What periods make up the prenatal period?
The pre-embryonic period
The embryonic period
The fetal period
How long is the prenatal period?
The first 38 weeks of human development
How long is the pre-embryonic period?
weeks 1-2 of the prenatal period
How long is the embryonic period?
weeks 3-8 of the prenatal period
How long is the fetal period?
weeks 9-38 of the prenatal period
What is another term used for prenatal period?
Gestational period
What is embryogenesis?
The developmental processes that occur in the pre-embryonic and embryonic periods.
What stages make up embryongenesis?
Cleavage
Gastrulation
Organogenesis
What happens during fertilization?
The male's sperm and the female's secondary oocyte unite to form a single diploid cell called the zygote.
What time period does the pre-embryonic stage of development span?
From fertilization in the uterine tube through completion of implantation into the wall of the mother's uterus
Give the sequence of events in the pre-embryonic period.
Secondary oocyte + Sperm =
Zygote then,
Cleavage then,
Morula then,
Blastocyst then,
Implantation.
What is a zygote?
A diploid cell produced when ovum and sperm fuse.
What is cleavage?
Starting with zygote, cell division by mitosis occurs to increase cell number, but overall size of the structure remains constant.
What is a morula?
Structure that resembles a solid ball of cells; 16 or more cells are present, but there is no change in diameter from original zygote.
What is a blastocyst?
Hallow ball of cells; outer ring formed by trophoblast cells; inner cell mass (embryoblast) is cell cluster inside blastocyst.
What happens during implantation?
Blastocyte adheres to uterine lining; trophoblast cells penetrate within functional layer of uterus, and together they start to form the placenta.
Where does fertilization occur?
In the widest part of the uterine tube, called the ampulla.
What does the trophoblast become?
The fetal half of the placenta.
What does the Inner Cell Mass or Embryoblast become?
The embryo.
What does the mom's half of the placenta start out as?
The uterine wall.
What happens to the trophoblast during implantation?
The trophoblast subdivides into two layers: a cytotrophoblast which is the inner cellular layer of the trophoblast, and a syncytiotrophoblast which is the outer, thick layer of the trophoblast.
What does the syncytiotrophoblast do after it is formed?
It buries into the functional layer of the endometrium and brings the rest of the blastocyst with it.
What do the cytotrophoblast and the syncytiotrophoblast form?
They form the chorion.
What does the chorion do?
It creates the fetal part of the placenta.
What happens to the embryoblast on day 8?
The cells of the embryoblast begin to differentiate into two layers. A layer of small cuboidal cells adjacent to the blastocyst cavity is termed the hypoblast. A layer of columnar cells adjacent to the amniotic cavity is called the epiblast layer.
What are the hypoblast and the epiblast called?
Together these layers form a flat disc termed a bilaminar germinal disc.
What do the bilaminar germinal disc and trophoblast produce?
Embryonic membranes to mediate between them and the environment.
What are the embryonic membranes?
Yolk sac
Amnion
Chorion
What embryonic membrane comes from the hypoblast? What does it store?
The yolk sac. In humans it is an important site for early blood cell and blood vessel formation.
What embryonic membrane comes from the epiblast?
The amnion is a thin membrane that is formed from and continuous with the epiblast layer.
What does the amnion eventually do?
It encloses the entire embryo in a fluid-filled sac called the amniotic cavity to prevent embryo desiccation.
What forms the chorion? What does the chorion do?
The cytotrophoblast and the syncytiotrophoblast. These cells blend with the functional layer of the endometrium and eventually form the placenta.
Epiblast forms the ____________
Embryo
and
Amnion
Hypoblast forms the ___________
Yolk sac
What does the yolk sac do in humans?
It produces the earliest blood cells.
When does Gastrulation occur?
During the third week of development, immediately after implantation. It is the beginning of the embryonic period.
What is gastrulation?
Process by which the cells of the epiblast migrate and form the three primary germ layers, which are the cells from which all body tissues develop.
What are the three primary germ layers?
Ectoderm
Mesoderm
Endoderm
What does the process of gastrulation begin with?
The formation of the primitive streak.
What is the primitive streak?
A thin depression on the surface of the epiblast.
What is the second step of gastrulation?
Invagination. Cells detach from the epiblast layer and migrate through the primitive streak between the epiblast and hypoblast layers.
What is the layer of cells called after invagination?
The layer of cells between the epiblast and hypoblast becomes the mesoderm.
How does the endoderm come about?
Other migrating cells eventually displace the hypoblast and form the endoderm.
How does the ectoderm come about?
Cells remaining in the epiblast then form the ectoderm.
What are the two ways the embryo folds during growth?
Cephalocaudal folding
Transverse folding
What happens during cephalocaudal folding?
