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Fertilization and Development Be 21 - Be 30 Cruz, Canlas, Daroya, Estabaya, Hubilla, Jimenez, Patubo, Ramirez, Regala, Tuppil Theories… • Preformation – sperm already has all the organs even before fertilization • Epigenesis – animal develops from a shapeless egg Fertilization How in the world does it occur??!! Fertilization • Conception (start of gestation – carrying of offspring in womb) • Joining of egg and sperm (zygote) • Sperm Capacitation • Acrosomal Reaction • Cortical Reaction Sea Urchins • External fertilization • Sperm Capacitation – display hyperactivated motility • Prepares sperm for Acrosomal reaction Sea urchins • Acrosome – vesicle at the tip of sperm; releases contents by exocytosis • Acrosomal reaction – release of hydrolytic enzymes • Acrosomal Process – elongated structure that penetrates jelly coat of egg • Has proteins that adhere to vitelline layer (has protein receptors) of egg Sea Urchins Fast Block to Polyspermy • Spem and egg membranes fuse • Neuron-like electrical response from plasma membrane of egg • Sodium ions flow into the egg – Membrane potential • Depolarization Cortical Reaction • • • • Changes in cortex of egg (outer part) Egg’s ER releases Ca2+ into cytosol High concentration of Calcium ions Cortical granules fuse with plasma membrane – Content released in perivitelline layer (osmotic gradient) • Fertilization membrane – hardened vitelline layer (slow block to polyspermy) Sea Urchins Fertilization in Mammals • Egg cloaked in follicle cells • Zona Pellucida – like jelly coat in sea urchins • Has protein receptors (ZP3) for sperm head • Sperm releases acrosome by exocytosis and fuse membrane with egg • Depolarization – fast block to polyspermy • Cortical reaction – hardens zona pellucida Fertilization in Mammals Fertilization in Mammals Fertilization in Mammals • Unlike sea urchin, sperm and egg nucleus don’t fuse immediately • Envelopes of both nuclei disperse • Chromosomes from two gametes share common spindle apparatus during first mitotic division After fertilization…. PREGNANCY??!! During Pregnancy… • Mother’s organs get squished • Heart and lungs work harder to support both mother and baby • Stomach rotated about 45 degrees so can only hold small amounts of food • Baby needs food First Trimester • Cleavage(after 36 hours)- series of mitotic divisions • Embryo from this point until after nine weeks • Organogenesis (formation of organs) • Blastocyst(after 5 days)- fluid-filled • Trophoblast- outer layer of cells (membrane systems) • Inner cell mass- inner cells (embryo and fetus) • Implantation in the endometrium (lining of uterus) • Trimester – in three parts First Trimester • 4 weeks – stop of menstrual period • 5 weeks – beating heart; working placenta and umbilical cord • Waste and nutrient transfer • Human chorionic gonadotropin- hormone checked in pregnancy test and to detect fetal disorders • 7 weeks – own blood cells; start moving First Trimester • 9 weeks – Fetus (until birth) • 9 weeks – all organ, muscle and nerves are in place and functioning • 10 weeks – fingers and toes • 11 weeks – functioning liver, kidneys, intestines, brain and lungs • 12 weeks – vocal chords, brain, pain, urine, thumb sucking Second Trimester • • • • • • 13 weeks – fingerprints 14 weeks – first hair 15 weeks – taste 16 weeks – grasp, kick, somersault 18 weeks – genitals 20 weeks – hear and recognize mom’s voice Second Trimester • 22 weeks – hear, fingernails • 26 weeks – touch Third Trimester • 27 weeks – open eyes • 31 weeks – preference in music • 38-40 weeks – ready to go out (end of gestation) Baby is foreign… right??? Trophoblast • Thought of as a shield for the embryo • Has composition that can trigger immune response from mother • Counteract attacks from mother’s immune system – Block action of IL-2 – If too subtle, can cause abortion BABY DELIVERY!!! Delivery • Parturition (birth) happens when certain hormones trigger contractions (labor) • Cervix dilates after thinning • Umbilical cord - connection of baby to mother (BVs, respiration, etc.) – Cut after delivery • Placenta removed What happens when baby is born?? MILK!! • Lactation – postnatal care • Decrease levels of progesterone – Prolactin secretion • Oxytocin – control mammary glands to secrete milk Sources • http://www.vivo.colostate.edu/hbooks/pathphys/r eprod/fert/fert.html • http://www.baby2see.com/development/first_trim ester.html • http://www.baby2see.com/development/second_ trimester.html • http://www.baby2see.com/development/third_tri mester.html • Campbell, N.A, et al (1999). Biology. 5th edition. N.Y.: Pearson Edication, Inc. – Bejamin Cummings. • http://www.medterms.com