G.I organs Flashcards
Describe the abdominal oesophagus
Emerges through the right crus of the diaphragm at T10
Goes through the muscular part of the diaphragm which is important because it contributes to the formation of the Lower Oesophageal Sphincter which prevents gastro-oesophageal reflux
Passes from the oesophageal hiatus into the cardial orifice just left to the midline
What are the relations of the abdominal oesophagus
Anterior vagal trunk- left vagus nerve- rotation of gut during development moves these fibres anteriorly
Posterior vagal trunk- single trunk- right vagus nerve
Describe the arterial supply of the abdominal oesophagus
esophageal branches of the left gastric artery (celiac trunk)
esophageal branches from the left inferior phrenic artery (from the abdominal aorta)
Describe the stomach
Most dilated part of G.I tract
J-shaped
Lies between abdominal oesophagus and S.I
Found in epigastric, umbilical and left hypochondriac regions
Describe the different regions of the stomach
Fundus: superior to plane created by the cardial notch
Cardia: surrounds the opening
Body: bulk of the stomach, between the fundus and angular incisure
Pyloric antrum: between the pyloric canal and angular incisure
Pyloric canal: leads to the pyloric constriction where the pyloric sphincter controls flow to the duodenum
Describe the other features of the stomach
Greater curvature: most lateral curvature; point of attachment of gastrosplenic ligament and greater omentum
Lesser curvature: most medial curvature; point of attachment of lesser omentum
Cardial notch: superior angle created where the oesophagus enters
Angular incisure: bend on the lesser curvature
Describe the arterial supply to the stomach
Left gastric artery (celiac trunk)
Right gastric (hepatic artery proper)
Right gastro-omental artery (gastroduodenal artery)
Left gastro-omental (splenic artery)
Posterior gastric (splenic artery- variant)
What is important to remember about the stomach
Clinical note – on chest x-rays be aware that you can often see a gas bubble in the fundus of the stomach lying directly beneath diaphragm. Do not confuse this air bubble with air in the peritoneum, say from an intestinal perforation.
Describe the duodenum
Position: C-shaped structure adjacent to head of pancreas
Functional anatomy: lumen widest of small intestine, and all retroperitoneal apart from the first region
Above level of umbilicus
First part is attached to the liver via the hepatoduodenal ligament (part of lesser omentum)
Describe the superior part of the duodenum
aka ampulla; extends from pyloric orifice to neck of gallbladder, passing anterior to the bile duct, portal vein and IVC (only intraperitoneal part)
Just right to the body of L1
Describe the descending part of the duodenum
extends from neck of gallbladder to the lower border of vertebra LIII; crossed anteriorly by the transverse colon, and right kidney is posterior; contains the duodenal papillae
Major duodenal papilla: entrance of bile/pancreatic ducts
Minor duodenal papilla: entrance of accessory pancreatic duct (and junction of foregut/midgut)
Describe the inferior part of the duodenum
longest section, crossing IVC, aorta and vertebral column
It is crossed anteriorly by the superior mesenteric artery and vein
Describe the ascending part of the duodenum
passes upwards on the aorta to vertebra LII, terminating at the duodenojejunal flexure
What is the duodenal flexure surrounded by
surrounded by fold of peritoneum (suspensory ligament of the duodenum)
Describe the arterial supply to the duodenum
Branches from gastroduodenal artery
Branches from superior mesenteric artery
Describe clinical implications of the duodenum
The relations of the duodenum are important clinically. Anurysms can compress the duodenum or ulcers can erode into the walls of vessels.
