1. The First Week of Development: Fertilization part 1 DR
The First Week of Development: Fertilization part 1 DR. HAYTHEM ALI ALSAYIGH Assistant prof. Board clinical surgical anatomy F.I.M.B.S.-MB.CH,B College of Medicine –University of Babylon

3. Fertilization
Fertilization, the process by which male and female gametes fuse, occurs in the ampullary region of the uterine tube.
This is the widest part of the tube and is close to the ovary.
Spermatozoa may remain viable in the female reproductive tract for several days.
Only 1% of sperm deposited in the vagina enter the cervix, where they may survive for many hours.

4. Fertilization
Movement of sperm from the cervix to the oviduct is accomplished primarily by their own propulsion, although they may be assisted by movements of fluids created by uterine cilia.
The trip from cervix to oviduct requires a minimum of 2 to 7 hours, and after reaching the isthmus, sperm become less motile and cease their migration

5. FERTILIZAITION
At ovulation, sperm again become motile, perhaps because of chemo attractants produced by cumulus cells surrounding the egg, and swim to the ampulla where fertilization usually occurs.

6. FERTILIZAITION
Spermatozoa are not able to fertilize the oocyte immediately upon arrival in the female genital tract but must undergo
(a) Capacitation and
(b) The acrosome reaction to acquire this capability.

7. Capacitation
is a period of conditioning in the female reproductive tract
that in the human lasts approximately 7 hours. Much of this conditioning, which occurs in the uterine tube, entails epithelial interactions between the sperm and mucosal surface of the tube.

8. Capacitation
During this time, a glycoprotein coat and seminal plasma proteins are removed from the plasma membrane that overlies the acrosomal region of the spermatozoa.
Only capacitated sperm can pass through the corona cells and undergo the acrosome reaction.

9. The acrosome reaction, which occurs after binding to the zona pellucida, is induced by zona proteins.
This reaction culminates in the release of enzymes needed to penetrate the zona pellucida, including acrosin- and trypsin-like substances

10. Oocyte immediately after ovulation, showing the spindle of the second meiotic division. B. A spermatozoon has penetrated the oocyte, which has finished its second meiotic division. Chromosomes of the oocyte are arranged in a vesicular nucleus, the female pronucleus. Heads of several sperm are stuck in the zona pellucida. C. Male and female

11. D,E. Chromosomes become arranged on the spindle, split longitudinally, and move to opposite poles. F. Two-cell stage.

12. Fertilization summary
Fusion of M + F gametes
At the ampulary region
1% of sperms enter the cervix
2-7 hrs from cervix to isthmus
Chemoattractants sec by the cumulus cells >>> movements of the sperms again

13. Fertilization Sperm events prior to fertilization: Capacitation :
Occurs in uterine tube and last about 7 hrs
Epith interaction between sperm and mucosal surface of the tube
Result in removal of glycoprotein coat and seminal plasma protein from the plasma membrane that cover acrosomal region

14. Fertilization Sperm events prior to fertilization: Acrosomal reaction:
After binding Z P
Result in the release of acrosin and trypsin like substances

15. The acrosome
reaction, which occurs after binding to the zona pellucida, is induced by zona proteins. This reaction culminates in the release of enzymes needed to penetrate the zona pellucida, including acrosin and trypsin-like substances.

16. The phases of fertilization
Include phase:
phase 1, penetration of the corona radiata;
phase 2, penetration of the zona pellucida; phase 3, fusion of the oocyte and sperm cell membranes.

17. phase 1: Penetration of the Corona Radiata
Of the 200 to 300 million spermatozoa deposited in the female genital tract,
only 300 to 500 reach the site of fertilization. Only one of these fertilizes the egg.

18. phase 1: Penetration of the Corona Radiata
It is thought that the others aid the fertilizing sperm in penetrating the barriers protecting the female gamete.
Capacitated sperm pass freely through corona cells

19. The three phases of oocyte penetration
The three phases of oocyte penetration. In phase 1, spermatozoa pass through the corona radiata barrier; in phase 2, one or more spermatozoa penetrate the zona pellucida; in phase 3, one spermatozoon penetrates the oocyte membrane while losing its own plasma membrane. Inset shows normal spermatocyte with acrosomal head cap

