UNEFM, Medicina, Ingles III, Unidad IV, Text 3 Gallbladder

1. TEXT 3 GALLBLADDER
The gallbladder is a small storage organ located inferior and posterior to the liver. Though small in size, the
gallbladder plays an important role in our digestion of food. The gallbladder holds bile produced in the liver until it is
needed for digesting fatty foods in the duodenum of the small intestine. Bile in the gallbladder may crystallize and form
gallstones, which can become painful and potentially life threatening....
Anatomy of the Gallbladder
Gross Anatomy
Hollow, muscular and pear-shaped, the gallbladder is a small organ – only about 3 inches in length and 1.5 inches in width
at its widest point. The larger end of the gallbladder extends inferiorly and to the right while the tapered end points
superiorly and medially. The tapered end of the gallbladder narrows into a small bile duct known as the cystic duct. The
cystic duct connects to the common hepatic duct that carries bile from the liver. These ducts merge to form the common bile
duct that extends to the wall of the duodenum.
Microscopic Anatomy
The mucosa, which forms the innermost layer of the gallbladder, lines the gallbladder with simple columnar epithelial tissue.
The columnar epithelial tissue contains microvilli on its surface, increasing the surface area and allowing the lining to absorb
water and concentrate the dilute bile.
Beneath the columnar tissue is a thin lamina propria layer made of connective tissue and capillaries that support and
anchor the epithelial layer.
Deep to the lamina propria is the muscularis layer that contains smooth muscle tissue. Contraction of the muscularis pushes
bile out of the gallbladder and into the cystic duct.
Surrounding the muscularis is a thin layer of fibrous connective tissue that helps to reinforce and strengthen the wall of the
gallbladder.
Finally, the serosa forms the outermost layer of the gallbladder. The serosa is an epithelial layer that forms part of the
peritoneum, or lining of the abdominal cavity. The serosa gives the gallbladder a smooth, slick surface to prevent friction
between moving organs.
Physiology of the Gallbladder
Storage
The gallbladder acts as a storage vessel for bile produced by the liver. Bile is produced by hepatocytes cells in the liver
and passes through the bile ducts to the cystic duct. From the cystic duct, bile is pushed into the gallbladder by peristalsis
(muscle contractions that occur in orderly waves). Bile is then slowly concentrated by absorption of water through the walls
of the gallbladder. The gallbladder stores this concentrated bile until it is needed to digest the next meal.
Stimulation
Foods rich in proteins or fats are more difficult for the body to digest when compared to carbohydrate-rich foods (see
Macronutrients). The walls of the duodenum contain sensory receptors that monitor the chemical makeup of chyme (partially
digested food) that passes through the pyloric sphincter into the duodenum. When these cells detect proteins or fats, they
respond by producing the hormone cholecystokinin (CCK). CCK enters the bloodstream and travels to the gallbladder
where it stimulates the smooth muscle tissue in the walls of the gallbladder.
Secretion
When CCK reaches the gallbladder, it triggers the smooth muscle tissue in the muscularis layer of the gallbladder to
contract. The contraction of smooth muscle forces bile out of the gallbladder and into the cystic duct. From the cystic duct,
bile enters the common bile duct and flows into the ampulla of Vater, where the bile ducts merge with the pancreatic duct.
Bile then flows from the ampulla of Vater into the duodenum where it breaks the fats into smaller masses for easier
digestion by the enzyme pancreatic lipase.