Early Embryotic Development Flashcards
Learning Objectives
List the sequence of developmental events between fertilization and implantation
Appreciate the major changes that occur during the formation of the bilaminar disc
Give examples of abnormal implantation sites and be aware of the implications of ectopic pregnancy
Understand the major causes of congenital malformations
Where does fertilization start?
In the ampulla tube within 12 hours of ovulation
Are sperm and ovum haploid or diploid cells?
Haploid cells
Explain the process of fertilization
The sperm cell breaks into the zone pellucida which dissolves the acrosome of the sperm. The sperm and oocyte membranes then fuse together. After the pro nucleus of the male and female expands.
At the same time, the chromatids are replicating into 2 sister chromatids
Explain the process of the first week of development off a cell.
Mitosis of the maternal and paternal chromosomes line up on the spindle equator (metaphase)
chromatids seperate (anaphase)
Since the zona pellucida remains intact, there is no cell growth just a cleavage between the two new smaller cells
Explain the stages of cell replication after fertilization
2 cells replicates to 4 cells
At 8 cells the cells become less distinct and compact and develop gap junctions to communicate with each other
At 16 cells or the morula there is a ball of cells that travel along the uterine tube and arrives at the uterus.
There are about 30-40 cells when the morula arrives and the zone pellucida dissolves.
After the zona pellucida disappears, what do the inner and outer cells of the morula become?
Outer cells become trophectoderm and inner cells become inner cell mass
Explain what happens 4.5+ days after fertilization
The cells expand into a ring like structure with a large bunch of cells called the trophectoblast. Below is the inner cells. The thin like ring structure of cells is the trophectoderm. The empty space is called blastoceol
When is the best time to test for genetic diseases and what should be tested?
5-6 days after fertilization and test on the trophectoderm
Explain the steps of implantation (Refer to lecture slides for diagrams)
(5.5-6 days) Binding of the embryotic epithelium to the uterus epithelium occurs
(6-7 days) Implatation begins with the trophoblasts becoming invasive. (becomes (syncytiotrophoblast and cytotrophoblast). These invade into the uterine epithelium
(Day 8) Two layers form in the embryo- epiblast and hypoblast. Within the epiblast forms an amniotic cavity
(Day 9) Hypoblasts coat the blastocyst to form the primary yolk. Amniotic cavity is fully formed. (Can’t be seen on diagram) Extraembryotic mesoderm will soon form deep to trophoblast
(Day 11 and 12) New layer between yolk sac and cytotrophoblast has been formed and the chorionic cavity will form by fusion of these. Blood begins to fill the trophoblastic spaces
(End of week 2) Secondary yolk sac is created and remnants of the primary yolk sac remain
After implantation, what layers and cavities have been developed?
2 layers in the trophoblast: Syncytiotrophoblast
Cytotrophoblast
2 layers in the inner cell mass
Epiblast-ectoderm
Hypoblast-endoderm
2 cavities form
Amniotic cavity
Chorionic cavity
What is the main cause of the disease preeclampsia?
Cytotrophoblast invasion into spiral arteries of uterus is defective. This makes the spiral arteries very hard and increases blood pressure
What is ectopic implantation and where does it occur most often?
Eptopic implantation is when implantation doesn’t occur in the uterus body (ampulla most common). Other examples include the ovaries.
What are the causes of congenital malformation?
Environmental: Drugs/ chemicals
Infectious agents
ionizing radiation
Multifactorial or unknown reasons
Genetic reasons: Chromosome deletion, mutations etc.
