6- Chyme, pancreas and liver

Question 1

Describe the constituency of chyme as it enters the duodenum

Answer 1

Hypertonic
Acidic
Partially digested

Question 2

How does the tonicity of chyme change in the duodenum?

Answer 2

Duodenum permeable to water, so hypertonic chyme draws water out from ECF
Means chyme release has to be controlled or duodenum would be overwhelmed with water influx

Question 3

What does the duodenum secrete in response to chyme?

Answer 3

Scretin - stimulates pancreas to release HCO3
CCK - stimulates pancreas to release digestive enzymes
Causes gallbladder contraction and relaxes the sphincter of oddi

Question 4

How are pancreatic secretions controlled?

Answer 4

Sympathetic inhibits
Parasympathetic - Vagus X - stimulates
Hormones secretin and CCK

Question 5

What proteses are secreted from the pancreas?

Answer 5

Trypsin
Chymotrypsin
Elastase
Carboxypeptidase

Question 6

Describe the storage of pancreatic proteases

Answer 6

Produced in inactive form in acinar cells stimulated by CCK

Concentrated and stored in zymogen granules, membrane bound secretions containing inactive precursor of enzymes

Question 7

What do the duct cells secrete?

Answer 7

When stimulated by secretin
Aqueous component
Bicarbonate
To neutralise acidic chyme

Question 8

How do pancreatic secretions reach the duodenum?

Answer 8

Pancreatic duct then ampulla of vater (convergence of pancreatic and common bile duct)

Question 9

What effect will a gallstone at the common bile duct have?

Answer 9

Block gallbladder secretions

Block pancreatic secretions, active proteases will self digest the pancreas

Question 10

Describe the function of bile

Answer 10

Emulsifies fat in duodenum so they are readily digested by lipases secreted by pancreas

Question 11

Describe the structure of a liver lobule

Answer 11

Hexagonal arrangement
Triad at each corner: portal vein, hepatic artery and bile duct
Central vein in middle
Acinus (functional area

Question 12

How does blood flow in/out of the liver?

Answer 12

Inwards towards the central vein by portal vein/hepatic artery, then via sinusoids (space between hepatocytes)
Outwards along canaliculi, into bile duct and into duodenum

Question 13

Describe the structure of liver acini

Answer 13

Blood drains from periphery to centre, creating zones corresponding to proximity to arterial supply, 1 being closest, 3 furthest away

Question 14

Describe damage to the liver acini due to ischaemia

Answer 14

As zone 3 is furthest away from blood supply, will receive least oxygen so most damaged.

Question 15

Describe damage to liver acini due to toxicity

Answer 15

Zone 1 closest to blood supply so will be exposed to the highest concentration of toxin, sustain most damage

Question 16

How and why is bile stored?

Answer 16

Continuously produced by the liver but only needed intermittently to deal with chyme
Gallbladder stores (until CCK stimulates gallbladder contraction) and concentrates, which can produce gallstones

Question 17

What pathway does bile take?

Answer 17

Liver 
Gallbladder
Common bile duct
Ampulla of vater
Duodenum 
Terminal ileum 
Portal vein to liver

Question 18

What is the consistency of bile?

Answer 18

Bile acids and pigments - secreted into canaliculi by hepatocytes
Alkaline solution - secreted by bile ducts that have been stimulated by secretin

Question 19

What are bile salts?

Answer 19

Bile acids conjugated with amino acids (glycine and taurine)

Question 20

Why do bile acids need to be conjugated?

Answer 20

Not soluble at duodenal pH, so are functionally useless

Bile salts are amphipathic so allow for emulsification of lipids

Question 21

What are micelles and what is their function?

Answer 21

Micelles are the products of lipid breakdown surrounded by bile salts
Act as a vehicle to transport hydrophobic molecules to enterocytes

Question 22

Describe the entero-hepatic circulation of bile acids

Answer 22

Bile salts do not enter eneterocyte in duodenum
Reabsorbed in terminal ileum
Returned to liver in portal blood, where it is recycled

Question 23

What are chylomicrons and what is their function?

Answer 23

Lipoprotein found in enterocytes, combined with newly re-estified triglycerides, phospholipids and cholesterol
Function: Exocytose through basolateral membrane, carrying digested fats via the lymphatic system (too big to enter capillaries) to reach circulation

Question 24

What is steatorrhoea?

Answer 24

Pale, floating, foul smelling faeces due to undigested fat in faeces
Due to insufficient bile acid or pancreatic lipase secretions