2. The Human Body: Part 2 The Human Body: Part 2 An Every Day Miracle

3. First Stages of Development Fertilization: Occurs: in FALLOPIAN TUBE (within 24 h of ovulation) Only a few dozen of the best swimmers make it!! When the sperm reaches the egg, the acrosome releases enzymes to digest the jelly-like coating surrounding the egg The sperm then uses it’s tail to move into the egg

4. Fertilization Gametes (n) fuse to form a zygote (2n) Zygote = first SINGLE cell of new life Sperm nucleus 1n Egg nucleus 1n ZYGOTE 2n

5. Early Stages of Development ZYGOTE

6. Cell Cleavage Zygote undergoes mitotic divisions (cleavage) to form ball of cells called morula (16-32 cells) Morula develops into blastocyst (day 6) Zygote (2n) Morula (2n) Blastocyst (2n)

7. First Stages of Development Blastula (aka Blastocyst): a cavity opens up in the morula (space inside called “blastocoel”)  trophoblast: outer layer of blastocyst  Some cells will later develop into chorion, then placenta  Some cells develop into the amnion  inner cell mass: will develop into embryo  blastopore: indentation on blastula which allows gastrulation

8. From Ovulation to Implantation

9. Day 1: First Cleavage – cell divides by mitosis Day 4: 16 – 32 cell stage. Ball of cells is called a morula. Day 5: the cells of the morula begin to move around to form an inner and outer layer of cells. The outer layer of flattened cells (chorion) are important for implantation in the uterine lining. Day 6: The two layers of cells arrange themselves around a hollow fluid filled cavity called the blastocoel, the actual cell mass is called a blastocyst.

10. From Ovulation to Implantation Day 7: Implantation - The blastocyst, by means of villi and enzymes secreted by the chorion (a membrane that forms around it), implants itself in the uterine wall, resulting in pregnancy (gestation). The chorion secretes hCG, which stimulates the corpus luteum to produce progesterone and estrogen for the first 3 months. Stem cells from the blastula are undifferentiated and can be used for stem cell research.

11. zygote morula blastocyst chorion

12. Layers of the Blastocyst Outer layer of blastocyst forms 2 membranes: chorion- produces hCG amnion - fluid filled sac protecting fetus

13. How to remember the stages? Zebras Make Better Guacamole Every Friday Zygote – Day 0 (Sperm + egg) Morula – Day 4 (16 – 32 cells) Blastocyst – Day 6 **Implantation Outer layer (chorion) secretes hCG and forms placenta

14. How to remember the stages? Zebras Make Better Guacamole Every Friday Gastrula – Day 7 - 3 germ layers – ectoderm, mesoderm, endoderm. Neurulation – formation of neural tube which will form CNS. Embryo – Day 10 - chorion starts to form the placenta Fetus – week 8 – called fetus because all major organ systems have started to develop

15. Ectopic Pregnancy: Faulty Implantation In an ectopic pregnancy, a fertilized egg has implanted outside the uterus, usually in the fallopian tube. Severe bleeding and possible death of the mother can result from this type of pregnancy

16. Pregnancy Tests Outer layer of the blastocyst (the chorion) starts to secrete hCG. T his causes morning sickness & is the hormone measured in a pregnancy test! Pregnancy test: tests for the presence of hCG in the urine (sometimes the blood). Remember hCG: similar to LH – keeps corpus luteum secreting progesterone & estrogen!! Later on, the placenta secretes sufficient estrogen and progesterone

17. How can a miscarriage occur? For first 3 months progesterone comes from mother Baby starts making it’s own after 3 months If mom stops progesterone and baby does not start… –Miscarriage occurs

18. Gastrulation (~Day 7) Gastrulation is the process in which the inner cell mass of blastula turns into 3 germ layers (embryonic tissues) – the ( ectoderm, mesoderm, endoderm) embryo now called gastrula

