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Ovulation Fertilization. Maturation of sperm Sperms –Incapable of fertilizing the oocyte immediately after being released into the lumen of the seminefrous.

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Presentation on theme: "Ovulation Fertilization. Maturation of sperm Sperms –Incapable of fertilizing the oocyte immediately after being released into the lumen of the seminefrous."— Presentation transcript:

1 Ovulation Fertilization

2 Maturation of sperm Sperms –Incapable of fertilizing the oocyte immediately after being released into the lumen of the seminefrous tubules –Maturation In epidydimus

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4 Epidydimus –Fluid reabsorption Increase concentrations of sperm by 100 folds –Estrogen dependent –Quiescence of sperms Slow activity Movement depends on musculature –Addition of chemicals Glycoproteins –Coating of sperm surface

5 Maturation of sperm –Ability to move on its own –Nuclear condensation and loss of cytoplasm –Metabolism alteration External source –Increased mobility –Changes in cell membrane Increased charge (glycosylation) Changes in protein profile Changes in lipid composition (fluidity)

6 Maturation of sperm –Androgen dependent Very high concentrations (ABP) Conversion to DHT –Increased bioactivity –Entire process will take several months to few days

7 Movement of sperms Entering vas deference from epidydimus –Muscular contraction rather than fluid movement –Dense mass –Serve as reservoir of sperms Lost in urine if no ejaculation

8 Sperm in male reproductive tract Semen –Sperm plus seminal plasma Seminal plasma –Derived from accessory sex glands –Serves as fluid vesicle for transport Unnecessary for sperm function

9 Seminal plasma –Derived from accessory sex glands –Serves as fluid vesicle for transport –Serves as buffer Basic in nature Neutralizes acids –Provides nutrients Fluctose sorbitol

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11 Semen composition –Immune cells –Infectious agents

12 Deposition of semen into the female reproductive tract Coitus –Physiological changes Genitalia Other parts of body –Phases Described in humans by Johnson and Masters Four phases –Excitement (sexual arousal) –Plateau (intense arousal) –Orgasm (involuntary climax) –Resolution Absolute refractory phase in male –Immediately after orgasm

13 Excitement –Vasocongestion Penile erection (engorgement of corpora cavanosa and corpus spongiosum) Vaginal lubrication (transudation) Enlargement of labia minora and clitorus –Vaginal expansion –Tenting effect on uterus Upward movement of uterus and cervix Fibrilation of uterus (contraction) –Sex flush –Myotonia Increased muscle tension

14 Plateau –Increased testis size Elevated from the original position –Secretion of fluid Cowpers gland –Sex flushes –Engorgement of vaginal wall Orgasmic platform –Formation of seminal pool

15 Female orgasm –Rhythmic contraction Vaginal wall Uterus –Involuntary muscle spasm

16 Male orgasm –Contraction of accessory sex gland Collection of semen into the urethral bulb Contraction of bladder muscle Emission stage of ejaculation –Expulsion of semen/ejaculation Muscle contraction Reproductive tract contraction

17 Resolution –Returning of body to nonaroused state Size of genitals –Uptake of sperm by the cervix Dipping into the seminal pool as the uterus returns to the normal position Opening of cervical canal

18 Site of semen deposition –Varies among species Humans and cattle –Near external portion of cervix (cervical os) Uterus in other species –Formation of plug Enzymatic reaction –Prevent backflow of semen –Buffers –Prevent sperm from other males to fertilize eggs?

19 Transport of sperm to the oviduct Sperm must enter female reproductive tract and reside there for some time –Maximum fertility Sperm –Viable inside of reproductive tract 24 to 48 hours in human 30 to 48 hours in cows Oocyte –A finite life span 6 to 24 hours after ovulation in human Sperm must reach the oviduct at appropriate time in order to remain viable and fertile

20 Transport of sperm to the oviduct Semen –Deposited in the anterior part of the vagina near the cervix The majority of the sperm –Lost because of retrograde flow of the mucus out of the vagina –Killed because of the unfavorable environment for sperm survival in the vagina. Semen pool Preovulatry follicle

21 Transport of sperm to the oviduct Some of the sperm –Transported through cervical canal into the uterus within minutes after sperm deposition Rapid transport Rapid transport of sperm is caused by the contraction of myometrium (muscle layer of the uterus) and not by active movement of sperm –Sperm that enter the oviduct by rapid transport Often non-viable and unlikely to participate in fertilization.

22 Transport of sperm to the oviduct Many sperm –Trapped in the folds and crypts of the cervix Formation of sperm reservoirs within the cervix –Critical More sperm ultimately reach the oviduct when more sperm are available in the cervical reservoir Folds and crypts of the cervix

23 Transport of sperm to the oviduct Slow transport of sperm –After establishment of reservoir –Ensures the availability of sperm in the oviduct continuously Large number of sperms –Fails to reach the oviduct Many obstacles such as folding of the uterine endometrium and the narrow diameter of the uterotubal junction Presumably to prevent polyspermy (more than one sperm fertilizing the oocyte)

24 Transport of sperm to the oviduct Aggregation of sperms –The isthmus –Sperm remain in the isthmus until ovulation –Hyperactivation Rapid movement of tail and erratic swimming motion Near ovulation Essential for their upward movement toward the ampulla. Infundibulum Ampulla Isthmus Ampullary- isthmic Junction Uterotubal Junction

25 Transport of sperm to the oviduct Capacitation –Changes in cell surface of the sperm –Required for proper attachment and penetration of the zona pellucida when the sperm encounters the oocyte Infundibulum Ampulla Isthmus Ampullary- isthmic Junction Uterotubal Junction

26 Capacitated sperms –Acrosome reaction when encountering the oocyte Ability to bind and penetrate zona pellucida –Swelling of acrosome Fusion of acrosomal membrane –Exocytosis of acrosomal content Ca and cAMP dependent

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28 Acrosome reaction –Triggered by the protein in the zona pellucida ZP3 Sperms have receptors for ZPs –Increased Ca uptake –Release of hexosaminidase B (removal of ZP3)

29 Acrosome reaction –Must take place near the oocyte Reduced sperm viability

30 Fertilization Sperm encountering the oocyte –Migration through the remaining cumulus cells that surround the oocyte –Sperm binds to the zona pellucida Mediated by the sperm binding sites present on zona pellucida First polar body Cumulus cells

31 Fertilization Within minutes of binding, the sperm begins to penetrate the zona pellucida, and eventually fuses with the oocyte –Equatorial and postacrosomal region –Ca-dependent reaction –Immediately after the sperm fuses with the oocyte, the oocyte extrudes the second polar body –Oocyte becomes a haploid cell Second polar body Zona pellucida

32 Fertilization Once a sperm fuses with the oocyte, the zona pellucida becomes hardened –Release of Ca –Sperm binding sites disappear from the zona pellucida –Hardening of zona and loss of sperm binding sites are necessary in order to prevent polyspermy Head of sperm

33 Fertilization Membrane of the sperm head –Degraded and replaced by a new membrane Formation of a structure called the male pronucleus –The maternal half of chromosomes The female pronucleus. Male pronucleus Female pronucleus

34 Fertilization Male and female pronuclei move toward the center of the oocyte –Degradation of the membrane that surrounds each pronucleus –Mixing of maternal and paternal chromosomes Restoration of the total number of chromosomes Zygote


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