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16 Cards in this Set
- Front
- Back
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Describe the formation of the morula |
A fertilised ovum has a diploid no. of chromosomes so once 2nd meiotic division has been completed, stage of cleavage begins
Series of rapid mitotic divisions in which the ovum divides over 3 says resulting in a 16-cell embryo. Sphere of cells called morula. Each is pluripotent so can dif. to cells of any lineage |
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Describe the formation of the blastocyst |
The morula cavitates, forming the blastocyst:
the outer layer - trophoblast polarised inner cell mass - embryoblast blasteocoele cavity |
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Describe the process of blastocyst implantation |
Attaches to endometrium and invades wall by burrowing inside |
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Describe the process and result of neurulation |
Process by which the ectoderm gives rise to the neural tube and crests of developing brain & spinal cord. Ectoderm gives rise to neuroect.
~day 19 cranial end of primitive streak, underlying mesoderm & notochord induce ectoderm to form neural plate -> rounds up to form neural folds
~day 20 neural plate expands at caudal end, deepens to form neural groove from which neural tube forms (cran-25&caud-27 neuropore) |
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Defects that can occur during neural tube folding when doesn't fuse/somites do not entirely engulf |
Spina Bifida Occulta (Hidden) - Unfused vertbral arch gives bifid appearance to spine. Most common, often undiagnosed - Tufts of hair a clue. Normally harmless.
Spina Bifida Cystica - Meningocoele (type I): cystic swelling of the dura and arachnoid mater/meninges protrudes through vertebral arch defect - Myelomeningocoele: spinal chord protrudes through with meninges - Rachischiss: no meninges formed so raw neural tissue exposed on surface (neural plate spread out onto the surface)
Anencephaly: rostral end of neural tube fails to close - Mero-anencephaly: rudimentary brain tissue and partial formation of cranium - Holo-anencephaly: most common type where brain is completely absent - Cranio-rachischiss: anencephaly and bony defects in spine, as well as exposure of neural tissue as vault of skull fail to form
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Major events in Week 1 |
Fertilised ovum (zygote) undergoes mitosis
Formulation of morula
Formation of blastocsyt
Implantation |
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Major events in Week 2 |
Implantation
Bilaminar disc formation
Amniotic and yolk sacs |
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Major events in Week 3 |
(first missed period day 15)
Primitive streak formation (day 15) Gastrulation (Tri-laminar disc formation) Neural plate and groove formation/folding Somite formation |
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Major events in Week 4 |
Heart formation (beats) Eye and ear primordia Pharyngeal arches Neural tube formed and folds fused Upper limb growth begins |
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Major events in Week 5 |
Further eye development Feet and hand plates present Face begins to form Brain vesicles form ower limb growth begins |
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Major events in Week 6 |
Oral & Nasal cavities & upper limb form
External acoustic meatus forms
Digits begin to appear
Gut rotation |
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Major events in Week 7 |
Genital development starts
External ear forms
Palate forms
Gut rotation complete and return to abdominal cavity |
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Week 8 |
Most major organ systems formed
Human features recognisable
Heart functional |
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Origin of neural crest cells |
Found on lateral edge of the neural fold when neuroectoderm cells are continuous with the surface ectoderm. They detach from rest of neural groove before tube forms -> discrete aggregations of neural crest cells
Migration begins around 20-27 days when the neural tube is closing |
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Migration and tissue differentiation of neural crest cells from TRUNK region |
From TRUNK region of tube: - Migrate dorsally through epidermis to the ectoderm to form melanocytes in the skin and hair folllicles - Migrate ventrally to the anterior part of each somite to form sensory ganglia, sympathetic and enteric neurones, Schwann cells and adrenal medullary cells. |
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Migration and tissue differentiation of neural crest cells from CRANIAL folds |
From CRANIAL folds: Contribute to the craniofacial skeleton and connective tissues, cranial nerve ganglia and melanocytes |
