Embryology development Flashcards
What is involved in fertilisation?
- Fusion of the oogonium ( 3 polar bodies and 1 ovum) and the spermatogonium (4 sperm bodies)
- Sperm carries through pronucleus. Leaves behind organelles
- Ovum released by the ovary. Fertilised in fallopian tube
- ZYGOTE carried to uterine cavity by cilia
What happens in week 1
1-Zygote multiplies by mitosis to form MORULA
2-MORULA becomes BLASTULA
3- BLASTULA made up of inner cell mass, blastocystic cavity, TROPHOBLAST
What happens in week 2
1- blastula reaches endocrine cavity 2-TROPHOCYTE become CHORION 3-inner cell mass become flattened- BILATERAL DISC: EPIBLAST and HYPOBLAST. 4-Epiblast separated AMNIOTIC CAVITY 5-Hypoblast separates YOLK SAC
What is It and the function of the Chorion
Rearrangement of trophocyte
Mushy-no visible cell membrane
finger like projections
Function:
- implantation
- forms part of placenta
- release of HMC hormone-used to detect pregnancy
Differences between fraternal and identical twins
fraternal-dizygote:
- 2 sperm-2 ovum
- usually females release 1 ovum per month-in some cases more than 1
Identical-monozygote:
- 1 ovum-1 sperm
- division occurs at a later date
- can share placenta and amniotic cavity
Role and appearance of the placenta
-develops in 18-24 weeks
-smooth upper foetal surface, contains umbellical cord
-rough maternal surface
role:
-nutrition
-supply of gases + removal of waste
-immune
What happens in week 3 - general
1-Primitive streak forms from Epiblast
cells from primitive streak move in between epiblast and hypoblast
Forms axis of embryo.
2-Formation of trilaminar disc- specialised cells
What happens to the Ectoderm
1-Notochord formation
Dipping of cells from ectoderm-forms solid tube
2- Notochord releases chemicals which lead to formation of NEURAL TUBE
What happens when STI occurs
Cilia function impaired.
Zygote cannot be carried to endocrine cavity
Ectopian pregnancy
Where does the foetus get mitochondrial DNA from?
All organelles inherited from mother so all mDNA from mum- including possible diseases.
What happens to the mesoderm?
It separates into 3 layers:
- Lateral- forms the peritoneum, pleura and body cavities
- Intermediate- forms the urogenital system
- Paraxial
Paraxial segments into somites- innervated by a pair of spinal nerves.
Somites then develop into:
-Dermatomes-move under the epidermis to form the dermis
-Myotomes- form muscles
-Sclerotomes: form bones and vertebrae
What happens in weeks 4-8?
- Heart starts beating on day 24
- Gut formation from the endometrium
- Tube folding
- 43 pair of somites
- Urogenital system
What is teratogenesis and what does it involve?
Abnormalities during development which can be due to:
ENVIRONMENTAL: e.g. tobacco, drugs, infections
GENETIC: e.g. chromosome number/structure
When and what can increase the risk of teratogenesis?
How can it be prevented?
When: week 1-2: very high risk-will usually end in death week 3-8 : highest sensitivity to teratogens Week 9-32: risk decreases what? -Dosage -Exposure during critical periods -genetic conditions of the embryo Tests: -Prenatal: blood ultrasound invasive -Postnatal: hearing breathing
What does the gut give rise to (general)
Gut divides into foregut, mid gut and hindgut.
Ventral section of the foregut gives rise to the Lung buds and trachea in week 4.
