HHP3115 Unit 1 Notes Chapter 3 PDF

Chapter 3 – Basic Embryology Embryology: study of the origin and development of single individuals Prenatal period includes… - Embryonic period: first 8 weeks in utero - Fetal period: remaining ~30 weeks in utero Note: there is not a direct connection between oviduct and ovary Embryonic peri...

Chapter 3 – Basic Embryology Embryology: study of the origin and development of single individuals Prenatal period includes… - Embryonic period: first 8 weeks in utero - Fetal period: remaining ~30 weeks in utero Note: there is not a direct connection between oviduct and ovary Embryonic period: first 8 weeks post-fertilization - Major events: o Organs form 3 primary germ layers o The basic body plan emerges Week 1 events: - Conception: occurs in the lateral third of uterine tube - Zygote: fertilized oocyte (one cell) o Moves towards the uterus - Blastomeres: daughter cells formed from zygote o Formed via cleavage: cell division without growth o No growth because it occurs so fast, and it would become an ectopic pregnancy if it grew too big that it had to implant in Fallopian tube - Morula: cluster of 12-16 blastomeres - Blastocyst: fluid-filled structure containing ~60 cells o Outer layer of cells (trophoblast) – becomes the extraembryonic membranes o Inner clump of cells (inner cell mass) – becomes the person - Implantation into endometrium of the uterus occurs on DAY 6 Stone baby: resulted from sperm fertilizing the egg in gap between ovary and tube (resulting in ectopic pregnancy, but this time it was viable) - It found a blood supply and grew to be 32 weeks, but there was obviously no way for it to be delivered - Died after it couldn’t be delivered - Since the genetic material was different than mom, the body calcified around it (to isolate it), and it turned into a 4 pound calcified tumor Week 2 events: - Bilaminar embryonic disk: the inner cell mass is divided into 2 sheets o Epiblast: top layer o Hypoblast: bottom layer o Amniotic sac: formed by an extension of epiblast  Outer membrane forms amnion  Inner membrane forms amniotic sac cavity  Filled with amniotic fluid o Yolk sac: formed by an extension of hypoblast  Small part of it will eventually be incorporated into our digestive tube  In other animals, it’s used as a source of nutrition. But placental mammals have a placenta to nourish us, so we don’t need it Week 3 events: - Primitive streak: epiblast cells migrate inward via a process called gastrulation o Forms the gastrula o The side of the epiblast that forms the primitive streak becomes the tail end - Gastrulation causes the 3 germ layers to be formed: o Endoderm: formed by first migrating cells (replaces the hypoblast) o Mesoderm: second group of migrating cells (lands between epiblast and endoderm) o Ectoderm: cells left at the surface, which don’t migrate inward (formed by epiblast cells) - Notochord develops from mesoderm on the cranial side o This is a straight line that basically spans from end of the primitive streak to the opposite side of the gastrula (dark blue park o Induces neurulation in overlying ectoderm - Neurulation: ectoderm starts forming the brain and spinal cord o Neural plate: ectoderm thickens o Neural groove: ectoderm folds inward o Neural tube: a hollow tube forms o Cranial part of the neural tube becomes the brain - Neural crest cells: ectoderm that breaks off during neural tube formation o Forms sensory nerve cells, ganglia, and melanocytes - Somites: bulging patterns of mesoderm next to the notochord (“paraxial mesoderm”) o Our first body segments o Become vertebrae, ribs, and axial muscles - Intermediate mesoderm: just next to the paraxial mesoderm o Becomes the urogenital system Week 4 events: - Lateral folding occurs, giving us the future gut (digestive tube) o Yolk sac pinched off o Major derivatives of embryonic germ layers: - Week 5 events: - Head is 50% of body - Upper appendages, called paddles, begin to form By end of 2nd month (8 weeks), all organs have appeared - The placenta is also fully functioning Fetal period: week 9 post-fertilization to birth - Major events: organs grow in size and complexity Beginning of 3rd month: - Head growth begins to slow, and the body increases in length - Ossification centers appear in bones - Sex will soon be able to be determined 3rd and 4th month: - Fingers, eyes, ears, etc. form - Finally resembles a human th th 5 -7 months: - Mother begins to feel fetal movement - Really begins to look like a human (fingernails, eyebrows, etc. are being formed) - Still not viable to survive outside the womb, because the lungs lack surfactant (a detergent that breaks up water tension in alveoli, allowing them to remain inflated) -At around 22-24 (6 months) weeks the fetus could survive outside the womb 8 and 9th month: th - Fetus usually rotates so that head is pointed down towards the cervix (most inferior part of the uterus) -Around 38-40 weeks is full term (around 9-10 months)