4.0 bile salts, fat absoprtion pathways and their role in drug absorption

bile

digestive fluid produced by the liver and stored in the gallbladder

although mostly composed of water bile contains important substances such as

• bile salts

• cholesterol

• bilirubin

• phospholipids

the components of bile work together to emulsify fats

breaking them into smaller droplets to facilitate digestion and absorption

bile salts are derived from cholesterol,

these are the most important component for fat digestion

cholesterol excreted from the liver

in the form of bile

bilirubin

a by product of the breakdown of red blood cells, it gives bile its greenish-yellow colour

phospholipids

aid in the emulsification of fats alongside bile salts

bile salts are the most critical component of bile for the digestion and absorption of dietary fats and fat soluble vitamins

synthesised in the liver from cholesterol and stored in the gallbladder until released into the small intestine after a meal

functions of bile salts

• emulsification

• micelle formation

• facilitation of lipase action

emulsification

bile salts emulsify large fat globules into smaller droplets increasing the surface area for fat digesting enzymes

micelle formation

they help form micelles tiny droplets that allow fats and fat soluble vitamins ADEK to be transported and absorbed

facilitation of lipase action

pancreatic lipase, the main fat digesting enzyme, requires bile salts to efficiently break down fats into free fatty acids and monoglycerides

bile salts have both hydrophobic and hydrophilic parts

allowing them to interact with both fats AND water- this is the key to their emulsifying action

enterohepatic circulation

once bile salts have done their job in the small intestine they are reabsorbed into the ileum and returned to the liver via the portal vein for reuse, conserving resources