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Embryonic Development

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 17. Acrosomal Reaction. Occurs in order for sperm to fertilize the egg

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Embryonic Development

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  1. Embryonic Development AP Biology Unit 6

  2. Fertilization • The joining of sperm and egg  creates a zygote • Occurs in the fallopian tube (oviduct) • Cleavage starts after fertilization Slide 2 of 17

  3. 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 17

  4. 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 17

  5. General Stages of Development • Cleavage • Blastula (Blastocyst) Formation • Gastrulation • Organogenesis (including neurulation) Slide 5 of 17

  6. Cleavage • 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 17

  7. 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 17

  8. Gastrulation • Stage in which cells move to form tissue layers and body axes. • Animation Slide 8 of 17

  9. Gastrulation • 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 17

  10. Gastrulation • Ectoderm (outer most layer) • Becomes nervous system, skin, hair, nails, sweat and oil glands • Archenteron = earliest stage of digestive tract Slide 10 of 17

  11. Organogenesis • Neurulation (initiation of the nervous system) occurs at the beginning of organogenesis Slide 11 of 17

  12. 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 17

  13. Neurulation • Notochord = mesoderm that supports the developing embryo  becomes vertebrae Slide 13 of 17

  14. 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 17 Image taken without permission from http://medicalimages.allrefer.com/large/spina-bifida-degrees-of-severity.jpg

  15. Fetal Surgery for Spina Bifida

  16. 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 16 of 17

  17. Development at a Cellular & Molecular Level • Normal embryonic development regulated by • Expression of genes for tissue-specific proteins • Induction: nearby cells release signal molecules that trigger a specific path of development in other cells • Hox genes: control the expression of many other genes  involved in pattern/sequence development. • Apoptosis: certain cells undergo cell death to form structures like fingers and toes.

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