Fertilization SLO PDF

Fertilization SLO: By the end of this course, each student should be able to describe the early embryogenesis and the branchial arches and their derivatives. It is the union of the sperm with the mature ovum. Normally it occurs in the lateral one third of the Fallopian tube. Results of fertilization...

Fertilization SLO: By the end of this course, each student should be able to describe the early embryogenesis and the branchial arches and their derivatives. It is the union of the sperm with the mature ovum. Normally it occurs in the lateral one third of the Fallopian tube. Results of fertilization: 1. The zygote is formed (fertilized ovum). 2. The diploid number of chromosomes is restored (46). 3. Segmentation (cleavage division) begins immediately after fertilization while the fertilized ovum still in the uterine tube. 4. Sex determination (female xx -- male xy). Segmentation (cleavage): The zygote divides into 2 cells, 4 cells, 8 cells, 16 cells (morula) and lastly the blastocyst is formed. The blastocyst reaches the uterine cavity by the 5th day after fertilization. Implantation: It begins about the 6th day and is completed at the 12th day after fertilization. It occurs in the posterior wall of the fundus of the uterus. The cells are arranged into an inner cell mass and an outer cell mass (trophoblast). The inner cell mass will differentiate into two layers (ectoderm and endoderm). A third layer appears between the ectoderm and the endoderm known as mesoderm. General Anatomy & Embryology 71 Oocyte Sperm Zona pellucida Head Neck Middle piece Tail Fusion of sperm & ovum Zygote Two Four Morula Blastocyst Inner cell mass Outer cell mass Uterine tube Uterus Ovary Placenta Zygote Morula Blastocyst Implantation General Anatomy & Embryology 72 The intra--uterine life: It is the time that elapses between fertilization and the birth of a newly born infant. It is about 10 lunar months (280 days) and divided into three stages: 1. Germinal period (fertilized ovum): the first two weeks. It is characterized by the formation of the three germ layers; ectoderm, endoderm and mesoderm. 2. Embryonic period: from the 3rd week to the end of 8th week. It is characterized by the differentiation of the three germ layers into organs and systems. 3. Foetal period: from the 3 rd month to the end of pregnancy. It is characterized by the growth of the various organs and systems and the gradual appearance of the external features of the fetus. Congenital anomalies are liable to occur during the germinal and the embryonic periods.