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Visualizing Embryonic Development

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Rex Ivan Dela Cruz

on 22 January 2015

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Transcript of Visualizing Embryonic Development

Visualizing Embryonic Development
The First Eight Weeks

Gastrulation - the formation of the three primary germ layers in embryogenesis
Third-eighth weeks
trophoblast starts to secrete human chorionic gonadotropin (hCG) for four months;
Same function as LH (maintains corpus luteum) so that the endometrium doesn't shed.
Secretion of estrogen and progesterone continues, preventing menstruation
hCG stops
2nd week, amniotic activity forms
Organ formation
3rd-8th weeks, organs form
8th week, shape that is recognizably human
third week, mesoderm cells develop on the back of the embryonic disk, form notochord (skeleton)

After the neuralation, the heart forms on the eighteenth day and starts beating
Fourth week, blood cells, lungs, kidneys,
Week 20 - 36
At week 40, nine-month period is reached and the baby is ready to be delivered
The embryonic period of development:
takes place over the first eight weeks (2/3 of first trimester)
cells divide and become redistributed
tissues and organs form
The joining of male (sperm) and female (ova) gametes to form a single cell, called a zygote
Fetal Development
Animation: https://web.stanford.edu/group/Urchin/GIFS/norm-sp.gif
Implantation: http://www.ivfgenesis.com/images/cell-stages/natural-cycle.gif
A zygote...
has 23 pairs of chromosomes
is moving out through the oviduct
Mitosis causes the zygote to undergo cleavge
When zygote reaches 16 cells, it is called a morula
Reaches uterus 3-5 days after fertilization
By: Rex & Hazel
The fetal period of development:
takes place from the ninth week through birth
the body grows rapidly
organs begin to function and coordinate
Embryonic vs Fetal Development
Begins 30 hours after fertilization
Blastocyst - embryo which is implanted into the wall of the uterus; is made up of two cells: the trophoblast and the inner cell mass.
Cleavage - the process of cell division without enlargement of the cells
Fluid from uterus entering morula creates blastocyst
Day 5-9
Day 1-4
Day 1
Day 10-17
The inner cell mass flattens into the embryonic disk
The developing embryo is now called a gastrula.
The disk consists of two layers:
an outer ectoderm and an
inner endoderm
a middle mesoderm shortly forms in between
Tissues fold into distinct patterns
The three-layered embryo is transformed into a body with separate organs
By the eight week, the shape is recognizably human
During the third week, mesoderm cells develop along the back of the disk.
The nervous system develops from the ectoderm
5-7 days after fertilization, blastocyst attatches to endometrium, called implantation
Morphogenesis - the series of events that form distinct structures of a developing organism; gastrulation marks the beginning of the process
Differentitation - when a cell develops a particular shape to perform specific functions that are different from the functions of other cells
(hCG) is a hormone produced by the placenta, following implantation.
4th week after fertilization
Neurulation forms the neural tube, to become spinal cord and brain
Extra-embryonic Membranes
Structures responsible for protection, nutrition, respiration, and excretion:
Allantois, Amnion, Chorio, Yolk Sac, Placenta, Umbilical cord
chorionic villi extend into the uterine lining, establishing placenta
3rd-8th weeks

Differentitation - cellular process that enables a cell to develop a particular shape and to perform specific functions that are different from the functions of other cells
Yolk Sac
Umbillical cord
Fetus is attached to the uterine wall by the placenta
Metabolic exchange occurs
Fully developed at 10 weeks
Provides antibodies and hormones for the fetus
Develops from the Extraembryonic Mesoderm
Surrounds the yolk
Modifies yolk lipids into lipoproteins
Provides nourishment required for Embryonic growth
Develops from cells of the embryonic disk
Becomes filled with fluid which protects the embryo from:
- Shock Absorption
- Temperature Fluctuations
Eighth week, yolk sac shrinks and amnition sac enlarges, umbilical cord forms
Umbilical cord contains two arteries to transport oxygen, and one vein
In about 20% of all deliveries, the umbilical cord is looped around the baby's neck.
During birth, these membranes are expelled from the uterus, known as afterbirth,
Develops from Trophoblasts/Extramembryonic Mesoderm
Surrounds Embryo
Outermost Membrane
Chorion + Allantois = gas and nutrient exchange
Functions as waste removal (removes embryonic wastes produced by embyro)
Suspended from the abdominal area of the embryo
Contributes to the formation of the digestive system
2nd week after fertilization
Encloses all extra-embryonic membranes
Forms the fetal portion of the placenta
Prevents Extreme Dryness
Prevents limbs from sticking to the body

Woman is now said to be pregnant
5-7 days after fertilization, blastocyst attatches to endometrium
First trimester:
skeletal system
reproductive system
Second trimester:
nervous system
Third trimester:
digestive system
respiratory system
The End
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