Bio 225- Embryology

• Telolicithal


  large amount of yolk on the bottom of the egg
• somites


  Paired blocks of mesoderm just lateral to the notochord of a vertebrate embryo.
• Notochord


  A rod of tough, flexible material that runs the length of a creature's body, providing the majority of its support

  
• neural tube


  an embryonic structure with subdivisions that correspond to the future forebrain, midbrain, and hindbrainwhere the neural folds have fused

  
• tadpole stage

  
• neural fold stage of frog

  neural folds join to form the neural tube

  
• Frog Blastula

  
• frog embryo

  Lots of yolk, Uneven holoblastic cleavage withanimal pole (darker colour) and vegetal pole(paler). Gray crescent is opposite to the site ofsperm entry. Forms due to cytoplasm rotationcausing mixing from the two poles. Any cell fromthe first cleavage that receives a bit of the graycrescent can become a full frog embryo. Frogembryos have no primitive streak. Instead,gastrulation begins at the dorsal lip ofblastopore (forms at site of gray crescent).

  
• Deuterostomes

  Animals in which the blastopore becomes the anus ex: Sea stars, and vertebrates

  
• protostomes


  blastopore becomes mouthWorms, insects, and snails

  
• holoblastic cleavage


  A type of cleavage in which there is complete division of the egg, as in eggs having little yolk (sea urchin) or a moderate amount of yolk (frog).
• Mesolecithal


  moderate amount of yolk at vegetal pole
• vegetal pole


  The portion of the egg where most yolk is concentrated; opposite of animal pole.

  
• animal pole


  The portion of the egg where the least yolk is concentrated; opposite of vegetal pole.

  
• coelomic vesicles


  forming mesoderm (muscular, skeletal, cardiovascular, and reproductive systems derived from mesoderm)

  
• archenteron


  lined with endoderm (forming lining of digestive and respiratory systems)

  
• Ectoderm


  forms skin and nervous system

  
• gastrula


  an embryo at the stage following the blastula, when it is a hollow cup-shaped structure having three layers of cells.

  
• Blastopore

  opening of the archenteron. this will become the anus.

  
• Blastula

  cytoplasm of original egg divided up into many smaller cells (blastomeres) which can move around during gastrulation

  
• 2 cell stage

  holoblastic cleavage (entire zygote cleaves into two similar sized cells since it has a small amount of yolk equally distributed (isolecithal) throughout cytoplasm)

  
• Zygote

  Fertilization membrane

  
• The blastocyst consists of the inner cell mass (ICM) and outer layer of cells called trophoblast.
• Trophoblast is derived from the trophectoderm, which forms the placenta.
• The embryonic disc develops into three layers: ectoderm, mesoderm, and endoderm.
• Gastrulation involves the formation of three germ layers: ectoderm, mesoderm, and endoderm.
• Ectoderm gives rise to skin, nervous system, hair, nails, teeth, lens of eye, and glands that secrete sweat and mammary gland secretions.
• Ectoderm gives rise to skin, nervous system, hair, nails, teeth, and glands.
• Endoderm gives rise to lining of digestive tract, lungs, liver, pancreas, thyroid, parathyroid, thymus, and urinary bladder.
• Mesoderm gives rise to muscle tissue, bone, blood vessels, kidneys, adrenals, urogenital ducts, heart, pericardium, pleurae, and peritoneum.
• During gastrulation, the epiblast folds over itself to form the primitive streak, where the notochord will be formed.
• Neural crest cells are formed during gastrulation and migrate throughout the body to form various structures such as pigment cells, cartilage, bone, smooth muscle, peripheral nerves, and some parts of the brain and spinal cord.