development of peritoneum & foregut (part II) - stomach rotation

Question 1

how are the greater & lesser sacs formed? how are the omenta formed?

Answer 1

rotation of the stomach

Question 2

how does the primitive stomach rotate?

Answer 2

in 2 directions:
around longitudinal axis
around anteroposterior axis

Question 3

what does the rotation of the stomach result in?

Answer 3

1. greater & lesser curvature come to lie first on right & left side (longitudinal)
2. then cardia & pylorus move horizontally, pushing greater curvature inferiorly (anteroposterior rotate)

Question 4

what does anterior and posterior in embryo equal in adults?

Answer 4

superior & inferior

Question 5

what is the stomach fixed by? what does this means when the stomach rotates?

Answer 5

fixed by anterior & posterior abdominal wall (cranial & caudal), therefore anything around stomach will have to change as a result of the stomach rotating (knock on effects on structures nearby & pull anything attached to greater curvature with it)

Question 6

describe what happens to dorsal mesentery during rotation around longitudinal axis

Answer 6

dorsal mesentery containing the greater curvature rotates longitudinally from dorsal to left hand side

Question 7

describe what happens to ventral mesentery during rotation around longitudinal axis

Answer 7

ventral mesentery rotates longitudinally to anatomical right side (lesser curvature & omentum)

Question 8

what is the stomach attached to?

Answer 8

attached to anterior and posterior abdominal wall - because in the foregut

Question 9

what allows for the rotation of the stomach to occur?

Answer 9

pliable membrane - able to move and create complex fold in membranes

Question 10

describe what happens in rotation around anteroposterior axis?

Answer 10

1. dilation of foregut - where stomach will develop
2. stomach rotating - pushing down (inferior) almost to horizontal
3. (greater & lesser curvature produced)

Question 11

what happens to the dorsal mesentery in rotation around the longitudinal axis?

Answer 11

a bulge is created in the dorsal mesentery from membrane twisting to follow stomach wall - becomes greater curvature

Question 12

what happens to the dorsal mesentery in rotation around anteroposterior axis?

Answer 12

gives rise to the omental bursa (greater omentum) suspended from greater curvature of stomach (as that is where the dorsal mesentery was attached to the stomach)

Question 13

what is significant about greater & lesser sac?

Answer 13

continuous with each other & can communicate with each other
clinically: fluid in one can travel to the other

Question 14

what does rotation of the stomach result in?

Answer 14

1. puts vagus nerves anterior & posterior to the stomach instead of L & R
2. shifts cardia (superior) & pylorus (inferior) from midline (stomach lies obliquely - anteroposterior rotation)
3. contributes to moving lesser sac behind stomach
4. creates greater omentum

Question 15

what is a peritoneal reflection?

Answer 15

a change in direction:
1. from parietal peritoneum to mesentery
2. from mesentery to visceral peritoneum
etc.

Question 16

what are structures without mesentery called? why?

Answer 16

retroperitoneal - as they are not suspended within the abdominal cavity

Question 17

what are retroperitoneal structures specifically?

Answer 17

were never in the peritoneal cavity & never had a mesentery (EVER)

Question 18

what are secondarily retroperitoneal structures?

Answer 18

began development invested by peritoneum, had a mesentery, BUT with successive growth & development, the mesentery is lost through fusion at posterior abdominal wall

Question 19

where does the foregut extend from to?

Answer 19

from the lung bud to the liver bud

Question 20

what happens in the 4th week to the ventral wall of the foregut?

Answer 20

a respiratory diverticulum forms in the ventral wall of the foregut at the junction with the pharyngeal gut

Question 21

what does the respiratory diverticulum create?

Answer 21

1. respiratory primordium (ventrally - respiratory tract)

2. oesophagus (dorsally)

Question 22

what happens after the respiratory diverticulum has developed?

