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Prenatal Development

Prenatal Development. Chapter 3: Meiosis & Development Section 3.4: Prenatal Development. What are the steps of prenatal development?. Fertilization Cleavage Implantation Gastrulation Organogenesis Embryo development (week 1-8) Fetus development (week 9-40).

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Prenatal Development

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  1. Prenatal Development Chapter 3: Meiosis & Development Section 3.4: Prenatal Development

  2. What are the steps of prenatal development? • Fertilization • Cleavage • Implantation • Gastrulation • Organogenesis • Embryo development (week 1-8) • Fetus development (week 9-40)

  3. What happens during fertilization? • Capacitation- chemicals in female body activate sperm • Oocyte secretes chemical to attract sperm

  4. What happens during fertilization? • Sperm contact corona radiata- the covering of follicle cell that is protecting secondary oocyte • Acrosome on sperm bursts and enzymes begin eating through next layer of egg called zonapellucida • Conception occurs when sperm head meets cell membrane of egg • The egg cell membrane changes its charge which prevents other sperm from entering cell. • Fertilization membrane forms- this will hold cells together when they start dividing.

  5. What happens during fertilization? • Sperm loses its tail • Egg nuclear membrane degenerates • Sperm & egg chromosomes duplicate • Sperm & egg chromosomes meet, nucleus begins reforming creates zygote

  6. What happens during cleavage? • Cleavage- period of frequent cell division (mitosis) that begins about 24 hours after fertilization • Blastomere- 2-4 cells mass • Morula- 16 cell stage. Solid ball of cells • Blastocyst- cell division continues and cells push against outer edge and form a fluid filled cyst in center of blastocyst • A group of cells called the inner cell mass will begin accumulating on one side of the blastocyst- cells are beginning to differentiate • This entire process takes about 6-7 days.

  7. What happens during implantation? • Day 7, blatocystimpants into uterine lining • Outer layer of cells (trophoblast) from blastocyst secrete human chorionic gonadotropin (hCG) • hCG prevents menstruation • This is what a pregnancy test detects in urine or blood.

  8. What happens during gastrulation? • Amniotic cavity forms between inner cell mass and the trophoblast layer • Cells in the blastocyst and inner cell mass will begin to form layers • Outer layer of cells forms ectoderm • Inner layer of cells forms endoderm • Middle layer of cells forms mesoderm • Cells in each of these layers will differentiate and have different fates.

  9. What are the cell fates of the 3 tissue layers? • Ectoderm • Skin • Nervous tissue (brain & spinal cord) • Endoderm • Digestive organs • Liver • pancreas • Mesoderm • Muscle • Bone • Reproductive organs • Kidneys • Gastrulation ends around day 14

  10. What supportive structures are forming during the first two weeks? • Chorionic villi- finger-like extensions that extend into uterine wall and come close to mom’s blood stream. • Mom and baby’s blood stream NEVER mixes but anything in mom’s blood stream can diffuse into baby’s (and vice versa) • Baby sends wastes into mom’s blood stream • Yolk sac- makes blood cells • Allantois- makes umbilical blood vessels • Umbilical cord attaches to center of placenta • Placenta- fully formed by 10 weeks; links woman to fetus & secretes hormones to maintain pregnancy & sends nutrients & waste back & forth between mom and baby.

  11. What happens during organogenesis? • The ectoderm, endoderm, and mesoderm begin forming organs • Embryo is sensitive to environmental influences such as chemicals and viruses

  12. Week 3 • Heart begins to forms by day 18 • Primitive streak forms along back of embryo. This is a primitive notochord which will become spine • Notochord induces cells of ectoderm to fold and form hollow neural tube which eventually becomes brain & spinal cord • Neural tube seals around day 20.

  13. What is a neural tube defect? • If NT does not seal, Neural Tube Defect (NTD) will form. • Ex: Spina bifida • Brain or spine is exposed • Baby paralyzed from point of exposure down • Occurs due to lack of vitamin B or folic acid • Pregnant women encouraged to take folic acid supplements/vitamins during pregnancy to prevent NTD • NTD can be detected around 15 weeks with alpha fetoprotein (AFP) blood test that detects a protein from fetus’ liver that is leaked at a fast rate • If detected and caught early enough can sometimes be corrected with in utero surgery.

  14. Week 4 • Heart begins beating around day 23 • Leg and arm buds begin to form • Blood cells form & fill primitive blood vessels • Immature lungs and kidneys develop

  15. Week 5 & 6 • Enlarged head • Apoptosis sculpts fingers and toes • Eyes open but no eyelids or irises • Gene SRY on y chromosome of a boy will begin forming male hormones that stimulate formation of male organs

  16. Week 7 & 8 • Skeleton of cartilage is formed • Embryo is about size of a paper clip • After 8 weeks it is now called a fetus.

  17. Weeks 9-12 • Body proportions equal out • Bone begins to replace cartilage • Fetus begins coordinating muscle and nerves and begins to move • Fetus sucks thumb, kicks • Urinates & defecates into amniotic sac • Breathes in amniotic fluid • Week 12 ends 1ST TRIMESTER

  18. 2nd TrimesterWeeks 13-24 • Hair • Lanugo- downy hair all over body • Eyelashes • Eyebrows • Nipples • Nails • Week 15- gender determined • Skin appears wrinkled due to lack of fat & pink with new capillary formation • Can feel distinct movement • Baby is about 9 inches long

  19. 3rd TrimesterWeeks 25-40 • Fetal brain cells grow and form numerous connections to organs • Fat forms under skin • Digestive & respiratory systems mature • Premature babies often have respiratory diseases and have difficulty digesting milk

  20. How can genetic disorders or birth defects be detected? • Chorionic villi sampling- cells are removed from chorionic villi and tested for abnormalities in number or shape of chromosomes. • Done at 10 weeks • Amniocentesis- fluid from amniotic sac is removed by needle and test for abnormalities • Done at 14 weeks

  21. How do multiples form? • Monozygotic multiples- • Identical twins • Fertilized egg splits • Twins are genetically identical • Share placenta • Dizygotic multiples- • Fraternal twins • Two sperm fertilized two different eggs • Twins are genetically different • Different placentas

  22. What are conjoined twins? • Separation of egg cell begins to occur while organs are developing. • Attachment point depends on where split was occurring & what organs were developing at the time. • Ex: Brittany & Abigail Hensel

  23. Brittany & Abigail Hensel • Dicephalic twins- have two heads • Share- liver, bloodstream, all organs below navel, 3 kidneys • Separate- neck, head, heart, stomach, gallbladder, lungs, nervous system • Parents chose not to separate b/c one child usually dies during surgery

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