Exercise 8 Pig Embryo (Posterior Sections)

Comparative Vertebrate Embryology SY 2014-2015 PIG EMBRYO (POSTERIOR SECTIONS) Levels of the Lung Buds (Stem Bronchi) and Foreleg Buds

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Comparative Vertebrate Embryology SY 2014-2015

paired posterior cardinal (postcardinal veins)  most dorsal vein  lying in place of the common cardinal veins in preceding level foreleg buds  pair of bud-like tissue masses from the dorsolatersal sides of the body  made up of an outer layer ectoderm – thickened at its apex as the apical ridge; core of mesoderm  at its core, interconnections of the ventral rami of the cervical and thoracic spinal nerves form the branchial plexus; nerves of the forelimb branch out from this esophagus  small middle hole beneath the pair of dorsal aorta lung buds  pair of vesicles on both sides of the trachea mediastinum  thick partition of mesenchyme  enclosing the trachea and the lung pleural cavity  pair of coelomic cavities on each side of the mediastinum  where the lung buds developed parietal pleura  lining of the lateral wall of the pleural cavity visceral pleura  medial epithelial lining of th pleural cavity  will cover the lungs septum transversum  mesenchymal partition extending across the body

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Comparative Vertebrate Embryology SY 2014-2015 posterior vena cava  blood vessel  embedded on the right side of the septum transversum  posteriorly, occupies a dorsal position in the substance of the liver  also known as inferior vena cava ventricle  thick-walled mass below the septum transversum

Level of the Liver and the Stomach

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Comparative Vertebrate Embryology SY 2014-2015

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Comparative Vertebrate Embryology SY 2014-2015 spinal cord  segmental nature of the nerves – arise on either side of the spinal cord, definite and clear, arise from the spinal cord by the roots dorsal root  contains the spinal ganglion and the sensory neurons  fibers from the dorsal root ganglion leading to the dorsolateral wall of the spinal cord  also known as afferent or sensory root ventral root  made up of motor fibers from motor neurons of the basal plate of the spinal cord  fibers coming from the ventrolateral wall of the spinal cord  join the sensory root  also known as efferent or motor root three branches of the spinal nerve trunk  dorsal ramus – carries fibers associated with the dorsal parts of the body (skin, deep muscles of the back, spinal column), close to the junction of the sensory and ventral root, small bundle of fibers which passes dorsolaterally, also known as lateral ramus  ventral ramus – carries fibers associated with the ventral and lateral body wall, large bundle of fibers which passes ventrolaterally  ramus communicans – branch from thr ventral ramus, carries fibers to the viscera via the prevertebral sympathetic chain, passes medioventrally to the sympathetic ganglion located above the dorsal aorta and the branchial plexus (innervates the limbs) dorsal root ganglion  darkly nucleated body on both sides of the spinal cord mammary ridges  pair of elevations on the dorsolateral part of the body  took the place of the foreleg buds in the series  present between the foreleg and hindleg buds descending aorta  fused dorsal aorta, paired in branchial region  posterior to the pharynx, fuse to form the median dorsal aorta  sends branches to the different parts of the body of the embryo below the branchial region  sympathetic ganglion – pair of ganglion immediately dorsal to the descending aorta mesonephros  functional kidney at this stage  located on both sides of the descending aorta  retroperitoneal, lies posterior to the liver  mesonephric duct – large oval canal found along its ventral margin glomerulus  knots of blood capillaries  located at the lower medial side of each kidney  surrounded by very flat epithelium called Bowman’s capsule  glomerulus and Bowman’s capsule make up the Malpighian corpuscle or renal corpuscle

