GI Session 6 Flashcards
What surrounds the major duodenal papilla?
Sphincter of Oddi
How is the pancreas divided into exocrine and endocrine portions?
Exocrine ~90%
Endocrine ~2%
What does the exocrine portion of the pancreas secrete?
Acinus secretes enzymes
Duct secretes aqueous solution
What does the endocrine pancreas secrete?
Insulin
Glucagon
How is the pancreas innervated?
ANS: sympathetic stimulation inhibits secretion, parasympathetic via vagus stimulates secretion
Describe the pathway that leads to enzyme secretion by the acinus.
Hypertonicity and fats detected in duodenum –> vagus nerve and CCK activates –> active and inactive enzymes produced
Which enzymes are secreted in their active form?
Amylases
Lipases
What is a zymogen granule?
A membrane bound inactive precursor of an enzyme
How are zymogen granules formed?
Cis-trans RER –> Golgi –> condensing vacuole –> zymogen granules
What is the alt heavy of aqueous solution secretion from the duct cells in the pancreas?
Hypertonic chyme in duodenum –> secretin activated –> production and secretion of HCO3- into duodenal lumen
What transporter is used to move HCO3- into the duodenal lumen?
Cl-HCO3- exchanger
At high flow rates in the duodenum how does HCO3- secretion change?
More is secreted
What occurs in the blood due to HCO3- production by the pancreas?
Opposite of alkaline tide as H+ produced move into pancreatic venous drainage causing a transient decrease in pH
What is the function of the liver?
Energy metabolism
Detoxification
Plasma protein production
Bile secretion
What are the components of bile?
Mainly water Bile salts FA Cholesterol Proteins Pigments Alkaline juice
How much bile is secreted by the liver?
250 ml to 1 l per day
What forms 80% of liver mass?
Hepatocytes
How can hepatocytes be identified on histology?
Lots of rough and smooth ER, glycogen and stacks of Golgi membranes
What is the function of RER?
Protein production
What is the function of SER?
Fat processing and detoxification
What is the structural unit of the liver?
Lobule formed by collections of hepatocytes divided by invaginations of the liver capsule
What is the surgical importance of the liver lobules?
Similar to bronchopulmonary segments so can be removed individually causing minimal damage to remaining tissue
What is the functional unit of the liver?
Acinus formed by distance between two central veins to form the long axis and distance between portal triads for the short axis
What is zone 1 of an acinus at risk of?
Toxins
Why is zone 3 of an acinus at higher risk of hypoxia than toxin damage in comparison to zone 1?
Further away from arterial supply but closer to central vein
Describe how blood flows into the liver.
Venous portal blood and arterial blood in hepatic arteries –> central vein –> healthcare veins –> IVC
What are kupffer cells?
Stellate macrophages
Why are Kupffer cells present in the hepatic sinusoids?
All blood from gut drains through liver so presents possible pathogen entry
Describe the path of blood from branches of the hepatic portal vein to the IVC in a hepatic sinusoid.
Branch –> central canals which merge to form –> hepatic veins –> IVC
How does bile flow in the liver?
Flows outwards from canaliculi –> bile ducts at periphery –> duodenum
What secretes bile acid dependent bile into the canaliculi?
Hepatocytes
What is the contents of bile acid dependent bile?
Bile acids
Pigments
What secretes bile acid independent bile?
Duct cells
What is bile acid independent bile similar to?
Alkaline solution secreted by pancreatic duct cells
What stimulates secretion of bile acid independent bile?
Secretin
What are the two primary bile acids produced by the liver?
Cholic acid
Chenodeoxycholic acid
Apart from the liver where else are bile acids formed?
Gut
How do bile acids become bile salts?
Conjugation with glycine and taurine
What is the purpose of conjugating bile acids to become bile salts?
Gives them and amphipathic structure so they can act at the oil/water interface for emulsification of dietary lipid
Makes the soluble at duodenal pH
Why aren’t fats completely digested by enzyme action in the duodenum?
Tend to form large globules by the time they reach here so there is a small SA for enzymes to act on
What is the action of bile salts in large lipid globules?
Emulsify to increase SA available for lipases to act
What do bile salts from with products of lipid digestion?
Micelles containing cholesterol, mono glycerine sand free FA from lipid
How do emulsified lipids enter enterocytes?
Diffuse down concentration gradient and are re-esterified back into triglycerides, phospholipids and cholesterol
What halogens to the reformed lipids once in the enterocytes?
