Oral Histology and Embryology Lecture One PDF

ORAL HISTOLOGY AND EMBRYOLOGY LECTURE ONE ‫ محمد احسان جابك‬.‫د‬ ‫دكتوراه امراض الفم والوجه والفكين‬ B.D.S, MSc., Ph.D.  Embryogenesis (fertilized egg develops into an embryo) (First week( ( Ovulation, Fertilization and implant...

ORAL HISTOLOGY AND EMBRYOLOGY LECTURE ONE ‫ محمد احسان جابك‬.‫د‬ ‫دكتوراه امراض الفم والوجه والفكين‬ B.D.S, MSc., Ph.D.  Embryogenesis (fertilized egg develops into an embryo) (First week( ( Ovulation, Fertilization and implantation)  (first eight weeks))embryo) - shifts from a single-celled zygote into a multi- layered, multi- dimensional fetus with primitively functioning organs (ninth week))fetus) - recognizable external features and a more complete set of developing organs  (Week 1( - fertilization through uterine implantation Steps: 1-gamete approximation 2-contact and fusion of gametes 3-fertilization 4-mitotic cleavage of the blastomere 5-morula formation 6-blastocyst formation 7-implantation of the blastocyst  OVULATION is a complex interaction between pituitary gland in brain regular monthly cycles controlled by hypothalamus which secretes gonadotropins (follicle-stimulating hormone (FSH) and luteinizing hormone (LH)) which stimulate and control cyclic changes in the ovary Ovaries and the uterus work to create the perfect environment for ovulation (the release of an egg), sperm and egg to meet and fertilized egg to implant itself in the uterus.  Every month n the days preceding ovulation the pituitary gland, releases a hormone (FSH and LH) which tells the ovaries to produce a number of fluid-filled cysts called follicles, only one of these follicles reaches full maturity (graafian follicle )and only one oocyte is discharged (egg inside the follicle detaches itself the follicle swells, then it ruptures); the others degenerate and become atretic. After ovulation the follicle turns into the corpus luteum which serves as a temporary endocrine gland, by releasing female sex hormones namely progesterone and estrogen. Subsequently, the corpus luteum shrinks and forms a mass of fibrotic scar tissue, the corpus albicans. Cumulus oophorus a cluster of cells that surround the oocyte both in the ovarian follicle and after ovulation, the inner most layer of these cells is the corona radiate. Corona radiate is the inner most layer of cumulus oophorus ,it is a thick layer that surrounds the zona pellucida it is composed of proteins, carbohydrates and hyaluronic acid. Zona pellucida is the inner protective glycoprotein layer that surrounds the plasma membrane of mammalian oocytes.  FERTILIZATION - is the process of fusing a mature male gamete and a mature female gamete to form a single cell, the zygote  Prior to fertilization, sperm undergo a process of capacitation ( period of conditioning , involves epithelial interactions between the sperm and the mucosal surface of the tube) , only capacitated sperm undergo the acrosome reaction. Acrosome reaction: which occurs after binding to the zona pellucida, is induced by zona proteins and culminates in the release of enzymes (acrosin- and trypsin) needed to penetrate the zona pellucida  RESULTS OF FERTILIZATION A- Restoration of the diploid number of chromosomes, half from the father and half from the mother. Hence, the zygote contains chromosomes different from both parents. B -Determination of the sex of the new individual. An X-carrying sperm produces a female (XX) embryo, and a Y-carrying sperm produces a male (XY) embryo. C- Initiation of cleavage  MORULA FORMATION after fertilization, the resulting one-celled zygote will rapidly undergo multiple mitotic cleaves as it travels around four days to reach the uterine cavity. BLASTULATION(BLASTOCYST FORMATION)  The blastocyte possesses an inner cell mass (ICM) called embryoblasts which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblast. This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocele. Blastocele is the first cavity formed during embryonic development, Blastocyst is a mass of cells that is formed a few days after fertilization.  IMPLANTATION is a complex biochemical and mechanical process that begins in the first week of gestation and extends into the second week. subdivided into: 1-Period of apposition where the blastocyst establishes weak interactions with the uterine wall. 2-Attachment phase occurs when binding of blastocyst to the uterine epithelium is more established. 3-Invasion occurs when the blastocyst begins to burrow into the endometrium. THE END