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Download Development - MSU Denver
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Development Fertilization • The haploid sperm joins with the haploid egg to make a diploid zygote or embryo • Fertilization occurs in the oviduct • Sex of baby is determined at the time of fertilization Sperm fertilizing egg Fertilization • Fraternal twins are the result of 2 different eggs fertilized by 2 different sperm • Identical twins are the result of a single egg/sperm that subsequently splits into twins. These twins are genetically identical. • Ectopic pregnancy is a pregnancy in an abnormal site, usually when the fertilized egg gets stuck in the oviduct Cleavage • Day 1-4 pregnancy • Mitosis division that occurs in oviduct as embryo moves towards the uterus Cleavage Blastocyst • Day 5 • In uterus • Rearrangement of cells into outer cells destined to become the placenta • Inner mass of cells destined to become the baby Blastocyst • Implantation occurs on day 7-8 • Blastocyst burrows its way into mom’s endometrium for nourishment & protection • Embryo secretes HCG, Human Chorionic Gonadotropin, that serves to keep the corpus luteum making estrogen and progesterone. HCG • HCG is the basis for the do-it-at-home pregnancy test • Urine test • Highly accurate Gastrulation • Week 2 pregnancy • Germ layers form, which are layers of cells destined to become certain organs depending on their position Gastrulation Germ Layers • Ectoderm is outer layer destined to become nervous tissue and skin. • Mesoderm is middle layer destined to become skeleton, muscles, heart, blood, vessels…. • Endoderm is inner layer destined to become lungs and digestive structures. Cross section of embryo Neurulation • 3 weeks • Embryo is 2mm long • Neural tube forms resulting in brain and spinal cord Organogenesis • Week 4 • All major organs, arm/leg buds, have begun their formation First Trimester • Most organ development occurs during the first trimester (3 months) of pregnancy • This is the time when the embryo is most susceptible to damage. Embryo vs. Fetus • By the end of the second month, the embryo looks distinctly human, and is now called a fetus Growth • Second and third trimesters are primarily growth stages Placenta • Begins development at 4 weeks and becomes fully functional by 12 weeks • Provides nourishment and oxygen for fetus, removes fetal waste and makes estrogen and progesterone Placenta • Comprised of maternal tissue – the endometrium • Comprised of fetal tissue – the chorion Placenta • Umbilicus is comprised of arteries/vein that link the fetus to the placenta Fetal Amnion • Sac surrounding fetus • Filled with amniotic fluid that provides protection, facilitates movement, and keeps a warm temperature • An amniocentesis is a sampling of this fluid checking for chromosomal and genetic abnormalities. Gestation • = pregnancy • 9 full months; three trimesters Childbirth • Labor occurs when contractions are regular and occurring about every 30 min. • As contractions get stronger, amnion is ruptured and amniotic fluid is released (“water” breaking) Childbirth • Estrogen causes minor contractions forcing the baby’s head against mom’s cervix • Stretching of the cervix causes the release of OXYTOCIN which causes large contractions • Oxytocin is made in the hypothalamus but released from the pituitary Note the positive feedback cycle Childbirth • Relaxin, made by the placenta, relaxes cervix and birth canal Childbirth • As the contractions occur even after the baby is delivered, the afterbirth (placenta) is passed.
