Developemnt

Question 1

Describe the gut tube

Answer 1

• Endoderm lined tube • Runs the length of the body • Blind pouches at the head and tail
ends • Opening at the umbilicus • Splanchnic mesoderm covering

Question 2

What er teh embryonic divisions of he gut?

Answer 2

• Foregut and hindgut begin as blind diverticula
• Midgut has an opening at first and is continuous with the yolk sac
• These embryonic divisions have implications for blood supply and lymphatic drainage in the adult
Caudal most part if hindgut

Question 3

What are the derivatives of the foregut

Answer 3

Oesophagus Stomach Pancreas, liver & gall bladder Duodenum (proximal to entrance of bile duct)

Question 4

What are the derivatives of the midgut

Answer 4

Duodenum (distal to entrance of bile duct) Jejunum Ileum Cecum Ascending colon Proximal 2/3 transverse colon

Question 5

What are the derivatives of the hindgut

Answer 5

Distal 1/3 transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of bladder & urethra

Also holds the cloaca which is divided to give anorectal canal and urethra etc

Question 6

What are the implications of blood supply for the gut

Answer 6

• Arterial supply reflects
embryonic development • Each embryonic segment
receives blood supply from a
distinct branch of the abdominal
aorta

Question 7

What is the foregut, midgut and nindgut blood supply

Answer 7

Celiac trunk, SMA, IMA respectively

Question 8

What are 2 structures in the gut that have a mixed bld supply

Answer 8

– Duodenum
• Proximal to entry of bile duct
– gastroduodenal a & superior pancreaticoduodenal a (CT)
AND
• Distal to entry of bile duct
– inferior pancreaticoduodenal a (SMA)
– Pancreas
• Head
– superior pancreaticoduodenal a (CT)
AND
– inferior pancreaticoduodenal a (SMA)

Question 9

What is the intraembryonic coelom?

Answer 9

• Formed as the embryo folds
• Begins as one large cavity
• Later subdivided by the future diaphragm into abdominal
and thoracic cavities

Question 10

Describe the membrane of the intraembryonic coelom

Answer 10

• One membrane lining the whole
intraembryonic cavity
– Specialises as the cavities specialise
• pericardium
• pleural membrane

Question 11

Describe the peritoneal cavity development

Answer 11

• Peritoneum & peritoneal cavity
– the peritoneal membrane lines the abdominal
cavity and invests the viscera
• during development it grows, changes shape &
specialises
– the peritoneal “cavity” is a potential space only
• under normal conditions it should contain nothing Copyright © 20

Question 12

What is a mesentery

Answer 12

• What?
– double layer of peritoneum suspending the gut tube from the abdominal
wall
• Why?
– allow a conduit for blood and nerve supply
– allow mobility where needed - aka allow structures to move around in cavity

Question 13

How does a mesentery form?

Answer 13

• The new primitive gut is suspended within the intraembryonic coelom
– Splanchnic mesoderm surrounds new
gut
– Mesentery formed from a condensation of this mesoderm

Question 14

Where are the mesenteries located?

Answer 14

• Dorsal mesentery suspends the entire gut tube from the dorsal body wall
• Ventral mesentery ONLY in the region of the foregut - foregit tightly attached, but leaves a free edge

Question 15

What are the greater and lesser peritoneal sacs

Answer 15

• Dorsal and ventral mesenteries in the region of the foregut divide the cavity into left and right sacs in this region only
– the left sac contributes to the
greater sac 
– the right sac becomes the lesser sac
• comes to lie behind the stomach

Question 16

What are teh greater ad lesser omenta?

Answer 16

• Omenta are specialised regions of peritoneum 
• Greater omentum
– formed from the dorsal mesentery 
– first structure seen when the abdominal cavity is opened
anteriorly
• Lesser omentum
– formed from the ventral mesentery
– free edge conducts the portal triad

Question 17

What influences the position of the greater and lesser sacs?

Answer 17

Rotation around longitudinal acc is causes membrane to fold , as it then tilts on the anterior/posterior axis it drops drown

Question 18

What is a peritoneal reflection?

Answer 18

• What is a peritoneal
reflection?
– A change in direction
• from parietal peritoneum to mesentery
• from mesentery to visceral peritoneum 
• from visceral peritoneum
Innervation depends on where its is attaches

Question 19

What about structures with no mesentery/not in the perinoteal space?

Answer 19

• Structures that are not suspended within the abdominal cavity are retroperitoneal
– retroperitoneal
• were never in the peritoneal cavity & never had a mesentery – secondarily retroperitoneal
• began development invested by peritoneum, had a mesentery BUT, with successive growth & development, the mesentery is lost through fusion at posterior abdominal wall

Question 20

What happens to he foregut in week 4

Answer 20

• Extends from the lung bud to the liver bud
– ? Lung bud • In the 4th week, a respiratory diverticulum
forms in the ventral wall of the foregut at the junction with the pharyngeal gut
– Respiratory primordium (ventrally)
– Oesophagus (dorsally)

Question 21

How are the GI and resp tracts separated?

Answer 21

By the tracheoeophageal septum

Question 22

Wha are consequences of abnormal postioning of the tracheoespohageal septum?

Answer 22

variety of oesophageal abnormalities occurring in up to 1 in 3000 live births

Question 23

Give an overview of the development of he foregut-derived glands

Answer 23

• Liver and biliary system
– Ventral mesentery 
• Pancreas
– Components develop in both
• Uncinate process and inferior
head = ventral 
• Superior head, neck, body & tail = dorsal

Question 24

Describe the peritoneal reflections of the liver

Answer 24

See slide

Question 25

Describe the development of the duodenum

Answer 25

• Its shape is determined by rotation of the stomach • Rotation of the stomach pushes duodenum to right, then against posterior
abdominal wall • Therefore it becomes secondarily retroperitoneal

Question 26

What does secondarily retroperitoneal mean ?

Answer 26

• A structure that developed intraperitoneally whose mesentery was lost to fusion with posterior abdominal wall parietal peritoneum due to massive expansion of GI tract during development
• Fusion fascia

Question 27

What is fusion fascia

Answer 27

Fascia attaching structure to the abdominal wall, see slide, Can exploit to make structure mobile