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Comparative Vertebrate Embryology SY 2014-2015 mesonephric tubules  coiled tubules located at the outer lateral portion of each mesonephros  found connected at the corpuscles posterior cardinal veins  dorsolateral in the mesonephros  also known as postcardinal vein stomach  horizontally enlarged segment of the foregut  replaces the esophagus liver  large mass  has strands of cells (hepatic cord) and spaces between the strands (hepatic sinusoid)  divided into paired dorsal and ventral lobes posterior vena cava  large blood vessels  embedded in the substance of the liver  drains blood from the subcardinal sinus to be sent to the sinus venosus  receives blood from the ductus venosus  preceeding level, embedded in the septum transversum  posteriorly, found at the right side of the stomach, partly embedded on the dorsal portion of the liver  supported by the caval mesentery  also known as inferior vena cava or postcava ductus venosus  blood vessels ventral to the stomach  embedded between the dorsal and ventral lobes of the liver  formed by the invasion of the left and right umbilical veins by the liver cords  anteriorly, found emptying into the postcava dorsal mesogaster  part of the dorsal mesentery  holds the stomach in place  enlarges greatly in the adult  becomes the dorsal omentum of the adult  becomes aggregated with mesenchymal cells to form the spleen omental bursa  closed cavity to the right of the stomach  posteriorly, opens into the peritoneal cavity, opening is called epiploic foramen hepatogastric ligament  mesentery connecting the liver and the stomach  with hepatoduodenal ligament, constitute the lesser omentum of the adult falciform ligament  remnant of the ventral mesentery (lesser omentum)  attaches the liver to the ventral body wall

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Comparative Vertebrate Embryology SY 2014-2015 Level of the Common Bile Duct

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Comparative Vertebrate Embryology SY 2014-2015

somites  44 paired blocks from the posterior end of the myelencephalon to the tail  myocoel – lumen  myotome – dorsomedian part of the block, forms the skeletal muscles  dermatome – ventrolateral portion, forms the connective tissue of the dermis  sclerotome – ventromedian portion of the block, will migrate and surround the spinal cord and notochord, forms the vertebral column duodenum  small cavity  takes the place of stomach common bile duct  large thick-walled cavity  embedded on the dorsal lobe of the liver, to the right of the duodenum  posteriorly, enters the duodenum  but before doing so, gives off a rounded tube, cystic duct, below the bile duct, embedded on the ventral lobe of the liver  anteriorly, connected to a wider cavity, hepatic duct, that constricts to become the common bile duct posterior vena cava  more dorsally located  stays close to th right side of the dorsal mesentery almost at the right side of the descending aorta  drains blood from the subcardinal veins and the hepatic portal veins hepatic portal vein  blood vessel  embedded on the right lobe of the liver  earlier embryonic omphalomesenteric vein which drains blood from the intestine gonad rudiment  ridge-like thickening or swelling of the coelomic epithelium on the medial side of each mesonephric kidney big left and small right umbilical veins  blood vessels  embedded in the ventral lobe of the liver which lies on both sides of the cystic duct  anteriorly, join together in the lver as the ductus venosus

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Comparative Vertebrate Embryology SY 2014-2015 Level through the Gallbladder and Umbilical Cord

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Comparative Vertebrate Embryology SY 2014-2015

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Comparative Vertebrate Embryology SY 2014-2015 hepatic portal vein  mesentery between the dorsal and vnetral pancreatic rudiment, to the right of the duodenum  posteriorly, on the left side of the duodenum  continues as the superior mesenteric vein, to the intestinal loop which it drains  extends further into the umbilical cord as the common vitelline vein  drains further the yolk sac as the right and left vitelline veins  remains embedded on the dorsal mesentery dorsal pancreas  large mass  embedded in the dorsal mesentery above the duodenum  outgrowth from the duodenum, connected by duct of Santorini  also known as dorsal pancreatic rudiment ventral pancreas  mass embedded in the dorsal mesentery below the hepatic portal vein, to the right of the duodenum  develops as an outgrowth from the common bile duct, connected by duct of Wirsung – degenerates at once  also known as ventral pancreatic rudiment  dorsal and ventral pancreatic rudiments will fuse to form the pancreas gallbladder  cavity right below the dorsal mesentery bearing the duodenum  lies on a partially disappearing ventral lobe of the liver bounded by the pair of umbilical vein  continuation of the cystic duct paired umbilical veins  pair of blood vessels  took the position of the ductus venosus  right umbilical vein – smaller, degenerating  left umbilical vein – retain, where blood flows from the placenta  also known as allantoic vein cranial and caudal limb of the intestinal loop  protrusion of the intestinal loop into the extraembryonic coelom of the umbilical cord  cranial limb – more dorsal, anteriorly continuous with the duodenum, will become the small intestine  caudal limb – posteriorly continuous with the colon, will become the large intestine superior mesenteric vein and artery  blood vessels between the cranial and caudal intestinal limb, embedded in the mesentery  superior mesenteric vein – more dorsal  superior mesenteric artery – posterior ventrolateral branch of the descending aorta common vitelline vein  vein on top of the superior mesenteric vein  posterior section of the superior mesenteric vein left and right umbilical arteries  pair of blood vessels below the intestinal limbs  more dorsal than the 2 pairs of blood vessels below the limbs

