Special Embryology 3 - Speaker Deck

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Development of Midgut (Page 37)

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Anatomy of GIT developed from midgut

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Dr. Sherif Fahmy

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Buccopharyngeal membrane Cloacal membrane Hindgut Midgut Foregut L.S. in folded embryo Heart Vitelline duct Cloaca Dr. Sherif Fahmy Septum transversum

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Formation of midgut loop that has: ▪ Cranial limb. ▪ Caudal limb. ▪ Apex that is connected to definitive yolk sac by vittelo-intestinal duct. ▪ Superior mesenteric artery in its axis (between 2 limbs)

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Anomalies of Midgut 1- Anomalies of mesenteries: - Mobile cecum due to persistence of a mesentery. - Reto-colic pocket due to defective fusion of mesentery. 2- Body wall defect: - Omphalocele (congenital umbilical hernia). - Gastroschisis (protrusion of part of the stomach). - Infantile umbilical hernia (due to defective closure of umbilicus). 3- Stenosis or atresia of intestinal lumen 4- Subhepatic cecum and appendix

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5- Abnormal rotation of midgut loop A- Arrest of rotation after 90 degree - Colon and cecum are on the left side of abdomen. B- Rotation for 90 degree to opposite direction - Transverse colon is deep to duodenum. 6- Remenants of vitelline duct -Meckel’s diverticulum. -Vitelline cyst -Vitelline fistula.

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90 degrees rotation in anticlockwise. 90 degrees rotation in clockwise direction

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Development of Hindgut (Page 41)

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Parts of Gut Developed from Hindgut Dr. Sherif Fahmy

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Congenital Anomalies 1- Imperforate Anus: Failure of rupture of anal membrane. 2- Congenital megacolon (Hirschprung Disease): due to absence of parasympathetic ganglia in the wall of the colon. 3- Anorectal agenesis: defective formation of rectum & anal canal. 4- Recto-vesical, recto-uretheral or recto-vaginal fistula. Due to defective formation of uro-rectal fistula. 5- Anal agenesis with or without fistula.

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Development of Kidney and Ureter (Page 44)

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Stages of Development of the kidney: •Human kidney is developed from intermediate mesoderm and passes through 3 stages : 1- Pronephros 2- Mesonephros 3- Metanephros

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Notochord Septum transversum Somites Dr. Sherif Fahmy Intermediate mesoderm

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Revision of Male Genital System

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Tunica vaginalis Tunica albuginea Vas deferens Fibrous septa Seminiferous tubules Rete testis Efferent ductules (vasa efferentia) Convoluted efferent ductules (lobules) inside head of epididymis Testicular artery Pampiniform plexus Body Tail of epididymis Dr. Sherif Fahmy Beginning of vas deferens Vestigue of processus vaginalis Mediastinum testis Tunica vasculosa

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Pronephros & Mesonephros

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Fate of Mesonephros 1- Mesonephric tubules: – Males: form vasa efferentia, lobules of epididymis (head of epididymis) and paradidymis. – Females: form epoophoron and paroophoron. 2- Mesonephric duct: - Males: Appendix of epididymis, Epididymis, vas deferens, seminal vesicle, ejaculatory duct, ureter and trigone of urinary. - Females: Gartner duct, ureter and trigone of urinary bladder.

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Metanephros (Permanent Kidney) (Page 47)

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1- Metanephros: •It is caudal part of intermediate mesoderm in the pelvic cavity. It forms metanephric cap (blastema) which divides into small masses following divisions of the ureteric bud. Each mass is called renal vesicles. •Each vesicle will form Bowman’s capsule, proximal convoluted tubule, loop of Henel and distal convoluted tubules.

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2- Ureter: • It arises from dorsum of mesonephric duct. • It elongates dorso-cranially to be in contact with metanephros which will form the metanephric cap. • Upper end of the ureter divides to form 2 – 3 major calyces, which further divides into many minor calyces which divide into collecting tubules. • Each collecting tubules will be covered with a piece of the metanephric cap which form renal vesicles which forms rest of the nephron except the collecting tubules which is developed from dividing ureteric bud. • Collecting tubules communicate with the rest of the nephron.

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Changes of external features of developing kidney: • Ascend of the kidney: It ascends from pelvic cavity to its adult site in the lumbar region on posterior abdominal wall. This is done by dorso-cranial elongation of the ureter pushing the kidney. • Change of blood supply: during ascend. • Loss of fetal lobulation: surface of the kidney becomes smooth. • Change of direction of hilum: from anterior to medial.

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CONGENITAL ANOMALIES A- KIDNEY • Renal agenesis: Unilateral or bilateral. • Congenital polycystic kidney: due to failure of communication between collecting tubules and rest of the nephron. • Horse shoe kidney: due to fusion between lower ends of both kidneys. Ascent is arrested at level of L3 vertebra. • Pelvic kidney: due to failure of ascend. • Ectopic kidney: abnormal site of the kidney. • Aberrant renal artery: additional artery that supplying the kidney. • Persistence of fetal lobulation: surface of the kidney shows lobulations.

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CONGENITAL ANOMALIES B- Ureter • Bifid ureter: Splitting of the upper part of the ureter. • Double ureter: Two separate ureters due to formation of 2 ureteric buds.