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Exercise 46
Embryonic Development
Developmental stages of humans
Fertilization Zygote
It is a fertilized egg Diploid (2n)Female pronucleiMale pronucleiAmphimixis
Developmental stages of humans
Zona pellucidaSurrounds the zygoteDisappears when the blastocyst
reaches the uterine cavity Corona radiata
Granulosa cells surrounding the zona pellucicda
Disappears after fertilization
Fertilization
Developmental stages of humans
Cleavage Stages of the Cleavage
Blastomere Early cleavage
4-cells stage… Morula
16-32 cells stage
Developmental stages of humans
BlastocystCentral cavity appears – blastocystic
cavityInner cell mass (ICM) – forms the embryoTrophoblast – nourishes the developing
embryo Final product of cleavage
Developmental stages of humans Implantation
From day 7 to day 10 after the ovulation
The blastocyst will go from a floating stage to a complete implanted stage in the uterus
Developmental stages of humans Gastrulation The ICM will develop into three
primary germ layersEctoderm
• Forms the epithelia and nervous system
Developmental stages of humans
Mesoderm• Forms everything between the
ectoderm and the endodermEndoderm
• Forms the mucosa of the digestive and respiratory tract, etc
Endometrium will form the deciduas
Deciduas basalis-part of the endometrium beneath the ICM. It will form the maternal portion of the placenta
Deciduas capsularis – it is the rest of the endometrium surrounding the blastocyst.
Developmental stages
Developmental stages of humans Embryo
Until the 8th week Fetus
From 8th week to birth Trophoblast
Will develop villiWill differentiate into the chorion that
will form the fetal portion of the placenta
Developmental stages of humans
PlacentaChorionic villi + decidua basalis
Embryonic membranes (from the ICM)Amnion
• Encases the embryo• Amniotic cavity
• Amniotic fluid
Developmental stages
Developmental stages of humans
Yolk sac• Originates the embryo’s first blood
cellsAllantois
• Body stalk and later umbilical cord• Umbilical cord attaches the
embryo to the placenta
In uterus development
PlacentaFetal side
• Shine and smooth• Presence of large blood vessels
Maternal side• Spongy, torn-looking, rough
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