Chapter 3 - A - Embryology Lecture Notes PDF

HHP:1100 HUMAN ANATOMY Embryology: Events of the Pre-Embryonic Period  HHP:1100 Overview Human Anatomy Question: How do we go from a single fertilized egg to a complex human body? 2  HHP:1100 Overv...

HHP:1100 HUMAN ANATOMY Embryology: Events of the Pre-Embryonic Period  HHP:1100 Overview Human Anatomy Question: How do we go from a single fertilized egg to a complex human body? 2  HHP:1100 Overview Human Anatomy Question: How do we go from a single fertilized egg to a complex human body? To answer this question, we must first review: – Cell division (mitosis): increased cell number – Cell differentiation: transformation into specific cell types – Cell development: process by which cells become fully functional Embryology: developmental events that occur prior to birth 3  HHP:1100 Lecture Overview Human Anatomy 1. Overview of Embryology 2. Pre-Embryonic Period – Week 1 – Implantation – Formation of the Bilaminar Germinal Disc – Formation of the Extraembryonic Membranes – Development of the Placenta 4  HHP:1100 1. Overview of Embryology Human Anatomy The prenatal period is the first 38 weeks of human development – Sequence of events occurring from fertilization until birth – Divided into three developmental stages: 1. Pre-embryonic period 2. Embryonic period 3. Fetal period 5  1. Overview of Embryology HHP:1100 Human Anatomy Developmental Stages 1. Pre-embryonic period – First two weeks after fertilization of egg – Formation of a blastocyst – Ends with implantation in lining of the uterus 6  1. Overview of Embryology HHP:1100 Human Anatomy Developmental Stages 1. Pre-embryonic period 2. Embryonic period – Third through eighth weeks – All major organ systems begin to develop 7  1. Overview of Embryology HHP:1100 Human Anatomy Developmental Stages 1. Pre-embryonic period 2. Embryonic period 3. Fetal period – Ninth through thirty- eighth weeks – Growth and development continues – Ends at birth 8  2. Pre-Embryonic Period HHP:1100 Human Anatomy Week 1 We are going to assume sperm fertilize ovum After zygote is formed, it undergoes a series of mitotic divisions called cleavage 9  2. Pre-Embryonic Period HHP:1100 Human Anatomy Week 1 At 16-cell stage, the structure is called a morula Soon after morula enters uterine cavity, it becomes a blastocyst – Fluid-filled blastocyst cavity in its center 10  2. Pre-Embryonic Period HHP:1100 Human Anatomy Week 1 Review – Zygote – Cleavage – Blastocyst Blastocyst has two components: 1. Trophoblast 2. Embryoblast 11  2. Pre-Embryonic Period HHP:1100 Human Anatomy Week 1 Blastocyst Structures: 1. Trophoblast: outer ring of cells that will develop into the chorion 12  2. Pre-Embryonic Period HHP:1100 Human Anatomy Week 1 Blastocyst structures: 2. Embryoblast: cluster of tightly packed cells inside one side of the blastocyst that will form the embryo  Inner cell mass  Pluripotent: can differentiate into any cell type in the human body 13  2. Pre-Embryonic Period HHP:1100 Human Anatomy Implantation Within a week of fertilization, the blastocyst enters the uterus Invades superficial, functional layer of endometrium (lining of the uterus) By day 9, the blastocyst has completely burrowed into the uterine wall 14  2. Pre-Embryonic Period HHP:1100 Human Anatomy Formation of the Bilaminar Germinal Disc By day 8, cells of the embryoblast differentiate into two distinct types: 1. Hypoblast: layer of small cuboidal cells facing the blastocyst cavity 2. Epiblast: layer of columnar cells deep to the hypoblast Together, these two layers form a flat disc called the bilaminar germinal/embryonic disc 15  2. Pre-Embryonic Period HHP:1100 Human Anatomy Formation of the Extraembryonic Membranes The bilaminar germinal disc and trophoblast produce three extraembryonic membranes: 1. Yolk sac: serves as a site for early blood cell and vessel formation 16  2. Pre-Embryonic Period HHP:1100 Human Anatomy Formation of the Extraembryonic Membranes The bilaminar germinal disc and trophoblast produce three extraembryonic membranes: 2. Amnion: thin layer of cells that forms above and is derived from the epiblast  A fluid-filled amniotic cavity appears between the amnion and epiblast layer 17  2. Pre-Embryonic Period HHP:1100 Human Anatomy Formation of the Extraembryonic Membranes The bilaminar germinal disc and trophoblast produce three extraembryonic membranes: 3. Chorion: Outermost membrane responsible for formation of the placenta 18  2. Pre-Embryonic Period HHP:1100 Human Anatomy Development of the Placenta The placenta is a highly vascularized organ that serves as an interface between embryo or fetus and mother – Embryonic portion of the placenta is the chorion – Maternal portion is from the functional layer of the endometrium 19  2. Pre-Embryonic Period HHP:1100 Human Anatomy Development of the Placenta Main functions of the placenta: 1. Exchange of nutrients, waste products, and respiratory gases between embryo and mother 2. Transmission of maternal antibodies to embryo or fetus 3. Production of estrogen and progesterone to maintain uterine lining 20  HHP:1100 In Summary … Human Anatomy 21  HHP:1100 Learning Outcomes Human Anatomy You Should Be Able To … 1. differentiate cell division (mitosis), differentiation, development, and maturation 2. define the pre-embryonic, embryonic, and fetal periods in relation to time 3. provide an overview of the major events that occur during each prenatal period 4. describe the structural changes that occur from zygote, to morula to blastocyst 5. discuss the timing and importance of cleavage 22  HHP:1100 Learning Outcomes Human Anatomy You Should Be Able To … 6. compare and contrast the locations and end fates of the embryoblast and the trophoblast of the blastocyst 7. explain the process and timing of implantation 8. describe the process by which the embryoblast transforms into a bilaminar germinal disc 9. describe the formation and functions of the extraembryonic membranes (i.e., yolk sac, amnion, chorion) 10. list the maternal and fetal components to the placenta, 23 and its primary functions