Devt. Anat. Block C

• coalescence of coelomic spaces in the extraembyronic mesoderm during 2nd week of development
• subdivides lateral mesoderm into somatic mesoderm (associated with chorion/amniotic cavity) and splanchnic mesoderm (associated with endoderm around the yolk sac)

• outer layer of lateral mesoderm associated with chorion/amniotic cavity
• forms parietal layers (parietal pleura, parietal pericardium & parietal peritoneum)

• layers of lateral mesoderm associated with endoderm around yolk sac
• forms visceral layers (visceral pleura, visceral pericardium, & visceral peritoneum)

paraxial, intermediate, lateral

• coalescence of small coelomic spaces appearing in lateral mesoderm
• divides lateral mesoderm into somatopleure (superficial ectoderm + somatic mesoderm) and splanchnopleure (endoderm + splanchnic mesoderm)

• endoderm + splanchnic mesoderm
• forms gut & viscera (organs)

• superficial ectoderm + somatic mesoderm
• forms body wall & parietal layers

• anterior curve: pericardial cavity
• limbs of curve: pleural/peritoneal cavities (2)

• rostral/anterior curve of intraembryonic coelom
• surrounds developing heart

• connect pericardial cavity with pleural/peritoneal cavity
• dorsal to septum transversum
• lateral to developing gut

• separates the pericardial & pleural cavities from the peritoneal cavity
• formed from septum transversum (central tendon), pleuroperitoneal membranes (small dorsal portion), dorsal mesentery of esophagus (crura), body wall (peripheral edges)

• septum transversum
• pleuro-pericardial membranes (2)
• pleuro-peritoneal membranes (2)

suspends entired gut from posterior abdominal wall

disappears except at most caudal region of foregut to form falciform ligament of liver

ventral mesentery

• pleuropericardial membranes fuse with mesodermal mesenchyme ventral to esophagus
• separates pericardial cavity from pleural cavities

• septum transversum: central tendon
• pleuroperitoneal membranes: small dorsal portion
• dorsal mesentery of esophagus: crura of diaphragm
• body wall: peripheral edhes (muscular ingrowth mostly on dorsal aspect)

expansion of the pleural cavities into the lateral body wall causing portion of the body wall to form peripheral parts of the diaphragm

• sunken/funnel chest
• results from short central tendon of the diaphragm which pulls on the inferior portion of the xiphoid portion of the sterum creating a depression of the sternum & anterior chest and flaring of the costal cartilages of ribs 7-10

• results from failure of fusion of pleuroperitoneal membranes creating a hole (foramen of Bochdalek) posterolaterally (usually on left)
• Morgani hernia: failure of fusion between septum transversum & lateral body wall
• hiatal hernia: delay in descend of stomach
• Bochdalek hernia: posterolateral defect due to failure of fusion of pleuroperitoneal membranes
• abdominal contents in thoracic cavity, patient presents with "flat abdomen"
• negatively affects lung development

failure of fusion between septum transversum & lateral body wall

delay in descent of stomach (keeping hiatus larger)

posterolateral defect due to failure of fusion of pleuroperitoneal membranes

• central portion: phrenic n (C3,4,5)
• peripheral portions: lower intercostal nn

• endoderm: gives rise to epithelium & glands
• splanchnic mesoderm: gives rise to muscular & fibrous elements of gut tube

• head fold: involves mouth (stomodeum)
• tail fold: involves anus (proctodeum)
• lateral fold: pinches off dorsal aspect of yolk sac

pharynx, esophagus, stomach, proximal duodenum (proximal to bile duct), liver, pancreas, gallbladder

celiac trunk

superior mesenteric artery

inferior mesenteric artery

small intestines (including duodenum after common bile duct), cecum, appendix, ascending colon, proximal 2/3 of transverse colon

distal 1/3 of transverse colon, descending colon, sigmoid colon, rectum, upper part of anal canal

fusion of two sides forms tracheoesophageal septum dividing esophagus & laryngotracheal tube

• defect in esophageal development due to malformation of tracheoesophageal septum resulting in a blind end esophagus
• causes polyhydramnios (baby can't swallow)

malformation of the esophagus; communication between the esophagus & the respiratory tract

• defect of esophageal development in which there is a narrowing of the esophagus
• can lead to short esophagus & congenital hiatal hernias

• caudal part of foregut rotates 90* clockwise
• dorsal border forms greater curvature (moves to left)
• ventral border forms lesser curvature (moves to right)
• original left side - ventral
• original right side - dorsal
• left vagus n: anterior vagal trunk
• right vagus n: posterior vagal trunk

muscular hypertrophy of gastric pylorus causes constriction of pyloric region of stomach & leads to non-bilious projectile vomiting

• dorsal mesentery of the stomach
• elongates to form greater omentum

• lesser sac of peritoneum
• begins as a series of clefts in dorsal mesogastrium which coalesce forming a single cavity

• greater omentum (gastrosplenic ligament, gastrophrenic ligament, gastrocolic ligament)
• mesentery proper
• lienorenal ligament
• transverse mesocolon
• mesoappendix
• mesocecum
• sigmoid mesocolon
• phrenicolic ligament

• lesser omentum (hepatogastric & hepatoduodenal ligaments)
• falciform ligament & ligamentum teres hepatis

foregut & midgut

celiac trunk & superior mesenteric artery

partial recanalization of duodenum (parts 3 & 4) causing bilious vomit (stenosis below ampulla of Vater)

• no recanalization of duodenum
• bilious vomit (atresia below ampulla of Vater)
• double bubble sign: fluid building up in stomach & duodenal bulb

• liver bud of endoderm that grows ventrally from distal end of foregut & invades the septum transversum
• cranial portion: liver
• caudal portion: gallbladder
• stalk: cystic duct & common bile duct

12 weeks

first few bowel movements of an infant; contain a large amount of bile (dark green)

• ventral bud: uncinate process & inferior head of pancreas
• ventral bud + distal dorsal bud: main pancreatic duct
• proximal dorsal bud: accessory pancreatic duct

defect caused when the ventral pancreatic bud surrounds the descending duodenum upon rotation & causes obstruction of the duodenum

herniation, return, fixation

when the cranial and caudal limbs do a 90* clockwise rotation around the superior mesenteric artery

• regression of mesonephros
• reduced growth of liver
• relatively small abdominal cavity

• leads to fusion of layers of the greater omentum & fusion of greater omentum with transverse mesocolon
• establishes secondarily retroperitoneal structures

• 2,3,4 parts of duodenum
• pancreas
• ascending colon
• descending colon

• Ileal (Meckel's) diverticulum: incomplete obliteration of vitelline duct
• umbilicoilieal fistula
• omphaloceoele
• gastroschisis

• fuses with cloacal membrane
• divides cloaca into urogenital sinus & anorectal canal
• perineal body: in between

divides upper 2/3 of anal canal from lower 1/3

longitudinal ridge of intermediate mesoderm that runs along dorsal aorta; pushes out from the body wall into the coelom

part of urogenital ridge that runs the entire length of the embryo & gives rise to the urinary system

first kidney which begins development at beginning of 4th weeks but degenerates by the end of the 4th week

middle kidney which begins to form at end of 4th week

• definitive kidney; appears as small projection off mesonephric duct in 5th week
• develops from ureteric bud (metanephric diverticulum) & metanephrogenic blastema (metanephric mass)

• connect to mesonephric duct
• in females: degenerate (remnants - epoophoron & paroophoron)
• in males: develop into efferent ductules (remnant - paradidymis)

