Hepatobiliary system

Question 1

Where is the liver?

Answer 1

Top right hand quadrant of the abdomen

Question 2

Why is the liver’s proximity to the stomach, pancreas, and duodenum relevant?

Answer 2

Efficiency of processes

Question 3

The biliary tree

Answer 3

The biliary tree is a series of gastrointestinal ducts allowing newly synthesised bile from the liver to be concentrated and stored in the gallbladder (prior to release into the duodenum)

Question 4

Gallbladder

Answer 4

Small sac under the liver that branches from the common hepatic duct
Salts and water in bile are absorbed
Concentrates the bile organic molecules (5x)
Holds between 30 – 60 ml bile

Question 5

Most common cell in the liver

Answer 5

Hepatocytes, making up about 80%

Question 6

Hepatic portal vein

Answer 6

brings highly nutrient rich blood to liver

Question 7

Hepatic artery (??)

Answer 7

Brings oxygen rich blood to liver??

Question 8

Functions of the liver

Answer 8

Storage of nutrients e.g. vitamins, glycogen, minerals
Metabolism (enzyme activation): of nearly everything from digested nutrients to toxins to drugs
Endocrine function: hormone production (insulin-like growth factor, angiotensinogen, thrombopoietin); synthesis of plasma proteins such as albumin, clotting factors etc
Exocrine function: bile acids, bilirubin, cholesterol, nutrient signalling hormones
Processing and “recycling” of haemoglobin

Question 9

Discovery of bile acids

Answer 9

Earliest mention in Ebers Papyrus of the 16th century BCE
First chemical structures discovered in 1849 by Heinrich Otto Wieland

Question 10

Bile

Answer 10

secretory product from liver and bile ducts

Question 11

Functions of bile

Answer 11

Elimination of toxins, heavy metals and xenobiotics
Regulation of whole body lipid homeostasis
Bile salts stimulate peristalsis
Contributes to maintenance of duodenal pH
Signalling molecules

Question 12

Cholestasis

Answer 12

Liver toxicity associated with bile secretion abnormalities

Bile flows back into liver and causes toxicity (I think??)

Question 13

Components of bils

Answer 13

Bile acids (4-20mM in small intestine)
Similar electrolyte composition to plasma
Higher bicarbonate concentration
Phospholipids (Lecithin)
HCO3- and other salts
Cholesterol (around 80% is synthesises by the body and around 20% is consumed in the diet)
Bile pigments & small amounts of other metabolic end products
Trace metals (eg copper)
NB: Bile salts = sodium/potassium addition to bile acids

Question 14

Main two bile acids

Answer 14

Chenodeoxycholic acid
Cholic acid

Question 15

Biosynthesis of bile acids

Answer 15

Cholesterol -> Cholic acid or Chenodeoxycholic acid

Question 16

She’s going really fast check the pathways and stuff later I’m lost

Question 17

Primary bile acids - synthesised in the liver

Question 18

Secondary bile acids - by intestinal bacteria

Question 19

Bile’s role in lipid digestion

Answer 19

Emulsification and digestion of dietary triglyceride by lipase/colipase in the presence of bile acids
Formation of micelles in the presence of bile acids and movement of micelles to the enterocyte brush border
Cellular metabolism, chylomicron formation and entry into lymph

Question 20

Dietary fat

Answer 20

component of diet extracted by organic solvents

Question 21

Non-polar dietary lipids

Answer 21

Cholesteryl ester, hydrocarbons and carotene

Question 22

Polar dietary lipids

Answer 22

Insoluble non-swelling amphiphiles
Insoluble swelling amphiphiles
Soluble amphiphiles

Question 23

Insoluble non-swelling amphiphiles

Answer 23

Triacylglcyerol (triglycerides)
Diacylglycerol
Nonionized long-chain fatty acids
Cholesterol
Fat soluble vitamins

Question 24

Bile acids - role in lipid digestion

Answer 24

Soluble amphiphiles that solubilise polar lipids during digestion
Absorption of dietary lipids
Bile acids are amphipathic
Polar and non-polar faces
Anti-bacterial properties
Denaturing proteolysis
pH for enzyme function e.g. lipase/colipase

Question 25

Lipid digestion - emulsification

Answer 25

Fats in ingested food are insoluble in water Aggregate into large lipid droplets Stomach major site of emulsification Intestinal aggregates are 0.5 μm in diameter Emulsification: Mechanical disruption of lipid droplets Emulsifying agents – bile acids

Question 26

Lipid digestion - micelle formation

Answer 26

Emulsion droplets require further breakdown Bile salts play a role in formation of micelles (4-7 nm in diameter) Lipid molecules released from micelles diffuse into intestinal epithelium

Question 27

Importance of micellar solubilisation

Answer 27

Intestinal brush border Separated from bulk fluid phase by unstirred water layer Access across unstirred layer by diffusion Solubility of lipids is low so few gain access to the epithelium Micellar solubilisation increases aqueous concentration Rate of diffusion slower but more efficient in mixed micelles containing fatty acids

Question 28

Bilirubin metabolism

Answer 28

Biliverdin is water soluble, bilirubin is not Bilirubin mops up free radicals Bilirubin transported in complex to avoid excretion in urine Liver conjugates bilirubin (glucuronyl transferase) – water soluble Bacteria deconjugate bilirubin in the gut Most urobilinogen absorbed, stercobilin excreted in faeces ^^process generally happens in macrophages and other phagocytic cells

Question 29

Bile storage

Answer 29

Liver produces bile at a rate of 0.5 – 1 L/day (<- reprocessing takes much less energy that it would otherwise need) Bile secreted by hepatocytes into small ducts (bile canaliculi) Form a single duct - common hepatic duct Bile fills the common hepatic duct Overflow of bile enters the gallbladder During a resting/fasting state bile is stored in the gallbladder

Question 30

Bile secretion

Answer 30

Bile salt secretion is primarily controlled by the concentration of bile salts in the hepatic portal blood During a meal bile salts are absorbed from the intestine, causing ↑ plasma concentration ↑ plasma concentration leads to ↑ secretion into the bile canaliculi Secretion is greatest during and after a meal

Question 31

Bile caniculus

Answer 31

a thin tube that collects bile secreted by hepatocytes

Question 32

Hormonal control

Answer 32

Fat in duodenum stimulates CCK release, gall bladder contraction, relaxation of sphincter of Oddi Secretin stimulates alkaline bile secretion from bile ducts

Question 33

Neural control - parasympathetic stimulation

Answer 33

(during cephalic phase of digestion) Gall bladder contraction Relaxation of Sphincter of Oddi Increased bile formation

Question 34

Neural control - sympathetic stimulation

Answer 34

Relaxation of gall bladder Reduced bile secretion

Question 35

Enterohepatic circulation

Answer 35

synthesis and processing of BAs in the liver down the bile duct sphincter of odi i'm lost