Embryology Flashcards
What is the embryonic period?
The first eight weeks
What does the term zygote refer to?
A single cell embryo
Describe human fertilisation
1) Sperm binds in a human specific interaction with the zona pellucida glycoprotein (the thick transparent membrane surrounding a mammalian ovum before implantation).
2) Acrosomal enzymes released from sperm head allowing the sperm to digest its way into egg.
3) Egg and sperm plasma membrane fuse and sperm contents enter the egg.
4) Sperm entry triggers the completion of meiosis 2 and release of cortical granules by oocyte.
What is cleavage?
The first set of cell divisions in the early embryo
Describe blastocyst formation
This is the point where differentiation occurs
What is compaction?
The blastomeres begin to form tight junctions with one another, leading to deformation of their round shape and formation of a mulberry-shaped mass of cells called a morula. This change in shape of the embryo is called compaction.
Describe implantation
This is an active process driven by Trophoblast (cells forming outer layer of trophoblast).
The Trophoblast divides into: Cytotrophoblast and Syncytiotrophoblast.
The Syncytiotrophoblast secretes enzymes that allow the blastocyte to embed in the uterine wall.
By day 9 implantation is complete.
What is gastrulation?
The formation of the germ layers
What are the three primary germ layers?
Ectoderm, mesoderm and endoderm
What is the fate of the ectoderm?
Epidermis of the skin: hair, nails and associated glands, nervous system: brain, spinal cord, peripheral nerves.
What is the fate of the mesoderm?
this is divided into three regions:
- Paraxial Region- Axial skeleton, voluntary muscle, parts of dermis
- Intermediate Region- Urogenital Systems, Kidney and ureter, Gonads and associated structures
Lateral plate further subdivided
• Somatic Lateral Plate- Somatic Lining of body wall, most of dermis, parts of limbs
• Visceral Lateral Plate- Cardiovascular system, mesothelial covering of organs, smooth muscle
What is the fate of the endoderm
Lining of the gut tube, Lining of respiratory tract, Lining of the bladder and urethra.
How does a morulla differ from a blastocyst
Morulla is 3-4 days as opposed to 4-5 days
A blastocyst has a cavity in the middle morulla is simply spherical shaped