Most duodenal ulcers occur in the superior part (duodenal cap)
Describe the position of the jejenum
proximal 2/5ths of the small intestine (mostly LUQ)
Describe the position of the ileum
distal 3/5ths of the small intestine (mostly RLQ)
Compart the jejunum to the ileum
Walls: jejunum has thicker walls with more frequent and prominent circular folds (plicae circulares)
Lumen: jejunum is larger in diameter
Arterial arcades: more prominent in the ileum
Vasa recta: longer in the jejunal supply
Mesenteric fat: larger in the ileum
Describe the large intestine
extends from distal end of the ileum to the anus, absorbing fluids and salts to form faeces in gut
Describe the caecum
Right groin- with associated appendix
In right iliac fossa inferior to the iliocaecal opening
Intraperitoneal- due to its mobility not due to suspension by mesentery
Continues with ascending colon at entrance of ileum
Usually in contact with anterior abdominal wall and may cross pelvic brim to enter true pelvis
Appendix attached to posteromedial wall just inferior to end of ileum
Describe the colon
Ascending colon: continuation of the large intestine to the right colic flexure below the liver
Transverse colon: (intraperitoneal) crosses the abdomen to the left colic flexure below the spleen
Descending colon: passes to the left groin
Sigmoid colon: associated with the sigmoid mesocolon and joins to the rectum
Describe the appendix
Point of attachment is consistent with the highly visible free taeniae leading directly to the base of the appendix, but the location of the rest of the appendix varies
Surface projection of base is at the junction of the lateral and middle one-third of a line from the ASIS to the umbilicus (McBurney’s point)
People with appendicular problems may describe pain near this junction
Summarise the branches of the abdominal aorta that supply the G.I tract
3 UNPAIRED arteries arising from the anterior of the AORTA
COELIAC TRUNK = FOREGUT, liver, pancreas and spleen
SUPERIOR MESENTERIC ARTERY (SMA) = MIDGUT
INFERIOR MESENTERIC ARTERY (IMA) = HINDGUT
Describe the features of the large intestine
Omental appendices: peritoneal-covered accumulations of fat associated with the colon
Taeniae coli: segregation of longitudinal muscle into narrow bands
Haustra of colon: sacculations of the colon
Describe the coeliac trunk
Anterior branch of abdominal aorta
Arises immediately below the aortic hiatus
Anterior to upper part of L1
Immediately divides into left gastric, common hepatic and splenic arteries
Describe the branches of the coeliac trunk
Common hepatic artery (medium): supplies the stomach, liver and duodenum (via the gastroduodenal artery) Left gastric artery: (small) supplies the stomach (both surfaces- anastomoses with left gastric artery) Splenic artery (large): supplies the spleen and branches to supply the pancreas
Describe the superior mesenteric artery
Anterior branch of abdominal aorta supplying the midgut
Arises immediately below the celiac artery anterior to the lower part of L1
Crosses anteriorly by the splenic vein and neck of pancreas
Posterior to the artery are the left renal vein, uncincate process of pancreas and the inferior part of the duodenum
Inferior pancreaticoduodenal artery is first branch
it then gives off jejunal and ileal arteries on the left
Right:
middle colic, right colic and ileocolic arteries
Describe the branches of the SMA
Middle colic artery: supplies the transverse colon
Right colic artery: supplies the ascending colon
Ileocolic artery: supplies ascending colon and distal ileum
Ileal arteries: supply the ileum (longer vasa recta and more prominent arterial arcades)
Jejunal arteries: supply the jejunum (shorter vasa recta and less prominent arterial arcades)
Describe the inferior mesenteric artery
Anterior branch of abdominal aorta and supplies the hindgut
Arises anterior to L3
Initially descends along aorta before moving to the left
Branches include the left colic, several sigmoid and superior rectal artery
Describe the branches of the IMA
Left colic artery: supplies the distal 1/3rd of the transverse colon and the descending colon ( ascends retroperitoneally, before dividing into ascending and descending branches)
Sigmoid arteries: supply the sigmoid colon
Superior rectal artery: supplies the rectum
Describe the portal vein
The portal vein arises from the superior mesenteric and splenic veins posterior to the 1st part of the duodenum / pylorus of the stomach. It then runs in the free edge of the lesser omentum to the liver. It drains blood from all abdominal viscera and liver
Does not drain blood from rectum however
Describe the relations of the portal vein
Ascending towards the liver, it passes posterior to the superior duodenum and enters the right margin of the lesser omentum
As it passes through this part of the lesser omentum, it is anterior to the omental foramen and posterior to the bile duct (its right) and hepatic artery proper (left)
Describe the splenic vein
collects blood from the spleen, gastric veins, pancreatic veins and the inferior mesenteric vein
Describe the superior mesenteric vein
collects blood from the small intestine, ascending colon and transverse colon
Describe the inferior mesenteric vein
collects blood from the descending and sigmoid colon as well as the rectum, draining to the splenic vein
Describe the porto-systemic anastomoses
The portal-systemic anastomoses are where veins draining to the portal vein and the IVC communicate.
