Fertilization and Tubal Functions

8/12/2019 Fertilization and Tubal Functions

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Allows gamete interaction in the tubalvastness...with one oocyte

Allows for procreation with isolated act ofcoitus

Allows fertilization by the fittestsperm

Blocks multiple fertilization

Allows for genetic recombination

Fertilization is a process that:


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sexualactivity

gamete

transport

Fertilization

Male Female

gametogenesisspermatogenesis ovulation

patent vas

and urethra

patent fallopiantubes / normalcervix and uterus

erection andejaculation

coitus appropriate

of ovarian cycle


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Adequate # of healthysperms produced bysem. tubules

deposited at theupper vagina

penetrate cervicalmucous

travel throughuterus

Reach ampullary region

of fallopian tubes

FERTILIZATION

Fertilization


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The oocyte is viable for 12 to 24 hours

Sperm is viable 24 to 72 hours

For fertilization to occur, coitus mustoccur no more than:

Three days before ovulation 24 hours after ovulation

Fertilization


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Fertilization


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Gametogenisis (Oogenesis, Spermatogenesis)

Sperm and oocyte transport though the femalereproductive tract

Sperm capacitation, chemotaxis. Sperm penetration through the cumulus

Acrosome reaction, zona binding

Penetration of the zona

Sperm-oocyte membrane fusion

Cortical + zona reactions (polyspermy block)

Pronuclei formation/polar body formation

Steps in Human Fertilization


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Fate of ejaculated sperm Leak out of the vagina immediately after

deposition

Destroyed by the acidic vaginalenvironment Fail to make it through the cervix Dispersed in the uterine cavity or

destroyed by phagocytic leukocytes Reach the uterine tubes

Sperm Transport


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Sperm attrition in the femalereproductive tract


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Sperm ascend in cervical mucousmicrostructure - filtering action?

Sperm found in tube/peritoneal cavitywithin 5 minutes

Non-capacitated sperm stored in cervicalcrypts

Fertilizable lifespan ~ 72 hours

Sperm transport in the femalereproductive tract starts process ofcapacitation

Sperm Transport


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Freshly ejaculated sperm are incapable offertilizing an egg

Sperm capacitation acquisition of

- the ability to undergo the acrosomereaction

- the ability to bind the zona pellucida

- hypermotility

Sperm Capacitance


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The sperm membrane becomes lessstable

The sperm loses epididymally-derivedcoating factors The sperm gains the ability to respond to

oocyte chemotactic factors

The sperm develops a finite andshortened lifespan

With sperm capacitation;


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Oocyte enters fallopian tube within 15minutes of ovulation

Fimbriae find oocyte-granulosa complexadherent to ovarian surface

Oocyte fertilizable lifespan 24 hrs max

Oocyte Transport


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An ovulated oocyte is encapsulated by:

The corona radiata and zona pellucida Extracellular matrix


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Sperm binds to the zona pellucida and

undergoes the acrosomal reaction

-Enzymes are released near the oocyte- Hundreds of acrosomes release their

enzymes to digest the zona pellucida


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Acrosome of sperm contain hyaluronidase

an enzyme that digest a channel through thezona pellucida spermatozoa fuses with theova cell membrane


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Fusion of sperm and oocyteplasma membranes


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If more than one sperm is to penetrate theova the genetic complement would be 3n.

To prevent multiple sperm penetraion two

responses have evolved in the egg.

Fast block to polyspermy membranedepolarization prevents sperm from fusingwith the oocyte membrane

Slow block to polyspermy zonal inhibiting

proteins

Blocks to Polyspermy


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when the first sperm head penetrates the egg

massive influx of Na+is triggered

depolarization of the egg

Makes it positive inside

Repels positively charged sperms

Inhibit penetration of more sperms

Fast block to Polyspermy


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Depolarization of the egg

will repel positivelycharged sperms

triggers influxof Ca2+

exocytosis ofcortical vesicles

contents of vesicles,surround egg, swell with

water and gel

block entry ofother sperms

Fast block to Polyspermy


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Zonal inhibiting proteins (ZIPs):

- Destroy sperm receptors

- Cause sperm already bound toreceptors to detach

Slow block to Polyspermy


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Completion of Meiosis II and Fertilization

Upon entry of sperm, the secondaryoocyte:- completes meiosis II- casts out the second polar body

The ovum nucleus swells, andthe two nuclei approach eachother


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Completion of Meiosis II and Fertilization

When fully swollen, the two nuclei arecalled pronuclei

Fertilization when

the pronuclei fusetogether


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3 hours: meiosis II completed-second polarbody extruded

10 hours: protein synthesis begins

Maternal legacy:maternal mRNA involved in

early embryo protein synthesis(to blastocyst stage)

Post-fertilization events


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Preembryonic Development

The first cleavage produces two daughtercells called blastomeres

Morula the 16 or more cell stage(72 hours old)

By the fourth or fifth day the preembryo

consists of 100 or so cells

blastocyst


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IMPLANTATION

The blastocyst floats freely for abouta day in the uterine cavity before it implants( 5-7 days after ovulation)

3 day period of uterine receptivity(high P4/E2 ratio)

implantation leads to full-term pregnancy


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Inner cell mass will developinto the fetus

Trophoblasts will develop

into the placenta and externalmembranes.

Blastocyst

Implantation the floatingblastocyst has to becomeattached to theendometrium.


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Primitive Trophoblast differentiates into:

Cytotrophoblast

cells of the inner layer thatretain their cell boundariesSyncytiotrophoblast cells in the outer layerthat lose their plasma membranes and invade theendometrium

IMPLANTATION


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embryo

attach tomaternal tissue

fetal membranes

IMPLANTATION


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Embryonic/fetal cells are separated frommaternal tissues and blood by the layer ofcytotrophoblasts and syncytio-

trophoblasts.

Critical for nutrient exchange and toprotect the developing fetus frommaternal immunologic attack.

IMPLANTATION

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Fertilization and Tubal Functions