UNIT 2: GI tract Flashcards by Ellen NR

what does the foregut contain and what is its arterial supply?

oesophagus to middle duodenum (includes stomach, liver and pancreas)
- supplied by coeliac trunk

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what does the midgut contain and what is its arterial supply?

middle duodenum to proximal 2/3 of transverse colon (includes ascending colon/ caecum/ appendix/ jejunum/ ileum)
- supplied by superior mesentric artery

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what does the hindgut contain and what is its arterial supply?

distal 1/3 of transverse colon to anal canal (includes descending colon, sigmoid colon and rectum)
- supplied by inferior mesentric artery

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where does the coeliac trunk arise from?

abdominal aorta at level of T12 between crura of diaphragm

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what are the three major branches of the coeliac trunk?

left gastric artery
splenic artery
common hepatic artery

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what does the common hepatic artery divide into?

hepatic artery (proper) - branches into right and left as approaches porta hepatis of liver
gastroduodenal artery - ends as superior pancreaticoduodenal artery

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where does the right gastric artery branch from and what does this form with the left gastric artery?

branches from hepatic proper artery

anastomose to form inner arcade - supplies stomach (sits on lesser curve)

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what branches off the splenic artery?

posterior gastric artery - supplies the fundus and upper body of stomach
- left gastroepiploic (gastro-omental) artery

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where does the right gastroepiploic artery branch from and what does this form with the left gastroepiploic artery?

branches from gastroduodenal artery

anastomose to from outer arcade supplying stomach sits on greater curve

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what veins supply the stomach?

parallel to the arteries but arise from portal veins and drain into the hepatic portal venous system

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what compose the outer/ inner layers of interior of stomach?

outer: smooth muscle
inner: muscosa - in fundus - smooth but in pylorus forms longitudinal folds

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where does the esophagus pass ?

follows verterbral column (thoracic kyphosis) and passes through esophageal hiatus at level of T10 and terminates at esophagogastric junction at T11 (7th costal cartilage)

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how would you describe the peritoneum on the oesophagus?

describe the external layer on superior/ middle/ inferior parts

retroperitoneal

voluntary striated muscle
both
smooth muscle

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what innervates the oesophagus?

vagal trunks which form anterior/ posterior vagal nerves
thoracic sympathetic trunks via greater splanchnic nerves
periarterial plexus

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describe the arterial supply and venous drainage of the oesophagus?

supplied by esophageal branches of the left gastric artery and left inferior phrenic artery
venous drainage - portal venous system through left gastric vein

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describe the four parts of the duodenum

1) superior - anterolateral to L1
2) descending - sides of L2/3 around head of pancreas
3) inferior - anterior to IVC/ aorta and posterior to SMA/ SMV - level of L3
4) ascending - passes on left side of aorta from L3 to L2 -curves anteriorly to join jejunum at duodenojejunal flexure

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what is the duodenojejunal flexure supported by?

suspensory muscle (ligament of Treitz) - slip of skeletal muscle from diaphragm and smooth muscle from 3rd/ 4th parts of duodenum

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what are proportions of the jejunum to ileum?

jejunum -2/5 - upper left quadrant

ileum - 3/5 - lower left quadrant

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compare jejunum to ileum

jejunum- thick intestinal wall/ longer vasa recta/ less arcades/ red in colour
ileum - thin intestinal wall/ shorter vasa recta/ more arcades/ pink in colour

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what are the main branches of the superior mesentric artery?

inferior pancreaticoduodenal artery 
middle colic artery 
right colic artery 
ileocolic artery  
jejunal/ileal arteries

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what arteries supply the duodenum?