Liver or portal obstruction causes these veins to dilate widely, possibly leading to severe venous haemorrhage from oesophagus or rectum
Describe some porto-systemic anastomoses
Gastroesophageal junction- around cardia of stomach- where left gastric vein and its tributaries anastamose with tributaries to the azygos veins of the caval system
anus- superior rectal vein anastomoses with inferior rectal veins of systemic system
anterior abdominal wall around umbilicus- para-umbilical veins anastamose with veins of anterior abdominal wall
colic veins and posterior abdominal wall veins
What happens when the pressure in the portal system is elevated
venous enlargement (varices) tend to occur at the sites of portosystemic anastomoses and are called:
varicies at anorectal junction
esophageal varicies at the gastrooesophageal junction
caput medusae at the umbilicus
susceptible to trauma and once damaged may bleed profusely
Summarise the lympahtics
The lymphatic drainage of the bowel follows the arterial supply, not the venous drainage.
All lymph drains into the cisterna chyli.
Cisterna chyli is an elongated lymphatic sac located in front of the L1 & L2 bodies
The thoracic duct commences from the cisterna chyli
Describe the celiac trunk
Drains lymph from structures part of abdominal foregut
Drains to pre-aortic lymph nodes near origin of celiac axis (celiac nodes)
Also receive lymph from superior mesenteric and inferior mesenteric groups of pre-aortic lymph nodes where they all drain into cisterna chyli
Describe the superior mesenteric lymph nodes
Also recives lymph from inferior mesenteric lymph nodes
Summarise the innervation of the gut
Abdominal viscera supplied by AUTONOMIC nervous system.
Sensory fibres most important
Parasympathetic sensory (regulate reflex gut function):
VAGUS NERVE
PELVIC SPLANCHNIC NERVES (S2-S4)
Sympathetic sensory (mediate PAIN): THORACIC SPLANCHNIC (T5-T12) LUMBAR SPLANCHNIC (L1+L2)
List the splanchnic nerves
Greater Splanchnic: T5-9 Lesser Splanchnic: T10-11 Least Splanchnic: T12 Lumbar Splanchnic: L1-2 Pelvic Splanchnic: S2-4
Describe the thoracic and lumbar splanchnic sympathetic fibres
Thoracic- three nerves pass from sympathetic ganglia in along sympathetic trunk in the thorax to the prevertebral plexus and ganglia associated with the abdominal aorta and abdomen
Lumbar- two to four nerves from lumbar part of sympathetic trunk or ganglia
Describe the sacral splanchnic nerves
Pass from sacral part of sympathetic trunk or associated ganglia and enter the inferior hypogastric plexus- an extension of the prevertebral plexus.
Describe the pelvic splanchnic nerves
Carry pre-ganglionic PSNS fibres from anterior rami of S2-S4 and pass to the inferior hypogastric plexus, where some fibres pass upwards to the prevertebral plexus
PSNS innervation of hindgut
What does the abdominal prevertebral plexus receive
preganglionic PSNS and visceral afferents from vagus nerve
preganglionic sympathetics and visceral afferent fibres of lumbar and thoracic splanchnic nerves
preganglionic PSNS fibres from pelvic splanchnic nerves
Describe the vagus nerves
After entering the abdomen as anterior and posterior vagal trunks- they send branches to the abdominal prevertebral plexus- which contain preganglionic PSNS fibres and visceral afferent fibres
Provide PSNS innervation of foregut and midgut
Describe the role of visceral afferent fibres in the gut
Innervation: the sensory fibres are most important.
In the viscera:
Sensory fibres running with the sympathetic (T1-L2) mediate pain and control of sphincters
Sensory fibres running with the parasympathetic (vagus or sacral) are involved in reflex regulation of gut function
peristalsis