20. Fertilization Phases : Penetration of cor rad ======= of Z P
Fusion of oocyte and sperm cell membrane.

21. Fertilization Response of the egg to sperm entrance:
Cortical and zona reactions
Release of cortical granules containing lysosomal enzymes result in:
-impermeability of oocyte cell membrain
-alteration in structure and composition of Zona pillocidum
completion of meiosis II of the secondary oocyte
Metabolic activation of the egg:
the activating factors carried by the sperm

22. phase 2: penetration of the zona pellucida
The zona is a glycoprotein shell surrounding the egg that facilitates and maintains sperm binding and induces the acrosome reaction
Both binding and the acrosome reaction are mediated by the ligand ZP3, a zona protein
Release of acrosomal enzymes (acrosin) allows sperm to penetrate the zona, thereby coming in contact with the plasma membrane of the oocyte

23. Phase2
Permeability of the zona pellucida changes when the head of the sperm comes in contact with the oocyte surface.
This contact results in release of lysosomal enzymes from cortical granules lining the plasma membrane of the oocyte. In turn, these enzymes alter properties of the zona pellucida (zona reaction)

24. Phase2
to prevent sperm penetration and inactivate species-specific receptor sites for spermatozoa on the zona surface.
Other spermatozoa have been found embedded in the zona pellucida, but only one seems to be able to penetrate the oocyte

25. Fertilization

26. phase 3: fusion of the oocyte and sperm cell membranes
The initial adhesion of sperm to the oocyte is mediated in part by the interaction of integrins on the oocyte and their ligands, disintegrins, on sperm.
After adhesion, the plasma membranes of the sperm and egg fuse

27. phase 3: fusion of the oocyte and sperm cell membranes
Because the plasma membrane covering the acrosomal head cap disappears during the acrosome reaction,
actual fusion is accomplished between the oocyte membrane and the membrane that covers the posterior region of the sperm head

28. In the human, both the head and tail of the spermatozoon enter the cytoplasm of the oocyte, but the plasma membrane is left behind on the oocyte surface. As soon as the spermatozoon has entered the oocyte, the egg responds in three ways

29. the egg responds in three ways :
1. Cortical and zona reactions.
As a result of the release of cortical oocytegranules, which contain lysosomal enzymes,
(a) the oocyte membranebecomes impenetrable to other spermatozoa, and
(b) the zona pellucida alters its structure and composition to prevent sperm binding and penetration.
These reactions prevent polyspermy (penetration of more than one spermatozoon into the oocyte).

30. 2. Resumption of the second meiotic division
2. Resumption of the second meiotic division. The oocyte finishes its second meiotic division immediately after entry of the spermatozoon.
One of the daughter cells, which receives hardly any cytoplasm, is known as the second polar body; the other daughter cell is the definitive oocyte.
Its chromosomes (22+X) arrange themselves in a vesicular nucleus known as the female pronucleus.

31. Phase contrast view of the pronuclear stage of a fertilized human oocyte with male and female pronuclei. B. Two-cell stage of human zygote.

32. 3. Metabolic activation of the egg
3. Metabolic activation of the egg. The activating factor is probably carried by the spermatozoon.
Postfusion activation may be considered to encompass the initial cellular and molecular events associated with early embryogenesis.

33. The spermatozoon, meanwhile, moves forward until it lies close to the female pronucleus. Its nucleus becomes swollen and forms the male pronucleus

34. the tail detaches and degenerates. Morphologically,
the male and female pronuclei are indistinguishable, and eventually, they come into close contact and lose their nuclear envelopes

35. During growth of male and female pronuclei (both haploid), each pronucleus must replicate its DNA. If it does not, each cell of the two-cell zygote has only half of the normal amount of DNA. Immediately after DNA synthesis, chromosomes organize on

36. the spindle in preparation for a normal mitotic division
the spindle in preparation for a normal mitotic division. The 23 maternal and 23 paternal (double) chromosomes split longitudinally at the centromere, and sister chromatids move to opposite poles, providing each cell of the zygote with the normal diploid number of chromosomes and DNA
As sister chromatids move to opposite poles, a deep furrow appears on the surface of the cell, gradually dividing the cytoplasm into two parts

37. The main results of fertilization are as follows:
Restoration of the diploid number of chromosomes, half from the father and half from the mother. Hence, the zygote contains a new combination of chromosomes different from both parents.
Determination of the sex of the new individual. An X-carrying sperm produces a female (XX) embryo, and a Y-carrying sperm produces a male (XY) embryo. Hence, the chromosomal sex of the embryo is determined at fertilization.
Initiation of cleavage. Without fertilization, the oocyte usually degenerates 24 hours after ovulation.

38. Fertilization summary
Results of fertilization:
1.restoration of diploid number of chromosomes in a new combination from the parent.
2.determination of the sex either XY male or XX female.
3. Initiation of cleavage.

39. CLEAVAGE
Once the zygote has reached the two-cell stage, it undergoes a series of mitotic divisions, increasing the numbers of cells.
These cells, which become smaller with each cleavage division, are known as blastomeres .
Until the eight-cell stage, they form a loosely arranged clump .

40. Development of the zygote from the two-cell stage to the late morula stage. The two-cell stage is reached approximately 30 hours after fertilization; the four-cell stage is reached at approximately 40 hours; the 12- to 16-cell stage is reached at approximately 3 days; and the late morula stage is reached at approximately 4 days. During this period, blastomeres are surrounded by the zona pellucida, which disappears at the end of the fourth day. 16

41. CLEAVAGE
After the third cleavage, however, blastomeres maximize their contact with each other, forming a compact ball of cells held together by tight junctions .

42. CLEAVAGE
This process, compaction, segregates inner cells, which communicate extensively by gap junctions, from outer cells.
Approximately 3 days after fertilization, cells of the compacted embryo divide again to form a 16-cell morula (mulberry).

43. CLEAVAGE
Inner cells of the morula constitute the inner cell mass, and surrounding cells compose the outer cell mass.
The inner cell mass gives rise to tissues of the embryo proper, and the outer cell mass forms the trophoblast, which later contributes to the placenta.

44. The Nuclei Fuse Together

45. What happens now? summary
Development of the zygote
The zygote undergoes a series of mitotic cell divisions called cleavage.
The stages of development are: Fertilized ovum (zygote)  2-cell stage  4-cell stage  8-cell stage  16 cell stage Morula  Blastocyst

46. Cleavage (divide via mitosis) forms the 2 cell stage

47. They split again to form the 4 cell stage

48. And again to form the 8 cell stage…

49. And eventually form a Morula

50. Next it becomes a blastocyst

51. Blastocyst formation
About the time the morula enters the uterine cavity, fluid begins to penetrate through the zona pellucida into the intercellular spaces of the inner cell mass.
Gradually, the intercellular spaces become confluent, and finally, a single cavity, the blastocele, forms .

52. Blastocyst formation
At this time, the embryo is a blastocyst. Cells of the inner cell mass, now called the embryoblast, are at one pole, and those of the outer cell mass, or trophoblast, flatten and form the epithelial wall of the blastocyst .
The zona pellucida has disappeared, allowing implantation to begin.
In the human, trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa on about the sixth day .

53. Blastocyst formation
New studies suggest that L-selectin on trophoblast cells and its carbohydrate receptors on the uterine epithelium mediate initial attachment of the blastocyst to the uterus.
Selectins are carbohydrate-binding proteins involved in interactions between leukocytes and endothelial cells that allow leukocyte “capture” from flowing blood

54. cell human blastocyst showing inner cell mass and trophoblast cells. B
cell human blastocyst showing inner cell mass and trophoblast cells. B. Schematic representation of a human blastocyst recovered from the uterine cavity at approximately 4.5 days. Blue, inner cell mass or embryoblast; green, trophoblast. C. Schematic representation of a blastocyst at the sixth day of development showing trophoblast cells at the embryonic pole of the blastocyst penetrating the uterine mucosa. The human blastocyst begins to penetrate the uterine mucosa by the sixth day of development
Trophoblast over the embryoblast pole begin to penetrate the uterine ep about the 6th day.

55. Blastocyst formation
A similar mechanism is now proposed for “capture” of the blastocyst from the uterine cavity by the uterine epithelium.
Following capture by selectins, further attachment and invasion by the trophoblast involve integrins, expressed by the trophoblast and the extracellular matrix molecules laminin and fibronectin.
Integrin receptors for laminin promote attachment, while those for fibronectin stimulate migration.

56. Blastocyst formation
These molecules also interact along signal transduction pathways to regulate trophoblast differentiation, so that implantation is the result of mutual trophoblastic and endometrial action.
Hence, by the end of the first week of development, the human zygote has passed through the morula and blastocyst stages and has begun implantation in the uterine mucosa.

