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 IVFAhmed M. Isa, Ph.D., HCLD (ABB), REM (ACE)Assistant Professor , Head of IVF Lab

Department of Obstetrics & GynecologyKing 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 Systemor the “Semen Factory”

Seminal Fluid Components

1. Sperms: From the Epididymis. Normally, 2-5% 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, mucous (increase sperm mobility. Contributes to the cohesive jelly-like texture of semen.), pre-ejaculate

Cowper’s fluid (a lubricant), and 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 countless.

• In humans, spermatogenesis from start to end takes about 64 days before a sperm is ready for ejaculation 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 Anterior

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 millions of the1ry 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, i.e. metaphase stage of meiosis II.

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, then it moves slowly along it, then down into the uterus.

ConceptionBack 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 few hundreds 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 take 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 (mostly species specific) that bind to the sperm.

b. Responds to the Acrosin to let the sperm cell into the oocyte cytoplasm.

c. Inactivate its ligands to prevent poly-spermia.

Finally they have met!

Conception

Conception3. 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.

Embryo Cleaving Stages

Embryo stages:

From day-2 after insemination until D-5 ( D-6, or D-7 in some cases).

Day-1 is the two-pronuclei stage and the one-cell zygote stage (later on the day).

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 a blastocyst stage embryo:

1.hatches out, in 1-2 days of its arrival to the uterine cavity,

2.attaches itself to the uterine wall,

3. penetrates its epithelium, and gradually

4. integrates its blood circulation with the mother’s circulation, through the placenta.

Implantation

• Endometrium Readiness & Receptivity:

• Very critical for conception.

• Normal endometrium is 10–14 mm thick at implantation time, in mid-luteal phase.

• By then, it has reached its maximum secretory activity, and has become rich in glycogen and lipids.

Implantation

• The window of endometrial receptivity is much preferred at days 16–20 of a 28-day menstrual cycle.

• The blastocyst loosely adheres to the endometrial epithelium, a process called apposition, 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 lining on their thorough path to the basement membrane.

– endometrial lining lift itself off, to allow the trophoblast to intimate itself underneath the epithelium.

– fusion of the trophoblast with uterine lining, on its way towards the basement membrane.

Stages of Embryo Implanta-tion within the Endomet-rium

ImplantationGoal 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.

الله !! بحان ُس�

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.