GI Tract

Question 1

What is the Gastrointestinal Tract?

Answer 1

The digestive system is made up of the gastrointestinal tract—also called the GI tract or digestive tract

The GI Tractis a series of hollow organs joined in a long, twisting tube from the mouth to theanus. The hollow organs that make up the GI tract are the mouth,oesophagus, stomach, small intestine, large intestine, and anus.

The liver, pancreas, and gallbladder are the solid organs of the digestive system.

Question 2

What is the Oesophagus?

Answer 2

25 cm long, 2cm diameter, muscular tube.
Connects pharynx to the stomach
Three constrictions:
Cervical constriction
Thoracic constriction
Diaphragmatic constriction
Passes through the oesophageal hiatus (diaphragm) at T10 level
Terminates by entering cardiac orifice of stomach at T11 (abdominal oesophagus is 1.25 cm wide)
Arteries, veins, lymphatics and innervation

Question 3

What is the arterial supply to Oesophagus?

Answer 3

Arterial supply; Thoracic part, Abdominal part- left gastric artery and left inferior phrenic artery

Question 4

What is the venous supply to the Oesophagus?

Answer 4

Veins; through left gastric vein to the portal venous system, through oesophageal veins to the systemic veins (azygous veins)

Question 5

What is the lymphatics of the Oesophagus?

Answer 5

Lymphatics; left gastric – coeliac lymph nodes

Question 6

What is the nerve supply for the Oesophagus?

Answer 6

Nerves; Oesophageal plexus-vagal trunks and thoracic sympathetics trunks via greater splanchnic nerve.

Question 7

Where is the stomach located?

Answer 7

Right and left upper quadrants or epigastric, umbilical and left hypochondriac

Question 8

What are the parts of the stomach?

Answer 8

Cardiac opening : Superior opening or inlet of the stomach. In the supine position, the cardial orifice usually lies posterior to the 6th left costal cartilage, 2-4 cm from the median plane at the level of the T11 vertebra.
Fundus: the dilated superior part that is related to the left dome of the diaphragm . The cardiac notch is between the oesophagus and the fundus. The fundus may be dilated by gas, fluid, food, or any combination of these. In the supine position, the fundus usually lies posterior to the left 6th rib in the plane of the MCL.
Body: the major part of the stomach between the fundus and pyloric antrum.
Pyloric part: the funnel-shaped outlet of the stomach; its wider part, the pyloric antrum, leads into the pyloric canal, its narrower part . The pylorus is the distal sphincteric region of the pyloric part. It is a marked thickening of the circular layer of smooth muscle that controls flow of the stomach contents through the pyloric orifice

2 curvatures: Lesser curvature and greater curvature

Question 9

What are the relations of the stomach - Stomach bed?

Answer 9

The stomach is covered by peritoneum.
Bare areas
The two layers of the lesser omentum extend around the stomach and leave its greater curvature as the greater omentum .
Relations: Anteriorly, diaphragm, left lobe of liver, and anterior abdominal wall.
Posteriorly, omental bursa and pancreas; the posterior surface of the stomach forms most of the anterior wall of the omental bursa .
Inferiorly, transverse colon .
Bed of the stomach, formed by the structures forming the posterior wall of the omental bursa. From superior to inferior, the bed of the stomach is formed by the left dome of the diaphragm, spleen, left kidney and suprarenal gland, splenic artery, pancreas, and transverse mesocolon

Question 10

What is the embryological rotation of the mid gut?

Answer 10

An understanding of the rotation of the midgut clarifies the adult arrangement of the intestines. The primordial gut comprises the foregut, midgut, and hindgut.
Pain arising from foregut derivatives—oesophagus, stomach, pancreas, duodenum, liver, and biliary ducts—localizes in the epigastric region.
Pain arising from midgut derivatives—the small intestine distal to bile duct, caecum, appendix, ascending colon, and most of the transverse colon—localizes in the periumbilical region.
Pain arising from hindgut derivatives—the distal part of the transverse colon, descending colon, sigmoid colon, and rectum—localizes in the hypogastric region.
For 4 weeks, the rapidly growing midgut, supplied by the SMA, is physiologically herniated into the proximal part of the umbilical cord . It is attached to the umbilical vesicle (yolk sac) by the omphaloenteric duct (yolk stalk). As it returns to the abdominal cavity, the midgut rotates 270° around the axis of the SMA . As the relative size of the liver and kidneys decreases, the midgut returns to the abdominal cavity as increased space becomes available. As the parts of the intestine reach their definitive positions, their mesenteric attachments undergo modification . Some mesenteries shorten and others disappear (e.g., most of duodenal mesentery). Malrotation of the midgut results in several congenital anomalies such as volvulus (twisting) of the intestine

Question 11

What is the Duodenum?

