3. Peritoneal and GI development 2

Question 1

What are the physicochemical factors of drugs and how does it impact its absorption?

Answer 1

Weak bases: 
-Ionised in acidic pH
-Absorbed in SI
-Ionisation in plasma
Weak acids
- Unionised in acidic pH
-BUT also absorbed in small intestine due to large SA

Question 2

What is the embryological reasoning behind the falciform ligament and lesser omentum having free, inferior borders?

Answer 2

The ventral mesentery just ends about half-way along the duodenum

Question 3

Foregut:
Extends from what to what?
Supplied by which vessel?
Gives rise to which structures?
What may occur on abnormal tracheo-oesophageal development?

Answer 3

The foregut extends from the mouth to just distal to the developing liver

Supplied by Coeliac trunk; refers pain to epigastrium (T7 to 9)

Foregut gives rise to the: oesophagus (which gives the respiratory diverticulum that forms the trachea and lungs); stomach; proximal duodenum; liver and biliary system; pancreas; and spleen

Abnormal tracheo-oesophageal development gives rise to TO fistula etc (or TEF, American esophagus)

Question 4

Describe the sequence of events during the formation of the stomach from the foregut

Answer 4

By the 4th week of development the stomach appears – dilation of foregut

It rotates about both a longitudinal and an AP axis:

• 90 degrees clockwise around the longitudinal axis so the left side faces anteriorly, and lesser curve faces to the right, while greater curve faces left
• AP axis so the pyloric part comes to lie on the right and oesophago-gastric junction slightly left, so that the greater curve faces left and inferior

Question 5

Describe the sequence of events during the formation of the duodenum from the foregut

Answer 5

The duodenum forms from the foregut and beginning of midgut
Initially it is found in the midline but the rotations of the stomach also cause the duodenum to rotate and swing to the right
It then “falls” on to the posterior abdominal wall and becomes retroperitoneal
During development the duodenum lumen becomes obliterated by a proliferation of cells, then it is re-canalized

Question 6

Describe the sequence of events during the formation of the liver and gallbladder from the foregut

Answer 6

3rd week
The liver develops from an endodermal bud, it penetrates the ventral mesentery and septum transversum and gives rise to the hepatic ducts and gallbladder
The ventral mesentery directly in contact with the liver becomes its visceral peritoneum and the bare area of the liver is where it contacts the diaphragm with no intervening peritoneum

Question 7

Describe the sequence of events during the formation of the pancreas from the foregut

Answer 7

The pancreas forms from dorsal and ventral endodermal buds from the duodenum; the rotation of the latter causes the ventral bud to migrate around to lie behind and fuse with the dorsal bud so that the adult pancreas lies in the curve of the duodenum

The ducts of the dorsal and ventral buds unite to form the main pancreatic duct.

While the accessory duct is the remnant of the duct of the dorsal bud

Question 8

How does an obstructive annular pancreas form?

Answer 8

In embryological developement of the foregut if the ventral pancreas may form as 2 lobes

Question 9

As the stomach is rotated around it’s longitudinal axis, what happens?

Answer 9

Its posterior aspect (that will become the greater curve) rotates to the left, so that the dorsal mesentery i.e. mesogastrium (that will become the greater omentum) is thrown to the left as well; and a potential space (omental bursa or lesser sac) is left posterior to the stomach and lesser omentum

Question 10

What are the boundaries of the epiploic foramen?

Answer 10

Anteriorly: free border of the
lesser omentum, with the bile duct, the hepatic artery proper, and the portal vein

Posteriorly: inferior vena cava

Superiorly: caudate process of the caudate lobe of the liver

Inferiorly: first part of the duodenum

Question 11

Boundaries and relations of the lesser sac

Answer 11

Anteriorly: caudate lobe 
of liver; lesser omentum; stomach
Posteriorly: pancreas 
Laterally: left kidney and adrenal gland; 
on the right the epiploic 
foramen

It extends upward as far as
the diaphragm and downward it may extend a little way between the layers of the greater omentum
le

Question 12

How is the greater omentum formed?

