Bile formation is an osmotic secretory process that is driven by the active concentration of bile salts in the bile canaliculi. Bile acids are produced from cholesterol and prior to being excreted from hepatocytes are bound to specific amino acids allowing them to exist as bile salts. One side of the bile salt molecule is negatively charged (hydrophilic) whilst the other is hydrophobic allowing bile salts to form micelles once a certain bile salt concentration has been reached.

Biology 2e is designed to cover the scope and sequence requirements of a typical two-semester biology course for science majors. The text provides comprehensive coverage of foundational research and core biology concepts through an evolutionary lens. Biology includes rich features that engage students in scientific inquiry, highlight careers in the biological sciences, and offer everyday applications. The book also includes various types of practice and homework questions that help students understand—and apply—key concepts. The 2nd edition has been revised to incorporate clearer, more current, and more dynamic explanations, while maintaining the same organization as the first edition. Art and illustrations have been substantially improved, and the textbook features additional assessments and related resources.

By the end of this section, you will be able to do the following:

Explain the processes of digestion and absorption
Compare and contrast different types of digestive systems
Explain the specialized functions of the organs involved in processing food in the body
Describe the ways in which organs work together to digest food and absorb nutrients

The gall bladder stores bile produced in the liver. Bile is important in the digestion of lipids. The gall bladder forms as an outgrowth of the bile duct, as a secondary hollow at the posterior edge of the original hepatic rudiment. The cystic duct joins the common bile duct which enters the duodenum at the major duodenal papillae (with the pancreatic duct) on the dorsal surface of the duodenum.