The embryonic disc and amnion grow very rapidly, but the yolk sac doesn't grow at all. This differential growth causes the head and tail regions to fold on themselves.
Where does cephalocaudal folding occur?
In the head and tail regions.
What does cephalocaudal folding create?
The future head and buttocks.
Where happens during transverse folding?
Left and right sides of the embryo curve toward the midline.
What does transverse folding form?
Forms cylindrical trunk with endoderm most internal and ectoderm covering the exterior.
What does transverse folding create?
A cylindrical trunk or torso region of the embryo.
What does the ectoderm eventually become?
Epidermis (skin)
Nervous tissue
Cornea
Hair
Nails
What does the Mesoderm eventually become?
Muscle tissue
Heart
Kidneys
Reproductive organs
Connective tissue (BBCC)
Dermis
What does the Endoderm eventually become?
Digestive system
Respiratroy system
What is they cylindrical structure of mesoderm called?
The notochord.
Where does the notochord form?
Parallel and deep to the primitive streak.
What does the notochord do?
It influences some of the overlying ectoderm to begin to form nervous tissue via a process called induction.
What is induction?
One structure influences or induces another structure to change form.
What is neurulation?
The inductive action that transforms a flat layer of ectodermal cells into a hollow nervous system tube.
What is the first step in neurulation? When does it occur?
Ectoderm thickens in the midline, forming the neural plate. Mid week 3.
What is the second step in neurulation? When does it occur?
The neural plate develops a depression called the neural groove and two elevations called the neural folds. Late week 3.
What is the third step in neurulation? When does it occur?
Neural folds fuse to form the neural tube, while neural crest cells pinch off the neural folds and migrate to various ares of the body. Early week 4.
What does the neural tube eventually become?
The brain and spinal chord.
What is organogenesis?
Ogran development begins. Upper and lower limbs attain adult shape.
When does organogensis begin?
Once the three germ layers have formed and the embryo has undergone cephaocaudal and transverse folding.
Most organ systems have developed by week __________. How long is the embryo at this point?
eight
The embryo is approximately 1 inch long.
What is a teratogen?
Anything that causes a birth defect.
During what period is the baby most sensitive to teratogens?
During the embryonic period.
Why is the embryo so sensitive to teratogens?
Because the embryonic period includes organogenesis, exposure to teratogens can result in the malformation of some or all organ systems.
How many babies are born in the US with a serious birth defect?
3 in 100
What percent of birth defects are chromosomal?
10%
What percent of birth defects are monogenic (1 gene causes the defect)?
8%
What percent of birth defects are major environmental (radiation, chemicals, smoking, etc.)?
7%
What percent of birth defects are mutifactorial (multiple causes)?
25%
What percent of birth defects are caused by unknown factors?
50%
Fetal alcohol syndrome is one of ________________ birth defects.
few preventable
How much alcohol can be teratogenic?
A single alcoholic binge
What are the FAS attributes?
Growth retardation
Heart defects
Microcephally (small brain)
FAS is the leading cause of ________________.
mental retardation
What percent of babies born to mothers taking Accutane have serious birth defects?
25%
What percent of babies born to mothers taking Accutane are mentally disabled?
50%
What do we call cell doublings leading to the morula?
Cleavage
Name the two components of the blastocyst.
Inner cell mass (embryoblast) and trophoblast
Describe the formation of the three primary germ layers.
The three primary germ layers are the ectoderm, mesoderm and endoderm that are created from the epiblast during gastrulation. This process begins when the primitive streak forms on the dorsal side of the epiblast. Epiblast cells migrate through the primit
What structure stimulates the formation of the neural plate? What germ layer contains the structure?
Notochord; mesoderm
Name an organ or organ system that derives from each of the three primary germ layers.
� Ectoderm: brain, spinal cord, skin
� Mesoderm: muscles, bone, blood, cartilage, tendons, ligaments, fat, kidneys, ovaries, testes
� Endoderm: trachea, lungs, esophagus, stomach, pancreas, gallbladder, liver, small intestine, large intestine
Describe the two types of body folding.
Transverse folding turns a flat embryo into a tube-like embryo. Cephalocaudal folding creates the head and buttocks.
What occurs during the fetal period?
Growth of the fetus from one inch to around 20 inches. Growth and maturation of the internal organs.
What is a teratogen? When is the baby most susceptible to them?
A teratogen is any substance that can cause a birth defect. The baby is most sensitive to them during the embryonic period.
What is a premature birth?
Any birth before week 38
Infants born as early as week _____ can survive without lifesaving measures.
30
Infants can survive as early as week ____.
22 (This requires a lot of help)
For premature babies a ____________ means a greater chance of fetal demise.
lower birth weight