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Development

Dive into the intricacies of human fertilization, ejaculation, ovulation, and the early stages of development, including sperm structure, fertilization process, twins, implantation, and embryo formation. Explore key concepts and stages explained in detail.

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Development

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  1. Development

  2. Ejaculationthe release of semen -Approximately 2 teaspoons (10 mL) -280 million sperm -Most die in the vagina within minutes after ejaculation -Once they move through the cervix into the uterus, they can survive longer, up to 5 days. -Outside the body sperm will die within minutes.

  3. SPERM STRUCTURE • Head • contains nucleus • an organelle “cap” called an Acrosome (contains digestive enzymes) • Tail • flagellum – whipping motion provides motility. • Base of tail contains a coiled mitochondrion to provide power for movement.

  4. Capacitation: readying the sperm • Sperms cannot fertilize oocytes when they are newly ejaculated. • The acrosome is not active • Chemicals in the uterus cause the acrosome to become active

  5. Ovulation- Secondary oocyte (nuclues contains 1/2 the chromosomes) Folicle cells (make up the corona radiata) Zona pellucida (protects the “egg”)

  6. At the cervix • Helping the sperm: • At ovulation, the mucus that normally covers the opening of the cervix thins out • This allows sperm to pass through the cervical opening. • It is also thought to help guide the sperm

  7. Stage 1 of fertilization: • Sperm come in contact with the follicle cells of the corona radiata • Enzyme action from multiple acrosomes help sperm pass through • Flagella action also aids corona radiata penetration

  8. Stage 2 of fertilization: • Penetration of the zona pellucida around the oocyte: • Acrosomal enzymes: cause lysis of the zona pellucida • Once sperm penetrates zona pellucida, the zona reaction occurs: • This reaction makes the zona pellucida impermeable to other sperms. • Zona pellucida begins to harden • When more than one sperm manages to enter the ovum (dispermy = 2; triploidy = 3), the fetus nearly always aborts.

  9. Corona radiata Figure 7.8

  10. Stages 3 of fertilization: • Fusion of plasma membranes of oocyte and sperm • Causes action potential of the seconadary oocyte membrane • 2nd meiotic division of oocyte is completed • The secondary oocyte was previously arrested in metaphase of the 2nd meiotic division, and now forms the mature ovum and another polar body. • https://www.youtube.com/watch?v=_5OvgQW6FG4

  11. Twins: still 1 sperm per egg • Monozygotic (monoovular): • A fertilized, single egg splits into two developing zygotes at a very early stage. • Identical twins; same sex. • When the split takes place determines if they share the same placenta or same sac or both. • Dizygotic (polyovular): • Result from the fertilization by two sperm of two separate ova that have reached maturation at the same time. • Not identical twins; can be different sexes • Incidence increases with age of the mother

  12. Day 2 - 3 • Cleavage begins Cleavage is cell splitting • The cells continue “splitting” by mitosis • The size of the embryo does not change, but the number of cells does • This is all occurring in the oviduct • Zona pellucida is hard

  13. MORULA • Cleavage stage ends • now called a morula (Latin for raspberry) • It is a solid ball of cells (about the size of the tip of your pen) • It will continue to be called a morula as long as it is a “solid ball” Day 4 - 5

  14. Blastocyst • The Morula hollows out as cells move outward. • The inside fills with liquid (the liquid is produced by the cells) • Cells are too many and too small to be seen at this point • This is now a blastocyst Early blastocyst day 5

  15. Inside the Blastocyst Parts of the blastocyst: • Inner Cell mass: will become develop into the child • Blastocoel: empty space of liquid is inside (-coel means empty space) • Trophoblast: outer layer of cells which will become membranes

  16. Human Hatching The blastocyst will “hatch” from the hardened zona pellucida .1 - .2 mm Day 6-7

  17. Implantationembryo attaches to uterine lining • Embryo produces pregnancy hormone (hCG)(human chorionic gonadotropin ) • Found in blood and urine Approximately 8-9 days after fertilization

  18. Hormonal Control of Pregnancy • Initially the trophoblast cells secrete Human Chorionic Gonadotrophin (HCG) • Functions of HCG: • Prevents the degeneration of the corpus luteum • Stimulates the growth of the CL. • Increase secretion of both estrogen and progesterone • Prevents mestruation

  19. Small chorionic villa (finger-like projections) grab on to the endometrium

  20. These projections make contact with the maternal blood supply, becoming the pipeline through which the fetus derives nutrients and oxygen, and rids itself of carbon dioxide and wastes. The placenta has not formed yet.

  21. The process of: Gastrulation • A hole forms at the top of the blastocyst near the inner cell mass • This hole is called the blastopore • Cells begin to migrate inward forming layers • The blastocyst is now becoming a gastrula

  22. Cell to cell interaction lines up the cells properly • 3 layers are formed Ectoderm Mesoderm Endoderm

  23. Differentiation • Cells are now committed • Each layer will only become what it has been programmed to become (by your DNA)

  24. Neurulation At 19 dys – photo about 25 dys: 2.5 mm • Brain and spinal cord are forming • The skull will not completely close until months after birth • WHY? • What do we call these spots?

  25. Brain regions can be found • Neural groove, which will become the spinal column • Heart begins to develop • Hematopoiesis begins • https://www.youtube.com/watch?v=wnnhMZtCvnQ Neurula Day 28 2-3.5 mm

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