2 Introduction:Fertilization is the process of union of mature male gamete (sperm) with mature female gamete (ovum) to produce new cell of life which is called (zygote) through chain of events in the oviduct (fallopian tubes). Indeed, interruption of any event will cause fertilization failure.
3 Folliculogenesis and ovulation: Folliculogenesis is the maturation of the ovarian follicle, describes the progression of a number of small primordial follicles into large mature follicles under the influence of FSH prior to puberty.Ovulation By the end of the follicular phase the mature follicle will develop and rupture, excrete the oocyte with some granulosa cells into oviduct. The oocyte is now competent to undergo fertilization.Ruptured follicle will transformed into the corpus luteum, that produce large amount of progesterone that helps to prepare the uterus for implantation of fertilized eggIn absence of fertilization corpus luteum degenerates.
4 Image showing phases of follicle development and ovulation: Mohamad J. (according to Gougeon A (1986). "Dynamics of follicular growth in the human.)
5 3d animation about folliculogenesis and ovulation:
6 Hormonal control of folliculogenesis and ovulation: Mohamad J. (according to H. J. Bearrden and J. W. Fuquay,2000 Applied Animal Reproduction.)
7 Ovum structure:Mohamad J. (according to McRorie and Williams,1974 Ann. Rev. Biochem.)
8 Mechanisms of ovum transport: Fimbria on terminal oviduct--acts as funnel to receive ovumFluids (abdominal cavity and that escaping from follicle during ovulation) serve as medium for free-floating ovumCilia lining oviduct and muscular contractions assists in moving ovum to site of fertilizationThe site of fertilization on most farm animals is (ampullary-isthmic junction) while in human is (ampulla) region.Image show goat reproductive system
10 Species Fertile life 8-12 hours 16-24 hours Fertile life of ovum:Estimate fertile life of ovum in different mammals is shown in table(1):SpeciesFertile lifeCow8-12 hoursSheephoursSwinehoursHumanhoursH. J. Bearrden and J. W. Fuquay,2000 Applied Animal Reproduction.Adapted from [Hamner, McLaren, Dukelow and Riegle
11 Mating process :Is the period when female receptive and will stand for mating with males during estrous phase of estrous cycle, the main purpose of mating is deposition of fertile semen into female genital tract after ejaculation, characteristics of ejaculate in different mammals is shown in table(2):speciesSite of semen depositionVolume of ejaculate (ml)Sperm concentration (billion/ml)No. of sperm reaching site of fertilizationCowVagina41Sheep2SwineCervix and uterus1250.200FewHuman3.50.120Adapted from [Blandau, R. J., in “Handbook of Physiology” (R. O. Greep, ed.)Vol. II, sect. 7, p Williams & Wilkins, Baltimore, Maryland , (1974)]Arthur C. Guyton, 2006
12 Time of ovulation in different mammals shown in table(3): Deposition of semen into female tract must be closely synchronized with ovulation to ensure the incidence of fertilizationTime of ovulation in different mammals shown in table(3):speciesTime of ovulationCow10-12 hours after end of estrous phaseSheepLate of estrous phaseGoatFew hours after end of estrous phaseSwineMid-estrous phaseHumanDay(14) after initiation of menstrual cycleH. J. Bearrden and J. W. Fuquay,2000 Applied Animal Reproduction.
13 Mechanisms of sperm transport: Pass into cervix by own movement As the sperm enter the cervix, orient themselves into current of thin mucus during estrusMyometrium moves them through the uterusMoved through oviduct by cilia of oviduct and uterine contractions and a thin fluid secreted by glandular cells.Image show goat reproductive system
14 Species Fertile life 24-48 hours 30-48 hours Fertile life of sperm:Estimate fertile life of sperm in different mammals is shown in table(4):SpeciesFertile lifeCow24-48 hoursSheephoursSwineHuman28-48 hoursH. J. Bearrden and J. W. Fuquay,2000 Applied Animal Reproduction.Adapted from [Hamner54a, McLaren, Dukelow and Riegle
15 Fertilization events: a) Sperm capacitation:Freshly ejaculated sperm are unable to fertilize an egg. Rather, they must first undergo a series of changes known as capacitation. Capacitation is associated with removal of adherent seminal plasma proteins, reorganization of plasma membrane lipids and proteins.
16 b) Acrosome reaction:The acrosome reaction involves breakdown and fusion of outer acrosome membrane with the plasma membrane of the sperm. This results in formation of vesicles and release of enzymes needed for sperm to penetrate the cumulus oophorus and corona radiata as well as zona pellucida . during the penetration process the acrosome is lost with only the inner acrosomal membrane remaining around the sperm head.
17 c) Sperm penetration:Sperm cell penetrate cumulus oophorus by the enzyme (hyaluronidase) released during acrosome reactionSperm cell penetrate corona radiata by the enzyme (corona-penetrating enzyme) also released during acrosome reaction.Sperm cell penetrate zona pellucida by the acrosin (trypsinlike enzyme) also released during acrosome reaction.Mohamad J. (according to McRorie and Williams,1974 Ann. Rev. Biochem.)
18 Then membrane of sperm fuses with the vitelline membrane of the egg, the egg cytoplasm around the area of contact surrounds the sperm head and incorporating it into the eggThe nucleus of sperm is then release into the egg cytoplasm without the tail
19 Animation show entrance of sperm nucleus into the egg
20 d) Consequences of fertilization: In most mammals after releasing the sperm nucleus into egg cytoplasm it stimulates the diffusion of cortical granules into the previtelline space, the erection of a barrier to prevent fertilization by more than one sperm will occur, this process is called zona reaction and vitelline block.Then the male and female pronuclei are formed and unite (syngamy) to establish the diploid one cell zygote.
22 Time of formation of zygote (hours) Time of formation of zygote and time required to entry the fertile ovum into uterus in different mammals is shown in table(5):SpeciesTime of formation of zygote (hours)Entry to uterus (days)Cow0-243-4Sheep0-382-4Goat0-304Swine0-15Human3-Adapted from [Brinster, R. L., J. Anim. Sci. 38, 1003 (1973)]-Times estimated from ovulation
23 Post fertilization events: The first of many changes following fertilization is to become multicellular, and the one-cell embryo rapidly cleaves into 2, 4, 8 and more cells. It then starts to do some interesting things like develop a discrete inside and an outside. Finally, the embryos of many species start to secrete hormones that ensure their survival - a process called maternal recognition of pregnancy.
25 References:Al-Dahash S. Y. A. and fathallah M. F. (1982) veterinary Gynecology and female genital diseases. Mousel university.Arthur, G.H: Noakes, D. E: pearson. H.and Parkinson, T. J. (1996). Veterinary reproduction obstetric. 7th ed. W. B. sounders co. , London.Austin, C. R., in “fertilization” (C. B. Metz and A. Monroy, eds.), p.437. Academic Press, New York, 1969.Barros, C., and franklin, L. E., J. Cell Biol. 37, C13 (1968).Biggers, J. D., J. Reprod. Fert. Suppl (1971).Boling, J. L., in “the mammalian oviduct” (E. S. E. Hafez and R. J. Blandau. Eds.), p. 163 Univ. of Chicago Press, Chicago, Illinois, 1969)Fortune J, Cushman R, Wahl C, Kito S (2000). "The primordial to primary follicle transition.". Mol Cell Endocrinol 163 (1-2): PMIDGougeon A (1986). "Dynamics of follicular growth in the human: a model from preliminary results.". Hum Reprod 1 (2): PMIDHafez, B and Hafez., E. S. E. (2002) reproduction in farm animal. 7th ed. Kiawah island, South Carolina.