Embryology Flashcards
Embryonic period
First 8 weeks of prenatal period
Where major organs are formed from three primary germ layers
Fetal period
Remaining 30 weeks
Organs continue to develop in size and complexity
Tube within a tube
Inner tube- digestive and respiratory tracts
Outer tube- consist of muscles and bones
Bilateral symmetry
Most body structures are paired with some exceptions
What has Dorsal hollow nerve cord and what does it develop into?
All vertebrate embryos have a hollow nerve cord that develops into the brain and spinal cord
What does the Notochord form into
Embryonic notochord forms just deep to the spinal cord and is quickly replaced by the vertebrae which makes up spinal column or backbone
Segmentation
Outer tube of the body develops into segments which are repeating units of similar structures
Oocyte
Female reproductive cell
Cleavage
Multiple cell division of zygote
Morula
Cluster of 12-16 cells formed by day 4
What are Blastocyst and their characteristics
Cluster of 60 cells
Will implant in the uterus around day 6
Fluid filled cavity in the center and inner cell mass and trophoblast
Inner cell mass
Cluster of cells on one side of the cavity
Will form the embryo
In some pregnancies The inner cell mass of a single blastocyst will split into two causes
Identical twins
Trophoblast
Layer of cells surrounding the cavity and inner cell mass
Help form the placenta
By day 9, inner cell mass have divided into
Two sheets of cell known as the bilaminar embryonic disc
The ____ form the bilaminar embryonic disc which give rise to the embryo
Epiblast and hypoblast
What are Epiblast and what’s do they form
Cells form most of the embryo
Forms amniotic sac
Amnion
Outer membrane of amniotic sac
What is Amniotic fluid
Fluid that acts to cushion the developing embryo up until birth
Hypoblast
Extension of the hypoblast form yolk sac
What does Yolk sac develop into
Give rise to digestive tract
Gastrulation
During week 3 the bilaminar embryo develops into 3 layers known as embryonic disc
Endodrerm
Day 14-15 the primitive steak appears on the dorsal surface of the Epiblast
Epiblast cells migrate toward the primitive streak and displace the hypoblast to become the endoderm
How does Mesoderm form
Day 16 some Epiblast cell burrow down from the primitive stream to form the mesoderm
Ectoderm
Epiblast cells that remain on the dorsal surface become the ectoderm
Neurulation
Development of brain and spinal cord
Primitive node
Swelling at the end of the primitive streak
What appears on day 16 and by day 18 it reaches the cranial or cephalic region of the embryo
Notochord
Presence of the notochord includes the ectoderm in the dorsal midline to thicken and become
Neural plate
Neuro plate starts to fold inward to become the
Neural groove
Neural groove depends into a
Neural tube
What does Neural tube do
Closest off at the neck and proceeds cranially in caudally
Neural crest cells
Originate from ectoderm and form nerve cells
Anencephaly
Developmental disorder when neural tube fails to close cranially
The rain does not develop in the baby is either stillborn or dies
Associated with low maternal folate levels
What are the different regions of the mesoderm by the end of week 3
Somites, intermediate mesoderm, lateral plate
where are Somites and what do they form
Area of mesoderm closest to the notochord forms segmental bulges Visible on the dorsal surface
Intermediate mesoderm
Series of spherical segments attached to Somites 
Lateral plate
Most lateral part of mesoderm remains unsegmented but splits into two sheets
Somatic and splanchnic mesoderm
Somatic mesoderm
Next to ectoderm
Splanchnic mesoderm
Next to endoderm
Coelom
Wedged like space the form between the two layers
Will become serous cavities of the ventral body cavity
Folding occurs during week 4 body goes from a flat disk to
3D cylinder shape by folding into a tube
Growth of Somites causes sides of embryo to join
Head and tail regions fold under expanding the brain and spinal cord
Derivatives of ectoderm
Ectoderm becomes the outer tube: brain, spinal cord and skin epidermis
Derivatives of endoderm
Endoderm becomes the inner epithelial lining of the inner tube: gut and respiratory tubes
Derivatives of mesoderm
Somites divide into three parts
Sclerotome
Produce vertebrae and ribs
Dermatome
Produce skin dermis in dorsal body
Myotome
Produces muscles and help form the limb buds
Intermediate mesoderm
Forms kidneys and gonads
Somatic mesoderm
Gives rise to skin dermis in ventral body and helps form the limb buds
Splanchnic mesoderm
Gives rise to digestive and respiratory tubes, heart and blood vessels
Around day 28/ week 5-8 what happens
Limb buds start to appear
Head enlarges and face starts to appear
Most major organs are formed during the second month of development so that any disruption during this time can result in birth defects
When can heartbeat be detected
By 6-7 weeks by ultrasound
Week 9-12 month 3 is when what happens
Brain continues to enlarge
Trunk and limbs elongate
Bone marrow starts to produce blood cells
Lungs begin to develop and fetus inhaled and exhales the amniotic fluid instead of air
When can sex be determined
Month 3
Weeks 13-16 month 4
Bone formation begins in vertebrae
Myelin start to form around nerve cells
Kidneys form
Weeks 17-20 month 5
Brain grows
When does quickening start
Month 5
Weeks 21-30 months 6-7
Lungs complete development and start to produce pulmonary surfactant at end of month 6
Premature infants born before month 6 may die from respiratory distress
week 31-38 month 8-9
Skin thickens and fat accumulates
Immune systems begins to develop
Normal birth
