3 First Week of Human Development E-learning

8/3/2019 3 First Week of Human Development E-learning

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First Week of HumanFirst Week of HumanDevelopmentDevelopment


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Fertilization & formation of

the ??

Cleavage of the zygote

Morula

Blastocyst formation

Initiation of Implantation


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FertilizationFertilization

The process during which a male gamete (sperm) unites with afemale gamete (oocyte) to form the zygote (1st embryonic cell)

Sperm + Oocyte = Zygote

Location:Ampulla of uterine tube

Time:

Within 24 hrs of ovulation


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Phases of FertilizationPhases of Fertilization

1. Passage of the sperm through corona radiata

Hyaluronidase from ??

2. Penetration of zona pellucida

Acrosomal enzymes (acrosin: proteolytic enzyme)

lysis of zona pellucida path for the sperm

* Zona reaction: changes in the properties of Z.P. that makes it

impermeable to other sperms

3. Fusion of plasma membranes of oocyte & sperm

inner part of head & tail of the sperm enter the

cytoplasm of the oocyte


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4. Formation of male pronucleus

- sperm nucleus enlarge & become

rounded

- tail degenerates

5. Fusion of pronuclei and

formation of the zygote


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In Vitro FertilizationIn Vitro Fertilization

Aspiration of several oocytesfrom the ovaries

Placement of oocyte in a special

culture medium containing sperms

Fertilization & cleavage of the zygote

are monitored

Transfer of the cleaved cells(4-8 cell)to the uterus

(2-3 cleaved zygotes are transferred)


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Cleavage of The ZygoteCleavage of The Zygote

Repeated mitotic divisions of the zygote into many cells

(Blastomeres)

Compaction:

at 8-10 blastomeres stage, cells become tightly aligned to forma compact ball.

Morula (like mulberry):

The developing human with

12 blastomeres formed

~ 4 days after fertilization

* when it is time to enter the uterine cavity


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Blastocyst FormationBlastocyst Formation

Early blastocyst: (late Day 4)

Uterine fluid passes through Z.P.to form fluid-filled space in center

Late blastocyst: (Day 5)

Z.P. is shed at day 5

blastomeres separated into:

1. Trophoblast:

outer cell layer = placenta

2. Inner cell mass:a group of blastomeres gathered atperiphery

give rise to the embryo = embryoblasts


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Initiation of ImplantationInitiation of Implantation

At 6th day:Blastocyst attaches to endometrial epithelium

Trophoblasts divide & specialize into 2 parts:

Cytotrophoblastsinner layer of cells

Syncytiotrophoblast layer:

outer layer of multinucleated protoplasmic mass

of tissue (no cell boundaries).Fxn.:

- production proteolytic enzymes??

- Secretion of HCG (later on, 2nd week)??


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Syncytiotrophoblast

Cytotrophoblast


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Summary of First WeekSummary of First Week


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Early Spontaneous AbortionEarly Spontaneous Abortion

Implantation is a critical stage that may fail to occur & result in

early abortion

Due to:

- inadequate estrogen & progesterone secretions- chromosomal abnormalities (defects in dividing cells)

Signs:

- delayed menstrual cycle for several days

- unusual profuse flow

* Rate ~ 45%


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Ectopic PregnancyEctopic Pregnancy

Ectopic: out of place

Implantation & development of the embryo outside the uterine cavity

(extrauterine implantation)

Due to:

Impaired movement of the zygote through uterine tube.

(scar, inflammation, abnormal anatomy)

Location:

~ 95% in ut. Tube (ampulla or isthmus), However

* twice more frequent in smoking women

nicotine paralyzes the cilia in epith. lining


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Ectopic PregnancyEctopic Pregnancy

signs:- Acute abdominal pain (distention)

- Abnormal bleeding

- Rupture of the tube & internal hemorrhage

Rx.:

Surgical removal

Anticancer drug (methotrexate)

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3 First Week of Human Development E-learning