57. UTERUS AT TIME OF IMPLANTATION The wall of the uterus consists of three layers:
(1) endometrium or mucosa lining the inside wall;
(2) myometrium, a thick layer of smooth muscle; and
(3) perimetrium, the peritoneal covering lining the outside wall
From puberty (11 to 13 years) until menopause (45 to 50 years),

58. the endometrium undergoes changes in a cycle of approximately 28 days under hormonal control by the ovaries.
During this menstrual cycle, the uterine endometrium passes through three stages,
the follicular or proliferative phase,
the secretory or progestational phase,
and the menstrual phase.

59. The proliferative phase begins at the end of the menstrual phase, is under the influence of estrogen, and parallels growth of the ovarian follicles. The secretory phase begins approximately 2 to 3 days after ovulation in response to progesterone produced by the corpus luteum. If fertilization does not occur, shedding of the endometrium (compact and spongy layers) marks the beginning of the menstrual phase. If fertilization does occur, the endometrium assists in implantation and contributes to formation of the placenta. Later in gestation, the placenta assumes the role of hormone production, and the corpus luteum degenerates

60. At the time of implantation, the mucosa of the uterus is in the secretory phase), during which time uterine glands and arteries become coiled and the tissue becomes succulent. As a result, three distinct layers can be recognized in the endometrium
: a superficial compact layer,
an intermediate spongy layer,
and a thin basal layer.

61. Normally, the human blastocyst implants in the endometrium along the anterior or posterior wall of the body of the uterus, where it becomes embedded between the openings of the glands .
If the oocyte is not fertilized, venules and sinusoidal spaces gradually become packed with blood cells, and an extensive diapedesis of blood into the tissue is seen.
When the menstrual phase begins, blood escapes from superficial arteries, and small pieces of stroma and glands break away.
During the following 3 or 4 days, the compact and spongy layers are expelled from the uterus, and the basal layer is the only part of the endometrium that is retained .
This layer, which is supplied by its own arteries, the basal arteries, functions as the regenerative layer in the rebuilding of glands and arteries in the proliferative phase

63. At the end of menstrual phase;
Date
Follicular changes
Uterine changes
At the end of menstrual phase;
under the influence of estrogen secretion
Maturation of the follicles
Proliferative changes to form 3 mucosal layers; the basal, intermediate spongy, and superficial compact layers.
Begins 2-3 days after ovulation;
under the influence of progesterone secretion
Formation of corpus luteum after ovulation and secrete estrogen and progesterone.
Secretory changes where the uterine gland and arteries are enlarged and coiled.
If no fertilization occur
Degeneration of corpus luteum.
Venules and siusoidal spaces gradually packed with blood and extensive blood diapedesis into the tissues.
Beginning of Menstrual phase where blood is escape with shedding of the compact and spongy layers of the mucosa.

66. Clinical Correlates
Contraceptive Methods

67. Contraceptive methods
1.barrier technique:
male condom covering the penis
female condom lining the vagina
vaginal diaphragm
cervical cap
contraceptive sponge.

68. Contraceptive methods

69. Contraceptive methods

70. Contraceptive methods
2.contraceptive pills:
Intake of pills containing estrogen and progesterone hormones for 21 days will inhibit FSH and LH secretion.
Male pills :synthetic androgen
Drug RU-486 (mifepristone)
3.depo-provera : progestin compound may inhibit ovulation for 5 yrs(subdermal) or 23 months(IM)

71. Contraceptive methods
4.intrauterine contraceptive devices
5.surgical vasectomy or ligation of the uterine tubes.
6. Fertility Awareness Methods
calendar rhythm method (-11 from the long, -18 from the short)
Standard days method (26-32 days cycle, cycle beads)8-19 days unsafe

72. INFERTILITY Normal SFA according to WHO VOLUME ≥ 2.0 ML pH 7.2-7.8
CONCENTRATION
≥ 20x106/ML
MOTILITY
≥ 50% with forward progression, or
≥ 25% with rapid progression
within 60 minutes of ejaculation
MORPHOLOGY
>30% WITH NORMAL MORPHOLOGY
Liquification
Takes minutes to liquefy

73. Male infertility may be a result of
insufficient numbers of sperm and/or poor motility.
Normally, the ejaculate has a volume of 2 to 6 mL, with as many as 100 million sperm per milliliter.
Men with 20 million sperm per milliliter or 50 million sperm per total ejaculate are usually fertile.
Infertility in a woman may be due to a number of causes, including occluded uterine tubes (most commonly caused by pelvic inflammatory disease),
hostile cervical mucus,
immunity to spermatozoa,
absence of ovulation, and others.

