BL S9 Embryology Flashcards
What is embryology?
The study of the progression from a single cell to a baby in 9 months.
Including the molecular, cellular and structural factors involved.
What is ovulation?
What happens to the endometrium in prep for ovulation?
What is the role of fimbrae?
What moves the egg along the Fallopian tube?
Where does fertilisation occur specifically?
If the egg isn’t fertilised what happens to it?
What occurs 2 week after ovulation?
The discharge of an egg from the ovary.
Thickens
Move egg to neighbouring Fallopian tube.
Contractions in tube wall and ciliates epithelium of tube.
Ampulla
Absorbed by the body
Uterus lining shed through vagina - menstruation.
Describe the various selective pressures on sperm in its journey through to fertilise the egg.
5 points.
- Some flow out of vagina
- May become trapped in cervix mucous and folds.
- Uterus - resident immune cells - destroy sperm
- Half go down wrong Fallopian tube
- Sperm act against motion of cilia.
In the uterus what moves the sperm towards the egg?
Uterine contractions.
Where does capacitation occur and what 2 things does it involve?
Uterus
Destabilisation of the acrosomal sperm head allowing it penetrate the outer later of the egg.
Changed to tail that allow for increased mobility - hyperactive.
What is the outermost layer of the egg?
Corona radiata
Once sperm reach zona pellucida what do they do?
What is the perivitelline space and what is its significance?
Bind to specialised sperm receptors which causes digestive enzymes to be released.
Fluid filled matrix between zona pellucida and egg cell membrane.
First sperm to make contact will fertilise the egg.
What measures are in place to stop polyspermy?
Egg cell membrane changes preventing other sperm from attaching.
Zona pellucida hardens trapping sperm and they can no longer attach to it.
Egg releases chemical push away sperm
How long must sperm be introduced into the female reproductive tract prior to ovulation?
How long are sperm viable?
How long is secondary oocyte viable?
5 days
5days
12-24 hours
What are sperm not immunologically rejected by the body?
Contact between sperm and blood must be made to trigger immune response.
Sertoli cells form extensive tight junctions between them to avoid contact between blood and sperm cells.
Define
Embryonic Age
Gestational age
Germinal Stage
Embryonic period
Foetal period
Time since fertilisation
Time since last menstruation - embryonic age + 2 weeks.
Fertilisation to end of second week.
Start of 3rd to end of 8th week.
Start of ninth to birth at 28 weeks.
Overall what occurs in week 1?
Oocyte fertilised by sperm in ampullary region and implant in the superior posterior uterine wall.
Overall what occur in week 2?
Trophoblast differentiates into
- Syncitiotrophoblast
- Cytotrophoblast
Embryoblast differentiates into bilaminar disc:
- Epiblast
- Hypoblast
Overall what occurs in week 3?
Primitive steak forms
Gastrulation occurs
Neuralation
Overall what occurs in week four?
Somitogenesis - organisation of the paraxial mesoderm
Folding
Describe briefly the following week 1 processes.
Cleavage
Compaction
Cleavage - First mitotic division forms 2 blastomeres - continues - morula forms - 16 blastomeres
Compaction - differentiation to 2 cell types
- embryo blast
- trophoblast
Both pluripotent and blastocyst cavity forms also.
Describe the following week 1 processes:
Hatching
Implantation
Polyspermy threat declined - blastocyst hatches out of zona pellucida to allow for growth and implantation
Conceptus (8 embryonic cells + 99 trophoblast cells) penetrates through uterine mucosa simple columnar epithelium and implant in the uterine stroma
After implantation has occurred, what closes the gap that was opened by the conceptus?
How is access of the maternal vasculature allowed for?
What forms the primitive yolk sac?
What pushes away the primitive yolk sac from the cytotrophoblast?
How is the secondary yolk sac formed?
What forms the chorionic cavity?
The secondary yolk sac forms the connecting stalk and what else?
What is the role of the connecting stalk?
Fibrin clot
Lacunae of syncitiotrophoblast becomes continuous with maternal sinusoids.
Uteroplacentalk circulation begins.
Hypoblast and exocoelomic membrane form the primitive yolk sac.
Extraembryonic mesoderm
Primary yolk sac pinches off.
Spaces within the extraembryonic mesoderm.
Definitive yolk sac
Joins bilaminar disc to the cytotrophoblast
Describe the location of the primitive streak and primitive node.
Primitive streak forms on the dorsal surface of the epiblast.
Primitive node forms at cephalic end.
Describe the process of gastrulation.
What is structurally distinct about one of the layers formed?
Epiblast cells migrate to the primitive streak and invaginate.
Hypoblast displaced and 3 new layers are formed.
- Ectoderm
- Mesoderm
- Endoderm
Mesoderm has gaps for mouth and anus.
How is the notochord formed?
What is the role of the notochord.
Action of ciliated cells at the primitive node during gastrulation cause former epiblast cells to migrate to cranial end of primitive steak and form the notochord.
Drives neuralation.
In week 4 segmentation occurs, describe this process.
What differentiates first?
What is derived from each tome etc.
Mesoderm - arranged into discrete zones and areas.
Paraxial mesoderm segments into 31 pairs of somites.
Somites differentiate to form
- Myotomes - skeletal muscle derived from this
- Dermatomes - area of skin innervated by 1 spinal nerve
- Sclerotomes - forms bones.
Sclerotomes differentiate first leaving dermomyotomes.
- myotome proliferates
- dermatome disperses
What does the organisation of paraxial mesoderm into somites give rise to?
Repeating structures:
- Ribs
- Vertebrae
- Intercostal muscle
- Spinal cord segments
What does folding in week 4 achieve?
Creates dorsal, ventral distinction Creates a ventral body wall Embryo suspended in amniotic sac Creates the interembryonic coelom Pull connecting stalk ventrally
What does cephalocaudal folding achieve?
What does lateral folding achieve?
Heart moves away from cranial end towards the future chest.
Creates primordium of the gut - intraembryonic coelom
Describe the process of neuralation.
Notochord - diffusion limited signalling molecules
Signal to above ectoderm cells to differentiate into neuroectoderm cells.
Causing thickening of ectoderm in this region
- neural plate forms
Edges of neural plate rise and curl - neural tube forms.
What can be said about the structure of the neural tube?
Wider at cephalic end compared to caudal end.
What is situs inversus and what is its cause?
Complete reverse mirror image viscera
Occurs as result of immobile cilia in primitive node.
What it derived from the ectoderm?
Organs and structures that maintain contact with the exterior.
Epidermis
Nervous system
What derives from the mesoderm?
Muscle
Cartilage
Bone
Vasculature
What derives from the endoderm?
Epithelium of GI and Respiratory tract
Panachyma of gland
Internal structures
What is teratogenesis?
The process by which congenital malformations are produced in a foetus.
