Anatomy of bleeding in the GI tract Flashcards
describe the components of the large intestine, from proximal to distal.
- Colon = caecum = appendix = ascending colon = transverse colon = descending colon = sigmoidal colon
- rectum
- anal canal
- anus
what are 3 functions of the large intestine?
1) defence
= commensal bacteria
2) absorption
= H20 and electrolytes
3) excretion
= of formed stool
describe the colons anatomical position.
= intra-peritoneal (quite mobile)
= secondarily retro-peritoneal
= intra-peritoneal (highly mobile as it has its own mesentery)
= secondarily retro-peritoneal
= intra-peritoneal (quite mobile as it has its own mesentery)
- inferior to liver
- inferior to spleen
what are paracolic gutters?
= spaces between the colon and the abdominal wall
how many paracolic gutters are there?
= 2; right and left
- located between lateral edges of ascending and descending colon and abdominal wall
what are the paracolic gutters part of?
= greater sac of peritoneal cavity
what re paracolic gutters potential sites for?
= pus collection
- similar to sub-phrenic or hepatorenal recesses
what are 3 distinguishing features of the colon?
1) omental appendices
2) teniae coli
3) haustra
describe the teniae coli.
= 3 distinct longitudinal bands of thickened smooth muscle, from caecum to distal end of sigmoid colon
= coming together at the appendix
True or False.
Splenic flexure, usually, lies more superior that hepatic flexure.
True
what are omental appendices?
= small, fatty, projections
how are haustra formed?
= by tonic contractions of tenaie coli
what is used as a contrast in radiology and how is it administered?
= barium
- administered via an enema
(enema = procedure in which liquid is injected via the rectum)
where do the caecum and appendix lie?
= in the right iliac fossa
describe the position of the appendix?
= variable (accounts for why patients have differences when presenting with appendicitis)
= often retro-caecal
where is the appendiceal orrifice?
= on postero-medial wall of caecum
where does the appendiceal orrifce correspond with?
- corresponds to McBurney’s point on the anterior abdominal wall
- 1/3 of the way between right ASIS to umbilicus
- maximum tenderness in case of appendicitis
where does the sigmoidal colon lie?
= in left iliac fossa
describe the mesentery fo the sigmoidal colon?
= long mesentery (sigmoid mesocolon)
- giving it a considerable degree of movement
what is a negative side to the long mesentery possessed by sigmoidal colon?
= the sigmoidal colon is at risk of twisting around itself
sigmoidal volvulus
what is sigmoid volvulus and what does it result in?
= when the sigmoidal colon twists round itself
= resulting in bowel obstruction
- bowel at risk of infarction if left untreated
describe where the abdominal aorta lies?
= midline, retroperitoneal structure
- lying anterior to vertebral bodies and to left of IVC
how many midline branches does the abdominal aorta have?
= 3 midline branches
- ceoliac trunk (foregut organs)
- superior mesenteric artery (midgut organs)
- inferior mesentery artery (hindgut organs)
what do the lateral branches of the abdominal aorta supply?
= kidneys/adrenal glands
= gonads (testes/ovaries)
= body wall (posterolateral)
what does the abdominal aorta bifurcate into?
= common iliac (L4)
- further bifurcates to internal and external iliac
Name 6 branches of the superior mesenteric artery.
- jejunal and ileal arterries
- appendicular
- ileocolic branches
- right colic artery
- middle colic artery
- inferior pancreaticoduodenal
look at the image of the superior mesenteric artery, slide 10.
describe the difference between the jejunal and ileal arteries?
Jejunum
= longer vasa rectae
= larger and fewer arcades
Ileum
= shorter vasa rectae
= smaller and many arcades
Name 3 branches of inferior mesenteric artery.
- left colic artery
- sigmoidal artery
- superior rectal artery
look at the image of the superior mesenteric artery, slide 12.
what is the marginal artery of drummond?
= arterial anastomoses between the branches of the superior mesenteric artery and inferior mesenteric artery
what could these anastomoses help prevent?
= they could help prevent intestinal ischaemia by providing an alternative (collateral) route by which blood can travel
what does the superior rectal artery, a bunch of inferior mesenteric artery, supply?
= hindugtt extends too proximal half of the anal canal (the pectinate linen)
what is the remainder of the GI tract supplied by?
= the internal iliac artery
- there is an anastomoses between these vessels
what are the bodies 2 main venous systems and what do they drain?
1) hepatic portal system
= drains venous blood from absorptive part of GI tract & associated organs to liver for ‘cleaning’
2) systemic venous system
= drains venous blood from all other organs and tissues into the superior or inferior vena cava
what does the inferior vena cava (retro-peritoneal) drain?
drains cleaned blood from the hepatic vein into the right atrium
what does the hepatic portal vein and splenic vein drain?
Hepatic portal vein
= drains blood from foregut, midgut and hindgut structures to the liver for first pass metabolism.
Splenic vein
= drains blood from foregut structures to hepatic portal vein
what does the superior mesenteric and inferior mesenteric vein drain?
Superoir mesenteric vein
= drains blood from midgut structures to hepatic portal vein
Inferior mesenteric vein
= drains blood from hindgut structures to splenic vein
describe the 3 clinically important sites of venous anastomosis between the systemic and portal venous system?
= at these sites, the presence of small collateral veins means blood can flow both ways;
- either into systemic or portal venous system
- there are no valves in these veins
- normally there is very little blood flow within these collateral veins
what are the 3 parts to the portal-system anastomoses?
1) distal end of oesophagus
2) skin around umbilicus
3) rectum/anal canal
describe what the inferior and superior part of the distal end of the oesophagus drains?
inferior part
= drains into hepatic portal vein
Superior part
= drains into azygous vein
describe the skin around umbilicus.
= connection between para-umbilical veins and small epigastric veins
- para-umbilical veins to hepatic portal vein along the round ligament of liver
- epigastric vein drains to caval system
describe the rectum/anal canal?
= rectum and superior anal canal drains to inferior mesenteric vein
- inferior parts of GI tract drains to the internal iliac veins
what is portal hypertension and what can cause it?
= elevation of blood pressure in the portal system
Can be caused by;
- liver pathology (cirrhosis)
- tumour compressing HPV
what does portal hypertension lead to?
= reversal of blood flow
what does a larger volume of blood flow to these anastomotic (collateral) areas cause?
= them to become varicosed
what are 2 clinical features of portal hypertension?
1) oesophageal varices
- dilated sub-mucosal collateral veins
2) caput medusae
- dilated para-umbilical and dilated epigastric veins
what is haematemesis?
= vomiting up blood
what are the options for the causes of haematemesis?
1) peptic ulcer in wall of stomach or duodenum
- erodes through the mucosa
- stomach or duodenum fills with blood
2) bleeding from oesophageal varives
- abnormal dilated veins
- thin walls, therefore the potential to rupture
= filling oeosphagus with blood
- formation often due to pathology affecting portal venous system
