27.25
Bile
La bile è un fluido corporeo fondamentale, caratterizzato dal suo colore giallo-verde e dalla sua natura alcalina. Prodotta nel fegato, viene trasport…
La bile è un liquido alcalino giallo-verde secreto dal fegato nei dotti epatici destro e sinistro e quindi nel dotto epatico comune. Da qui, può prendere due percorsi.
La bile può entrare nel dotto cistico, portando alla cistifellea, oppure può fluire nel dotto biliare, convergendo allo sfintere di Oddi al duodeno.
Quando lo sfintere è chiuso, la bile viene restituita alla cistifellea, dove viene immagazzinata e concentrata fino al momento del bisogno.
Quando i grassi alimentari raggiungono il duodeno, la cistifellea si contrae e lo sfintere di Oddi si apre, rilasciando la bile nel duodeno.
Qui, i sali biliari emulsionano i lipidi alimentari formando micelle, favorendo la digestione e l'assorbimento dei lipidi.
Inoltre, l'alcalinità della bile neutralizza l'eccesso di acido gastrico nel chimo.
Oltre a elettroliti, trigliceridi e fosfolipidi, la bile contiene anche bilirubina, un pigmento giallo formato come sottoprodotto della degradazione dell'emoglobina nei globuli rossi morenti.
La bilirubina viene metabolizzata dai batteri del colon, producendo urobilinogeno e stercobilinogeno, conferendo alle feci il suo colore marrone.
View the full transcript and gain access to JoVE Core videos
Q1: Where is bile produced and how does it travel through the digestive system?
The liver secretes bile into the right and left hepatic ducts, which converge into the common hepatic duct. From there, bile either enters the cystic duct leading to the gallbladder for storage or flows directly into the bile duct. Both pathways converge at the sphincter of Oddi at the duodenum, where bile is released into the small intestine during digestion.
Q2: What role does the sphincter of Oddi play in bile regulation?
The sphincter of Oddi controls bile flow into the duodenum. When closed, it redirects bile to the gallbladder for storage and concentration. When dietary fats reach the duodenum, the sphincter opens and the gallbladder contracts, releasing concentrated bile into the small intestine to aid in lipid digestion.
Q3: How do bile salts help with fat digestion?
Bile salts emulsify dietary lipids by forming micelles, which break large fat droplets into smaller particles. This increases the surface area available for enzymatic breakdown and facilitates mechanical and chemical digestion in the small intestine, making lipids easier to absorb.
Q4: What is bilirubin and where does it come from?
Bilirubin is a yellow pigment formed as a byproduct of hemoglobin breakdown in dying red blood cells. It is a key component of bile and gives bile its characteristic yellow-green color. After reaching the colon, bilirubin is metabolized by colonic bacteria into stercobilinogen, which gives feces its brown color.
Q5: How does bile neutralize stomach acid in the duodenum?
Bile is an alkaline liquid that neutralizes excess stomach acid, or chyme, as it enters the duodenum. This alkaline environment protects the small intestine from acid damage and creates optimal conditions for digestive enzymes to function effectively during nutrient absorption.
Q6: What are the main components of bile besides bile salts?
Bile contains electrolytes, cholesterol, triglycerides, phospholipids, and bilirubin. These components work together to support fat digestion and absorption while also serving as a vehicle for eliminating bilirubin and other waste products from the body through the digestive system.
Q7: When is bile released from the gallbladder?
Bile is released from the gallbladder when dietary fats enter the duodenum. This triggers gallbladder contraction and opens the sphincter of Oddi, allowing stored and concentrated bile to flow into the small intestine where it immediately begins emulsifying lipids for digestion and absorption.