Development of the Digestive System Flashcards
What happens during week 1?
Fertilisation to implantation
What happens during week 2?
Bilaminar germ disk formation
Which gene is a transcription factor for establishing left sidedness?
PTX2
What happens during week 3?
Trilaminar germ disk formation -gastrulation
CNS induction
Neurulation
Makes ectoderm, mesoderm and endoderm
What process happens during week 3 to 8?
Organogenesis
What structures originate from the embryonic ectoderm?
Skin, CNS, PNS, ear and nose
What structures originate from embryonic endoderm?
Epithelial lining of the resp. system, GIT, glands, liver, pancreas, thyroid, urinary bladder
What structures originate from embryonic mesoderm?
Muscles, bones, cartilage, dermis, vascular system, urogenital system, spleen
When is the gut tube formed?
3rd and 4th week
What does lateral plate mesoderm give rise to?
Parietal and visceral mesoderm
How is the gut tube closed?
At cranial end by oropharyngeal membrane
At caudal end by cloacal membrane
Describe the molecular regulation of the craniocaudal organisation of the gut?
Secretion of sonic hedge hog (SHH) by the gut endothermal cells - creates signalling pathway fir HOX gene
What is HOX gene expression do?
In gut mesoderm
Causes craniocaudal organisation of the gut
What is the mesentery?
There is ventral and dorsal
Hangs the gut tube from the body wall
Double layers of peritoneum
What is the origin of the mesentery?
Mesodermal
What does the mesentery enclose?
Intraperitoneal organs
Where does the oesophagus develop from?
Cranial part of the gut tube
Foregut
Lung bud develops from ventral wall of the foregut
Tracheo-oesophageal ridge between
How is the stomach developed?
Foregut caudal to oesophagus dilates to form stomach
Creates the greater and lesser curvatures
Explain the rotations if the stomach when developing
90 degree clockwise around longitudinal axis
Rotation along antero-posterior axis
What is the mesogastrium?
The mesentery which attaches the stomach to the dorsal and ventral wall
How is the omental bursa behind the stomach formed?
Rotation along the longitudinal axis pulls the dorsal mesentery to the left
What does the greater and lesser omentum connect?
Greater - liver and stomach
Lesser - down from stomach along greater curvature to become 4 layers
Explain the formation of the duodenum
Formed from caudal part of foregut and cranial part of midgut tube
What arteries supply the duodenum?
Coeliac trunk and superior mesenteric artery
What are hepatocytes and biliary epithelia formed from?
Endodermal origin
What is the origin of kupffer cells, haematopoietic cells and CT?
Mesodermal origin
What is the origin of the spleen?
Mesodermal at week 5
In spleen, what happens at week 15-17?
Colonised T-lymphocytes
In spleen, what happens at week 23?
The B cell precursors arrive and spleen starts its lymphoid function
What is the origin of the pancreas?
Endodermal at week 5
What happens at week 6 when developing the pancreas?
As duodenum rotates the ventral bud also moves close to dorsal bud
Major papilla formed
What is the major papilla?
Bile duct and major pancreatic duct
What does the midgut contain?
Extends from opening of bile duct into the duodenum to proximal 2/3rds of transverse colon
How is the primary intestinal loop formed?
Anti-clockwise rotation at week 6
Intestine develops in umbilical cord and moves back to abdominal cavity at week 10
What is the vitelline duct?
Connects the ilium with yolk sac up to the 12-14th week
What does the midgut loop develop into?
Part of duodenum, jejunum, ileum, ascending colon, and 2/3rds of transverse colon
When does cecal bud form?
Week 6
What are common anomalies in the midgut?
Stenosis, malrotation - reversed rotation
Describe omphalocele
Failure of retraction of herniated intestinal loop through umbilical ring at week 10
What could be caused from Vitelline duct remaining?
Fistula, cyst,, ligament or Meckel’s diverticulum
What is formed from hindgut endodermal development?
Distal 1/3 of transverse colon, descending colon, sigmoid colon, rectum and upper part of anal canal
What is formed from hindgut ectodermal development?
Lower part of anal canal and anal orifice
When does the cloacal membrane rupture?
Week 7
What are some developmental anomalies of the hindgut?
Urorectal fistula, rectovaginal and rectoperineal fistula
Imperforated anus
