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PREGNANCY & HUMAN DEVELOPMENT Mutiara Budi Azhar Faculty of Medicine Sriwijaya University Embryology Embryology is a science that studies the normal development as well as birth defects of a human being in the maternal uterus. Dr MBA Pregnancy and Human Development 2 Historical gleanings Hippocrates, Father of Medicine, first recorded embryological studies; bird embryo can be likened to that of man. Aristotle: studied chick and other embryos, which resulted from union of semen with menstrual blood. Dr MBA Pregnancy and Human Development 3 From Egg to Fetus Pregnancy – events that occur from fertilization (conception, conceptio) until the infant is born. Conceptus – the developing offspring. Gestation period – from the last menstrual period until birth. 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 Dr MBA Pregnancy and Human Development 4 Relative Size of Human Conceptus Dr MBA Pregnancy and Human Development 5 Gametes and Gametogenesis Dr MBA Pregnancy and Human Development 6 Gamete A gamete (from Ancient Greek γαμετης; translated gamete = wife, gametes = husband) is a cell that fuses with another gamete during fertilization (conception) in organism that reproduce sexually. In species which produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual which produces the larger type of gamete—called an ovum (or egg)—and a male produces the smaller tadpole-like type—called a sperm. Dr MBA Pregnancy and Human Development 7 Gamete. Cont’ Anisogamy or heterogamy: the condition wherein females and males produce gametes of different sizes: in humans, the human ovum is approximately 20 times larger than the human sperm cell. Isogamy is the state of gametes from both sexes being the same size. Dr MBA Pregnancy and Human Development 8 Gamete. Cont’ The name gamete was introduced by the Austrian biologist biologist Gregor Mendel Gametes carry half the genetic information of an individual, one chromosome of each type. In human an ovum can only carry X chromosom (of the X and Y chromosom) As a sperm can carry either an X or a Y, males have the control of the gender of any resulting zygote as the genotype of the sex-determining chromosomes of a male must be XY and a female XX. Dr MBA Pregnancy and Human Development 9 The Human Life Cycle Haploid: pertaining to a single set of unpaired chromosomes or an organism or cell that comprises of a single set of chromosomes Diploid: Contain two homologous sets of chromosomes Dr MBA Pregnancy and Human Development 10 Gametogenesis Dr MBA Pregnancy and Human Development 11 Spermatogenesis Dr MBA Pregnancy and Human Development 12 Ooogenesis Dr MBA Pregnancy and Human Development 13 Spermatogenesis Dr MBA Pregnancy and Human Development 14 Oogenesis Dr MBA Pregnancy and Human Development 15 Sperm Meiosis Dr MBA Pregnancy and Human Development 16 Spermatozoa Spermatozoa Dr MBA Pregnancy and Human Development 17 Oocyte Dr MBA Pregnancy and Human Development 18 hypothalamus GnRH anterioir pituitary FSH LH Mid-cycle peak of LH (triggers ovulation) hypothalamus Blood levels of FSH (purple) and LH (lavender) anterior lobe of pituitary gland FSH LH growth of follicle estrogens LH ovulation corpus luteum progesterone, estrogen Blood levels of estrogens (light blue) and progesterone (dark blue) endometrium of uterus estrogens progesterone, estrogen menstruation Days of one menstrual cycle (using 28 days as the average duration) Dr MBA FOLLICULAR PHASE OF MENSTRUAL CYCLE LUTEAL PHASE OF MENSTRUAL CYCLE 19 Fertilization Dr MBA Pregnancy and Human Development 20 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 Dr MBA Pregnancy and Human Development 21 Sperm Transport and Capacitation Fates of ejaculated sperm – – – – Leak out of the vagina immediately after deposition Destroyed by the acidic vaginal environment Fail to make it through the cervix Dispersed in the uterine cavity or destroyed by phagocytic leukocytes – Reach the uterine tubes Sperm must undergo capacitation before they can penetrate the oocyte Dr MBA Pregnancy and Human Development 22 Acrosomal Reaction and Sperm Penetration An ovulated oocyte is encapsulated by: – The corona radiata and zona pellucida – Extracellular matrix Sperm binds to the zona pellucida and undergoes the acrosomal reaction – Enzymes are released near the oocyte – Hundreds of acrosomes release their enzymes to digest the zona pellucida Dr MBA Pregnancy and Human Development 23 Acrosomal Reaction and Sperm Penetration. Cont.’ Once a sperm makes contact with the oocyte’s membrane: – Beta protein finds and binds to receptors on the oocyte membrane – Alpha protein causes it to insert into the membrane Dr MBA Pregnancy and Human Development 24 Acrosomal Reaction and Sperm Penetration. Cont.’ Dr MBA Pregnancy and Human Development 25 Blocks to Polyspermy Only one sperm is allowed to penetrate the oocyte Two mechanisms ensure monospermy – Fast block to polyspermy – membrane depolarization prevents sperm from fusing with the oocyte membrane – Slow block to polyspermy – zonal inhibiting proteins (ZIPs): Destroy sperm receptors Cause sperm already bound to receptors to detach Dr MBA Pregnancy and Human Development 26 Completion of Meiosis II and Fertilization Upon entry of sperm, the secondary oocyte: – Completes meiosis II – Casts out the second polar body The ovum nucleus swells, and the two nuclei approach each other When fully swollen, the two nuclei are called pronuclei Fertilization – when the pronuclei come together Dr MBA Pregnancy and Human Development 27 Events Immediately Following Sperm Penetration Dr MBA Pregnancy and Human Development 28 Preembryonic Development Dr MBA Pregnancy and Human Development 29 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) Dr MBA Pregnancy and Human Development 30 Preembryonic Development. Cont.’ Blastocyst – a fluid-filled hollow sphere composed of: – A single layer of trophoblasts – An inner cell mass Trophoblasts take part in placenta formation The inner cell mass becomes the embryonic disc Dr MBA Pregnancy and Human Development 31 The Period of the Zygote Zygote blastocyst Cell differentiation % of blastocysts that fail to implant? Dr MBA Pregnancy and Human Development 32 The Period of the Zygote. Cont.’ Outer layer of blastocyst develops into: – – – – Amnion Chorion Placenta Umbilical cord **note that these structures actually develop during the period of the embryo Dr MBA Pregnancy and Human Development 33 Implantation Dr MBA Pregnancy and Human Development 34 Implantation Begins six to seven days after ovulation when the trophoblasts adhere to a properly prepared endometrium The trophoblasts then proliferate and form two distinct layers – Cytotrophoblast – cells of the inner layer that retain their cell boundaries – Syncytiotrophoblast – cells in the outer layer that lose their plasma membranes and invade the endometrium Dr MBA Pregnancy and Human Development 35 Implantation. Cont.’ The implanted blastocyst is covered over by endometrial cells Implantation is completed by the fourteenth day after ovulation Dr MBA Pregnancy and Human Development 36 Implantation of the Blastocyst Dr MBA Pregnancy and Human Development 37 Implantation of the Blastocyst. Cont.’ Dr MBA Pregnancy and Human Development 38 Implantation of the Blastocyst Dr MBA Pregnancy and Human Development 39 Implantation of the Blastocyst. Cont.’ Dr MBA Pregnancy and Human Development 40 Implantation of the Blastocyst. Cont.’ Dr MBA Pregnancy and Human Development 41 Implantation of the Blastocyst. Cont.’ Viability of the corpus luteum is maintained by human chorionic gonadotropin (hCG) secreted by the trophoblasts hCG prompts the corpus luteum to continue to secrete progesterone and estrogen 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 Dr MBA Pregnancy and Human Development 42 Hormonal Changes During Pregnancy Dr MBA Pregnancy and Human Development 43 Placentation Dr MBA Pregnancy and Human Development 44 Placental Development Dr MBA Pregnancy and Human Development 45 Placentation Formation of the placenta from: – Embryonic trophoblastic tissues – Maternal endometrial tissues Dr MBA Pregnancy and Human Development 46 Placentation. Cont.’ The chorion develops fingerlike villi, which: – Become vascularized – Extend to the embryo as umbilical arteries and veins – Lie immersed in maternal blood Decidua basalis – part of the endometrium that lies between the chorionic villi and the stratum basalis Dr MBA Pregnancy and Human Development 47 Placentation. Cont.’ capsularis – part of the endometrium surrounding the uterine cavity face of the implanted embryo. The placenta is fully formed and functional by the end of the third month. Embryonic placental barriers include: Decidua – The chorionic villi – The endothelium of embryonic capillaries Dr MBA Pregnancy and Human Development 48 Placenta • Permits the exchange of materials between the bloodstream of the fetus and that of the mother • Produces progesteron; gradually take over the role of corpus luteum. The placenta also secretes other hormones – human placental lactogen, human chorionic thyrotropin, and relaxin. Dr MBA Pregnancy and Human Development 49 Placentation. Cont.’ Dr MBA Pregnancy and Human Development Figure 28.7a-c 50 Placentation. Cont.’ Dr MBA Pregnancy and Human Development Figure51 28.7d Placentation. Cont.’ Dr MBA Pregnancy and Human Development Figure 28.7f 52 Germ Layers Dr MBA Pregnancy and Human Development 53 Gastrulation During the 3rd week, the two-layered embryonic disc becomes a three-layered embryo The primary germ layers are ectoderm, mesoderm, and endoderm Primitive streak – raised dorsal groove that establishes the longitudinal axis of the embryo Dr MBA Pregnancy and Human Development 54 Germ Layers • The blastocyst develops into a gastrula with three primary germ layers: ectoderm, endoderm, and mesoderm. • Before becoming three-layered, the inner cell mass subdivides into the upper epiblast and lower hypoblast: these layers form two of the four embryonic membranes Dr MBA Pregnancy and Human Development 55 Gastrulation. Cont.’ • As cells begin to migrate: – The first cells that enter the groove form the endoderm – The cells that follow push laterally between the cells forming the mesoderm – The cells that remain on the embryo’s dorsal surface form the ectoderm • Notochord – rod of mesodermal cells that serves as axial support Dr MBA Pregnancy and Human Development 56 Three Germ Layers* • Endoderm – formed from migrating cells that replace the hypoblast • Mesoderm – formed between epiblast and endoderm • Ectoderm – formed from epiblast cells that stay on dorsal surface *All layers derive from epiblast cells! Dr MBA Pregnancy and Human Development 57 Primary Germ Layers Serve as primitive tissues from which all body organs will derive. Ectoderm – nervous system, skin, hair, sensory receptors. Endoderm – digestive system, lungs, urinary tract, other internal organs. Mesoderm – muscles, bones, circulatory system, reproductive system, excretory system. Endoderm and ectoderm are securely joined and are considered epithelia. Dr MBA Pregnancy and Human Development 58 Derivatives of Germ Layers Dr MBA Pregnancy and Human Development 59 Embryonic Membranes Amnion – epiblast cells form 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 Dr MBA Pregnancy and Human Development 60 Embryonic Membranes. Cont.’ Yolk sac – hypoblast cells that form 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 Dr MBA Pregnancy and Human Development 61 Embryonic Membranes. Cont.’ 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 Dr MBA Pregnancy and Human Development 62 Embryonic Period Dr MBA Pregnancy and Human Development 63 Embryonic Period Dr MBA Pregnancy and Human Development 64 Embryo at 4 Weeks Dr MBA Pregnancy and Human Development 65 Face Development from 5½ to 8 Weeks Dr MBA Pregnancy and Human Development 66 The Period of the Embryo. Cont.’ By 4th week, heart has formed and begun to beat Becomes more human in appearance during 2nd month Sexual differentiation during 7th – 8th weeks Dr MBA Pregnancy and Human Development 67 The Period of the Fetus Dr MBA Pregnancy and Human Development 68 The Period of the Fetus Final 7 months of pregnancy Fetus Digestive and excretory systems functional Sex detected by ultrasound by end of 3rd month Kicks and movements strong enough to be felt Organ systems mature rapidly during final 3 months Dr MBA Pregnancy and Human Development 69 The Period of the Fetus. Cont.’ Dr MBA Pregnancy and Human Development 70 Fetus at 9 Weeks Dr MBA Pregnancy and Human Development 71 Fetus at 11 Weeks Dr MBA Pregnancy and Human Development 72 Fetus at 16 Weeks Dr MBA Pregnancy and Human Development 73 Fetus at 18 Weeks Dr MBA Pregnancy and Human Development 74 Fetus at 20 Weeks Dr MBA Pregnancy and Human Development 75 Fetus at 28 Weeks Dr MBA Pregnancy and Human Development 76 Fetal development Dr MBA Pregnancy and Human Development 77 Twins Dr MBA Pregnancy and Human Development 78 The Period of the Fetus. Cont.’ Viable between 22-28 weeks Receives antibodies Assume upside-down position in final weeks – Weight of head – Shape of uterus Dr MBA Pregnancy and Human Development 79 A Brief View of Prenatal Development Dr MBA Pregnancy and Human Development 80 A Brief View of Prenatal Development. Cont.’ Dr MBA Pregnancy and Human Development 81 Developmental Events of the Fetal Period Dr MBA Pregnancy and Human Development 82 Developmental Events of the Fetal Period Dr MBA Pregnancy and Human Development 83 Table 3.1 (2 of 3) Developmental Events of the Fetal Period Dr MBA Pregnancy and Human Development 84 Table 3.1 (3 of 3) Trends in Development Cephalocaudal Trend Proximodistal Trend Dr MBA Pregnancy and Human Development 85 Teratogens Dr MBA Pregnancy and Human Development 86 Susceptible period Dr MBA Pregnancy and Human Development 87 Teratogens Root word means “formation of monsters” Harm isn’t always simple or straightforward Amount and length of exposure Genetic makeup of mother/baby Presence of several negative factors Dr MBA Pregnancy and Human Development 88 Teratogens. Cont.’ Same defect different teratogens One teratogen different defects Some effects seen later Age of baby Sensitive period Dr MBA Pregnancy and Human Development 89 Dr MBA Pregnancy and Human Development 90 Teratogens. Cont.’ Paternal influences often overlooked – – – – – – Dr MBA Direct and indirect effects Second hand smoke Chemicals Cocaine can “hitchhike” Smoking, alcohol, drug use sperm Diets low in vitamin C Pregnancy and Human Development 91 Other Factors Teratogens. Cont.’ Exercise Nutrition Emotional stress Rh blood incompatibility Maternal/Paternal age – Older less fertile, more risk of disorders – Younger increased risk of prematurity, infant death Dr MBA Pregnancy and Human Development 92 Other Factors Teratogens. Cont.’ Infectious diseases Prenatal care Previous births Dr MBA Pregnancy and Human Development 93 Congenital malformations (Birth defects) Dr MBA Pregnancy and Human Development 94 Chemical: nitrite, benzol; lead, arsenic, cadmium, mercury, etc. Drugs: thalidomide (amelia and meromelia), Dr MBA Pregnancy and Human Development 95 Drugs: aminopterin (anencephaly, hydrocephalus, cleft lip); streptomycin (deafness). Hormones: estrogens, progestins Social drugs: cigarettes (small babies); alcohol (fetal alcohol syndrome). Dr MBA Pregnancy and Human Development 96 Perinatal Environment Environment surrounding birth Stages of childbirth – Contractions – Delivery – Afterbirth Newborn appearance Dr MBA Pregnancy and Human Development 97 Birth Labor Oxytocin Uterine contractions Dr MBA Pregnancy and Human Development 98 Perinatal Environment Assessing the Newborn – Apgar scale – 1 minute and 5 minutes after birth Dr MBA Pregnancy and Human Development 99 The Apgar Test Dr MBA Pregnancy and Human Development 100 Perinatal Environment Assessing the Newborn – Neonatal Behavioral Assessment Scale (NBAS) Several days after birth 20 inborn reflexes Reactions to comforting and social stimuli Unresponsiveness may indicate neurological problems Can be a parent teaching tool Dr MBA Pregnancy and Human Development 101 Perinatal Environment Complications – Anoxia Severe cerebral palsy, mental retardation Mild irritability, motor/cognitive delays Chances have been reduced with fetal monitoring Respiratory distress syndrome – Complicated delivery Forceps Cesarean Medications Dr MBA Pregnancy and Human Development 102 Preterm and Small-for-Date Preterm = born more than 3 weeks early, but appropriate weight for time in womb Small-for-Date = underweight due to slow fetal growth – Greater risk than preterm – Causes include smoking, drug use, stress, lack of prenatal care, multiple births, social support Postterm = born after 42 weeks Dr MBA Pregnancy and Human Development 103 Thank you very much for your kind attention Dr MBA Pregnancy and Human Development 104