Germinal
Vesicle stage, GV (1st Arrest).
• Only at puberty, those primary oocytes
resume development, usually one or a few,
at each menstrual cycle.
Oogenesis (Cont.):
• They grow and complete meiosis l,
forming a larger haploid secondary oocyte
and a small polar body, each bears one
set of chromosomes.
• In humans (and most vertebrates), first
polar body degenerates.
• The secondary oocyte immediately
proceeds to meiosis II, but again stops at
metaphase II (2nd Arrest), and known as
Mll oocye.
Oogenesis (Cont.):
• Only if fertilization occurs will meiosis II ever
be completed.
• Entry of the sperm triggers the completion of
meiosis II,
• where the secondary oocyte ejects the
second polar body, and becomes a fertilized
egg with 2 pronuclei, its own and the sperm’s.
• The 2 pronuclei fuse in one at the zygot stage
Oogenesis (cont.):
• Egg maturation to the MII stage takes place
within the follicle, a fluid-filled envelope of
cells surrounding the developing egg.
• The ripening follicle also serves as an
endocrine gland. Its cells make a mixture
of steroid hormones collectively known as
Estrogens. Estrogens are responsible for
the development of the secondary sexual
characteristics of girls at puberty and
maintains them thereafter.
Female Reproductive System
Section of the ovary
1. Germinal epithelium.
2. Central stroma.
3. Peripheral stroma.
4. Bloodvessels.
5. Vesicular follicles in
their earliest stage.
6, 7, 8. More advanced
follicles.
9. An almost mature
follicle.
9'. Follicle from which the
ovum has escaped.
10. Corpus luteum.
Oogenesis: a simplified graph for one chromosome
Oogenesis
• Animated oogenesis, and
• Animated comparison between
spermatogenesis and
oogenesis
Ovulation
• Occurs about two weeks after the onset
of bleeding in a regular 28-day
menstruation cycle.
• In response to an LH surge, the follicle
discharges the secondary MII oocyte.
• The oocyte is swept into the open end of
the fallopian tube and move slowly down
into the uterus.
Conception
Back again to the sperms!
• The sperms are in the caudal epididymis
approximately 64 days after the initiation
of their spermatogenesis.
• Sperm viability preservation during
storage requires:
1. Adequate testosterone levels.
2. Maintenance of the normal scrotal
temperature, 36°c.
Conception
• Sperm as an ejaculate component:
• The alkaline pH of semen activates the
sperms and protects them from the relatively
high acidic environment of the vagina.
• The human, sperm can be found in the
fallopian tube ~5 minutes after insemination.
• Of an average of 200 to 300 millions sperm
deposited into the vagina, only a few hundred
achieve proximity to the egg.
Conception
• Fertilization starts with sperm
capacitation, that is characterized by:
1) acquiring hyper-motility.
2) binding to the zona pellucida.
3) undergoing the acrosome reaction
to penetrate thorough into the
oocyte.
Conception
• At acrosome reaction, breaking down and merging
of the plasma membrane and the outer acrosomal
membrane takes place, so the acrosin enzyme
digests the zona to let the sperm head contents only
into the oocyte.
Conception
• The Egg and its Environment:
• The oocyte, at the time of ovulation, is
surrounded by the sticky granulosa cells
(the cumulus oophorus).
• The zona pellucida, a none-cellular porous
layer of glycoproteins (secreted by the
oocyte), separates and protects the fragile
oocyte from the surrounding environment.
Conception
• The fimbriae at the end of the fallopian tubes
sweep the ovaries’ surfaces and pick up the
egg once it is out of its follicle.
• The egg spends about 80 hours in the
fallopian tube, 90% of which is at the junction
of the ampulla and the isthmus.
• It is in this location that fertilization and
dispersion of the cumulus cells are
completed.
Conception
The Fimbriae always scans the ovary surface for
any discharged mature eggs.
Conception
• If fertilization is to happen, then it is a few
minutes for the ovum & sperm to meet! The
ovum however can keep its readiness for
about half a day then it starts to degenerate.
• Within 2–3 minutes after ovulation, the oocyte
is in the ampulla of the fallopian tube awaiting
the sperms, that arrive within 5 minutes of
their deposition into the cervix.
• Tubal transport of the egg/embryo depends
on the circular smooth muscles contractions
and the cilia-induced flow.
Conception
• The exact fertilizable life of the human mature
oocyte is unknown, but the most estimated
range is between 12 to 24 hours, at the most.
• Detailed steps of fertilization:
1. Cumulus oophorus expansion that helps:
a. increase the chances of an encounter with
sperms.
b. facilitate sperm passage through the cumulus
cells, which is driven by its hyper-motility.
2. The acellular zona pellucida has three major
functions in the fertilization process:
a. activates the Sperm Ligands- which are,
with some exceptions, species specificthat bind with sperms.
b. reacts with the Acrosin of the Acrosome
to let the sperm cell into the oocyte
cytoplasm.
c. then, undergoes further Zona Reaction to
inactivate its ligands so only one sperm can
penetrate.
