Development of the GI Tract

Question 1

The structures in the primitive embryo

Answer 1

Ectoderm
Mesoderm
Endoderm

Question 2

What does the ectoderm form

Answer 2

Brain, spinal cord, skin, epithelia

Question 3

What does the mesoderm form

Answer 3

Connective tissues, bones, cartilage, blood, muscle

Question 4

What does the endoderm form

Answer 4

Guts

Question 5

Formation of the primitive gut

Answer 5

Trilaminar disk folds in on itself
Left of ectoderm forms brain
Right of ectoderm forms bottom of spinal cord

Left of endoderm forms pharynx, oesophagus, stomach, duodenum
Middle of endoderm forms jejunum, ileum, caecum, asc colon
Right of endoderm forms desc colon, caecum, rectum

Top of allantois forms part of urinary tract

Question 6

Structure of the embryo once the trilaminar disk folds in on itself

Answer 6

Coelomic cavities form peritoneum either side of gut tube

Question 7

Structure and function of the mesenteries

Answer 7

Double fold of peritoneum forms mesentery
Allows blood vessels like abdominal aorta, blood supply => gut tube
Foregut only has ventral mesentery
Fore, mid, hind gut has dorsal mesentery

Aorta
Dorsal mesogastrium
Gut tube
Ventral mesogastrium

Question 8

The vitelline duct and allantois, blood supplies

Answer 8

Mid and hind gut don’t have anterior connection, connected to yolk sac and allantois, form umbilical cord

Coeliac trunk supplies foregut, comes off aorta
Superior mesenteric artery supplies midgut, part of umbilical cord and vitelline duct
Inferior mesenteric artery supplies hindgut

Umbilical arteries pass into umbilical cord

Question 9

Structure of the foregut

Answer 9

Pharynx, oesophagus
Lower respiratory tract
Stomach
Duodenum
Liver, pancreas
Biliary apparatus

Question 10

Pharynx formation

Answer 10

Empty canal
Canal filled up with cells
Vacuoles form in canal
Forms canal

Question 11

Problems in pharynx formation

Answer 11

Stenosis = lumen too narrow
Duplication = 2 canals form, bacteria can accumulate
Atresia = canal is closed off

Question 12

Lower respiratory tract formation

Answer 12

Respiratory diverticulum buds off from oesophagus
Tracheooesophageal septum forms during separation
Forms pharynx and trachea
Trachea forms lung buds

Question 13

Problems in oesophagus and trachea formation

Answer 13

Atresia of oesophagus
Fistula formation between trachea and oesophagus
Atresia and fistula formation

Question 14

Development of pancreas

Answer 14

Dorsal pancreas buds off on L
Ventral pancreas, gall bladder and hepatic system branch off from bud on R
Ventral pancreas grows and rotates around joins w dorsal pancreas to form 1 pancreas (becomes the asinate process)
Ductal system passes from dorsal pancreas to ventral pancreas into duodenum

Question 15

Structures in the midgut

Answer 15

Duodenum, distal to bile duct opening
Jejunum and ileum
Caecum and appendicitis's
Asc colon
Proximal 2/3 of transverse colon

Question 16

Midgut umbilical herniation

Answer 16

Midgut = cranial limb
Hindgut = caudal limb

Stage 1 = elongation
Intestines herniate out due to rapid growth and
Stage 2 = 90 degree anticlockwise twist
Stage 3 = 180 degree anti clockwise twist, elongated tubes brought back into abdominal cavity
Eventually large bowels are on the right, small bowel ends up on left

Question 17

Abnormal midgut rotation

Answer 17

Reversed rotation
Non rotation
Mixed rotation

Question 18

Reversed rotation

Answer 18

Stage 3 reversed, clockwise

Duodenum in front of large bowel instead of the other way around

Question 19

Non rotation

Answer 19

Small bowels and large bowels end upon opposite sides

Transverse colon bunched up

Question 20

Mixed rotation

Answer 20

Caudal, cranial limb movement not coordinated, no rotation
Intestinal loops form volvulus
Twists blood supply to gut, dies

Question 21

Omphacoele

Answer 21

More space in umbilical cord than abdominal space

Intestines end up in umbilical cord instead

Question 22

Gastroschisis

Answer 22

Intestines end up in area lateral to umbilical cord

Potentially linked to mother’s cocaine and drug use

Question 23

Meckels diverticulum

Answer 23

2 inch out pouching of small bowel, 2 feet from iliocaecal junction
Left over from umbilical cord, vitelline duct is not fully absorbed

Question 24

Structures in hindgut

Answer 24

Distal 1/3 of transverse colon
Desc colon
Sigmoid colon
Rectum
Superior part of anal canal
Epithelium or urinary bladder, most of urethra

Question 25

Structure of the hind gut region

Answer 25

Urogenital septum between but doesn’t separate hind gut and cloaca
Urogenital septum between vitelline duct and allantois
Cloaca covered by cloacal membrane

Question 26

Function of cloaca

Answer 26

Forms rectal canal, urethra, blind ended by membrane

Only opens up when membrane broken

Question 27

Development of hindgut region

Answer 27

Urogenital septum separates urinary and rectal exits
Cloacal membrane thins
Proximal allantois => proximal urinary bladder
Proximal anal canal formed from hindgut
Distal anal canal formed from proctodeum