Embryology of the GI Flashcards
omphalocele
A new born baby born with herniation of abdominal viscera through an
enlarged umbilical ring
how long is the process of fertilisation to implantation in week 1
51/2 to 6 days
what occurs during week 2
bilaminar germ disk is formed
which gene is a transcription factor for establishing left sidedness
PTX2
what occurs during week 3
trilaminar germ disk formation (gastrulation)
what 3 processes occur during week 3
gastrulation
CNS induction
Neurulation
what three parts make up the trilaminar germ disc
ectoderm
intraembryonic mesoderm
endoderm
organogenesis
organ malformation can happen during this period from exposure to any teratogenic substance
when can organogesis occur
week 3-8
teratogens
drugs
virus
thalidomide (limb deformities)
what structures originate from ebryonic ectoderm
Skin (epidermis, hair, nail), CNS,PNS, sensory epithelia of the eye,ear, nose & other structures (pituitary,mammary and sweat glands, enamel of teeth),adrenal medulla etc.
what structures originate from embryonic endoderm
Epithelial lining of Respiratory system, GIT, glands, liver (hepatocyte and biliary epithelium), pancreas,
thyroid, parathyroid parenchyma, urinary bladder etc.
Embryonic mesoderm
- muscles, bones,cartilage, dermis, vascular system, urogenital system except bladder, spleen, liver
mesenchyme, adrenal cortex etc.
when does the development of the gut tube occur
during the 3rd and 4th week drom the endodermal lining of the yolk sac
what gives rise to parietal and visceral mesoderm
lateral plate mesoderm
what does parietal layer line
body cavity
what does visceral layer line
gut tube
what happens to the connection of the gut tube with the yolk sac over time
it becomes smaller until it is only connected at umbilical cord by vitelline duct
when does the connection between the gut tube and yolk sac no longer exist
12-14 weeks
what is the gut tube closed by at the cranial end
oropharyngeal membrane
what is the gut tube closed by at the caudal end
cloacal membrane
sonic hedgehog signalling pathway
secretion of SHH by gut stimulates expression of HOX gene
craniocaudal organisation of gut
Instructs what it should become - eg small intestine, large intestine or cloaca
mesentery
ventral and dorsal
double layers of peritoneum
hangs the gut tube from body wall
encloses organs (intraperitoneal)
what does the foregut include
extends from lung bud diverticulum to bile duct opening of the duodenum, consists of pharync oesophagus stomach and perennial part of duodenum
what does the oesophagus develop from
cranial part of the gut tube
where does the lung bud develop from
ventral wall of the foregut
4 weeks
Tracheo- oesophageal
septum (ridge)
The formation of a tracheoesophageal septum will divide the ventral trachea from the dorsal esophagus.
Failure to separate will result in tracheoesophageal fistula
what forms the stomach
foregut dilates to form the stomach
week 4
creates lesser and greater curvatures
what is the longitudinal rotation of the stomach
90 degrees rotation
what is the second rotation of the stomach
Rotation along antero-posterior axis
how is the stomach attached to both the ventral and dorsal wall
a mesentery called mesogastrium
what does rotation along the longitudinal axis do to the mesentery
pulls the dorsal mesentery to the left
creates omental bursa behind the stomach (lesser sac)
what is the duodenum formed from
caudal part of the foregut and the cranial part of the midgut tube
blood supply of duodenum
Both coeliac trunk and
superior mesenteric artery
retroperitoneal and duodenum
anatomical space (sometimes a potential space) behind (retro) the peritoneum
duodenum is retroperitoneal except from the duodenal cap
what week of gestation is the liver bud formed
week 3
hepatocytes, biliary epithelia
endodermal in origin
Kupffer cells, haematopoietic cells and connective tissue
mesodermal origin (septum
transversum)
Falciform ligament and lesser omentum
develops from ventral mesentery
Gall bladder and cystic duct
(endodermal origin)
what week of gestation does bile form
12th week
spleen
mesodermal origin
week 5
spleen in Weeks 15 to 17
colonised by T lymphocytes
spleen in week 23
the B-cell precursors arrive and spleen starts it’s lymphoid function
pancreas
endodermal in origin (wk-5)
what happens as the duodenum rotates
the ventral bud also moves close to the
dorsal bud (wk-6)
(bile duct and major pancreatic duct)
Major papilla
Incomplete separation of lung bud
oesophageal atresia and tracheo-oesophageal
fistula
what are some development abnormalities of the foregut?
Obliterated bile duct, distended hepatic duct
Duplication of gall bladder
Accessory pancreatic duct
where does the midgut extend to and from?
from opening of bile duct into the duodenum to proximal 2/3rds of the transverse colon
describe the formation of the primary intestinal loop?
Anti-clockwise rotation
Physiological herniation of intestinal loop (Wk-6)
Vitelline duct connects the ilium with yolk sac (up to 12th-14th wk)
Intestinal loops begin to move back into the abdominal cavity (wk-10)
what develops around week 6 during formation of primary intestinal loop?
cecal bud develops
what occurs after Intestinal loops begin to move back into the abdominal cavity (wk-10)
The midgut loop elongates and will differentiate into part of the duodenum, jejunum, ileum, ascending colon, and two- thirds of the transverse colon
what are common developmental abnormalities of the midgut?
Common anomalies: stenosis, malrotation etc.
omphalocele
Failure of retraction of herniated intestinal loop through umbilical ring at week-10
what happens when the vetelline duct persists
In 2-4% people a small vitelline duct persists
May form fistula/cyst / ligament/Meckel’s dive
describe the development of the hindgut
Endodrmal origin: Distal 1/3rd transverse colon, descending colon, sigmoid colon, rectum and upper part of the anal canal.
*Ectodermal origin: Lower part of the anal canal and anal orifice
what is the origin of the cranial part of the anal canal
endodermal
what is the origin of the caudal part of the anal canal
ectodermal
what happens to the cloacal membrane at week 7 gestation
it ruptures
what are the developmental abnormalities of the hindgutt?
urorectal fistula
rectovaginal fistual
rectoperineal fistula
imperforate anus
