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Embryonic Development. AP Biology Unit 6. Fertilization. The joining of sperm and egg  creates a zygote Occurs in the fallopian tube (oviduct) Cleavage starts after fertilization. Slide 2 of 15. Acrosomal Reaction. Occurs in order for sperm to fertilize the egg

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embryonic development

Embryonic Development

AP Biology

Unit 6

  • The joining of sperm and egg  creates a zygote
  • Occurs in the fallopian tube (oviduct)
  • Cleavage starts after fertilization

Slide 2 of 15

acrosomal reaction
Acrosomal Reaction
  • Occurs in order for sperm to fertilize the egg
  • the sperm releases digestive enzymes from the acrosome in its head to digest into the egg.
  • When the sperm and egg membranes come into contact, they fuse and allow the sperm to enter.
  • receptors on the egg membrane that are species-specific (usually) and ensure correct fertilization.

Slide 3 of 15

sperm entry into egg
Sperm Entry into Egg
  • Once the sperm enters the egg, many different things happen
    • Egg blocks any more sperm from entering
    • Egg is metabolically activated to start development (DNA Replication, more Protein Synthesis and Cellular Respiration)
    • Egg and sperm nuclei fuse = diploid nucleus

Slide 4 of 15

general stages of development
General Stages of Development
  • Cleavage
  • Blastula (Blastocyst) Formation
  • Gastrulation
  • Organogenesis (including neurulation)

Slide 5 of 15

  • Rapid cell division
  • Not much time for cells to grow in between divisions
  • Cells at this stage are totipotent stem cells—can become any kind of cell.

Slide 6 of 15

blastula formation
Blastula Formation
  • A blastula (hollow ball of cells) forms when some of the cells in the center pull away from one another to form a fluid filled cavity in the center (blastocoel)
    • Also called a blastocyst
    • It is at this stage when it implants into the uterus

Slide 7 of 15

  • Stage in which cells move to form tissue layers and body axes.
  • Animation

Slide 8 of 15

  • Endoderm (inner most layer)
    • Forms digestive tract, respiratory tract, pancreas liver
  • Mesoderm (middle layer)
    • Forms muscle, bones, excretory system, circulatory system, most of reproductive system

Slide 9 of 15

  • Ectoderm (outer most layer)
    • Becomes nervous system, skin, hair, nails, sweat and oil glands
  • Archenteron = earliest stage of digestive tract

Slide 10 of 15

  • Neurulation (initiation of the nervous system) occurs at the beginning of organogenesis

Slide 11 of 15

steps of neurulation
Steps of Neurulation
  • Neural plate forms as ectoderm thickens and flattens on the posterior side.
  • Edges of the neural plate move towards each other to form the neural tube
  • The edges of the plate fuse together to form a tube
  • The neural tube detaches from the rest of the ectoderm

Slide 12 of 15

  • Notochord = mesoderm that supports the developing embryo  becomes vertebrae

Slide 13 of 15

neural tube defects
Neural tube defects
  • Anencephaly (folds don’t fuse at the top forebrain can’t form properly)
  • Spina Bifida (folds don’t fuse at the bottom  can cause major spinal problems as amniotic fluid flows over the open area)

Slide 14 of 15

Image taken without permission from http://medicalimages.allrefer.com/large/spina-bifida-degrees-of-severity.jpg

development in mammals
Development in Mammals
  • As a mammalian fetus develops, it also forms a series of membranes that surrounds the embryo
  • These membranes (like the amnion) function to help nourish and protect the embryo.
  • The formation of these membranes is thought to be a evolutionary adaptation to living on land

Slide 15 of 15