Embryology Flashcards
How many weeks is from conception to birth
38 weeks
What are the 3 periods of birth
- Pre - Embryonic period - 1st week
- Embryonic period - weeks 2 to 8
- Fetal period - weeks 9 to 39 ( 3 trimesters )
What happens during the Pre Embryonic period
Fertilization in ovary to Implantation in uterus = GLASTISIS
Not really an embryo - just a cluster of cells
What happens during the Embryonic period
- Multicellular Blastocyst to recognizable Vertebrate
- Organogenesis
- Developing embryo and creating something that looks like a liferform
What happens during the Fetal period
- Major growth of existing structures – everything increases in size + a few new ones/structures/organs produced
When do you become fertile
Not fertile until 2 weeks after last menstrual period – when you get pregnant
So its 38 weeks rather than 40 weeks
SO embryology occurs when pregnant women give birth- take date from last menstrual period
What is unique about whats produced at the end of the embryonic period
No matter what its coming from – human or mouse, we all roughly look the same at end of embryonic period - we’re just different sizes
What is the period where most organs are produced
Embryonic period
When was most of what we are created
During 1st 8 weeks
What happens during fetal period
Pretty much look like a human = end of embryonic period - have facial features
What are the cellular events that occur in embryonic development
- Cell Addition by Mitosis or ‘Cleavage’
(2) Cell Movement & Migration
(3) Programmed Cell Death or ‘Apoptosis’
What cell size is cell addition by mitosis or cleavage
From a single cell to >5 x 1012 cells
Doenst expand in size - only replicates
What happens during cell movement and migration
Forms layered, folded &/or tubular structures
Need those cells to move around and migrate to form different organs and structures in body – otherwise one lump of cell
What happens during programmed cell death or Apoptosis
Regression & elimination of tissues that are no longer required
Many times when cells and structures developed in developing embryo needed at that point of time but not needed when premature adult or human – develop and serve their function but those cells have to die off through apoptosis
Example of apoptosis in a tissue during embryonic development
- When eye developing – lens of eye coming and forming but at that time you have no aqueous humour production so there is no O2 and nutrients supply = blood vessel branching out of optic nevre – goes through cavity in middle of eye – vitreous and forms a basket of blood vessels – tunica vascularis lentis = provides o2 and nutrient supply for developing lens but when ciliary body matures , you get production of aqueous humour – that bathes lens with nutrietns and o2 so tunica vascularis lentis isn’t needed anymore so it dies – apoptosis
What is apoptosis
Programmed cell death - when the cell dies off
What happens during day 0
The zygote forms
Maternal and Paternal nuclei has fused
Sperm breaks down as it burrows its way inside - releasing its nucleus inside
What is the transparent capsule of the membrane called
Zona pellicuda - capsule/membrane that wasn’t around blasteocyst
How does a zygote form
Sperm or egg successfully found each other - sperm successfully eat its way through the membrane and the egg is implanted itself into the ovary
How many pairs of chromosomes in diploid
23
What happens during Day 1
Zygote divides/ cell splits to form 2 blastomeres
When it splits it doesnt double in size due to the 2 fused nuclei
Surrounded by membrane, separating inside capsule
What happens during week 1 - pre embryonic period
- Cleavage: daily series of binary cell divisions: blastomeres increase to 4, 8, 16 cells etc
- Moves down oviduct to uterine cavity, ‘wafted’ by cilia on oviduct epithelium - migration of cells and forming separate structures
- Instead of 1 cell dividing, both cells go through mitosis
What is produced at 3 days
Mast ball of cells - MORULA
What is cleavage
- Daily series of binary cell divisions
- 4 cells divide to create 8
- Every time you divide its exponential growth - v quick
How many days does it take for egg to get to Fallopian tube
7 days
Why are the eggs not stationary during week 1
As it goes through these divisions as ovaries are released into Fallopian tube
What is the Fallopian tube lined with and why
Ciliated columnar epithelial cells
Cilia is wafting - wants to move the egg down the Fallopian tube into the uterine cavity
How long does it take for egg to get to uterine cavity during 1st week of embryonic period
7 days
What is inside blastocyst
Internal cavity - filled with blasticium – fluid those cells are secreting
What happens during days 5 to 6
Blastocyst rearrange structure and segregate into 2 separate regions
What are the 2 sub regions of cells of the blastocyst
(1) Inner mass = Embryoblast
forms the Embryo (‘blast’: Gr,‘maker’)
(2) Outer layer = Trophoblast
forms the Placenta (‘tropho’: Gr,’feeder’) . Separated by fluid (blastocele)
What is embryoblast
Embryo maker – little spot of cells makes embryo
Inner cell mass
What is trophoblast
Feeder maker
All the cells around the outside
What happens during days 7 t o 10
- Zona pellucida ( translucent capsule ) ruptures = allows blasteocyst/trophoblast cells to invade uterine walls of uterus
- Trophoblast cells begin invading the epithelium & stroma of the maternal uterine wall
What is the placenta of trophoblast
- Outer layer
- Interphase between maternal bloody supply and embryo bloody supply – takes what it wants – o2 and nutrients from mothers blood supply and
And gives it to embryo – feeder
What happens during days 5 to 7
Blastocyst implanted into the uterine wall
Entering embryonic period - going into uterine wall
- Zona Pellucida ruptures - allows trophoblast cells to attach and migrate inbetween columnar epithelium of uterine wall
Where does embryo develop
Inside the mothers tissue - embeded into uterine stroma into connective tissue
NOT in uterus cavity
What happens during week 2
- Division of the Embryoblasts and Trophoblasts into 2 further cell types
- Cells proliferate
- Trophoblast cells buried deeper and deeper into uterine walls until whole blastocyst is inside the epithelium
- Membranes being broken down between cells – migrate as a big mass intothe stroma
What do Embryoblasts divide into
Into 2 layered disc/ cell types
- Epiblast,
- Hypoblast,
What do Trophoblasts divide into
Into 2 divisions/ cell types:
- Cytotrophoblast
- Syncytiotrophoblast