2.1 Development of the gut 1+2 Flashcards
what are the 3 layers of the trilaminar disc?
ectoderm
mesoderm
endoderm
what is formed from the ectoderm?
skin hair epidermis nails nerve tissue
what is formed from the endoderm?
inner epithelial lining of GI
respiratory tract
urinary tract
reproductive tract
what 3 segments does the mesoderm develop into?
paraxial mesoderm
intermediate mesoderm
lateral mesoderm
what does the paraxial mesoderm give rise to?
somites
- skeletal muscle
- cartilage
- vertebrae
what does the intermediate mesoderm give rise to?
gonads and kidneys
what does the lateral plate mesoderm give rise to?
splits into two sections.
splanchnic section forms viscera
somatic section forms body tissue
what process does the embryo begin in the 4th week?
lateral folding
craniocaudal folding
what does lateral folding achieve?
creates ventral body wall
primitive gut becomes tubular
what does cranio caudal folding achieve?
creates cranial and caudal pockets from yolk sac endoderm
what are blind diverticula?
the blind ends at the cranial and caudal ends of the primitive gut tube
what is the opening into the umbilicus from the midgut called?
the vitelline duct
what are the 3 embryonic divisions of the primitive gut tube?
foregut
mid gut
hindgut
what are the structures of the foregut
oesophagus stomach pancreas liver bile ducts gallbladder midpoint of the second part of the duodenum lower respiratory tract
what are the structures of the midgut
distal duodenum jejunum ileum caecum ascending colon 2/3 of transverse colon
what are the structures of the hindgut
distal 1/3 of the transverse colon descending colon sigmoid colon rectum upper anal canal cloaca
why is it a problem if the vitelline duct persists after birth ?
- meckels diverticulum - outpouching in small intesting - favoured area for carcinogens
- connection between midgut and umbilicus
what does the intraembryonic coelom form?
the abdominal and thoracic cavities, which are seperated by the developing diphragm
what is the splanchapleuric mesoderm?
where the splanchnic portion of the lateral mesoderm adheres to the endoderm of the gut. Forms viscera
what is the somatopleuric mesoderm?
where the somatic portion of the lateral mesoderm adheres to the ectoderm to create body walls and dermis
what structures are formed from the mesodermal membrane sorrounding the intraembryonic coelom?
pericardium
pleural membrane
peritoneum
what is a mesentery?
a double fold of peritoneum suspending the gut tube and viscera from the abdominal wall
what is the purpose of mesenteries?
allow a conduit for blood and nerve supply
allow mobility where needed
what embryonic structure forms the mesenteries?
condensation of splanchnic mesoderm
describe the difference between the ventral mesentery and the dorsal mesentery
dorsal mesentery = supplies the entire aspect of the gut
vental mesentery = only suspends the foregut
what structure does the right sac of the foregut peritoneum become?
becomes the lesser sac the lies behind the stomach
what does the left sac of the foregut peritoneum become?
the greater sac
what are omenta?
specialised regions of periotoneum
what forms the greater omentum
the dorsal mesentery
what forms the lesser omentum
ventral mesentery
what does the free edge of the lesser omentum conduct?
the portal triad
what are the consequences of the rotation of the stomach?
Puts the vagus nerves anterior and posterior to the stomach (instead of left and right)
• Shifts cardia and pylorus from the midline
• Stomach comes to lie obliquely
• Contributes to moving the lesser sac behind the stomach
• Creates the greater omentum
how do retroperitoneal structures vary from secondary retroperitoneal structures
retroperitoneal were never in the peritoneal cavity and never had a mesentery
secondarily retroperitoneal began development invested by peritoneum. Had a mesentery but with successive development, the mesentery is lost through fusion at posterior abdominal wall
when does the buccopharyngeal membrane rupture?
in the 4th week to form the mouth
when is the anus formed?
in the 7th week by the rupture of the cloaca
what is the blood supply to the foregut?
coeliac artery
what is the blood supply to the mid gut?
the superior mesenteric artery
what is the blood supply to the hindgut?
the inferior mesenteric artery
what is the function of the tracheoesophageal septum
to cleave the respiratory bud from the oesophagus in the foregut at the 4th week of development
what can happen if there is a problem with tracheoesophageal septum development?
blind-end oesophagus
tracheoesophageal fistula
what changes happen to the lumen of the gut during development?
5TH week = lumen closes due to endoderm proliferation
9th week = recanalisation of the gut lumen
describe the development of the stomach
develops on the dorsal aspect of the foregut before being rotated 90 degrees to lie obliqely
why do visceral and parietal peritoneum localise pain differently
visceral peritoneum derived from the splanchnic mesoderm = vague pain
parietal peritoneum derived from the somatic mesoderm = can localise pain
where does the spleen develop in the embryo?
in the dorsal mesentery of the foregut
where does the liver develop in the embryo?
in the ventral mesentery of the foregut
how does the foregut rotate in development?
90 degrees clockwise
what does the right and left vagus nerves become?
right vagus = posterior vagal trunk
left vagus = anterior vagal trunk
what is the connection between the greater and lesser sac called?
the foramen of winslow / epipolic foramen
where is the falciform ligament?
remenants of the ventral mesentery, anterior wall of abdomen to the liver
where is the lesser omentum
mesentery between the liver and the stomach
where is the gastrosplenic ligament?
connection from the stomach to the spleen
where is the splenorenal mesentery?
between the spleen and the posterior abdominal wall
how does the pancreas develop?
Develops in 2 buds
Ventral section buds from the hepatic diverticulum. Larger dorsal bud branches from the foregut beneath the stomach. ventral bud moves around posteriorly to sit beneath the dorsal bud when the foregut rotates. buds fuse.
Describe the development of the duodenum
Develops from the caudal foregut and cranial midgut.
Shape determined by rotation of stomach. Becomes secondary retroperitoneal