Fetal Membranes & Twins Lecture Notes PDF

 Fetal membranes 1. Amniotic cavity Definition: Cavity filled with amniotic fluid surrounding the embryo Development: wy...

 Fetal membranes 1. Amniotic cavity Definition: Cavity filled with amniotic fluid surrounding the embryo Development: wy  During the 2nd week,  Its floor is formed by epiblasts  Its roof is formed by amnioblasts & somatic extra-embryonic mesoderm  During the 3rd week, it communicates with the yolk sac da through neurenteric canal  During the 4th week, after folding it completely surrounds the embryo Amniotic fluid en Definition: Fluid filling amniotic cavity Amount: one liter at birth Structure:  99% water H Source: 1.amnioblast 2.placenta 3.fetal kidney main source” R.  1% (organics, inorganic salts, fetal epithelium) Circulation:  Amnioblast & placenta produce fluid in amniotic cavity → fetus swallow the fluid. D  Excess water passes via urinary system to amniotic cavity again  Waste products return to maternal blood Anatomist “folding & fetal membranes”  Function: 1. Prevent infection 2. Protect against trauma 3. Control body temperature 4. Maintain electrolyte balance 5. Allow free movement & prevent body adhesion 6. Allow symmetrical growth Protrude via cervix causing its dilatation during labor 8. When rupture, fluid wash vagina wy 7. Anomalies: Oligo-hydramnios: Definition: Fluid less than 0.5 liter Cause: da  Placental insufficiency  Renal agenesis  Urinary tract obstruction en Character: Fetal adhesion & anomalies Poly- hydramnios Definition: Fluid more than 2 liter Cause: H  Idiopathic “commonest cause”  Fetal cause: esophageal atresia  Maternal cause: diabetes R. Character:  Maternal & fetal distress  True knots of umbilical cord D Anatomist “folding & fetal membranes”  2. Yolk sac Definition: Cavity related to ventral surface of embryo Development wy  During the 2nd week, primary yolk sac has  Floor is formed by hausser membrane & splannchininc extra-embryonic mesoderm da  Roof is formed by hypoblast  During the 3rd week, 2nd yolk sac has communicates en with amniotic cavity through neurenteric canal  During the 4th week, after folding H  Part of yolk sac become incorporated inside baby to form gut R.  Part of yolk sac remains outside the baby forming definitive yolk sac  Both remain connected by vitello-intestinal duct D Anatomist “folding & fetal membranes” Anomalies:  Vitelline band: the vitelline duct is obliterated but not degenerated.  Vitelline fistula: persistence of whole vitelline duct.  Vitelline sinus: persistence of the distal part of vitelline duct. wy  Vitelline cyst: persistence of the middle part of vitelline duct.  Meckel’s diverticulum: Cause: persistence of the proximal part of vitelline duct. da Feature:  Occurs in 2% of people. en  Two times more in males than females.  Two inches long.  Two feet from the ileocecal junction. H  Contain ectopic gastric or pancreatic tissue. R. D Anatomist “folding & fetal membranes” Function: 1. Allantois: Definition: extension from caudal part of yolk sac into umbilical cord Fate: wy  Extra-embryonic part: degenerates  Intra-embryonic part” urachus”  Medial part: form apex of urinary bladder da  Distal part: form median umbilical ligament Anomalies:  Urachal sinus: persistence of the distal part of urachus. en  Urachal cyst: persistence of the middle part of urachus.  Urachal diverticulum: persistence of the proximal part of urachus. H  Urachal fistula: persistence of whole urachus. 2. Before function of placenta: Yolk Sac was responsible for nutrition to embryo R. 3. Before function of liver: Yolk Sac has haemopiotic function “RBCs formation” 4. Cells of gut migrate to gonads to form germ cells D Anatomist “folding & fetal membranes”  3. Umbilical cord Development :  During the 2nd week, the cord appears in the form of connecting stalk  During the 4th week, after folding it is carried from caudal end to ventral surface of the baby wy Structure: Primitive umbilical cord:  Length: 50 cm  Diameter: 1cm:  Attached to central part of placenta da  Structure:  Connecting stalk covered with amniotic sheath “ formed of extra-embryonic mesoderm which become loose → Wharton jelly” en  Allantois  Umbilical vessels “2 umbilical arteries & left umbilical vein”  Definitive yolk sac & vitello-intestinal duct Changes after birth:  H  Physiological hernia “6th -10th week” Allantois → median umbilical ligament & apex of urinary bladder R.  2 umbilical arteries → medial umbilical ligament  Left umbilical vein → ligamentum teres of liver  Definitive yolk sac & vitello-intestinal duct → degenerate D Anatomist “folding & fetal membranes” Anomalies According to attachment: wy  Eccentric: attached to placenta away from center  Marginal: attached to placental margin  Vilamentous: attached away from placenta da According to number: 2-3 umbilical cord According to knots  False: no placental circulation affection en  True: placental circulation stop causing fetal death According to length  Long: cause true knots formation H  Short: cause premature separation of umbilical cord Exomphalmus “omphalocele” : persistent physiological hernia after 10th week R. According to structure: the cord may contain 2 veins D Anatomist “folding & fetal membranes”  4. Chorion  Structure: Syncytiotrophblast, Cytotrophoblast & Somaric extra-embryonic mesoderm wy  Development:  Primary villi formed of syncytiotrophblast & Cytotrophoblast  Secondary villi formed of syncytiotrophblast & Cytotrophoblast da & Somaric extra-embryonic mesoderm  Tertiary villi formed of syncytiotrophblast & cytotrophoblast & Somaric extra-embryonic mesoderm & fetal blood vessels en  Types & Fate:  Chorion leave: chorion towards decidua capsularis Fate: Degenerates H  Chorion frondosum: chorion towards decidua basalis R. Fate: Form fetal part of placenta  Function:  Anchoring villi: fixation of the embryonic sac to the endometrium D  Absorbing villi: exchange of gases & materials between fetal & maternal blood. Anatomist “folding & fetal membranes”  5. Placenta Parts  Fetal part: formed by chorion frondosum wy  Maternal part: formed by Decidua basalis Structure Macroscopic structure: da  Shape: discoid  Diameter: 20cm  Thickness: 2 cm  Weight: 1/6 of baby weight "1/2 kg" en  Surfaces:  Maternal: Has cobblestone appearance  Fetal: Smooth with umbilical cord attached to it H Microscopic structure: Placental barrier  Definition: membrane separating maternal & fetal blood  Structure: R.  Before 20th week: Syncytiotrophblast & Cytotrophoblast & extra-embryonic mesoderm & fetal blood vessel  After 20th week: Syncytiotrophblast & extra-embryonic D mesoderm & fetal blood vessel  Late in pregnancy: Syncytiotrophblast, & fetal blood vessel Anatomist “folding & fetal membranes” Function  Protective: Protect fetus against maternal organism  Respiratory: Gas exchange by simple diffusion via placental barrier wy  Excretory: Fetus get rid of urea & uric acid by simple diffusion  Nutritive: All nutrition reach the embryo through the placenta  Secretory: hormonal secretions:  Human chorionic gonadotropin “HCG”: till 4th month to maintain corpus luteum to produce progesterone da  Progesterone: after 4th month  Melanin  Relaxin: before labour to relax the cervix en  Estrogen: before labour to increase sensitivity of endometrium to oxytocin  Lactogen: to stimulate milk formation Anomalies  Site of placenta: H  Number: placenta succentriata: accessory placenta  Placenta previa: see before R.  Placenta percreta: chorionic villi penetrate myometrium to surrounding organs  Site of umbilical cord attachment See umbilical cord D  Shape: Zonary, Irregular, Bipartite & Tripartite Anatomist “folding & fetal membranes”  Twins Definition: delivery of more than one embryo wy Cause :  Hereditary  Medical: administration of exogenous gonadotropin Types : Dizygotic Monozygotic da Incidence 70% 30% Source 2 oocyte + 2sperm = 2 zygote 1 oocyte + 1 sperm = 1 zygote Sex Appearance Viable Similar en Genetically Non - identical Identical Character Finger print According to stage of separation: Fetal membranes H Diamniotic dichorionic  At 2 cell stage: Diamniotic dichorionic"2 amnion, 2 chorion, 2 placenta" "2 amnion, 2 chorion, 2 placenta"  At blastocyst stage: Diamniotic monochorionic "2 amnion, 1 chorion, 1placenta" Conjoined twins:  At Bilaminar stage: Monoamniotic monochorionic"1amnion, 1chorion, 1placenta" R.  Cause: incomplete separation of embryonic disc  Character: twins may fuse at:  Head :cranio-pagus  Thorax: thoraco-pagus D  Ventral surface  Dorsal surface Anatomist “Twins” Anatomist “Twins”