Finally
they
have
met!
Conception
Conception
3. Meiosis II resumes and is completed,
approximately 3 hours after sperm cell
penetration.
• The 2nd polar body is released and leaves
the egg with a haploid complement of
chromosomes. But,
• the addition of a chromosome-set from the
sperm restores chromosome diploid number
in the fertilized egg, that will start cleaving.
Conception- Embryo Cleaving Stages
Embryo stages
from day 2 after
fertilization until
day 5, 6, or even 7.
Day one is the twopro-nuclei stage
and the one-cell or
zygote stage.
Female Reproductive Hormones,
Ovulation, and Conception in Humans
• Offspring Genotypes
possibilities are 50% to
50% male to female.
• However, Phenotype
possibilities are just
unlimited.
• As Crossovers and
hopefully balanced
Translocations are
also probable.
Implantation
• By definition, implantation is the process by
which an embryo at its blastocyst stage:
1. hatches out, in 1-3 days of arrival to the
uterine cavity,
2. attaches itself to the uterine wall,
3. penetrates its epithelium, and gradually
4. integrates with the circulatory system of the
mother through the placenta.
Implantation
• Endometrium Readiness & Receptivity:
• Very critical for conception.
• Normal endometrium is 10–14 mm thick at
implantation time, in the mid-luteal phase.
• By then, it’s reached its maximum secretory
activity, and becomes rich in glycogen and
lipids.
Implantation
• The window of endometrial receptivity
period is restricted to days 16–20 of a 28day menestrual cycle.
• The blastocyst loosely adheres to the
endometrial epithelium, a process called
apposition stage, which most commonly
occurs on the endometrium of the upper
posterior wall of the uterus.
Implantation
• Possible types of interaction between
implanting trophoblast and uterine epithelium:
– trophoblast cells intrude the uterine epithelium on
their thorough path to the basement membrane.
– endometrial epithelial cells lift off the basement
membrane, an action that allows the trophoblast
to intimate itself underneath the epithelium.
– fusion of the trophoblast with some uterine
epithelial cells, on its way to the basement
membrane.
Stages of
Embryo
Implantation
within the
Endometrium
Implantation
Goal Achieved!
• The purpose of placental invasion is to
remodel the uterine tissues and
vasculature, establishing a structure that
would allow and maintain a mother-fetus
interchange, enough to sustain the fetus,
until it becomes a baby ready to get out.
!! ‫سبحان هللا‬
ُ
Introduction to In Vitro
Fertilization or IVF
•
•
•
•
•
•
What is infertility?
Whose fault is it?!
It is a disease not a shame.
How to find out the reason?
How to propose the treatment?
Treatment ranges from: 1) just counseling,
2) IUI with natural cycle, 3) IUI with
ovulation stimulation, 4) conventional IVF,
5) IVF/ICSI, till finally, 6) IVF/ICSI/ PGD.
Placenta
• After implantation is complete, the trophoblast
further differentiates along two main pathways,
giving rise to
– Villous trophoblast
– extravillous trophoblast.
• The villous trophoblast, as its name suggests,
gives rise to the chorionic villi of the placenta,
and primarily functions in the transport of oxygen
and nutrients between the fetus and mother.
Placenta
• The extravillous trophoblast migrates into the
decidua and myometrium and also penetrates
maternal vasculature.
• The mechanisms leading to trophoblast invasion
into the endometrium are similar to the
characteristics of metastasizing malignant cells.
Placenta
Placenta
• As the growth of embryonic and extraembryonic
tissues continues, the blood supply of the
chorion facing the endometrial cavity is
restricted, and consequently the villi in contact
with the decidua capsularis cease to grow and
degenerate.
• This portion of the chorion becomes the
avascular fetal membrane that touches the
decidua parietalis (chorion laeve)
Placenta
• At approximately 1 month after conception,
maternal blood enters the intervillous space from
the spiral arteries in fountain-like bursts.
Placental Hormones
• HUMAN CHORIONIC GONADOTROPIN
– Rescue and maintenance of function of the
corpus luteum
– Promote male sexual differentiation
– Stimulation of the maternal thyroid gland
– Promotion of relaxin secretion
– Promote uterine vascular vasodilatation and
myometrial smooth muscle relaxation
Placental Hormones
• HUMAN PLACENTAL LACTOGEN
– Maternal lipolysis and an increase in the levels of
circulating free fatty acids
– An anti-insulin or "diabetogenic" action
– A potent angiogenic hormone; it also may play
an important role in the formation of fetal
vasculature
Placental Hormones
• Chorionic Adrenocorticotropin
• Relaxin
• Parathyroid Hormone-Related Protein
• Growth Hormone Variant
• Etc.