Download What is embryonic development? -The sequence of events that

What is embryonic development?
-The sequence of events that gradually changes a
Zygote into a functional organism
Zygote- Fertilized egg
Embryo- an organism in the early stages of development
(up to week 8)
Fertilized Egg Stage:
After fertilization, zygote begins
A series of cell divisions called
CLEAVAGE (mitosis)
Fertilization
Fertilized egg divides by MITOSIS
-Zygote DOES NOT grow in size
Solid Ball Stage (Morula):
-Result of cleavage
-About 100 tiny cells. All identical
Blastula Stage:
-Solid ball rearranges. All cells pushed
To the outside creating a hollow ball
(1 cell thick and filled with fluid)
Stem cells are taken at this point. 5 days
After fertilization
-Specialized changes that transform embryonic cells
Into specialized cells, tissues and organs
Gastrula Stage:
Gastrulation occurs:
Cells push in on one side of blastula,
forming a two layered embryo
3 Primary Germ Layers
form giving rise to organs
and tissues
Primary Germ Layer
Ectoderm
(Outer Layer)
Mesoderm
(middle layer)
Endoderm
(Inner Layer)
Structures Give Rise To
-Nervous System, skin, hair, nails
-Muscles, Circulatory, and Skeletal Systems
Sex organs (testes and ovaries)
-Lining of digestive and respiratory
Tracts, parts of liver and pancreas
Bird Embryo:
Chorion & Allantois (Chorioallantoic
Membrane):
-Combine to help embryo exchange
Gases and remove wastes
Yolk Sac:
-Surrounds the yolk which is the food source for
The embryo
Amnion:
-Surrounds embryo, protects it, and holds it in a
Solution of salt water (similar to the ocean)
Human embryo:
The following extraembryonic membranes develop AFTER
Implantation (embryo burrows in uterine lining):
Chorion:
Connects to uterine wall
Amnion:
Contains amniotic fluid which surrounds and
Protects the embryo (shock absorbency)
Combination of fetal and maternal tissue that
Placenta:
Nourishes the embryo by providing it with
Oxygen and nutrients and removes wastes
*** The blood of the fetus and mother NEVER mix.
They are close enough for DIFFUSION to occur.
Umbilical Cord:Connects the placenta to the fetus (at
Belly button). Transports oxygen, nutrients,
And wastes between fetus and mother
(placenta)
How do the placenta and the umbilical cord work together?
-Nutrients, oxygen, and wastes diffuse across the
Placenta. The umbilical cord transports these materials
between the fetus and the placenta.
1 egg + 1 sperm (egg splits giving
Identical Twins: rise to 2 separate zygotes with
Identical DNA)
Fraternal Twins: 2 eggs and 2 sperm cells
(2 eggs released and each fertilized
with a different sperm cell)
Involves 3 Processes that ALL begin with fertilization:
1. Growth-
Increase in # of cells by MITOTIC CELL
DIVISION (no increase in size)
2. Development- As cells develop they move within the
embryos body and arrange themselves
into specific layers
3. Differentiation- Each cell becomes specialized to
Perform specific tasks
(heart cells, brain cells, skin cells
given their identity)
Meiosis Fertilization
Birth
Mitosis Differentiation
(Creates gametes)
(zygote)
(growth/development)
How long does human pregnancy last?
-About 266 days of development (fertilization to birth)
called the GESTATION PERIOD
1st Trimester:
-All organ systems begin to form
-Most critical time; most
Sensitive to outside influences
6 Weeks
-1st detectable brain waves
8 weeks
-Now called a FETUS (living
organism in the later stages
of development. Week 8
and on)
-Eyes well developed and
fingers lengthen
12 Weeks
-End of 1st trimester
-Fetus able to move
(mother unable to sense)
14 Weeks
2nd Trimester:
-Rapid body growth
-Fetus more flexible
with movement
18 Weeks
-Phases of sleep and
awakening
At 20 weeks (5 months):
-May suck thumb
-Rapid brain development
21 Weeks
-Fetus begins to kick
- 8” in length
24 Weeks
-Response to light and
sound from outside the
uterus
-End of 2nd trimester
32 Weeks (8 months)
3rd trimester:
-Mass more than
triples
-During 8th month
Eyes open/close
-Fully mature at 35
Weeks (20”)
-Perfect hearing
What are some of the first signs of birth?
-”water breaks” (Amniotic sac breaks and fluid is released
Into the vagina)
-Muscular contractions cause cervix to widen (dilate)
-Baby moves further from the uterus towards the
vagina
What is afterbirth?
-The placenta separates from the uterus and exits
through the vaginal canal
What are some dangers facing a fetus?
-Radiation (X-rays)- may stop cell division
-Genetic mutations (chromosome #)
-Infectious Illness (can lead to brain damage, miscarriage)
-Inadequate Diet
-Harmful Lifestyle- (smoking, drugs, alcohol, std’s)
may lead to still birth, brain damage, low birth weight,
mental retardation, learning disabilities
Artificial Insemination-Donor sperm is inserted into vaginal canal of
female during ovulation and internally fertilizes the
egg in the oviduct
-Baby contains ½ of mother’s DNA and ½ from the donor
In Vitro Fertilization-Sperm and egg are combined EXTERNALLY
-Embryo implanted into female’s uterus for development
Amniocentesis-Technique used to extract fetal cells and examine
DNA for possible genetic defects (can be risky)
Cloning-Technique in which the nucleus is removed from a
Normal body cell and used to replace the nucleus of
An egg cell
-Egg is implanted into female’s uterus for development
-Offspring is IDENTICAL to parent (no variation)
-Offspring ages faster than normal
-Not successful in humans as to date (moral and
ethical issues involved)
Stem Cell Research-UNDIFFERENTIATED embryonic cells are removed
(around day 5) and treated with chemicals to develop
into specific tissues and organs
-Moral and ethical debates
-Belief is that this technique can be used to
cure many diseases and disorders