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Terms in this set (54)
What is a gamete?
A sperm or an egg (23 chromosomes)
What is a oocyte?
A female gametocyte or germ cell involved in reproduction.
Where is the ampullary region?
Towards the ovary end of the fallopian tube.
When does fertilisation occur?
12-24 hours after ovulation
Where does fertilisation occur?
What is a zygote?
The ovum after fertilisation (22 pairs of autosomal chromosomes and 1 pair of sex chromosomes)
Give a brief summary of what happens in the first week of fertilisation.
Zygote and Morula form, implantation and blastocyst formation.
What happens during the first 3 days after fertilisation?
1. Zygote commences a series of mitotic cells divisions (cleavage divisions), dividing into blastomeres.
2. Day 3= 16 cell Morula formed and reaches uterus
During these cleavage divisions in the zygote, does it enlarge?
No, it just becomes more and more compact.
What is a morula?
An early stage embryo consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida.
What is the zona pellucida?
Glycoprotein layer surrounding the plasma membrane of mammalian oocytes, preventing entry of subsequent sperm during fertilisation. Remains until Blastocoel formation.
On day 3 the morula undergos a process termed "compaction", what does this mean?
Cell to cell contact is maximised through tight junctions
Inner cells are segregated from outer cells.
What is the newly compacted inner cell mass known as?
What is the newly compacted outer cell mass known as?
What does the embryoblast give rise to?
The entire embryo
What does the Trophoblast give rise to?
Forms the outer layer of the blastocyst and contributes to the development of the placenta.
What process transforms the Morula to the blastocyst?
Pumping of fluid from outside to inside. Uterine fluid passes between the outer cells; the inner cells mass gravitates to one end of this cavity.
What is the blastocoel?
Is the fluid-filled central region of a mammalian blastocyst.
What day does the blastocyst implant onto the uterine wall?
Day 5 1/2 - 6
How does the blastocyst implant onto the uterine wall?
Proteolytic secretions from the trophoblast (outer cell mass) erode the lining of the uterus and cells from the trophoblasts invade the space created. Blastocyst thus becomes embedded into the uterine wall.
What happens in the 2nd week of fertilisation?
Placentation and Bilaminar germ disc formation
What starts to occur on the the 8th day?
1. Trophoblast differentiates into 2 parts as it works its way deeper into the uterine wall:
- Syncytiotrophoblast (leading portion, in red)
-Cytotrophoblast (cells adjacent to embryo)
What is the syncytiotrophoblast?
The invasive, multinucleated and cytoplasmic layer of the trophoblast. (Individual cells lose their cell membranes to form a multinucleate synzitium).
What occurs on the 9th day of placentation?
Further enzymatic activity of the Syncytiotrophoblast embeds blastocyst deeper into the uterine wall. Blastocyst is completely embedded into uterine wall.
What occurs during the 10th day of placentation?
Lacunae make contact with maternal sinusoidal blood vessels in the uterine wall, establishing placental circulation.
By day 12 what happens to the lacunae?
They stop growing and fuse to form large interconnecting spaces called lacunar networks. Capillaries in the endometrium (uterine wall) surrounding the developing embryo dilate forming maternal sinusoids.
What is the Bilaminar germ disc?
Inner cell mass (embryoblast) differentiates into two layers which form the bilaminar germ disc (shown as implantation proceeds):
Epiblast- layer of columner cells facing the cytotrophoblast.
Hypoblast- small flattened cells, face the blastocoel.
What 2 cavities are formed?
1. Amniotic cavity- dorsal the epiblast
2. Yolk sac cavity- ventral to the hypoblast
What is the extraembryonic mesoderm?
Day 12- A loose agglomeration of cells that appear and spread along the inner surface of the cytotrophoblast and surround
the embryonic disc.
Extraembryonic mesoderm between the cytotrophoblast and yolk sac forms a loose tissue with large vacuoles that later unite to become the _____________ _________.
What is the function of the extraembryonic coelom?
Plays a crucial role in nutrition of the developing embryo until a vascular system is established.
What other event occurs as the extraembryonic coelom forms?
More solid area of the extraembryonic mesoderm remains which connects the embryo to the trophoblast, this the connecting stalk which is the first sign of the umbilical cord.
What occurs in the third week of fertilisation?
What happens to the bilaminar germ disc in gastrulation?
It forms a trilaminar germ disc.
What are the layers of the trilaminar germ disc?
ectoderm, mesoderm and endoderm
What happens to one end of the embryonic disk in gastrulation? What does this indicate?
It thickens at one end forming the prechordal plate. This indicates the future of head of the embryo and shows head and tail polarity.
After the prechordal plate forms the primitive streak forms. Explain the process?
Epiblastic cells at tail end divide and migrate towards midline forming a multilayered structure. These cells start to sink below the surface of the embryo to form the primitive streak.
Once the primitive streak is established __________ inhibit the ___________ of any other structures
How is the endoderm layer formed?
When epiblast cells reach the midline, break way from plate of epiblasts and turn downwards into the plane between the epiblasts and the hypoblasts. They then migrate down to the hypoblast and displace cells creating endoderm.
What day is the endoderm formed?
What happens on day 16?
The next wave of migrating epiblastic cells spread outwards between the epiblasts and endoderm to form the intraembryonic mesoderm. Also the Notochord forms.
What is the primitive node?
The movement of mesoderm cells is limited initially to the inferior one third of the embryonic disc. The superior end of the disc is known as the Primitive node.
What is the Notochord and how does it form?
Epiblast cells migrate and invade the primitive node. They stay together to form a blind-ending midline tube, under the midline.
What happens on day 17?
-Notochord gradually enlarges, reaching the prechordal plate.
-The epiblast layer now become known as the ectoderm.
What happens on day 19 onwards?
The neural tube forms
How does the neural tube form?
-The notochord has an inductive effect on the ectoderm.
- This leads to the formation of the neural plate which infolds to form the neural folds and grooves. The neural folds eventually fuse to form a tube.
What is Spina Bifida?
Failure of fusion of the neural folds to form the neural tube. So there is incomplete closing of the backbone and membranes around the spinal cord.
What do you understand by the term "Neural Crest"
- A population of transient multipotent cells found within the neural folds that give rise to a diverse lineage.
- They originate along the length of the embryo.
- They separate and migrate to different parts of the embryo from the cranial to caudal parts.
List 5 things that the neural crest cells give rise to in the oro-facial region.
- Dermis, smooth muscle and fat
- Facial skeleton
- Brachial (pharyngeal) arches
- Odontoblasts of developing teeth
- Cartilage (nose, middle ear and face)
Give examples what neural crest cells give rise to in the rest of the body.
Cranial nerve ganglia
C cells of the thyroid gland
Dermis of the face and neck
Arachnoid and pia mater
What is the fate of the endoderm layer?
Lining of the lungs, parts of the tongue, urethra and associated glands, bladder and digestive tract.
Fate of mesoderm layer?
muscles, bones, lymphatic tissue, spleen, blood cells, heart, lungs and reproductive and excretory systems except elements of the neural crest.
Fate of ectoderm?
Skin, nails, hair, lens of eye, lining of the internal and external ear, URT, elements of the oral cavity, tooth enamel, anus, pituitary gland, mammary gland. Neural crest.
Good Video links
https://www.youtube.com/watch?v=bIdJOiXpp9g (2nd week)
https://www.youtube.com/watch?v=3AOoikTEfeo (3rd week)
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