1st/ 2nd - coeliac trunk- gastroduodenal and superior pancreaticoduodenal arteries
3rd/ 4th - superior mesentric arteries - inferior pancreaticoduodenal arteries

what veins drain duodenum?

hepatic portal veins- drain directly or indirectly via splenic or superior mesentric veins

what nerves innervate the duodenum?

vagus (parasympathetic)

greater/lesser splanchic nerves - coeliac/ mesentric plexuses (sympathetic)

what structures form the large intestine?

cecum, appendix, colon, rectum and anal caal

where is the cecum found? describe its features

blind pouch in right lower quadrant - right iliac fossa - inferior to ileocecal valve - no mesentery but entirely enveloped by peritoneum

where is the appendix found?

extends from posteromedial aspect of cecum inferior to valve - base of appendix found at Mcburneys points- 1/3 of distance from the anterior iliac superior spine to umbilicus - has short mesentery = mesoappendix (posterior side of ileum)

what arteries/veins supply the cecum and appendix?

cecum - ileocolic appendix - appendicular venous drainage for both by ilecolic vein

give features of the colon

teniae coli - 3 longitudinal thickened bands of muscle fibres from base of appendix to rectosignoid junction and form continuous layer around the rectum haustra - sacculations/ pouches - formed from teniae coli smooth internally - no villi

describe the attachment of the ascending and descending colon to the posterior abdominal wall

peritoneum covers anterior and lateral sides attaches them to wall - short mesentery

describe the attachments of the transverse colon

attached to diaphragm by phrenicocolic ligament | - has transverse mesocolon lies along inferior border of pancreas

where is the sigmoid colon located?

iliac fossa at level of S3 long mesentery = sigmoid mesocolon

what are the three main branches of the inferior mesentric artery?

left colic artery sigmoid arteries superior rectal artery

which arteries supply the parts of the colon?

ascending: ileocolic/ right colic artery transverse: middle colic artery descending: left colic sigmoid: sigmoid arteries

What is the function of the caecum?

reservoir for chyme - receives the ileum

What is the name of the collateral supply of the colon?

marginal artery of Drummond - formed from anastomosis of terminal branches of SMA & IMA - vasa recta branch from this

What is the venous drainage of the colon?

corresponding veins - empty into hepatic portal vein

What is a volvulus? describe the clinical signs and treatment

where the intestine twists on itself - colicky pain, abdominal distension, absolute constipation Rx: decompression or resection if perforated

What level does the rectum begin at?

level of S3

Describe the two flexures of the rectum

- sacral flexure: follows curve of the sacrum and coccyx | - anorectal flexure - formed from the tone of the puborectalis muscles - contributes to faecal continence

Describe the ampulla of the rectum

last segment of the rectum - continous with the anal canal | - relaxes to accumulate & temporarily store faeces until defecation

describe the peritoneal coverings of the rectum

superior 1/3 - anterior/ lateral sides middle 1/3 - anterior only posterior 1/3 - no peritoneum

describe the reflections of the peritoneum in males and females

- male: rectovesical pouch - reflection from rectum to posterior bladder wall - female: rectouterine pouch (pouch of Douglas) - reflection from rectum to posterior vagina & cervix

describe the arterial supply of the rectum

- superior rectal: IMA continuation - middle rectal: internal iliac branch - inferior rectal: internal pudendal

describe the venous drainage of the rectum

corresponding veins but superior drains into the portal venous system and middle/ inferior drain into systemic venous system - anastomosis between portal and systemic veins form site of portocaval anastomosis

describe the innervation of the rectum

- sympathetic: lumbar sphlanchnic + sup/ inf hypogastric plexus - parasympathetic: S2-4 (via pelvic splanchnic and inferior hypogastric plexus)

describe the anal canal

it is located in the anal triangle and it is collapsed by internal and external anal sphincters to prevent passage of faecal material

describe the two anal sphincters

- internal anal sphincter: formed from thickening of involuntary circular smooth muscle in the bowel wall ( surrounds upper 2/3) - external anal sphincter: voluntary muscle overlaps the internal and blends with the puborectalis muscle (surrounds lower 2/3)

where is the anorectal ring found?

junction of rectum & anal canal (fusion of sphincters & puborectalis)

describe the histology of the anus

- superior aspect - columnar epithelium - inside canal - longitudinal folds = anal columns joined at inferior ends by anal valves => form pectinate line which divides the anus into two parts

what epithelium found below the pectinate line?

non-keratinised stratified smooth epithelium (anal pecta) this transitions into true skin at the level of the inter-sphincteric groove

describe the vasculature of the rectum

- above pectinate line: superior rectal artery/ vein | - below pectinate line: inferior rectal artery/ vein