• AKA Wolffian duct
• empties into cloaca
• in females: degenerates (remnants - appendix vesiculosa, duct of Gartner)
• in males: forms vas deferens, epididymis, seminal vesicles & ejaculatory duct (remnant - appendix epididymis)

intermediate mesoderm

external iliac branches - abdominal aorta branches - renal arteries

multiple renal arteries can exist if arteries do not degenerate properly; can lead to hydronephrosis

connects to cloaca; constricts proximal end to form urachus

extends from the apex of the bladder to the umbilicus (median umbilical fold)

invagination of ectoderm that fuses with urorectal septum dividing area into urogenital membrane (anteriorly) & anal membrane (posteriorly)

point where urorectal septum  pushes through cloaca & makes contact w/ skin

mesenchyme that pushes through & divides the cloaca into urogenial sinus & anorectal canal

• vesical part: forms majority of urinary bladder (both sexes)
• pelvic part: forms entire female urethra; forms prostatic & membranous male urethra
• penile part: forms penile (spongy) male urethra

represents portion of bladder where mesonephric ducts were incorporated; becomes overgrown by endoderm

• abscence of kidney due to failure of ureteric bud to form
• unilateral: other kidney will undergo compensatory hypertrophy
• bilateral: incompatible with life

kidneys are filled with cysts & nonfunctional

kidney fails to undergo ascent & remains functional

inferior mesenteric artery causes midline obstruction; blocks complete ascent of fused kidneys

ureters end in places other than bladder (vagina, prostate, urethra)

• cysts: improper closure of allantois in region of umbilicus
• sinus: discharge of clear cyst fluid near umbilius
• fistula: constant discharge of urine & cyst fluid from bladder & cyst

incomplete closure of musculature of the abdominal wall that causes exposure & erosion of anterior wall of bladder; urine is constantly secreted

• cortex: mesoderm
• medulla: ectoderm + NCC invasion

develop in medulla of suprarenal glands from NCCs

abnormal increase in testosterone production by adrenal glands

• undergo similar development in both male & female
• external cortex & internal medulla
• stage occurs in development of gonads, ducts & external genitalia

Mullerian duct; forms alongside mesonephric duct (gonads develop medial to both ducts)

• antimullerian hormone
• AKA mullerian inhibiting substance
• secreted by Sertoli cells to inhibit development of paramesonephric duct, driving it to apoptosis in males

testes determining factor: present on the Y chromosome driving development in male direction

interstitial cells that develop in the mesenchyme outside of primary sex cords; responsible for secretion of testosterone by the 8th week of development

• inward proliferation of mesothelium into mesnchyme; colonized by PCGS
• males: become seminiferous cords
• females: obliterated & replaced by secondary sex cords

projection of the peritoneum that pusches down the muscle & fascia into future scrotum

peritoneal layers that remain with testis in adult after processus vaginalis has been obliterated

herniation of gut into scrotum through patent processus vaginalis (indirect hernia)

failure of testes to descend; spermatogenesis may be affected

presence of excess fluid in persistant process vaginalis

presence of blood in persistant processus vaginalis; collection of blood in tunica vaginalis

veins of pampiniform plexus are elongated & dilates (usually on left)

hernia occuring as an adult due to maintained connection between peritoneal cavity & tunica vaginalis (patent processus vaginalis)

• male: testes, seminiferous tubules, rete testis, sertoli cells, leydig cells
• female: ovary, primordial follicles, rete ovarii

• male: gubernaculum testis (testicular ligament)
• female: round ligament of the uterus, ovarian ligament

• male: efferent ductules, paradidymis
• female: epoophoron, paroophoron

• males: appendix epipdidymis, epididymis, ductus deferens, seminal vesicles, ejaculatory duct
• females: appendix vesiculosa, duct of Gartner
• both: ureter, pelvis, calices & collecting tubules

• male: appendix testes
• female: uterine tubes, uterus, cervix, superior 1/3 of vagina, hydatid of Morgani

• male: bladder, prostate gland, prostatic urethra, prostatic utricle, membranous urethra, bulbourethral glands, penile urethra
• female: inferior 2/3 vagina, bladder, urethra, urethral & paraurethral glands, greater vestibular glands

• male: seminal colliculus
• female: hymen

• male: glans & body of penis
• female: clitoris

• male: ventral aspect of penis
• female: labia minora

• male: scrotum
• female: labia majora & mons pubis