Embryogenisis Flashcards
Definition of embryogenisis
Development and formation of an embryo from fertilised egg- zygote
What are the boundaries for the pre-embryonic stage
0-2 weeks
What does the pre-embryonic stage begin with
Zygote
Formed from sperm and egg
Defintion of totipotent cells
Cells that can differentiate into anything
Definition of pluripotent cells
Cells that become more specialised as development continues
What is the zona pellucida
Protective layer surrounding plasma membrane of oocyte
What is the function of the zona pellucida
Prevents polyspermy during fertilisation
What is the name of the structure that prevents polyspermy during fertilisation
Zone pellucida
What are the 6 parts to the pre-embryonic stage
Cleavage
Morula formation
Blastocyst formation
Blastocyst hatching
Implantation
Formation of bilaminar disk
Formation of 2 cavities
What occurs during the cleavage of the pre-embryonic stage
24 hours post fertilisation
First mitosis division of zygote
What occurs during morula formation of the pre-embryonic stage
Cells are referred to as blastomeres until there’s 16 cells present- called morula
What occurs during blastocyst formation of the pre-embryonic stage
Cells of morula differentiate into 2 types of cells
Inner cell mass into embryoblasts
Outer cell mass into trophoblast cells- form placenta and hormone production
Cavity is formed- fluid enters morula- called blastocele
What occurs during blastocyst hatching of the pre-embryonic stage
Blastocyst reaches uterus
Hatches from zona pellucida ready for implantation
What occurs during implantation of the pre-embryonic stage
Zygote implants into endometrium- invades tissue
Develops blood supply from maternal circulation
Ensures embryo has nutrients and waste removed
What occurs during formation of two cavities of the pre-embryonic stage begin
Amniotic cavity- eventually surrounds foetus
Primitive yolk sac- forms some of the supporting tissues needed for developing embryo
What are the different types of twins
Monozygotic and dizygotic
Describe how monozygotic twins arise
Identical twins
1 zygote splits
Timing of split affects number of placentas and amniotic cavities
Incomplete splitting leads to conjoined twins
Describe how dizygotic twins arise
Non-identical twins
2 eggs
Fertilised by 2 different sperms
Different genetic material
Will have different placentas and amniotic sacs
What are the 2 stages of the embryonic stage
Gastrulation
Neurulation
When does gastrulation occur
At week 3
What occurs during gastrulation of the embryonic stage
Begins with formation of primitive streak
Then formation of primitive node
Cells from epiblast migrate towards primitive streak and pass through it and develop new layers of cells beneath epiblast
1st layer replaces hypoblast- becomes endoderm
More cells migrate- sit between epiblast and endoderm- mesoderm also forming notochord
Epiblast cells become-ectoderm
What occurs during neurulation of the embryonic stage
Notochord signals to overlying ectoderm to thicken- forms neural plate
Causes it to be raised at the edges forming neural folds
Folds fuse at midline- form neural tube
Neural tube detaches from ectoderm and is now within mesoderm
During fusion of neural folds- neural crest cells detach- eventually become peripheral NS
What is formed from the endoderm
Form cells that line internal tracts
Epithelia that line- GI and respiratory tract, lungs, urethra, bladder
Contribute towards glandular parts of liver and pancreas
What does the mesoderm form
Bones, cartilage, connective tissue and muscles
Cardiovascular, urinary, reproductive and lymphatic systems
Dermis of skin
