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