embryol - Embryology University of Hargeisa- Somaliland Dr...

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www.medicalppt.blogspot.com Embryology University of Hargeisa- Somaliland Dr Mohamed Hussein Mohamed (Qabile), MD PUBLISHED BY www.medicalppt.blogspot.com
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www.medicalppt.blogspot.com INTRODUCTION Embryology Embryology: In its widest sense is applied to the various changes which take place during the growth of an animal from the egg to the adult condition. It is, however, usually restricted to the phenomena, which occur before birth. Embryology may be studied from two aspects (1) that of ontogeny which deals with the development of the individual; and (2) that of phylogeny, which concerns itself with the evolutionary history of the animal kingdom. Developmental Periods: Human development is divided into two: 1. Prenatal (before birth): the main developmental changes occur during prenatal phase. 2. Postnatal: (after birth). Embryological Terminology: The following terms are commonly used in discussions of developing humans: Oocyte (ovum, egg): the female germ or sex cell produced in the ovaries. When mature, the oocyte is called a secondary oocyte or mature oocyte. Sperm (spermatozoon): Refers to the male germ cell produced in the testes (testicle). Zygote: This cell results from the union of an oocyte and a sperm during fertilization. A zygote is the beginning of a new human being. Cleavage: This is the series of mitotic cell divisions of the zygote that result in the formation of early embryonic cells – blastomeres. The size of the cleaving zygote remains unchanged because at each succeeding cleavage division the blastomeres becomes smaller.
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www.medicalppt.blogspot.com Morula: This solid mass of 12 to about 32 blastomeres is formed by cleavage of a zygote. Blastocyst: After the morula enters the uterus from the uterine tube (fallopian tube), a fluid filled cavity– develops inside it. This change converts the morula into a blastocyst. Implantation: The process during which the blastocyst attached to the endometrium and subsequently embeds in it. Gastrula: During gastrulation (transformation of a blastocyst into a gastrula), a three layered embryonic disc forms (third week). The three germ layers of the gastrula ectoderm, mesoderm and endoderm, subsequently differentiate into the tissues and organs of the embryo. Neurula: The early embryo during the third and fourth weeks, when the neural tube is developing from the neural plate. Embryo: The developing human during its early stages of development. The end of the eighth week ( 56 days. Conceptus: The embryo and associated membranes. Primordium: The beginning or first discernible indication of an organ or structure. Fetus: After the embryonic period (eight weeks), the developing human is called a Fetus: During the fetal period (ninth week to birth), differentiation and growth of the tissues and organs formed during the embryonic period occur. Abortion (miscarry):
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embryol - Embryology University of Hargeisa- Somaliland Dr...

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