Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Human Anatomy & Physiology SEVENTH EDITION Elaine N. Marieb Katja Hoehn PowerPoint ® Lecture Slides prepared by Vince Austin, Bluegrass Technical and Community College C H A P T E R 28 Pregnancy and Human Development P A R T A

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From Egg to Embryo  Pregnancy – events that occur from fertilization until the infant is born  Conceptus – the developing offspring  Gestation period – from the last menstrual period until birth

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From Egg to Embryo  Preembryo – conceptus from fertilization until it is two weeks old  Embryo – conceptus during the third through the eighth week  Fetus – conceptus from the ninth week through birth

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Relative Size of Human Conceptus Figure 28.1

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Accomplishing Fertilization  The oocyte is viable for 12 to 24 hours  Sperm is viable 24 to 72 hours  For fertilization to occur, coitus must occur no more than:  Three days before ovulation  24 hours after ovulation  Fertilization – when a sperm fuses with an egg to form a zygote

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sperm Transport and Capacitation  Fates of ejaculated sperm:  Leakage  Low pH of vagina  Failure to reach cervix  Destroyed by phagocytosis/lost in cavity  Failure to reach tubes  Sperm must undergo capacitation before they can penetrate the oocyte

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 28.2a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Completion of Meiosis II and Fertilization  Upon entry of sperm, the secondary oocyte:  Completes meiosis II  Casts out the second polar body  Fertilization – when the pronuclei come together

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Events Immediately Following Sperm Penetration Figure 28.3

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cleavage and Implantation  Cleavage – rapid mitosis of the zygote following fertilization.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Preembryonic Development  The first cleavage produces two daughter cells called blastomeres  Morula – the 16 or more cell stage (72 hours old)  By the fourth or fifth day the preembryo consists of 100 or so cells (blastocyst)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Preembryonic Development  Blastocyst – a fluid-filled hollow sphere composed of: 1. A single flattened layer of cells called trophoblasts 2. An inner cell mass  Trophoblasts take part in placenta formation  The inner cell mass becomes the embryonic disc

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cleavage: From Zygote to Blastocyst Figure 28.4

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Implantation  6-7 day  trophoblast implants into the endometrium – high levels of estrogen and progesterone  2 layers implant in endometrium

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Implantation  blastocyst is covered over by endometrial cells  completed by the fourteenth day after ovulation

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Implantation of the Blastocyst Figure 28.5a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Implantation of the Blastocyst Figure 28.5b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Implantation  corpus luteum -secrete estrogen and progesterone  Chorion – developed from trophoblasts after implantation, continues this hormonal stimulus  Between the second and third month, the placenta:  Assumes the role of progesterone and estrogen production  Is providing nutrients and removing wastes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormonal Changes During Pregnancy Figure 28.6

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Placentation  Formation of the placenta from:  Embryonic trophoblastic tissues  Maternal endometrial tissues  These form the chorion

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Placentation  The placenta is fully formed and functional by the end of the third month

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Placentation  Embryonic placental barriers allow for passage of nutrients but the blood does not intermix  The placenta also secretes other hormones – human placental lactogen, human chorionic thyrotropin, and relaxin

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Placentation Figure 28.7a–c

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Placentation Figure 28.7d

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Placentation Figure 28.7f

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Germ Layers  Inner cell mass produces 4 membranes during the first 2-3 weeks of development  Amnion, yolk sac, allantois, chorion

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Embryonic Membranes  Amnion – a transparent membrane filled with amniotic fluid  Provides a buoyant environment that protects the embryo  Helps maintain a constant homeostatic temperature  Amniotic fluid comes from maternal blood, and later, fetal urine

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Embryonic Membranes  Yolk sac – a sac on the ventral surface of the embryo  Forms part of the digestive tube  Produces earliest blood cells and vessels  Is the source of primordial germ cells

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Embryonic Membranes  Allantois – a small outpocketing at the caudal end of the yolk sac  Structural base for the umbilical cord  Becomes part of the urinary bladder  Chorion – helps form the placenta  Encloses the embryonic body and all other membranes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Gastrulation  During the 3 rd week, the two-layered embryonic disc becomes a three-layered embryo – gastrulation  Primitive streak – raised dorsal groove that establishes the longitudinal axis of the embryo  The primary germ layers are ectoderm, mesoderm, and endoderm

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Gastrulation  Notochord – rod of mesodermal cells that serves as axial support

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Primary Germ Layers  Ectoderm – forms structures of the nervous system and skin epidermis  Endoderm – forms epithelial linings of the digestive, respiratory, and urogenital systems  Mesoderm – forms all other tissues