Bile Intro Flashcards
What is the “Unstirred Water Layer”?
The polar area that is closest to the Intestinal Walls caused by Laminar Flow, Mucus, and HCO3
What is the issue with Lipid reabsorption in the Small Intestine?
Although they can easily diffuse into Enterocytes WITHOUT the use of Transporters, Lipids are hydrophobic/non-polar so they CANNOT get through the Unstirred Water Layer to access the Enterocytes
Where is Bile synthesized?
Bile is synthesized in the Hepatocytes of the Liver
Primary Bile:
- Where is it synthesized
- What does it consist of?
- Name of a common type?
- What is it used for?
- Primary Bile is synthesized in the Hepatocytes of the Liver
- Cholesterol Backbone, excess Phospholipids, Bilirubin, and a Conjugated Amino Acid (Taurine or Glycine)
- Cholic Acid (most common type)
- Amphipathic so it emulsifies lipids and “Taxis” them across the Unstirred Water Layer
What enzyme synthesizes Cholesterol? How can it be blocked?
- HMG CoA Reductase in the Liver synthesize Cholesterol
2. Statin drugs block HMG CoA Reductase, therefore blocking Cholesterol synthesis
Describe the makeup of Primary Bile:
Primary Bile is AMPHIPATHIC and consists of:
- Cholesterol Backbone
- Excess Phospholipids
- Bilirubin
- Taurine or Glycine (conjugated Amino Acid that makes up the polar end)
What is Secondary Bile?
Bile that has been acted on by Intestinal Bacteria in the lower GI Tract that is NO LONGER AMPHIPATHIC so it has a hard time crossing the Unstirred Water Layer to reach Enterocytes
Bile is nearly “Isotonic” to Plasma which means what?
BILE IS A GREAT BUFFER
Bile and Plasma have nearly the same osmolarity which means that if Bile is secreted, it brings water with it. This causes “Solvent Drag” which pulls solutes (Na+, Cl-, and HCO3-) with the water as well that buffer acidic chyme leaving the stomach. This makes Bile an effective buffer.
What is Solvent Drag?
An important process that buffers acidic chyme leaving the stomach so that enzymes can act on it
“As Bile is secreted it pulls Water and the Water pulls Solutes (Na+, Cl-, and HCO3-) which makes Bile an effective Buffer”
When is Bile secreted and what purpose does it serve?
- We ingest food which activates the Vagus Nerve
- PNS causes the Hepatocytes in the Liver to increase Bile secretion AND it relaxes the Sphincter of Oddi
- CCK is produced in the Duodenum and it increases Bile production, contracts the Gallbladder, relaxes the Sphincter of Oddi, and stimulates Pancreatic Enzymes
- Bile enters the Duodenum and forms a protective barrier around the lipids and emulsifies them to increase Surface Area for digestion
- Pancreas secretes Proteases as inactive Zymogens, Pancreatic Lipase (lipid digestion), and Pancreatic Amylase (starch digestion)
- Tryspinogen (one of the inactive Zymogens) is activated by Enterokinase (EK) into Trypsin
- Trypsin activates the other Protease zymogens yielding Chymotrypsin, Carboxypeptidase, and Colipase
- Colipase binds to the hydrophilic ends of the Bile surrounding Lipids and opens a “door” for the Lipase to enter and hydrolyze lipids
- The Micelle is officially formed as the Bile now surrounds lipids that have been hydrolyzed by the Pancreatic Lipase
- Bile “Taxis” the hydrolyzed Lipid through the “Unstirred Water Layer” and drops it off to the Enterocytes.
- Lipids diffuse through the Enterocytes
- Bile continues this process as long as Chyme is present in the Small Intestine up until the Terminal Ileum where transporters uptake Primary Bile to be recycled.
- Recycled Bile is put into the PORTAL SYSTEM to be circulated back to the Liver
- About 10% of Bile is lost into the Feces with each cycle to rid the body of Cholesterol, Bilirubin, and random wastes
- When the meal is done and there is no longer Chyme present in the Duodenum, CCK is reduced and Bile secretion is stopped.