Answer 11

25cm, widest and fixed, C shaped contour. Starts at the pyloric end and ends at duodenojejunal junction L2 vertebra 2-3cm left to midline, partially retroperitoneal.
Four parts:
1st part 5cm, first 2cm called ampulla has mesentery and is mobile
2nd part 7-10 cm, right side of the vertebral column, L3, head of pancreas is medial, right colic flexure is lateral, hepatopancreatic ampulla, minor duodenal papilla.
3rd part 6-8cm crosses L3 and abdominal aorta. and
4th part 5 cm, aorta is medial to it, L2

Question 12

What are the arteries of the duodenum?

Answer 12

Arteries: The coeliac trunk, via the gastroduodenal artery and its branch, the superior pancreaticoduodenal artery
The superior mesenteric artery, through its branch, the inferior pancreaticoduodenal artery

Question 13

What are the veins of the duodenum?

Answer 13

Veins: Follow the arteries and drain into the hepatic portal vein, through the superior mesenteric and splenic veins

Question 14

What are the lymphatics of the duodenum?

Answer 14

Lymphatics:
Pyloric lymph nodes, lie along the gastroduodenal artery , the anterior lymphatic vessels drain into the pancreaticoduodenal lymph nodes, located along the superior and inferior pancreaticoduodenal arteries.
Superior mesenteric lymph nodes, The posterior lymphatic vessels pass posterior to the head of the pancreas and drain into the.
Efferent lymphatic vessels from the duodenal lymph nodes drain into the celiac lymph nodes.

Question 15

What are the nerves of the duodenum?

Answer 15

Nerves: Vagus and greater and lesser (abdominopelvic) splanchnic nerves by way of the celiac and superior mesenteric plexuses. The nerves are next conveyed to the duodenum via periarterial plexuses extending to the pancreaticoduodenal arteries

Question 16

What are the Jejunum and ileum?

Answer 16

6-7 m long, duodeno-jejunal flexure to ileocaecal valve
attached to the posterior wall by the mesentery
Jejunum located – mainly in the umbilical region
Ileum located – hypogastric and pelvic regions.
Mucous membrane (epithelium, lamina propria & muscularis mucosae); submucosa, muscularis externa (circular and longitudinal muscles) and Serosa.

Question 17

What are the vessels of the small intestine?

Answer 17

Superior mesenteric artery arises at L1, 1cm inferior to celiac artery- 15-18 Jejunal and ileal arteries forming loops with in the mesentry and give rise to vasa recta
Superior mesenteric vein- ends posterior to the neck of pancreas, unites with the splenic vein to form the portal vein.
Lymphatics- lacteals that drain in the lymphatic vessels and then groups of lymph nodes- Juxtaintestinal, mesenteric and superior central, efferents travel to the Superior mesenteric lymph nodes.

Question 18

What are the nerves of the small intestine?

Answer 18

Nerves- SMA nerve plexus, Sympathetics- T8- T10 segments, through sympathetic trunks and abdominopelvic splanchnic nerves, synapse at the celiac and SMA ganglia
Parasympathetics- Posterior vagal trunks, myenteric and submucosal plexuses in the intestinal walls.
Sympathetics-reduce the peristalsis and secretory activity, vasocontrictive and parasympathetics- increases secretomotor activity.
Sensory fibers are sensitive to distension.

Enteric plexuses:-
Myenteric plexus between circular/longitudinal muscles.
Submucosal Meissner’s plexus submucosal surface of the circular layer of muscle.

Sympathetic nerves -> TS to T9 -> sympathetic trunks -> splanchnic nerves -> coeliac ganglia ->postsynaptic sympathetic nerves
Generally inhibits peristalsis, but stimulates the sphincters and muscularis mucosae

Parasympathetic nerve -> vagus (CN X) (posterior vagal trunk) ->intrinsic postsynaptic neurons.
Generally augments peristalsis and inhibits the sphincters

Referred Pain
Refers to the periumbilical (peri = around) region or central epigastrium

Question 19

What is the large gut?

Answer 19

1.5m
Function: Absorption of fluid and solutes
Caecum, appendix, ascending, transverse, descending, sigmoid and rectum.
Omental appendices (epiploicae) – small adipose projections, Teniae coli -Longitudinal muscle layer concentrated into three bands – (free tenia ; tenia omentalis; taenia mesocolica) , Haustrations - semilunar folds and large caliber lumen.

Question 20

Where is the large gut located?

Answer 20

Caecum - right inguinal region (2.5cm), S1/L5
Ascending colon, right side of posterior abdominal cavity from cecum to right lobe of liver
Right colic flexure- hepatic flexure
Transverse colon, right to left colic flexure.
Left colic flexure-splenic flexure
Descending colon, left colic flexure to left iliac fossa
Sigmoid colon- iliac fossa to S3 15cm from anus is the rectosigmoidal junction.
Rectum and anal canal

Question 21

What are the vessels of the large gut?

Answer 21

Blood Vessels
Arteries: caecum, appendix, ascending colon, 2/3 of transverse colon. – SMA
1/3 transverse colon, descending and sigmoid colon, rectum and upper anal canal - IMA. Veins: the same as the arteries.
Lymphatics
ascending and transverse colon lymphatics drain into the superior mesenteric nodes, which finally drain into the thoracic duct
Transverse, descending and sigmoid lymphatics drain into the inferior mesenteric lymphatic system.
Innervation
caecum, appendix, ascending colon, 2/3 transverse colon:-
sympathetic :- coeliac and superior mesenteric ganglia
parasympathetic:- vagi
1/3 transverse colon, sigmoid colon and rectum:-
sympathetic:- lumbar part of the trunk, superior hypogastric plexus
parasympathetic:- pelvic splanchnic nerves

Question 22

What is the Caecum (or Cecum)?

Answer 22

Caecum – 7.5cm large blind pouch, below the ileocaecal valve and located in the right iliac fossa.
No mesentry although completely covered by peritoneum.
Caecum starts the process of fluid & electrolyte reabsorption.
Iliocaecal valve – frenula of the ileum
Vermiform appendix – 6-10 cm blind intestinal diverrticulum. Mesoappendix, usually appendix is retrocecal
Arterial supply; Ileocolic artery of the SMA and appendicular artery and venous drainage from the SMV and ileocolic veins
Lymphatics to the ileocolic and SMA nodes

Question 23

What is the ascending colon?

Answer 23

Ascending colon- narrower than cecum, retropeitoneal on posterior abdominal wall, right paracolic gutter on the lateral side.
Arterial supply- Ileocolic, right colic and middle colic artery of SMA that form marginal arteries.
Veins- ileocolic, right colic veins to SMV
Lmphatics – epicolic and paracolic nodes to the superior mesenteric lymph nodes
Nerves- Superior mesenteric nerve plexus.

Question 24

What is the transverse colon?

Answer 24

Longest
Most mobile
Transverse mesocolon
Arterial supply- middle and right colic arteries (SMA), and left colic artery through the anastomoses
Veins SMV
Lymphatics- middle colic lymph nodes to SM lymph nodes
Nerves- Superior mesenteric nerve plexus.

Question 25

What is the descending and sigmoid colon?

Answer 25

Hindgut- Left colic flexure to the left iliac fossa
Retroperitoneal- anterior and lateral peritoneum
Paracolic gutter on the lateral side
Sigmoid colon- S shaped, iliac fossa to S3, Intraperitoneal .
Sigmoid mesocolon- V shaped attachment
Arteries- Left colic and sigmoidal arteries IMA.
Veins- Left colic vein to IMV flowing to splenic vein and into the hepatic portal vein.
Lymphatics- epicolic and paracolic to left colic and then to the Inferior mesenteric nodes
Nerves- Sympathetics (L1-3 via the inferior mesenteric ganglion) are from the lumbar splanchnic nerves. Parasympathetics- – S2—4 pelvic splanchnic nerves via inferior hypogastric plexuses.

Question 26

What is the rectum and the anal canal?

Answer 26

Rectum is fixed terminal part of large gut.
Starts at S3, attachment of sigmoid mesentry
Tenia of sigmoid colon spread to continue in the rectum
Lateral flexures- Left superior and inferior and right intermediate.
Dilated terminal part is known as the Ampulla of rectum
Superior third is covered with peritoneum anteriorly and laterally. Rectovesical and rectouterine pouches and pararectal pouches formed
Arteries- Superior rectal> IMA, Middle rectal> internal iliac, and inferior rectal > internal pudendal.
Veins- Superior rectal vein> portal veins, Middle and inferior rectal in the systemic veins. Internal and external rectal venous plexuses.
Nerves- Sympathetics> Lumbar splanchnic nerves and the hyogastric plexuses around the IMA. Parasympathetics> S2-S4 via pelvic splanchnic nerves and left and right hypogastric plexuses.