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Summary Human Embryology and Developmental Biology – Lecture 1
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Human Embryology and Developmental Biology – Lecture 108-02-2018
The cycle of life:
- Embryonic stage Fertilization of the oocyte birth
- Juvenile stage Growth metamorphosis larva
- Adult stage Fertile individuals reproduction
- Ageing stage Growing old physiological death
All cell movements/cleavages are highly conserved.
Animal models:
- Handy to investigate genes, processes, etc.
- Easy to breed, fast life cycle, etc.
The principles of development are highly conserved amongst the animal kingdom
(from organism to organism).
- Are able to phenocopy human diseases precisely
Examples of animal models:
- Xenopus laevis (kikker)
- Brachydanio rerio (zebrafish)
- Chicken
- C. elegans
- Drosophila Melanogaster
Developmental stages:
1. Cleavage
Fertilized egg (zygote) mitosis blastomeres
Volume of the cells stay the same, the cells only get smaller and smaller after the
occurring cleavages. The cells do not grow in size yet.
2. Blastulation
Ordening of blastomeres, formation of blastocoel.
3. Gastrulation
Morphogenic movements of blastomeres.
, Formation of 3 embryonic germ layers;
Endoderm, ectoderm, mesoderm.
Everything develops from the 3 embryonic germ layers.
4. Organogenesis
Differentiation of the 3 embryonic germ layers formation of organs.
Cleavage:
The cell cycle takes longer as development proceeds The further the cell cycle,
the slower cleavages occur.
Ootypes and patterns of cleavage (distribution of egg yolk):
Ootypes:
- Isolecithal (iso = equal, uniform)
- Mesolecithal (meso = middle)
- Telolecithal (telo = end)
- Centrolecithal (centro = center)
Patterns of cleavage:
Main patterns:
- Holoblastic (holos = complete, blastos = germ)
- Meroblastic (meros= part)
Specific patterns:
- Radial
- Spiral
- Discoidal
- Superficial
Isolecithal ootype is common in mammals and nematodes.
Centrolecithal ootype is common in most insects.
The first two cleavages of blastomeres occur from animal to vegetal pole.
Big: macromeres
Between: mesomeres
Tiny: micromeres
A blob of cells with cavity in the middle: blastocoel. The cavity appears, due to re-
organization of the blastomeres, during blastulation.
Unequal/displaced radial cleavage: above equator.
Discoidal meroblastic cleavage: on top of the yolk. (e.g. zebrafish).
Xenopus (kikker) has a holoblastic cleavage pattern.
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