19. Gastrulation (~Day 7) Cells begin to differentiate (change) to form specific organ systems!

20. PBS Nova: Miracle of Life

21. The Embryo Takes Shape

22. 3 Germ Layers Ectoderm (outer): skin(epidermis), hair, nails, nervous system, eye, ear Mesoderm (middle): muscle, bones, gonads, kidneys, outer layer of digestive & respiratory tracts, circulatory system Endoderm (inner): thyroid gland, liver, pancreas, inner layer of digestive & respiratory tracts, bladder How to remember? Mesoderm My Big Green Kangaroo Drives Race Cars Endoderm Three Lions Paddle Down Blue River

23. Neurulation: formation of neural tube  develops into brain and spinal cord Becomes the primative curve of the spine

24. http://www.pbs.org/wgbh/nova/sciencenow/0305/03.html

25. Summary of Events After Implantation Days 7-10 Days 10-14 Days 15-21 Day 21 Week 4 Weeks 5 – 8 Gastrulation begins – major cellular reorganization into the three germ layers “Gastrula” stage is when different genes will be turned on to express different organs in the later stages of the pregnancy Pregnancy fully established Amniotic cavity forms Yolk sac forms Embryo forms from embryonic disc Chorion starts to form the placenta Emergence of the body plan “Primitive streak” starts to form (at site of Gastrulation) becomes mesoderm Neural Groove forms (future brain and spinal cord) Heart begins to beat Eyes, ears and lower limbs begin to develop Teeth, palate, external genitalia begin to develop

26. After week 8/9, embryo is called a fetus because all the major organs have started to develop.

27. Extra-Embryonic Membranes: formed after implantation 1. Chorion: outer membrane of blastula fetal contribution to placenta secretes hCG until 2nd trimester (first 3 months) gas/nutrient/waste exchange 2. Amnion: inner membrane of outer layer of blastula becomes fluid-filled sac that protects embryo from infection and impact and temperature fluctuations

28. Extra-Embryonic Membranes: formed after implantation 3. Allantois: forms the foundation of the umbilical cord Becomes part of the bladder 4. Yolk sack: in other animals, provides nutrients Small in humans (forms blood cells)

29. Extra-Embryonic Membranes

30. Extra-Embryonic Membranes Practice

31. Cat Fetus  1. umbilicus,  2 amnion,  3 allantois  4 Yolk sac  5 embryo part of placenta  6 maternal part of placenta (endometrium)

32. Placenta Placenta: allows exchange of some substances between mother and fetus from mother: nutrients, oxygen, antibodies, viruses, drugs, alcohol from fetus: metabolic wastes (CO 2, urea) NO exchange of blood cells

33. Placenta formed when villi from chorion extend into endometrium not fully developed until the 2nd trimester secretes estrogen & progesterone during the 2nd & 3rd trimesters Progesterone prevents contractions Progesterone and estrogen cause growth of the endometrium

35. The Placenta The placenta will function as the: Lungs: exchange O 2 and CO 2 Small Intestine: provide nutrients Kidneys: remove nitrogenous wastes (urine)

36. Umbilical Cord Rope-like structure that forms after 8 weeks Runs from the belly button of the fetus to the placenta Contains 2 arteries and 1 vein 2 arteries carry deoxygenated blood… from fetus to mother Vein carries oxygenated blood… from mother to fetus Normally arteries carry oxygenated blood Only 2 exceptions exist…pulmonary artery & umbilical artery!!! The umbilical cord naturally has a twist to it since the veins are longer than the arteries The umbilical cord can wrap around the neck during delivery

37. Placenta Baby (fetus) Mother 2 umbilical arteries Carry CO 2, wastes… 1 umbilical vein Carries O 2, nutrients… Exchange occurs here – diffusion, active transport… maternal veins Carry CO 2, wastes… away from fetus Maternal artery Carries O 2, nutrients … to fetus Fetal Circulation Summary.

38. Umbilical Arteries (2) carrying deoxygenated blood Cervical plug (mucus) Umbilical Vein (1) carrying oxygenated blood Amniotic Fluid Placenta Chorion Important diagram to be able to label! –Be able to label the 2 umbilical arteries & umbilical vein –2 arteries are twisted around vein. Uterus Amnion Umbilical Cord

39. http://www.pbs.org/wgbh/nova/miracle/program.html