Week 7: General Emryology Flashcards
What is the human development time of a zygote?
-30 hours
What is the human development timeline of a morula (ball of cells)?
-30 hours to 4 days
What is the human development time of a Blastula?
Day 4 to Day 7
What is the human development timeline of a gastrula?
Day 7 to Week 3
What is the human development timeframe of an embryo?
Week 3 to Week 8
what is the human development timeline of a foetus?
-Week 8 to week 40 (birth)
What is rostral? (Nomenclature in embryology)
Head end (cranial or superior)
What is caudal? (Nomenclature in embryology)
Tail end (inferior)
What is dorsal? (Nomenclature in embryology)
Back (posterior)
What is ventral? (Nomenclature in embryology)
Front (anterior)
What is proximal (Nomenclature in embryology)?
Structures near the body centre
What is distal? (Nomenclature in embryology)
Structures further from the body centre (e.g. hand is distal to elbow)
What is the order of stages from fertilisation to implantation (days 1-6) ?
Fertilisation, cleavage, morula, blastocyst, implantation (of blastocyst into the endometrium of the uterus)
What is fertilisation?
The process where a sperm fuses with an ovum creating a zygote which eventually leads to the development of an embryo
What is the difference between diploid and haploid? §
Haploid single set of chromosomes (23), Dipliod has two sets of chromosomes (23 form each parent, 46 in total)
What is a zygote cell?
When the ovum nucleus and sperm head nucleus (pronuclei) fuse intermixing their chromatin, to form a diploid nucleus= zygote cell
What are the stages of Cleavage?
- zygote undergoes rapid mitotic divisions (cleavage)
- 2 cell stage on day 1
- 4 cell stage on day 2
- 16 cells by day 3, this is called the Morula (solid ball of cells)
What is a blastocyst cell?
- what is the embryoblast?
- what is the trophoblast?
- day 4-5, morula enters uterine cavity
- at 32 cell stage, fluid enters morula, collects between blastomeres & reorganises them around the blastocyst cavity (fluid-filled space)
- When a blastocyst cavity has formed, the tissue is called a Blastocyst (which contains 100’s of cells), from which 2 cell populations arise;
1. Embroyblast (inner cell mast)= will become the embryo
2. Trophoplast (outer cell layer, is blastocyst wall) = will become outer chorionic sac (surrounds foetus, site of mother-foetus nutrient/waste exchange)
What is implantation?
The ovum enters the fallopian tube and travels along towards the endometrium where implants (5-6 days after fertilisation)
What is the zone pellucida?
Thick glycoprotein layer surrounding the oocyte plasma membrane, by day 5 the blastocyst hatches from the Zona Pellucida by enzymatically digesting a hole and squeezing through it. This shedding of ZP is essential to permit implantation into the endometrium
What is the inner cell mass?
- In the blastocyst, the Inner Cell Mass (embryoblast) will ultimately form the embryo (orientates with endometrium)
- The ICM is the source of embryonic stem cells (capable of forming all embryonic cell types)
What is the trophoblast??
Outer cell layer of blastocyst (forms placenta and adnexa)
What happens on day 6 after fertilisation?
-blastocyst rolls (actually grows) until Inner Cell Mass lines up with endrometrium
What are the two distinct layers that the trophoblast form into?
- Cytotrophoblast (inner layer eventually forms primary chronic villi)
- Syncytiotrophoblast (outer layer, invades endometrium so direct contact with maternal blood and main communicator between foetus and mother)
What are the two distinct layers of the inner cell mast?
-Epiblast- forms 3 germ layers (ectoderm)
-Hypoblast - transient layer replaced by endoderm
Together epiblast + hypoblast form the Bilaminar embryonic disc
What is gastrulation?
Formation of trilaminar embryo (3 layers) (week 3)
- Early phase in mammalian embryonic development where bilaminar embryonic disc (2 layers, hypo + epi)
- three layer structure called Gastrula, eventually will form embryo’s entire body organs and tissues
What are the three layers of the Gastrula?
- Ectoderm (external layer) : epidermis (skin), nervous system (PNS, CNS), retina, nose and ears, hair, nails
- Mesoderm (middle layer) : dermis, bones, cartilage, connective tissue, cardiovascular/reproductive/lymphatic system, muscle (Striated smooth and cardiac), kidneys and spleen
- Endoderm (internal layer):digestive system, liver, pancreas, inner layers of lungs
What is primitive streak formation?
Forms 2 germ cell layers, endoderm and mesoderm, start to organise front, head, back, tail of embryo, left/right orientation (body axis)
- migrating epiblast cells
- embryo then starts folding
