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The gallbladder is a small, hollow organ that is situated beneath the liver in humans. It is a pear-shaped muscular membranous sac that stores and concentrates bile, a fluid that is received from the liver and is important in digestion. The gallbladder wall is composed of a number of layers, including a muscular layer formed by smooth muscle, which contracts to expel bile from the gallbladder. The smooth muscle of the gallbladder can be affected by various diseases, including cholesterol gallstone disease, which is characterised by decreased contractility of the gallbladder smooth muscle.
| Characteristics | Values |
|---|---|
| Description | The gallbladder is a small, hollow organ that stores and concentrates bile, a fluid that is received from the liver and is important in digestion. |
| Shape | Pear-shaped |
| Capacity | 50 ml or 1.7 fluid ounces |
| Location | Beneath the liver |
| Muscular layer | The gallbladder has a muscular layer formed by smooth muscle, with fibres that lie in longitudinal, oblique and transverse directions. |
| Muscular layer function | The muscle fibres contract to expel bile from the gallbladder. |
| Muscular layer regulation | Gallbladder tone is regulated by spontaneous muscle activity, hormones, neurotransmitters, and other compounds. |
| Disorders | Common disorders include gallstones, cholecystitis (inflammation), and cholesterol gallstone disease. |
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What You'll Learn
The gallbladder is a muscular membranous sac
The gallbladder is a small, hollow organ that sits beneath the liver. It is shaped like a pear and has a capacity of about 50 ml (1.7 fluid ounces). The gallbladder is also known as the cholecyst and its function is to store and concentrate bile, a fluid produced by the liver, before releasing it into the small intestine.
The innermost layer of the gallbladder wall is the epithelium, which is lined by a single layer of columnar cells with an apical brush border of microvilli. Underneath the epithelia is a thin layer of connective tissue called the lamina propria. Together, these two layers are known as the mucosa. The mucosa is curved and collected into tiny outpouchings called rugae. The Rokitansky-Aschoff sinuses are deep outpouchings of the mucosa that can extend through the muscular layer.
The submucosa is another thin layer of loose connective tissue with smaller blood vessels. It contains elastin fibres, lymphatics, and glands that secrete mucus. The perimuscular layer is a layer of connective tissue that surrounds the muscular layer. The outer layer of the gallbladder is the serosa, a thick layer that is continuous with the peritoneum, which lines the abdominal cavity.
Gallbladder neurons receive two types of synaptic inputs: fast excitatory postsynaptic potential (EPSP) and slow EPSP. The release of acetylcholine is the principal means of neuronally mediated contraction of the gallbladder smooth muscle. Tachykinins also produce a direct, concentration-dependent contraction of the gallbladder muscle strips.
Disruption of gallbladder smooth muscle function is an early feature of cholesterol gallstone disease. Decreased gallbladder smooth muscle contractility is a hallmark of this disease, along with alterations in bile composition and inflammation of the gallbladder wall.
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It stores and concentrates bile
The gallbladder is a small, hollow organ that stores and concentrates bile before it is released into the small intestine. The gallbladder is pear-shaped and is situated beneath the liver. The gallbladder has a capacity of about 50 ml (1.7 fluid ounces). The inner surface of the gallbladder wall is lined with mucous-membrane tissue similar to that of the small intestine.
Bile is a fluid that is received from the liver and is important for digestion. The absorption of water and inorganic salts from the bile by the cells of the mucous membrane causes the stored bile to be about five times, but sometimes as much as 18 times, more concentrated than when it was produced in the liver. The bile flows into the cystic duct and gallbladder, where it is stored and concentrated until it is needed for digestion. When food enters the duodenum, the common duct's sphincter opens, the gallbladder contracts, and bile enters the duodenum to aid in the digestion of fats.
The gallbladder wall is composed of several layers. The innermost surface of the gallbladder wall is lined by a single layer of columnar cells with a brush border of microvilli, very similar to intestinal absorptive cells. Underneath the epithelia is a thin layer of connective tissue, the lamina propria. The muscosa is curved and collected into tiny outpouchings called rugae. A muscular layer sits beneath the mucosa. This is formed by smooth muscle, with fibres that lie in longitudinal, oblique and transverse directions, and are not arranged in separate layers. The muscle fibres here contract to expel bile from the gallbladder.
The gallbladder is subject to many disorders, including gallstones, which are formed by material that cannot be dissolved, usually cholesterol or bilirubin. Gallstones can cause significant pain and are often treated with the removal of the gallbladder. Disruption of gallbladder smooth muscle function is an early feature in the development of cholesterol gallstone disease.
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The gallbladder has a muscular layer
The gallbladder is a small, hollow organ that is situated beneath the liver in humans. It is pear-shaped and has a capacity of about 50 ml or 50 millilitres. The gallbladder is a muscular membranous sac that stores and concentrates bile, a fluid that is received from the liver and is important in digestion. The gallbladder wall is composed of a number of layers.
