Chapter 24 Development of digestive and respiratory system

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Chapter 24 Development of digestive and
respiratory system
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• digestive and respiratory system derived from
  primitive gut
• /foregut
• /midgut
• /hindgut
• ---epi. of digestive and respiratory system
  derived from endoderm
• ---CT and MT of digestive and respiratory system
  derived from splanchnic or visceral mesoderm

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1. Development of digestive system

• 1) derivatives of pharyngeal pouch
• ---pharyngeal pouch
• /outpocketings of endodermal lining of the
  primary pharynx (extends from the buccopharyngeal
  membrane to the tracheobronchial diverticulum)
• /5 pairs

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• ---derivatives of pharyngeal pouch
• ? First pharyngeal pouch
• ---distal portion widen into a sac-like
  structure-middle ear cavity, the branchial
  membrane form tympanic membrane or eardrum
• ---proximal part remain narrow to form the
  pharyngotympanic or Eustachian tube

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• ? Second pharyngeal pouch
• ---distal portion obliterated
• ---remaining part proliferate and form primordium
  of the palatine tonsil

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• ? Third pharyngeal pouch
• ---dorsal portion differentiates into inferior
  parathyroid gland
• ---ventral part cells differentiates and form
  two cell cords, fuse with each other behind the
  thorax to give rise to the promordium of the
  thymus

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• ? Fourth pharyngeal pouch
• ---dorsal portion forms superior parathyroid
  gland
• ---ventral portion degenerates
• ? Fifth pharyngeal pouch
• ---gives rise to the ultimobranchial body,
  immigrate into thyroid and differentiate into
  parafollicular cells

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• development of thyroid gland
• ---thyroid primordium by the 4th week,
  endodermal proliferation of the floor of
  primitive pharynx, then descends in front of the
  primitive pharynx as a bilobed diverticulum
• ---thyroglossal duct a narrow canal connecting
  primitive pharynx with thyroid primordium, by the
  6th week, becomes solid and disappears.

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• ---foramen caecum
• ---thyroglossal cyst and fistula a cystic
  remnant of the thyroglossal duct, may be found at
  any point along the migratory path followed by
  the thyroid gland sometimes a thyroglossal cyst
  is connected to the outside by a fistulous canal,
  called thyroglossal fistula

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• 2) development of esophagus and stomach
• ? development of esophagus
• ---derived from primitive gut extending from the
  laryngotracheal diverticulum to stomach
• ---with the descent of the heart and lungs, it
  lengthens rapidly
• ---muscular coat, formed by surrounding
  mesenchyme
• /striated in upper two-thirds
• /smooth in lower one-third

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• ? development of stomach
• ---by 4th week, appears as a fusiform dilation of
  foregut

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• ---greater and lesser curvatures by the 5th
  week, posterior part of stomach grow faster than
  the anterior portion
• ---by 7-8th week, around the longitudinal axis,
  the stomach carries out a 90clockwise rotation,
  its left side to face anterior

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• ---rotation around the transverse axis, the
  caudal(pyloric) end of the stomach moves upward
  and to the right the cephalic( cardiac)end moves
  downward and to the left

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• ? development of intestine
• a. midgut derivatives
• ---duodenum formation
• /formed by terminal part of foregut and the
  cephalic part of the midgut
• /C-shaped ventrally, rotates to the right

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• ---midgut loop by 5th week, midgut grow rapidly
  to form a U-shaped loop, its apex connects with
  yolk sac by way of the narrow vitelline duct
• /cephalic limb
• /caudal limb

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• ---physiological umbilical herniation during the
  6th week, midgut loop grow rapidly, enter the
  umbilical coelum---extra-embryonic coelom( in
  umbilical cord)

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• ---by 6-8th week, midgut loop rotates 90 around
  an axis formed by the superior mesenteric artery
  in a counterclockwise direction, move cephalic
  limb to right, caudal limb left

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• ---caecal swelling a conical dilation of the
  caudal limb, form caecum and appendix

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• ---by 10th week, midgut loop return to the
  abdominal cavity, simultaneously rotates 180 in
  a counterclockwise direction, move cephalic limb
  to left, caudal limb right

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• ---cephalic limb develop into jejunum and most
  part of ileum

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• ---caudal limb terminal part of ileum, caecum,
  appendix, 2/3 transverse colon

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• b. hindgut derivatives
• ---give rise to 1/3 transverse colon, descending
  colon, sigmoid

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• ---cloaca dilation of terminal part of hindgut,
  connect with allantois, closed by cloacal
  membrane

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• ---urorectal septum by 6-7th week, mesenchyma
  between hindgut and allantois proliferates and
  form a transverse ridge, divided the cloaca into
  urogenital sinus and anorectal canal