74. INFERTILITY
is a problem for 15-30% of couples Causes: 1.low number of sperms 2.poorly motile sperms. 3.obstructed uterine tubes mostly by pelvic inflammations. 4.hostile mucosa of uterine cervix. (guaifenesin drug) 5.absence of ovulation.

75. One percent of all pregnancies in the United States occurs using Assisted Reproductive Technology (ART). Off spring from these conceptions show increases in prematurity (<37 weeks' gestation), low birth weight (<2,500 g), and infant mortality. Most of these adverse outcomes are caused by increased rates of multiple births (twins, triplets, etc.) common in ART pregnancies.
Recent studies indicate, however, that even among singleton births from ART, there are increases in low birth weight and malformed infants.
Some of the approaches used for ART include the following:

76. Assisted reproductive technologies (ART)
infertility
Treatment:
Assisted reproductive technologies (ART)
(in which both the eggs and sperm are handled in the laboratory).

78. infertility 1. In Vitro Fertilization. (IVF)
2.Gamete IntraFallopian Transfer (GIFT)
3.Zygote IntraFallopian Transafer (ZIFT)
4.IntraCytoplasmic Sperm Injection. (ICSI)
5. Intra Uterine Insemination.(IUI)

79. infertility

80. infertility

81. Adverse Outcomes Potentially Associated with ART
Spontaneous abortions
Multiple births
low birth weight (<2500 gm)
preterm delivery (<37 weeks gestation) (even among singleton births)
Birth defects
Developmental disabilities
Childhood malignancies

82. Embryonic Stem Cells
Embryonic stem cells (ES cells) are derived from the inner cell mass of the embryo.
Because these cells are pluripotent and can form virtually any cell or tissue type, they have the potential for curing a variety of diseases, including diabetes, Alzheimer's and Parkinson's diseases, anemias, spinal cord injuries, and many others.
Using animal model research with stem cells has been encouraging. For example, mouse ES cells in culture have been induced to form insulin-secreting cells, muscle and nerve stem cells, and glial cells. In whole animals, ES cells have been used to alleviate the symptoms of Parkinson's disease and to improve motor ability in rats with spinal cord injuries.

83. ES cells may be obtained from embryos after in vitro fertilization, a process called reproductive cloning. This approach has the disadvantage that the cells may cause immune rejection, because they would not be genetically identical to their hosts. The cells could be modified to circumvent this problem, however.
Another issue with this approach is based on ethical considerations, as the cells are derived from fertilized viable embryos.

84. As the field of stem cell research progresses, scientific advances will provide more genetically compatible cells, and the approaches will be less controversial. Most recently, techniques have been devised to take nuclei from adult cells (e.g., skin) and introduce them into enucleated oocytes.
This approach is called therapeutic cloning or somatic nuclear transfer. Oocytes are stimulated to differentiate into blastocysts, and ES cells are harvested.
Because the cells are derived from the host, they are compatible genetically and because fertilization is not involved, the technique is less controversial.

85. Adult Stem Cells
Adult tissues contain stem cells that may also prove valuable in treating diseases.
These cells are restricted in their ability to form different cell types and, therefore, are multipotent, not pluripotent, although scientists are finding methods to circumvent this disadvantage.
Adult stem cells isolated from rat brains have been used to cure Parkinson's disease in rats, suggesting that the approach has promise.
Disadvantages of the approach include the slow rates of cell division characteristic of these cells and their scarcity, which makes them difficult to isolate in sufficient numbers for experiments.

86. Abnormal Zygotes
The exact number of abnormal zygotes formed is unknown because they are usually lost within 2 to 3 weeks of fertilization, before the woman realizes she is pregnant, and therefore are not detected.
Estimates are that as many as 50% of pregnancies end in spontaneous abortion and that half of these losses are a result of chromosomal abnormalities.
These abortions are a natural means of screening embryos for defects, reducing the incidence of congenital malformations. Without this phenomenon, approximately 12% instead of 2% to 3% of infants would have birth defects.
With the use of a combination of IVF and polymerase chain reaction (PCR), molecular screening of embryos for genetic defects is being conducted. Single blastomeres from early-stage embryos can be removed, and their DNA can be amplified for analysis. As the Human Genome Project provides more sequencing information, and as specific genes are linked to various syndromes, such procedures will become more commonplace.

87. THE END