Embryology - Early Development Flashcards
What is the timeline of an embryo?
Developing organism during the first 8/40 weeks.
What is the timeline of a fetus?
After 8 weeks.
What happens during the embryonic period?
Most organs have differentiated.
What happens during the fetal period?
Time for the organs to undergo maturation.
When do congenital defects occur?
Typically in the embryo stage.
What is the first stages in the embryonic period?
Zygote (fertilised egg) undergoes cleavage to produce a morula.
What is the second stage i the embryonic period?
The morula travels along the uterine tube towards the uterus and it further divides and a fluid filled cavity appears. The morula becomes a blastocyst.
What is the third stage in the embryonic period?
6 days after fertilisation the blastocyst is implanted into the uterine mucosa.
What is the outer layer of cells in the blastocyst called?
Trophoblast.
What is the trophoblast destined to become?
Placental.
What are the remainder of cells in the blastocyst called?
Inner cell mass.
What does the inner cell mass attach to?
The inner layer of the trophoblast.
What does the inner cell mass divide into?
- Amnion.
- Yolk sac.
What separates the amnion and yolk sac?
Embryonic plate - mass of cells.
What will the embryonic plate differentiate into?
Tissues and organs of the embryo.
What is the amniotic aspect of the embryonic plate?
Ectoderm.
What is the yolk sac aspect of the embryonic plate?
Endoderm.
What is between the endoderm and ectoderm?
Primary mesoderm.
What is the secondary mesoderm derived from?
Cells of the ectoderm.
What grows in from the ectoderm towards the endoderm?
Notochord - axial rod of cells.
What is the dorsal surface of the embryonic plate?
Ectoderm and amniotic.
What develops on the dorsal surface of the embryonic plate?
Neural groove develops.
What happens with the neural groove?
The edges unite to form the neural tube. The tube becomes depressed below the surface.
Where does the brain and spinal cord develop from?
Neural tube.
Where is the neural crest formed from?
Cells from the edges of the groove that become isolated between the tube and the overlying ectoderm.
What will the neural crest develop into?
- Posterior root ganglia of spinal nerves.
- Corresponding ganglia of cranial nerves.
- Autonomic ganglia.
- Satellite cells of ganglia.
- Schwann cells of peripheral nerves.
- Chromaffin cells of suprarenal medulla.
How does the mesoderm lie?
In three longitudinal strips - alongside the notochord and neural tube.
What is the paraxial mesoderm?
The longitudinal strip nearest the midline.
What does the paraxial mesoderm become segmented into/
Masses of cells - mesodermal somites.
What do the mesodermal somites produce?
- Sclerotome - medially.
- Myotome - laterally.