Anatomy of Bleeding in the GI Tract Flashcards
large intestine components
colon
rectum
anal canal
anus
colon components
caecum appendix ascending colon transverse colon descending colon sigmoid colon
functions of the large intestine
defence- commensal bacteria
absorption- H20 and electrolytes
excretion- of formed stool
paracolic gutters locations
left and right
between lateral edge of ascending and descending colon and abdominal wall
what are the paracolic gutters part of?
peritoneal cavity
importance of parabolic gutters
potential sites for pus collection
distinguishing features of colon
omental appendices
tenure coli
haustra
omental appendices
small, fatty projections
teniae coli
3 distinct longitudinal bands of thickened smooth muscle, running from caecum to distal end of sigmoid colon
come together at the appendix
haustra
formed by tonic contraction of the teniae coli
caecum and appendix location
both lie in the right iliac fossa but location of the appendix is variable (most often retrocaecal)
what does the variation of the position of the appendix account for?
the different ways in which patients can present with appendicitis
where is the appendiceal orifice?
on posteromedial wall of caecum
what does the appendiceal orifice correspond to?
McBurney’s point (1/3 of the way between ASIS to umbilicus)
where does the sigmoid colon lie?
in the left iliac fossa
sigmoid colon
has a long mesentery which gives it a considerable degree of movement but also means it is at risk of twisting around itself
sigmoid volvulus
when the sigmoid colon twists round on itself resulting in bile obstruction
bowel at risk of infarction if left untreated
location of abdominal aorta
midline, retroperitoneal structure
lies anterior to vertebral bodies and to left of IVC
3 midline branches of abdominal aorta
celiac trunk
superior mesenteric artery
inferior mesenteric artery
what supplies the foregut organs?
celiac trunk
what supplies the midgut organs?
superior mesenteric artery
what supplies the inferior mesenteric 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 iliacs
what do the common iliacs further bifurcate into?
internal and external iliacs
branches of the superior mesenteric artery
appendicular ileocolic branches right colic artery middle colic artery inferior pancreaticoduodenal
jejunal arteries
longer vasa rectae
larger and fewer arcades
ileal arteries
shorter vasa rectae
smaller and many arcades
branches of the inferior mesenteric artery
left colic artery
sigmoid arteries
superior rectal artery
marginal artery of Drummond
arterial anastomoses between the branches of the SMA and the IMA
depending on the health of these and the speed at which obstruction occurs, these could help prevent intestinal ischaemia by providing an alternative (collateral) route by which blood can travel
blood supply to rectum and anal canal
superior rectal artery, a branch of IMA internal iliac artery middle rectal artery inferior rectal artery there is an anastomoses between these vessels
where does the hindgut extend to?
the proximal half of the anal canal (the pectinate line)
hepatic portal venous system
drains venous blood from absorptive parts of the GI tract and associated organs to the liver for ‘cleaning’
systemic venous system
drains venous blood from all other organs and tissues into the superior or inferior vena cava
inferior vena cava (retroperitoneal)
drains cleaned blood from the hepatic veins into the right atrium
hepatic portal vein
drains blood from the foregut, midgut and hindgut structures to the liver for first pass metabolism
splenic vein
drains blood from foregut structures to hepatic portal vein
superior mesenteric vein
drains blood from midgut structures to hepatic portal vein
inferior mesenteric vein
drains blood from hindgut structures to splenic vein
portal-systemic anastamosis
at these sites, the presence of small collateral veins means blood can flow both ways
no valves
normally little blood flow
three sites of portal-systemic anastomoses
skin around umbilicus
distal end of oesophagus
rectum/ anal canal
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 veins drain to caval system
distal end of oesophagus
inferior part drains to the hepatic portal vein
superior part drains to the azygous vein
rectum/anal canal
rectum and superior anal canal drains to inferior mesenteric vein
inferior part of GI tract drains to the internal iliac veins
portal hypertension
elevation of blood pressure in the portal system
what can cause portal hypertension?
liver pathology (cirrhosis) tumour compressing HPV
what does portal hypertension lead to?
reversal of blood flow
larger volume of blood flow to these anastomotic areas causes them to become varicosed
clinical presentation of portal hypertension
oesophageal varices
caput medusae
rectal varices
causes of haematemesis
bleeding from oesophageal varices
peptic ulcer in wall of stomach or duodenum
