Second Week Embryology PDF

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Mansoura University

Anatomist

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embryology human development implantation anatomy

Summary

This document details the second week of human embryo development. It covers topics such as implantation, anomalies, and the formation of the decidua. Relevant concepts about early pregnancy stages are included.

Full Transcript

2nd week Implantation  Definition: embedding blastocyst into endometrium  Site upper part of posterior uterine wall near fundus  Time : begin at the end of 1st week ti...

2nd week Implantation  Definition: embedding blastocyst into endometrium  Site upper part of posterior uterine wall near fundus  Time : begin at the end of 1st week till the end of 2nd week  Mechanism:  Loss of zona pellucida causes trophoblast exposure  Exposed trophoblast has 2 powers:  Adhesive power: to endometrium  Histolytic power: by enzymes that help blastocyst to digest endometrium.  Fibrin plug fill the digest part of endometrium Anatomist “second week”  Anomalies: Placenta previa: Implantation of blastocyst into lower uterine segment. It may be: 1. Placenta previa lateralis: Placenta is away from Internal os 2. Placenta previa marginalis: Placenta partially cover Internal os 3. Placenta previa centralis: Placenta is completely cover Internal os Ectopic pregnancy: Implant ion of blastocyst outside uterine cavity. It may be 1. Tubal "commonest type": Caused by early loss of zona pellucida or delayed transport of zygote 2. Ovarian: it may be Primary: implantation into ovary or Secondary: to tubal pregnancy rupture 3. Peritoneal “abdominal”: Mainly in recto-uterine pouch Anatomist “second week” Decidua  Definition : endometrium of pregnant uterus  Structure : as endometrium at secretory phase  Hormonal control : under effect of progesterone  Parts : Decidua capsularis: Definition: part of endometrium covering the fetus Fate: Fuse & Degenerate Decidua parietalis Definition: part of endometrium lining uterine cavity Fate: Fuse & Degenerate Decidua basalis: Definition: part of endometrium between fetus & myometrium Fate: Form maternal part of placenta Anatomist “second week” Blastocyst changes “Chorionic vesicle formation” 1.Trophoblast becomes: 1a.Syncytio-trophoblast: outer layer of trophoblast which: Produce proteolytic enzymes to erode the endometrium Secrets HCG "human chorionic gonadotropin" to keep coprpus luteum secreting progesterone for 4 months 1b.Cytotrophoblast: inner layer of trophoblast 2.Inner cell mass becomes Bilaminar disc formed of 2a.Epiblast: upper columnar layer 2b.Hypoblast: lower cuboidal layer 3.Blastocele becomes 3a.Amniotic cavity: between epiblast "form floor" & amnioblast "form roof" 3b.Primary Yolk sac: between hypoblast "form roof" & Hausser membrane "form floor" 4,Extra-embryonic mesoderm appears and divided by Extra-embryonic coelom into 4a.Somatic mesoderm: lining cytotrophoblast & covering amniotic cavity 4b.Splanchnic mesoderm: covering yolk sac N.B: Somatic & splanchnic mesoderm remain incontact at the caudal end of baby forming connecting stalk “umbilical cord” N.B: Chorion is formed of syncytiotrophoblast , cytotrophoblast & somatic extra-embryonic mesoderm Anatomist “second week”

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