Packaged as aporoteins–> chylomicrons
Describe the passage of chylomicrons from enterocytes into the L subclavian vein.
Exocytosis from basolateral enterocyte membrane –> lacteals –> lymphatic system –> thoracic duct –> L subclavian vein
Why don’t chylomicrons enter capillaries after exocytosis from enterocytes?
Too large
What are lacteals?
Lymph capillaries
How are bile salts recycled?
Remain in gut lumen until terminal ileum –> reabsorbed –> portal blood –> liver extracts
What is the purpose of recycling bile salts?
Reduces energy demand for constantly making new ones although this has to happen to some degrees as some are lost
What is the function of the gallbladder?
Store continuously produced bile until it is stimulated to release
Concentrate bile
What stimulates bile release from the gallbladder?
Detection of hypertonicity and lipid presence –> CKK release from duodenum –> sphincter of Oddi relaxes
How does the gallbladder concentrate bile it stores?
Removes water/ions
What causes faeces to be brown?
Hb broken down –> conjugated in liver to become soluble –> bile –> stercobilinogen –> brown faeces
What leads to steatorrhoea?
If bile salts or pancreatic lipases a not secreted in adequate amounts
Where does the SMA arise?
L1 vertebral level immediately inferior to coeliac trunk
What does the right colic artery supply?
Ascending colon
What does the middle colic artery supply?
Transverse colon
What lies anterior to the SMA?
Pylorus
Splenic vein
Neck of pancreas
What lies posterior to the SMA?
L renal vein
Uncinate process of pancreas
Inferior duodenum
Describe the arrangement of jejunal and ileal arteries.
Pass between layers of mesentery to freon anastomotic arches –> vasa recta
How do jejunal and ileal arteries compare?
Jejunal = fewer arterial arcades but longer vasa recta Ileal = more arterial arcades but shorter vasa recta
Describe the path of the inferior pancreaticoduodenal artery.
1st branch of SMA –> anterior and posterior branches –> anastomose with branches of superior pancreaticoduodenal artery from coeliac trunk –> supply inferior head of pancreas, uncinate process and duodenum
What does the ileocolic artery supply?
Ascending colon
Appendix
Caecum
Ileum
What is ligated in appendicectomy?
Appendicular artery from ileocolic artery
How is the ileocolic artery positioned?
Passes inferiorly and R
Where does the IMA arise?
L3 vertebral level, near inferior border of duodenum 3-4 cm from the aortic bifurcation
Is the IMA peritoneal, retroperitoneal or secondary retroperitoneal?
Retroperitoneal
What does the sigmoid artery supply?
Descending colon and sigmoid colon via 2-4 branches
What is the uppermost branch of the sigmoid arteries called?
Superior sigmoidal artery
How are the sigmoid arteries positioned?
Run inferiorly, obliquely and L –> cross over psoas major, L ureter and L internal spermatic vessels
What is the left colic artery?
1st branch of IMA
What does the left colic artery supply?
Distal 1/3 of transverse colon
Descending colon
How is the left colic artery positioned?
Anterior to psoas major, L ureter and L internal soermatic vessels then:
Ascending branch crosses L kidney anteriorly and enters T colon mesentery moving superiorly
Descending branch moves inferiorly and anastomoses with superior sigmoid artery
What can the IMA cause in the developing kidney?
Horseshoe kidney
Why does chyme become hypertonic in the stomach?
Exponential increases in the number of molecule present combined with impermeability of stomach wall to water
What is the superior rectal artery?
Most inferior branch of IMA supplying the rectum
Describe the passage of the superior rectal artery.
Crosses pelvic brim crossing L iliac artery and vein –> at S3 forms 2 terminal branches either side of rectum –> within wall smaller branches eventually communicate with middle and inferior rectal arteries
What is the marginal artery of Drummond?
Continuous arterial circle along inner border of colon with vasa recta extending to the colon
What forms the marginal artery?
Ileocolic Right colic Middle colic Left colic Sigmoid branches
What is the arc of Riolan?
Anastomosis of middle colic and left coli arteries
Describe the clinical relevance of the splenic flexure blood supply.
Watershed area due to dual blood supply from most distal branches of two large arteries –> more resistant to ischaemia in occlusion of one artery but more sensitive to systemic hypoperfusion
The junction of which two arterial supplies is found at the splenic flexure?
SMA+IMA
