Embryology weeks 1-4 Flashcards
Pre-embryonic period
Period during which implantation occurs
Embryonic period
Period during which major organ systems are formed
Fetal period
Period characterized by growth
When is the pre-embryonic period?
Weeks 1-2
When is the embryonic period?
Weeks 3-8
When is the fetal period?
Weeks 9-38
When is the embryo most susceptible to teratogens?
Embryonic period
When is embryo not sensitive to teratogens?
Pre-embryonic period
Where does fertilization normally occur?
Ampulla (neck) of uterine tube
What must the sperm penetrate to fertilize the oocyte?
Zona pellucida
What is a zygote?
Sperm and egg
Rapid mitotic cell division without increasing in size
cleavage
How long for an egg to travel the length of the uterine tube?
5 days
Layer of cells surrounding the oocyte
Corona radiata
First phase of fertilization
Sperm penetrates corona radiata
Second phase of fertilization
Sperm penetrates zona pellucida
Glycoprotein coat that facilitates binding of sperm
Zona pellucida
Which layer blocks fertilization by multiple sperm?
Zona pellucida
Third phase of fertilization
Germ cell membranes fuse, triggering completion of meiosis by the ovum
How many cells must be present for the developing embryo to be a morula?
16
Two groups that morula separates it cells into
Trophoblast cells (outer layer of cavity) and embryoblast (inner cells)
Embryo with a hole in the middle
Blastocyst
What allows blastocyst to implant on uterine lining?
Enzymatic degradation of the zona pellucida
Two layers that the embryoblast differentiates into
epiblast and hypoblast
Two layers of the trophoblast
cytotrophoblast and syncytiotrophoblast
Cytotrophoblast
contains actively dividing cells
Syncytiotrophoblast
layer that invades maternal capillaries
hormone produced by syncytiotrophoblasts
human chorionic gonadotrophin (hCG)
Structure epiblast cells surround
amniotic cavity
Structure hypoblast cells surround
yolk sac
What does embryo exist as at the end of week 2?
Bilaminar (two layered) disc
Which cell type (epi or hypoblast) becomes dorsal?
Epiblast
Process of forming three embryonic germ layers and body axes of embryo
gastrulation
Groove at caudal end of epiblast that establishes 3 axes of embryo
primitive streak
Raised area at the cranial end of the streak
Primitive node
Germ layer created between the epiblast and hypoblast
Mesoderm
Germ layer created by migrating epiblast cells replacing hypoblast
Endoderm
Germ layer created by cells remaining at the epiblast
Ectoderm
Structure that induces development of the nervous system and parts of vertebral column
Notochord
One site of epiblast and hypoblast juncture (future mouth)
oropharyngeal membrane
One site of epiblast and hypoblast juncture (future anus)
Cloacal membrane
In neurulation what does notochord induces overlying ectoderm to become?
Neural plate
What does the neural plate close off to become?
Neural tube
Where does the neural tube first fuse?
The midregion of the embryo
Structures from the surface ectoderm (2)
epidermis of skin and glands
Structures from the neural tube (2)
brain and spinal cord
Structures from the neural crest cells (2)
Peripheral nervous system and bones of the face
Three columns of mesoderm from medial to lateral
paraxial mesoderm, intermediate mesoder, and lateral plate
Two layers the lateral plate separates into
Visceral and somatic layer
Cells that blood cells develop from
hemangioblasts
What are the four places hemangioblasts arise from youngest to oldest
Yolk sac, liver, spleen, bone marrow
What causes longitudinal folding?
Rapid growth of brain
What does the yolk sac eventually become?
The GI tract/gut tube
three regions of the gut tube
foregut, midgut, hindgut
Which column of mesoderm differentiates into somites?
Paraxial
Which column of mesoderm forms urogenital system?
Intermediate
Which column of mesoderm forms limb bones, heart, and blood vessels?
Lateral
