BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 27 Reproduction and Embryonic Development Modules – 27.19

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gestation is pregnancy –It begins at conception and continues until birth –Human gestation is 266 days (38 weeks or 9 months) –Mouse gestation is 1 month –Elephant gestation is 22 months The embryo and placenta take shape during the first month of pregnancy HUMAN DEVELOPMENT

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Human development begins with fertilization in the oviduct Figure 27.16A Cleavage starts Fertilization of ovum Oviduct Secondary oocyte Ovulation Ovary Blastocyst (implanted) Endometrium Uterus

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cleavage produces a blastocyst –A blastocyst is a fluid-filled cavity –The inner cells of the blastocyst form the baby –The outer cells form the embryo trophoblast Figure 27.16B ENDOMETRIUM Inner cell mass Cavity Trophoblast

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The trophoblast secretes enzymes to enable the blastocyst to implant in the uterine wall Figure 27.16C ENDOMETRIUM Future embryo Future yolk sac Multiplying cells of trophoblast Trophoblast UTERINE CAVITY Blood vessel (maternal)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gastrulation occurs and organs develop from the ectoderm, endoderm, and mesoderm Figure 27.16D Mesoderm cells Amniotic cavity Amnion Chorion Yolk sac

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Meanwhile, the four embryonic membranes develop –Amnion –Chorion –Yolk sac –Allantois Figure 27.16E Chorion Amnion Allantois Yolk sac Chorionic villi EMBRYO: Ectoderm Mesoderm Endoderm

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The embryo floats in the fluid-filled amniotic cavity, while the chorion and embryonic mesoderm form the embryo’s part of the placenta The placenta’s chorionic villi absorb food and oxygen from the mother’s blood Figure 27.16F Placenta Allantois Yolk sac Mother’s blood vessels Amniotic cavity Amnion Embryo Chorion Chorionic villi

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The placenta allows for a variety of substances to pass from mother to fetus –Protective antibodies –German measles virus –HIV –Drugs (prescription and nonprescription) –Alcohol –Chemicals in tobacco smoke

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings First trimester –First three months –The most rapid changes occur during the first trimester Human development from conception to birth is divided into three trimesters Figure 27.17A, B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Second trimester –Increase in size of fetus –General refinement of human features Figure 27.17C, D

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Third trimester –Growth and preparation for birth Figure 27.17E

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hormonal changes induce birth –Labor is controlled by a positive feedback mechanism –Estrogen released from the ovaries increases the sensitivity of the uterus to oxytocin Childbirth is hormonally induced and occurs in three stages

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Oxytocin is a powerful stimulant for the smooth muscles of the uterus –Oxytocin also stimulates the placenta to make prostoglandins that stimulate the uterine muscles to contract even more Uterine contractions stimulate the release of more and more oxytocin and prostoglandins

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 27.18A ESTROGENOXYTOCIN from ovaries From fetus and pituitary Induces oxytocin receptors on uterus Stimulates uterus to contract Stimulates placenta to make PROSTAGLANDINS Stimulates more contractions of uterus Positive feedback

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings There are three stages of labor Dilation of the cervix is the first stage –Cervix reaches full dilation at 10cm –Longest stage of labor (6-12 hours or longer) Figure 27.18B, part 1 Dilation of the cervix 1 Placenta Umbilical cord Uterus Cervix

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Expulsion is the second stage –Period from full dilation of the cervix to delivery of the infant –Uterine contractions occur every 2-3 minutes –Mother feels urge to push down with her abdominal muscles –Infant is forced down and out of uterus and vagina within a period of 20 minutes Figure 27.18B, part 2 Expulsion: delivery of the infant 2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The delivery of the placenta is the final stage of labor –Usually occurs within 15 minutes after the birth of the baby Figure 27.18B, part 3 Delivery of the placenta 3 Umbilical cord Uterus Placenta (detaching)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hormones continue to be important after the baby and placenta are delivered –Decreasing progesterone and estrogen levels allow the uterus to return to its pre-pregnancy state –Oxytocin and prolactin stimulate milk secretion

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Reproductive technology –Hormone therapy can increase sperm or egg production –Surgery can correct blocked oviducts Assisted reproductive technology –In vitro fertilization (IVF) Surrogate motherhood Connection: Reproductive technology increases our reproductive options Figure 27.19