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Comparative Vertebrate Embryology SY 2014-2015 allantois  cavity between the left and right umbilical arteries  finds its way out of the umbilical cord to join the urogenital sinus tail  lowermost portion  contains the spinal cord Level through the Urogenital Sinus and Umbilical Cord

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Comparative Vertebrate Embryology SY 2014-2015 subcardinal veins  veins on the ventromedian border of the mesonephros, ventral to the descending aorta  converge with each other by forming a subcardinal anastomosis of the subcardinal sinus on the area where mesonephros is in contact with each other  posterior or inferior vena cava – where blood contained from the posterior region enters, new channel to the heart  posterior portion of the postcardinal vein regress mesocolon  prominent mesentery  holds the caudal limb of the intestinal loop (small cavity, lowermost portion of the mesentery) mesonephric duct  pair of excretory duct of the mesonephros  found on each ventral limit of the mesonephros  posteriorly, continuous with the urogenital sinus urogenital sinus  inverted U-shaped structure  constitute the tail  both ends lead to the mesonephric duct rectum  cavity below the urogenital sinus, separated by the cloacal septum  cloacal septum not yet complete, urogenital sinus and rectum are still continuous towards the posterior section umbilical veins  prominent blood vessels on both sides of the umbilical cord  a pair right below the mesonephric duct, a pair on both sides of the upper mesenchymal mass that contains the tail  continuous with each other umbilical arteries  medial blood vessels below the mesocolon, lying on both side of the middle cavity, allantois  posteriorly, continuous with descending aorta allantois  flattened canal on the ventral wall of the urogenital sinus  emerges form the umbilical cord  joins the urogenital sinus umbilical cord  lightly stained area  holds the allantois, vitelline blood vesels, umbilical blood vessels, and the cranial limb of the intestinal loop  Wharton’s jelly – gelatinous connective tissue, matrix of the umbilical cord

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Comparative Vertebrate Embryology SY 2014-2015 Level of the Hindlimb Bud

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Comparative Vertebrate Embryology SY 2014-2015 hindleg bud  prominent thickenings on the lower portions of the sections  consist of an outer layer ectoderm and an inner core of somatic mesoderm  apical ectodermal ridge – thickened ectoderm pair of mesonephric duct  a pair close to the mesonephros, a pair at the lower level of the hindleg bud mesocolon  mesentery that holds at its higher level the caudal limb of the intestinal loop and at it lower level the colon ureter  small duct  emerges form the dorsal portion of the mesonephric duct  posteriorly, expands as the renal pelvis surrounded by a mass of cells called nephrotome Level through the Spinal Nerve

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Comparative Vertebrate Embryology SY 2014-2015

spinal ganglia  separates masses of nerve cell body on both sides of the neural cavity ventral roots of the spinal nerves  below the spinal ganglia  do not bear any spinal ganglion sclerotome  undulated portions next to where the spinal ganglia or ventral roots of the spinal nerves are  made of dense caudal portion and less dense cranial portion  vertebra formed by fusion of the caudal half of the sclerotome with the cranial half of the next caudal sclerotome myotome  indented area left of the undulation of the sclerotome  less dense dermatome  outermost dense area  covers the myotome  undulated but opposite to that of the sclerotome epidermis  ouer covering of th body intersegmental arteries  paired branches of the dorsal aorta on either side of the neural tube

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