Starting from Day 8, blastocyst progressively invades into the endometrial stroma and there is formation of: 2 layers in Trophoblast: 1. Inner mononulcear Cytotrophoblast (Cellular) Mitotic figures are found in the cytotrophoblast – hence generate primary chorionic villi into the syncytiotrophoblast. 2. Outer multinucleated Syncytiotrophoblast (Syncytium – cells have fused) Mitotic…
Tag: Embryology
PGMEE, MRCS, USMLE, MBBS, MD/MS
Embryology Week 1: Cleavage to Implantation
Following events occur in the zygote formed in the week zero of development: Cleavage Approximately 24 hours after fertilization the zygote begins with the first cleavage division. Series of mitotic divisions of the zygote (occurs in fallopian tube) to form small daughter cells called blastomeres. Characteristics of cleavage in humans:…
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Embryology Week 0: Gametogenesis, Ovulation and Fertilization
Gametogenesis – formation of gametes from primitive germ cells Spermatogenesis, begins at puberty and occurs in seminiferous tubules (spermiogenesis occurs in sertoli cells). One spermatogenesis takes an average of 74 days to complete. Oogenesis Stages Spermatogenesis Migrate at 6th week of development 1. Primordial Germ Cells / PGCs (46, 2n) – epiblast…
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Germ Layer Derivatives – Mnemonics
Principle of Germ Layer Segmentation Ectoderm gives further rise to neuroectoderm and neural crest cells. Endoderm remains intact. Mesoderm gives further rise to paraxial mesoderm (somitomeres and 35 pairs of somites), intermediate mesoderm, and lateral mesoderm: General Rule for Germ Layer Derivatives Ectodermal derivatives: 1. Everything that makes you attractive: Skin, hair,…
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Branchial Apparatus (Pharyngeal arches and pouches) : Mnemonics
Synonym: Pharyngeal apparatus Mnemonic: CAP covers from out to in Pharyngeal arches are equivalent of gill arches in fish that develop in a cranio-caudal sequence. Derivatives of Pharyngeal or Branchial Apparatus Pharyngeal cleft Pharyngeal arch Pharyngeal pouch Ectoderm Mesoderm Neural crest Cranial Nerves Arteries Endoderm 1st External Auditory Meatus…