Answer 22

the respiratory diverticulum bulges out of the ventral wall of foregut, tracheoesophageal septum then develops to close off the division of ventral and dorsal, creating separate tubes for oesophagus and respiratory tract

Question 23

what are some of the consequences of abnormal positioning of the tracheoesophageal septum?

Answer 23

1. proximal blind - end oesophagus (immediately symptomatic in babies - they aspirate, difficulty feeding)
2. tracheoesophageal fistula (abnormal passageway between trachea & oesophagus)

Question 24

what happens to the stomach once it has rotated into the correct position?

Answer 24

growth:

1. slight dilation of distal foregut indicates position of stomach primordium (embryonic stomach)
2. faster growth of dorsal border - creates greater curvature

Question 25

what happens after faster growth of greater curvature?

Answer 25

stomach rotates, changing position of the dorsal & ventral mesentries

Question 26

what does 'stomach rotates, changing position of the dorsal & ventral mesentries' achieve?

Answer 26

1. omental bursa formed | 2. lesser sac displaced posteriorly from right (right to back - lesser, left to front - greater)

Question 27

what are foregut-derived glands formed in the ventral mesentery?

Answer 27

liver biliary system part of pancreas (uncinate process & inferior head)

Question 28

what are the foregut-derived glands formed in the dorsal mesentery?

Answer 28

pancreas (superior head, neck, body and tail)

Question 29

where does the liver develop from?

Answer 29

earliest GI tract associated gland | develops from hepatic bud within ventral mesentery

Question 30

how much of abdomen does liver occupy during development?

Answer 30

large proportion

Question 31

what has the greatest impact on foregut region during development?

Answer 31

growth of liver & movement of stomach (& growth of stomach)

Question 32

What are the peritoneal reflections of the liver?

Answer 32

1. bare area (top - area where organ opens up, can put hand around) 2. falciform ligament (anterior - ligament attaching liver to ventral body wall) 3. lesser omentum (posterior liver)

Question 33

which part of the liver does not have visceral peritoneum covering? why?

Answer 33

difficult to free liver from diaphragm - doesn't have visceral peritoneum at surface touching diaphragm, because enclosed by (coronary, left & right triangular ligaments) - consequence of growth and development at the same time of diaphragm, so diaphragm covers bare area of liver

Question 34

where does the duodenum develop from?

Answer 34

caudal foregut and cranial midgut (has precursors from both sections) - split at bile duct

Question 35

how does the duodenum develop?

Answer 35

grows rapidly, forming C-shaped loop when stomach rotates (duodenum was attached to inferior stomach prior anteriorposterior rotation, so when rotated to become oblique, the duodenum forms a C shape bend, which wraps around the head of the pancreas)

Question 36

how is the lumen of the duodenum throughout development?

Answer 36

lumen is obliterated (from AP rotation of stomach?) and then recanalised (re-opened) by the end of the embryonic period

Question 37

what does rotation of the stomach do to the duodenum aside from form C-shape around head of pancreas?

Answer 37

pushes duodenum to right, against POSTerior abdominal wall

Question 38

what are secondarily retroperitoneal structures?

Answer 38

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

Question 39

what forms in secondarily retroperitoneal structures?

Answer 39

fusion fascia forms (where organ and mesentery was pushed into posterior abdo wall)

Question 40

what is fusion fascia?

Answer 40

a double connective tissue band derived from the fusion of closely apposed surfaces of peritoneum as a result of degeneration of the lubricating serous layer between them (even visceral peritoneum fuses with posterior abdominal wall)

Question 41

what can you do to secondarily retroperitoneal structures?

Answer 41

because they were once peritoneal structures and once had mesentery, they can be remobilised (in dissection)

Question 42

what are examples of secondarily retroperitoneal structures of the foregut?

Answer 42

duodenum (except duodenal cap) pancreas (head within C-shape of duodenum) (duodenum pushed out by developing GI and enlarging stomach & liver & rotation of stomach)