Download Chapter 24 Development of digestive and respiratory system

Chapter 24
Development of digestive
and respiratory system
* 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
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
---derivatives of pharyngeal pouch:
① First pharyngeal pouch:
---distal portion: widen into a sac-like structuremiddle ear cavity, the branchial membrane
form tympanic membrane or eardrum
---proximal part: remain narrow to form the
pharyngotympanic or Eustachian tube
② Second pharyngeal pouch:
---distal portion: obliterated
---remaining
part
proliferate
and
primordium of the palatine tonsil
form
③ 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
④ Fourth pharyngeal pouch:
---dorsal portion: forms superior parathyroid
gland
---ventral portion: degenerates
⑤ Fifth pharyngeal pouch:
---gives rise to the ultimobranchial body,
immigrate into thyroid and differentiate into
parafollicular cells
*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.
---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
2) development of esophagus and stomach
① 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
② development of stomach
---by 4th week, appears as a fusiform
dilation of foregut
---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 90°clockwise
rotation, its left side to face anterior
---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
③ 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
---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
---physiological umbilical herniation: during
the 6th week, midgut loop grow rapidly,
enter the umbilical coelum---extraembryonic coelom( in umbilical cord)
---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
---caecal swelling: a conical dilation of the
caudal limb, form caecum and appendix
---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
---cephalic limb: develop into jejunum and
most part of ileum
---caudal limb: terminal part of ileum, caecum,
appendix, 2/3 transverse colon
b. hindgut derivatives
---give rise to 1/3 transverse colon,
descending colon, sigmoid
---cloaca: dilation of terminal part of hindgut,
connect with allantois, closed by cloacal
membrane
---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
---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
3) development of liver and pancreas
①development of liver and gall bladder
---hepatic diverticulum: by beginning of 4th
week, endodermal proliferation of end of
the foregut
---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
---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
② 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
---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
---main pancreatic duct, together with the
common bile duct, enters the duodenum
at the site of the major papilla
4) congenital malformations of the digestive
tract
① atresia or stenosis of digestive tract: caused
by failure of recanalization or improper
recanalization, mostly in esophagus and
duodenum
② 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
③ 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
---vitelline ligament: vitelline duct persist as a
fibrous cord, will cause intestinal obstruction
---Mcekel’s
diverticulum:
caused
by
persistence of a shore length of the vitelline
duct, that remains attached to ileum
④ 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
⑤imperforate anus, rectal atresia and
rectal fistula:
---imperforate anus: results from failure
rupture of anal membrane
---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
⑥ abnormal rotation of the intestinal loop:
nonrotation or reversed rotation of the
midgut
⑦ atresia of the gall bladder and bile
ducts:
results
from
failure
of
vacuolization of the epithelial cords or
reopen
⑧ 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
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
---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
2) congenital malformations
① tracheal stenosis or atresia : caused by
failure of reopen or unequal division of the
foregut
② tracheoesophageal fistula; imcomplete
development
or
deviation
of
tracheoesophageal
septum,
with
esophageal atresia
③ hyaline membrane disease( respiratory
distress
syndrome):
incomplete
development of type II alveolar cells, a
membrane-like substance is formed
from the injured pulmonary cells
④ pulmonary agenesis and pulmonary
hypoplasia: