GI: anatomy of the GI tract Flashcards
What are the 4 regions of the stomach?
- Cardia – surrounds the superior opening of the stomach at the T11 level.
- Fundus – the rounded, often gas filled portion superior to and left of the cardia.
- Body – the large central portion inferior to the fundus.
- Pylorus – This area connects the stomach to the duodenum. It is divided into the pyloric antrum, pyloric canal and pyloric sphincter. The pyloric sphincter demarcates the transpyloric plane at the level of L1.
Describe the anatomical relations of the stomach
Superior: Oesophagus and left dome of the diaphragm
Anterior: Diaphragm, greater omentum, anterior abdominal wall, left lobe of liver, gall bladder
Posterior: Lesser sac, pancreas, left kidney, left adrenal gland, spleen, splenic artery, transverse mesocolonv
What are the roles of each of the 4 regions of the stomach?
- Fundus: stores undigested food and digestive gases
- Body: secretes pepsinogen (chief cells) + hydrochloric acid (parietal cells)
- Pylorus: secretes mucus, gastrin and pepsinogen
What are the 2 sphincters of the stomach?
Inferior oesophageal sphincter:
- T11 level
- marks the transition point between the oesophagus and stomach
- allows food to pass through the cardiac orifice and into the stomach
- not under voluntary control
Pyloric sphincter:
- lies between the pylorus and the first part of the duodenum.
- controls of the exit of chyme
- an anatomical sphincter- contains smooth muscle, which constricts to limit the discharge of stomach contents
What is the name of the membrane which supports the abdominal viscera and state 2 structures consisting of this membrane which attach to the stomach
Double layered membrane called the peritoneum supports most of the abdominal viscera and assists with their attachment to the abdominal wall.
The greater and lesser omenta are two structures that consist of peritoneum folded over itself (two layers of peritoneum – four membrane layers).
Describe the position and attachments of the greater and lesser omenta
GREATER OMENTUM
Hangs down from the greater curvature of the stomach and folds back upon itself where it attaches to the transverse colon
LESSER OMENTUM
Continuous with peritoneal layers of the stomach and duodenum
This smaller peritoneal fold arises at the lesser curvature and ascend to attach to the liver.
State the roles of the greater and lesser omenta
Greater omentum:
- contains many lymph nodes and may adhere to inflamed areas
- Therefore plays a key role in GI immunity and minimising the spread of intraperitoneal infections.
Lesser omentum:
- attaches the stomach and duodenum to the liver.
Describe the arterial supply to the stomach
The arterial supply to the stomach comes from the celiac trunk and its branches.
Anastomoses form along the lesser curvature:
- Right gastric – branch of the common hepatic artery, which arises from the coeliac trunk.
- Left gastric – arises directly from the coeliac trunk
….and along the greater curvature by the right and left gastro-omental arteries:
- Right gastro-omental – terminal branch of the gastroduodenal artery, which arises from the common hepatic artery.
- Left gastro-omental – branch of the splenic artery, which arises from the coeliac trunk.
Describe the autonomic innervation of the stomach
Parasympathetic nerve supply
- arises from the anterior and posterior vagal trunks
- this is derived from the vagus nerve.
Sympathetic nerve supply
- arises from the T6-T9 spinal cord segments
- passes to the coeliac plexus via the greater splanchnic nerve.
- It also carries some pain transmitting fibres.
Where does the small intestine extend?
Pylorus of the stomach to the ileocaecal junction, where it meets the large intestine at the ileocaecal valve.
State the 3 anatomical divisions of the small intestine
Duodenum- extraperitoneal, 25cm, C-shaped, wraps around head of pancreas. 4 parts- superior, descending, inferior, ascending
Jejenum- intraperitoneal, attached to the posterior abdominal wall by mesentery (a double layer of peritoneum).
Ileum- intraperitoneal, attached to the posterior abdominal wall by mesentery (a double layer of peritoneum).
Where is the most common site for duodenal ulceration?
The superior duodenum.
It ascends upwards from the pylorus of the stomach, and is connected to the liver by the hepatoduodenal ligament.
State 5 distinguishing features of the jejenum and the ileum
Describe the arterial supply of the duodenum
*Proximal to the major duodenal papilla –*
supplied by the gastroduodenal artery (branch of the common hepatic artery from the coeliac trunk).
*Distal to the major duodenal papilla –*
supplied by the inferior pancreaticoduodenal artery (branch of superior mesenteric artery).
Describe the arterial and venous supply to the jejenum and ileum
Superior mesenteric artery and vein
- Superior mesenteric artery* arises from the aorta at the level of the L1 vertebrae, immediately inferior to the coeliac trunk.
- Superior mesenteric vein* unites with the splenic vein at the neck of the pancreas to form the hepatic portal vein.
What are the 4 anatomical divisions of the colon?
Ascending- retroperitoneal, ascends superiorly from the cecum to the hepatic (R. colic) flexure.
Transverse- right colic flexure to the spleen, least fixed part of colon. Intraperitoneal- enclosed by the transverse mesocolon.
Descending- retroperitoneal but anterior to left kidney.
Sigmoid- left iliac fossa to the level of the S3 vertebra. Attached to the posterior pelvic wall by a mesentery – the sigmoid mesocolon (long, allows motility)
State 4 characteristic features of the colon that allow it to be distinguished from the small intestine
- Attached to the surface of the large intestine are omental appendices – small pouches of peritoneum, filled with fat.
- Running longitudinally along the surface of the large bowel are three strips of muscle, known as the teniae coli.
- The teniae coli contract to shorten the wall of the bowel, producing sacculations known as haustra.
- The large intestine has a much wider diameter compared to the small intestine.
Which arteries supply each divison of the colon?
As a general rule:
Midgut-derived structures = superior mesenteric artery
Hindgut-derived structures = inferior mesenteric artery.
- ASCENDING = ileocolic and right colic
- TRANSVERSE = right (SMA), middle (SMA), left (IMA) colic arteries
- DESCENDING = left colic
- SIGMOID = sigmoid arteries (branch of left colic)
Which veins supply each divison of the colon?
As a general rule:
Midgut-derived structures = superior mesenteric vein
Hindgut-derived structures = inferior mesenteric vein
- ASCENDING = ileocolic and right colic
- TRANSVERSE = right (SMV), middle (SMV), left (IMV) colic arteries
- DESCENDING = left colic
- SIGMOID = sigmoid veins (branch of left colic)
What are the 4 lobes of the liver?
right and left lobe, caudate lobe and quadrate lobe
Briefly explain the passage of blood through the portal circulation
- The SMV, IMV, and splenic vein drain venous blood from the GI tract to the liver via the hepatic portal vein
- The portal vein splits into the left and right branches
- On entering the liver, the blood drains into the hepatic sinusoids where it is screened by Kupffer cells (specialised macrophages) to remove any pathogens
Describe the 4 regions of the stomach
Cardia
- Surrounds the opening of the oesophagus into the stomach
Fundus
- area abover the level of the cardial orifice
- stores undigested food and digestive gasesr
Pylorus
- secretes mucus, gastrin and pepsinogen
Body
- Chief cells secrete pepsinogen
- Parietal cells secrete hydrochloric acid