The innermost surface of the gallbladder wall is lined by a single layer of columnar cells with a brush border of microvilli, very similar to intestinal absorptive cells. Underneath the epithelia is an underlying lamina propria, muscularis, perimuscular layer and serosa. The mucosa, the inner portion of the gallbladder wall, consists of a lining of a single layer of columnar cells, with cells possessing small hair-like attachments called microvilli. This sits on a thin layer of connective tissue, the lamina propria.
Gallbladder neurons receive two types of synaptic inputs, both of which are excitatory. The principal driving force for generating neuronal output from gallbladder ganglia to the smooth muscle is the vagal preganglionic axons. The release of acetylcholine is the principal means of neuronally mediated contraction of gallbladder smooth muscle. Electric field stimulation of nerves in gallbladder muscle strips elicits a contraction that is significantly diminished, if not blocked, by the muscarinic receptor antagonist, atropine.
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It sits beneath the liver
The gallbladder is located in the abdomen, beneath the liver. It is a small, hollow organ, shaped like a pear, and is responsible for storing bile produced by the liver. This bile is then released into the small intestine, specifically the duodenum, where it assists in the digestion of fats and certain vitamins. The gallbladder is divided into three sections: the fundus, which is the rounded base angled towards the abdominal wall; the body, which sits in a depression in the lower liver; and the neck, which tapers and connects to the cystic duct. The fundus and body lie in the gallbladder fossa, found beneath the junction of hepatic segments IVB and V.
The position of the gallbladder in relation to the liver can vary, with rare cases of variants such as within, above, on the left side of, behind, or detached/suspended from the liver being documented. The human gallbladder is typically grey-blue in colour and measures approximately 7 to 10 centimetres in length and 4 centimetres in diameter when fully distended. It has a capacity of about 50 millilitres.
The gallbladder wall is composed of several layers, including a muscular layer formed by smooth muscle. This muscular layer surrounds the mucosa, the inner portion of the gallbladder wall, which consists of a single layer of columnar cells with hair-like attachments called microvilli. The muscle fibres in the gallbladder contract to expel bile from the organ. The gallbladder receives signals to release bile when an individual eats, and this bile flows through ducts into the small intestine.
The gallbladder is susceptible to various issues, one of the most common being gallstones. These are formed when bile clumps together and solidifies, and they can cause significant pain, especially in the upper-right corner of the abdomen. Gallstones can vary in size, ranging from small to as large as a golf ball, and an individual may have just one or several. They are predominantly composed of hardened cholesterol, although they can also be formed from bilirubin, a byproduct of hemoglobin breakdown. Certain factors, such as being overweight, rapid weight loss, and a diet high in cholesterol and fat, can increase the likelihood of gallstone formation.
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Gallbladder smooth muscle function and dysfunction
The gallbladder is a small, hollow organ that sits beneath the liver in humans. Its function is to store and concentrate bile, which is produced by the liver, before releasing it into the small intestine. The gallbladder has a muscular layer formed by smooth muscle, which contracts to expel bile from the organ.
Gallbladder tone is regulated by spontaneous muscle activity, hormones, and neurotransmitters released by intrinsic neurons and extrinsic sympathetic nerves. The most direct means of gallbladder contraction is for the hormone cholecystokinin (CCK) to act on receptors located on the gallbladder's smooth muscle. CCK acts at several sites to promote functional gallbladder motility. However, it is unclear whether CCK receptors on gallbladder smooth muscle are a normal physiologic site of action for CCK. In vitro studies have shown abnormalities in the binding of CCK to plasma membrane CCK-1 receptors, alterations in the contraction of isolated smooth muscle cells, and decreased contractility of isolated smooth muscle strips and whole gallbladder preparations.
Gallbladder smooth muscle dysfunction is an early feature in the development of cholesterol gallstone disease. Gallstones are formed by material that cannot be dissolved, usually cholesterol or bilirubin. In patients with cholesterol gallstones, ex vivo analysis of gallbladders revealed smooth muscle cells that contained excess cholesterol in their plasma membranes. This excess cholesterol results in less contractility and decreased levels of scavengers of reactive oxygen species. Defects in contractility associated with cholesterol gallstones are reversible at an early stage.
Gallbladder smooth muscle dysfunction is also associated with chronic acalculous disease. In patients with this disease, in vitro studies have shown impaired gallbladder motility and increased stasis.
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Frequently asked questions
The gallbladder is a small, hollow organ that stores and concentrates bile, a fluid that is received from the liver and is important in digestion.
The gallbladder is a muscular membranous sac. It has a muscular layer formed by smooth muscle, with fibres that lie in longitudinal, oblique and transverse directions.
The gallbladder muscle contracts to expel bile from the gallbladder into the bile duct and then into the duodenum of the small intestine.