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• ---urogenital sinus ventral portion of cloaca,
  develops into bladder and urethra
• ---anorectal canal dorsal portion of cloaca,
  develops into rectum and upper segment of anal
  tube

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• 3) development of liver and pancreas
• ?development of liver and gall bladder
• ---hepatic diverticulum by beginning of 4th
  week, endodermal proliferation of end of the
  foregut

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• ---hepatic diverticulum extends into the septum
  transversum and divides into a large cephalic and
  a small caudal part
• ---cephalic part cells proliferate to give rise
  to hepatic cord and bile duct
• ---cystic diverticulum(caudal part) develop into
  gall bladder and cystic duct

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• ---the paired vitelline veins and umbilical vein
  form hepatic sinusoids
• ---at about 6th week, blood stem cell immigrate
  into liver from yolk sac, hemopoiesis begin

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• ? development of pancreas
• ---dorsal pancreatic bud and ventral pancreatic
  bud by the end of 4th week, arise from the
  endoderm of caudal part of the foregut
• ---dorsal pancreas, ventral pancreas
  pancreatic buds cells proliferate to give rise to
  acinus and ducts

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• ---the ventral pancreas rotates to right-dorsal
  direction and fuse with dorsal pancreas
• ---the ventral pancreas forms the inferior part
  of the head of the pancreas dorsal pancreas
  forms other part of pancreas

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• ---main pancreatic duct, together with the common
  bile duct, enters the duodenum at the site of the
  major papilla

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• 4) congenital malformations of the digestive
  tract
• ? atresia or stenosis of digestive tract caused
  by failure of recanalization or improper
  recanalization, mostly in esophagus and duodenum

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• ? congenital umbilical hernia caused by
  incomplete closure of the central part of the
  abdominal wall, the viscera return to the abdomen
  but herniated again during the fetal period

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• ? umbilical fistula and Meckel diverticulum
• ---umbilical fistula results from persistence
  of a patent vitelline duct, meconium or mucus may
  be found at the umbilicus
• ---vitelline sinus results when a small
  portion of duct remains and opens onto the skin
• ---vitelline cyst results when intermediate
  patent leaves

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• ---vitelline ligament vitelline duct persist as
  a fibrous cord, will cause intestinal obstruction
• ---Mcekels diverticulum caused by persistence
  of a shore length of the vitelline duct, that
  remains attached to ileum

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• ? congenital aganglionic megacolon results from
  the absence of ganglion cell of the
  parasympathetic ganglia, which cause failure of
  the distal segment to move the intestinal
  contents onward

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• ?imperforate anus, rectal atresia and rectal
  fistula
• ---imperforate anus results from failure
  rupture of anal membrane

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• ---rectal atresia due to a failure of the anal
  pit to develop or deviation of the urorectal
  septum in dorsal direction
• ---rectal fistula associate with an imperforate
  anus, between the rectum and the vagina or
  urinary bladder or urethra

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• ? abnormal rotation of the intestinal loop
  nonrotation or reversed rotation of the midgut
• ? atresia of the gall bladder and bile ducts
  results from failure of vacuolization of the
  epithelial cords or reopen

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• ? annular pancreas ventral pancreatic bud give
  rise to two branches, which rotate the duodenum
  in an opposite direction, the duodenum is
  completely surrounded by pancreatic tissue

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2. development of respiratory system

• 1) development of larynx, trachea and lung
• ---laryngotracheal groove by the begin of 4th
  week, shallow groove from the ventral wall of the
  foregut caudal to the hypobranchial eminence
• ---laryngotracheal diverticulum
  laryngotracheal groove deparated from foregut by
  the esophagotracheal septum

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• ---lung bud by the end of 4th week,
  laryngotracheal diverticulum forms two lateral
  outpocketings. By the 5th week, the right lung
  bud divides into three branches-main bronchi, and
  the left into two main bronchi. By the end of 2nd
  month, lobar bronchi divided into segmental
  bronchi. By the end of 6th month, approximately
  17 generations of subdivisions formed and give
  rise to terminal bronchi, respiratory bronchi and
  alveoli. By 7th month, type II alveolar cell
  appears.
• ---splanchnic mesoderm develops into the CT,
  cartilage, SM and visceral pleura

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• 2) congenital malformations
• ? tracheal stenosis or atresia caused by
  failure of reopen or unequal division of the
  foregut
• ? tracheoesophageal fistula imcomplete
  development or deviation of tracheoesophageal
  septum, with esophageal atresia

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• ? hyaline membrane disease( respiratory distress
  syndrome) incomplete development of type II
  alveolar cells, a membrane-like substance is
  formed from the injured pulmonary cells
• ? pulmonary agenesis and pulmonary hypoplasia