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General embryology introduction ( chapter 1)

General embryology introduction ( chapter 1)

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General embryology introduction ( chapter 1)

  1. 1. Human Embryology Chapter 1. Introduction SHAFIM AHMED
  2. 2. Embryology  What is Embryology? 1. Definition: the study of the origin and development of an organism. 2. focuses on the development that occurs in the prenatal period (gestational period)
  3. 3. Embryology  Prenatal period: before birth • 38 weeks(266days,9months) from conception to birth (average) “fetal” age • Gynecologic timing has been from LMP (last menstrual period) therefore refers to 40 weeks “gestational” age  Date of conception has been difficult to time  LMP is on average two weeks before ovulation
  4. 4. prenatal period  “Embryonic” period: ( embryo) 1.extends from fertilization through 8 weeks. week 1 starts with fertilization and extends through the first cell divisions that produce an embryo with one germ layer. week 2 produce two germ layers. week 3 produce three germ layers and folds those a recognizable three dimensional body form. week 4 through 8 (month 2) are the period of organogenesis.
  5. 5. 2.Week 4 is particularly important, as the initial set-up of all organ systems is completed in this week. All the major events of organ formation and formation of body regions occurs during the period of organogenesis, which is completed in the embryonic period.
  6. 6. “Fetal” period: 9 weeks – birth (fetus) • The major events that occur during the fetal period involve growth in the size of organs by rapid increase in cell number, as well as biochemical functional maturation. • Most organs begin with a basic form of functioning during the fetal period, but it is only for development of the organ itself usually. The most important is exception is the cardiovascular system. Mature functional status is not achieved in most organ untill after birth.
  7. 7. Prenatal Development Embryonic development fertilization - 8 weeks All major organs formed Fetal development 9 weeks – birth Organs grow larger and become more complex Postnatal DevelopmentPostnatal Development time period from fertilization to birth = gestationgestation
  8. 8. Relative Size of Human Conceptus Figure 28.1
  9. 9. Four mammalian embryos at variousFour mammalian embryos at various stages of development (HAECKEL):stages of development (HAECKEL): • A PigA Pig • B CowB Cow • C RabbitC Rabbit • D HumanD Human ““Please, note the similarities inPlease, note the similarities in the different developingthe different developing mammalian species!”mammalian species!”
  10. 10. Embryonic body axis terminology 1.The first axis formed is the cranial-caudal axis The cranial-caudal axis is established while the embryo is still a flat disk or sheet of cells, long before it fold into the three-dimensional structure. This axis runs from the future head to the future ”tail” end.
  11. 11. 2. The dorsal-ventral axis is established very shortly thereafter. The second major axis the dorsal-ventral, is formed as the body folds. This axis defines, respectively, the future” back” and “front” sides of both embryonic and adult bodies.
  12. 12. Significance of Embryology in medicine  The knowledge of the basic principles ofThe knowledge of the basic principles of development will assist the student in understandingdevelopment will assist the student in understanding relationships taught in gross anatomy, histology, andrelationships taught in gross anatomy, histology, and pathology courses, and will later serve the clinicianpathology courses, and will later serve the clinician in diagnosing certain conditions and in counselingin diagnosing certain conditions and in counseling congenital malformations (significance incongenital malformations (significance in gynecology/andrology and in molecular biology!).gynecology/andrology and in molecular biology!).
  13. 13. Content  General Embryology 1.Fertilization 2.Cleavage 3.Implantation 4.Formation Of The Germ Layers 5.Folding Of The Embryo 6.Derivatives Of The Germ Layers 7.External Appearance Of The Embryo And Fetus 8.Placenta  Special Embryology Systems development

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