Answer 12

As the dorsal mesentery is thrown left, the stomach rotates on its AP axis and the greater curve faces inferiorly. The dorsal mesentery is then dragged with it so that a big, double-layered fold of mesentery, the greater omentum, hangs off the greater curve

Question 13

Describe the sequence of events during the formation of the spleen from the foregut

Which two ligaments are formed, between which structures?

Answer 13

Spleen forms with the dorsal mesentery of the stomach

Lienorenal ligament: The mesentery between the spleen and the posterior abdominal wall (close to the kidney)

Gastrolienal / gastrosplenic ligament: the mesentery between the spleen and the stomach is the

Question 14

Greater omentum overlies which structures?

Answer 14

Transverse colon and intestine

Question 15

Midgut:
Commences and ends?
Supplied by?
By the 5th week...
Connected to the yolk sac via what?
Rapid growth leads to..

Answer 15

Commences immediately distal to the entrance of the bile duct into the duodenum and ends 2/3 along
transverse colon

Supplied by Superior Mesenteric Artery; pain refers to peri-umbilical region (T10)

By the 5th week the midgut is suspended from the dorsal abdominal wall as the primary intestinal loop
by a mesentery

It is connected to the yolk sac by the vitelline duct

Rapid growth of the intestinal loop causes its physiological herniation through the umbilicus and into the umbilical cord

Question 16

The primary intestinal loop of the midway undergoes growth and rotation, describe

Answer 16

The cranial limb of the loop grows and will become much of the jejunum and ileum

The loop rotates in a counter clockwise direction
90degrees in the physiological hernia

And then another 180degrees as the loop drops back into the abdomen at about 70 days (10 weeks)

Overall this is a total of 270degrees of rotation around the axis of the SMA

Question 17

Describe the migration of the caecum during midgut development?

Answer 17

Around 10 weeks

Initially, as the intestine drops back in to the abdomen, the jejunum lies to the left and the caecum is up in the right hypochondrium, adjacent to the liver

The caecum, with the appendix, then migrates inferiorly to the right iliac fossa

Question 18

What two congenital abnormalities can occur in embryological development o the midgut?

Answer 18

Partial / abnormal rotation of intestine

Vitelline duct fistula- Leading faecal discharge at umbilicus

Question 19

Name 3 conditions that occur during failure of recanalisation of GI tract?

Answer 19

Gastroschisis
Omphalocele
Umbilical hernia

Question 20

Hindgut:
Gives rise to?
Supplied by?
Divisions of the cloaca?

Answer 20

Gives rise to: the distal end of the transverse colon (1/3); descending colon; sigmoid colon; rectum and upper 2/3 anal canal

Supplied by inferior mesenteric artery; refers pain to suprapubic region (T12)

The most inferior part of the hindgut develops from the cloaca, which is divided by the mesodermal uro-rectal septum:
Anteriorly the cloaca develops into the urogenital system
Posteriorly the anorectal canal

Question 21

Describe the embryological development of the anal canal?

Answer 21

The distal aspect of the cloaca is closed by the anal membrane membrane
As the surrounding mesoderm and ectoderm proliferate, the anal part of the membrane sinks in to the anal pit
The membrane breaks down at 8 weeks, so that the proximal 2/3 of the anal canal is derived from the hindgut endoderm while the distal 1/3 is derived from ectoderm
The pectinate line marks the change in embryological derivation, blood and nerve supply

Question 22

What causes an imperforate anus?

Answer 22

1. The common origin of the anal canal and the urogenital organs means that fistulae between them may
2. Also the anal membrane may not break down

Both causing an imperforate anus

Question 23

What is Hirchsprung Disease?

Answer 23

Lack of normal development of the colonic innervation leads to a constricted, aganglionic segment of bowel, with a distended segment proximally (the innervation of which is normal)

Question 24

Define the term psychosomatic disorder

Answer 24

Psychosomatic disorders are disorders where emotional or psychological factors can impact on the symptoms

Question 25

Describe the signs and symptoms of irritable bowel syndrome (7)

Answer 25

• abdominal (stomach) pain and cramping, which may be relieved by defecation
• a change in bowel habits – such as diarrhoea, constipation, or sometimes both
• bloating and swelling of your stomach
• excessive wind (flatulence)
• occasionally experiencing an urgent need to go to the toilet
• a feeling that you have not fully emptied your bowels after going to the toilet
• passing mucus from your bottom