Summary: Samenvatting

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• 1 Cleavage

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• What are the two main patterns of cleavage?

  Holoblastic (complete) and meroblastic (incomplete) cleavage.

• What are the 4 forms of holoblastic (complete) isolethical (sparce, evenly distributed yolk) cleavage?

  1. Radial cleavage (stekelhuidigen (zoals see urchin) & amphioxus (=lancetvisje)
  2. Spiral cleavage (annelids (=ringwormen), mollusks (=weekdieren), flatworms) 
  3. Bilateral cleavage (tunicates (=manteldieren))
  4. Rotational cleavage (zoogdieren, nematoden)

• What are the types of meroblastic cleavage?

  Telolethical (dense yolk throughout most of cell)
  1. Bilaterial cleavage (cephalopod molluscs (=inktvis))
  2. Discoidal cleavage (fish, reptiles, birds)
  
  Centrolecithal (yolk in center of egg): superficial cleavage (most insects)

• 2 Gastrulation and blastulation

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• What are the three germ layers?

  Ectoderm, mesoderm and endoderm

• What are the 5 types of morphogenic rearrangements and explain them

  Invagination: infolding of a region of cells
  involution: inward movement of an expanding outer layer
  ingression: migration of individual cells from the surface layer into the inferior of the embryo
  Delamination: splitting of one cellular sheet into two more or less parallel sheets. 
  Epiboly: movement of epithelial sheets, usually of extodermal cells, that spread as a unit to enclose the deeper layers of the embryo.

• 3 Neurulation

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• What will eventually form from endoderm?

  The digestive and pulmonary system

• What will eventually form from mesoderm?

  Bones, some of the inner layers of the skin, urinary system, reproductive system and muscles (including cardiac muscle)

• What are the steps in the neurulation process?

  Formation neural plate - folding (neural fold) - elevation neural crest (neural groove) - convergence (neural folds apposing) - Neural tube - migration neural crest cells.

• What types of mesoderm are there and what are they responsible for?

  Intermediate mesoderm: kidney and gonads (geslachtsklieren)
  Chorda-mesoderm: notochord
  paraxial mesoderm: head & somites --> somites form sclerotome (cartilage), syndrotome (tendons), myotome (skeletal musle), endothelial cells and dermatome (dermis, skeletal muscle)
  Laterial plate mesoderm: splanchnic (circulatory system), somatic (body cavity) & extraembryonic

• 4 Cell specification, determination and morphogenesis

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• Explain the term 'cell specification'

  During early development, an embryonic cell is set on a path of molecular changes. It becomes comitted to certain fates, and passes through the following stages: specification --> determination --> differentiation.
  Cell specification is a term for the phenomenon of the embryonic cell being capable to differentiate autonomously when it is placed in a neutral environment. This means that there is something instinsic to the embryonal cell that makes sure it can specify.