Gallbladder
Encyclopedia
In vertebrates the gallbladder (cholecyst, gall bladder, Biliary Vesicle) is a small organ
that aids mainly in fat digestion
and concentrates bile
produced by the liver
. In humans the loss of the gallbladder is usually easily tolerated.
via the cystic duct
, which then joins the common hepatic duct
to become the common bile duct
. At the neck of the gall bladder is a mucosal fold called Hartmann's pouch, where gallstone
s commonly get stuck. The angle of the gallbladder is located between the costal margin
and the lateral margin of the rectus abdominis muscle
.
Unlike elsewhere in the intestinal tract, the gallbladder does not have a muscularis mucosae
.
containing fat enters the digestive tract
, it stimulates the secretion
of cholecystokinin
(CCK). In response to CCK, the adult human gallbladder, which stores about 50 mL of bile
, releases its contents into the duodenum
. The bile
, originally produced in the liver
, emulsifies
fats in partly digested food.
During storage in the gallbladder, bile becomes more concentrated which increases its potency and intensifies its effect on fats.
In 2009, it was demonstrated that the gallbladder removed from a patient expressed several pancreatic hormones including insulin. This was surprising because until then, it was thought that insulin was only produced in pancreatic β-cells. This study provides evidence that β-like cells do occur outside the human pancreas. The authors suggest that since the gallbladder and pancreas are adjacent to each other during embryonic development, there exists tremendous potential in derivation of endocrine pancreatic progenitor cells from human gallbladders that are available after cholecystectomy
.
s have gallbladders, whereas invertebrate
s do not. However, its precise form and the arrangement of the bile ducts may vary considerably. In many species, for example, there are several separate ducts running to the intestine, rather than a single common bile duct, as in humans. Several species of mammal
s (including horse
s, deer
, rats
, and various lamoid
s) and several species of bird
s lack a gallbladder altogether, as do lamprey
s.
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
that aids mainly in fat digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
and concentrates bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
produced by the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
. In humans the loss of the gallbladder is usually easily tolerated.
Human anatomy
The gallbladder is a hollow system that sits just beneath the liver. In adults, the gallbladder measures approximately 8 centimetres (3.1 in) in length and 4 centimetres (1.6 in) in diameter when fully distended. It is divided into three sections: fundus, body and neck. The neck tapers and connects to the biliary treeBiliary tree
The biliary tract is the common anatomical term for the path by which bile is secreted by the liver then transported to the first part of the small intestine, also known as the duodenum...
via the cystic duct
Cystic duct
The cystic duct is the short duct that joins the gall bladder to the common bile duct. It usually lies next to the cystic artery. It is of variable length...
, which then joins the common hepatic duct
Common hepatic duct
The common hepatic duct is the duct formed by the convergence of the right hepatic duct and the left hepatic duct . The common hepatic duct then joins the cystic duct coming from the gallbladder to form the common bile duct...
to become the common bile duct
Common bile duct
The common bile duct is a tube-like anatomic structure in the human gastrointestinal tract. It is formed by the union of the common hepatic duct and the cystic duct . It is later joined by the pancreatic duct to form the ampulla of Vater...
. At the neck of the gall bladder is a mucosal fold called Hartmann's pouch, where gallstone
Gallstone
A gallstone is a crystalline concretion formed within the gallbladder by accretion of bile components. These calculi are formed in the gallbladder, but may pass distally into other parts of the biliary tract such as the cystic duct, common bile duct, pancreatic duct, or the ampulla of...
s commonly get stuck. The angle of the gallbladder is located between the costal margin
Costal margin
The costal margin, sometimes referred to as the costal arch, is the medial margin formed by the false ribs and one true rib -- specifically, from the seventh rib to the tenth rib....
and the lateral margin of the rectus abdominis muscle
Rectus abdominis muscle
The rectus abdominis muscle, also known as the "six pack", is a paired muscle running vertically on each side of the anterior wall of the human abdomen . There are two parallel muscles, separated by a midline band of connective tissue called the linea alba...
.
Microscopic anatomy
The different layers of the gallbladder are as follows:- The epithelium, a thin sheet of cells closest to the inside of the gallbladder
- The lamina propria, a thin layer of loose connective tissue (the epithelium plus the lamina propria form the mucosa)
- The muscularis, a layer of smooth muscular tissue that helps the gallbladder contract, squirting its bile into the bile duct
- The perimuscular ("around the muscle") fibrous tissue, another layer of connective tissue
- The serosa, the outer covering of the gallbladder that comes from the peritoneum, which is the lining of the abdominal cavity
Unlike elsewhere in the intestinal tract, the gallbladder does not have a muscularis mucosae
Muscularis mucosae
The lamina muscularis mucosae is the thin layer of smooth muscle found in most parts of the gastrointestinal tract, located outside the lamina propria mucosae and separating it from the submucosa....
.
Function
When foodFood
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
containing fat enters the digestive tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
, it stimulates the secretion
Secretion
Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
of cholecystokinin
Cholecystokinin
Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein...
(CCK). In response to CCK, the adult human gallbladder, which stores about 50 mL of bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
, releases its contents into the duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
. The bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
, originally produced in the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, emulsifies
Emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
fats in partly digested food.
During storage in the gallbladder, bile becomes more concentrated which increases its potency and intensifies its effect on fats.
In 2009, it was demonstrated that the gallbladder removed from a patient expressed several pancreatic hormones including insulin. This was surprising because until then, it was thought that insulin was only produced in pancreatic β-cells. This study provides evidence that β-like cells do occur outside the human pancreas. The authors suggest that since the gallbladder and pancreas are adjacent to each other during embryonic development, there exists tremendous potential in derivation of endocrine pancreatic progenitor cells from human gallbladders that are available after cholecystectomy
Cholecystectomy
Cholecystectomy is the surgical removal of the gallbladder. It is the most common method for treating symptomatic gallstones. Surgical options include the standard procedure, called laparoscopic cholecystectomy, and an older more invasive procedure, called open cholecystectomy.-Open surgery:A...
.
In animals
Most vertebrateVertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s have gallbladders, whereas invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s do not. However, its precise form and the arrangement of the bile ducts may vary considerably. In many species, for example, there are several separate ducts running to the intestine, rather than a single common bile duct, as in humans. Several species of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s (including horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s, deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
, rats
RATS
RATS may refer to:* RATS , Regression Analysis of Time Series, a statistical package* Rough Auditing Tool for Security, a computer program...
, and various lamoid
Lamoid
Lamoid is a group of South American camelids, which includes the guanaco, vicuna, alpaca and llama. The digestive system of lamoids is distinctive, with a noteworthy capability for digesting certain toxins. Furthermore, the gallbladder structure is absent in lamoids.-References:* Murray E. Fowler....
s) and several species of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s lack a gallbladder altogether, as do lamprey
Lamprey
Lampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...
s.
External links
- Diagram of Human Stomach and Gallbladder – Human Anatomy Online, MyHealthScore.com.
- www.newchronicles.webs.com/f/gastrointestinalphysiology – Gastrointestinal Physiology Review.