Embryology S1 Flashcards
What is the primitive streak and what is it important for?
A narrow groove that develops on the dorsal surface of the epiblast. It has an important role in the orientation of the embryo, determining the front and the back
Explain briefly how the mesoderm is formed
- Cells on the epiblast migrate towards the primitive streak, invaginating into the epiblast, displacing the hypoblast, creating three layers
- As more cells migrate through the streak, they spread laterally and cephalic (towards the head)
What is the function of the Zona pellucida
The glycoprotein shell that surrounds the oocyte that prevents polyspermy
What is the bilaminar disc?
Made up of the epiblast and the hypoblast; derived from the embryoblast
When is gastrulation complete?
Because development proceeds cephalocaudally (head to tail), gastrulation is not complete in the caudal region until week 4
Name the three germ layers within the trilaminar disc and their positions within
Endoderm - The innermost layer
Mesoderm - The middle germ layer
Ectoderm - The outermost layer
What is gastrulation
The reorganisation of the germ layers into the ectoderm, mesoderm and endoderm and hence, establishing the origin of all cells
Where is the cytotrophoblast found?
It is the placental membrane around the yolk sac
Name three derivatives of the mesodermal germ layer
Any from: Smooth, skeletal and cardiac muscle, connective tissue, bone, cartilage, blood and blood vessels and the urinary system
What is a germ layer?
A layer from which other developed tissues originate from
Where is the oocyte fertilised?
In the ampulla
What is a fertilised oocyte called?
Zygote
Name 3 important derivatives of the ectodermal germ layer
Any from: Skin, skin derivatives (including hair, nails, lens and cornea, mouth and anus lining)
(Embryology) What are the three periods of human development?
1) Pre-embryonic: 1-2 weeks
2) Embryonic: 3-8 weeks
3) Fetal: 9-38 weeks
(Embryology) What changes occur between fertilisation of the oocyte and compaction?
Zygote undergoes cleavage to form two blastomeres which make up the morula
(Embryology) On which day does compaction occur?
Day 4
(Embryology) What is the structure of the conceptus after compaction
Blastocyst:
- Inner cell mass - Embryoblast
- Outer cell mass - Trophoblast
- Blastocyst cavity
- inside zona pellucida
(Embryology) How many cells will go on to form the embryo?
8
(Embryology) What occurs on day 5?
Hatching - blastocyst moves out of the zona pellucida and is now no longer constrained and is free to enlarge and divide and interact with the uterine wall for implantation
(Embryology) Describe the process of implantation
Occurs on days 6-7. Interstitial process whereby the blastocyst invades the uterine wall and implants in the storm
(Embryology) What is the optimum site for implantation
Posterior uterine wall
(Embryology) What problems can arise if the zygote implants at an alternative site to the posterior uterine wall?
Placenta praevia- conceptus implants in the lower uterine segment , covering the cervix opening, requires a caesarean section
Ectopic pregnancy- usually occurs when zygote implants in fallopian tube, can quickly become life threatening
What changes occur on day 9?
Rapid development of the syncytiotrophoblast. Formation of the yolk sac
What stimulates the process of gastrulation
Appearance of the primitive streak, node and pit on the dorsal surface of the epiblast
What is the purpose of the notochord?
- Important signalling role
- Drives formation of nervous system
- Basis for axial skeleton
- Define the phylum Chordata
Describe notochord formation and development
Notochord emerges from the cranial end of the primitive pit and forms a thick rod along the mesoderm, defining the midline
What is the role of the notochord in the development of the neural tube in week 4?
Releases diffusion limited signalling molecules which stimulate thickening of the overlying ectoderm
This forms the neural plate
Edges of the plate are elevated above the plane of the disc and curl towards each other to form the neural tube
What is the fate of the notochord?
Goes on to form the spinal chord
What is the developmental and clinical significance of the myotome?
Developmental - Gives rise to muscle
Clinical - muscle or group of muscles supplied by a single spinal nerve
What is the developmental and clinical significance of the dermatome?
Developmental - Gives rise to dermis
Clinical - Single strip of skin supplied by a single spinal never
In which two directions does embryo folding occur?
Cephalocaudally and laterally
