This section is written in a specific format to conform to the principles outlined for each of the organs.
The gallbladder is a pear shaped structure whose major function is to store and concentrate bile produced by the liver, and to deliver the bile to the duodenum when activated to do so by cholecystokinin (CCK). CCK is a hormone produced by the duodenum in response to the presence of fat and protein. CCK causes the gallbladder to contract, and relaxes the sphincter of Oddi, which lies at the distal end of the common bile duct at its junction with the duodenum.
Just as the bladder is a storage space for urine, the gallbladder is a receptacle and storage space for bile. The liver is the factory that produces the bile, and the gallbladder is the storage facility for that factory. Its capabilities are limited to receiving and concentrating bile, and with muscular contraction it expels the bile in response to neurohormonal stimulation.
Unlike the urinary bladder whose absence would obviously inconvenience the human being significantly, the gallbladder is not missed when it is removed. While agenesis of the gallbladder is rare in humans, agenesis is normal in the pigeon, rat, and horse. When it is congenitally absent though, it is the associated conditions such as biliary atresia, rectovaginal fistula, imperforate anus, and absence of bony structures that have greater clinical relevance.
As Biological Unit
The gallbladder is a hollow organ with a muscular wall that consists of mucosa, muscularis and serosa (or adventitia).
Links and Connections
The gallbladder is connected to liver at the gallbladder fossa which not only allows anchorage and support, but also acts as the hilum of the gallbladder by enabling blood vessels, lymphatics, nerves, and ducts to connect directly to the liver. The systemic arterial connection usually originates from the right hepatic artery via the cystic artery, the systemic venous connections are via the cystic veins into the portal system, systemic lymphatics via hepatic nodal system, and nervous connections via sympathetic (celiac axis) and parasympathetic (vagus) systems. Hormonal connections include interaction with vasoactive intestinal polypeptide, (VIP) and CCK.
Units to Unity
The gallbladder is part of the hepatobiliary biliary system, which in turn is part of the gastrointestinal system. It is not a vital organ, and people can survive without it as evidenced by the inumerable number of people who have had their gallbladders removed, and who live quite comfortably without it.
Dependence and Independence
The gallbladder cannot function alone and requires the liver to produce the bile that it stores, and the centrally based innervations and signaling of the neurohormonal axis to instruct it when to empty and when to fill.
Time Growth and Aging
The gallbladder arises from the primitive endoderm at the junction of foregut with the midgut from tissue called the septum transversum. The septum transversum differentiates and eventually gives rise to the gallbladder, biliary tree, and the liver. The gallbladder ages well, though gallstones are relatively common in Western civilization, and overall bile flow decreases with age. The aging and sluggish biliary system is one of the proposed mechanisms in the pathogenesis of gallstone production.
The gallbladder lies within the peritoneal cavity of the abdomen in close association with the liver. It lies in a plane that divides the liver into right and left lobes.
The forces that govern gallbladder function are mostly mechanical in origin. The gallbladder fills passively by ongoing production of bile. Since the sphinter of Oddi is usually closed between meals, bile flow is forced into the gallbladder through the diminutive cystic duct since this offers the path of least resistance.
When fat or protein enters the duodenum, the CCK that is released, causes the gallbladder to contract and the sphincter of Oddi to relax, so that bile will now flow along a new path of least resistance which is via the common bile duct into the duodenum.
The interactions of the gallbladder with the rest of the body are fairly simple. The gallbladder acts as an intermediary between the liver and bile duct system on the upstream side, with the duodenum on the downstream side. The complex synthesis by the liver of bile salts from cholesterol is in contrast to fairly simple appearing interactions of the gallbladder. Passive filling during non stimulated phase, storage, absorbtion of water and concentration of bile, followed by active transient contraction as a response to a fatty meal is in essence the function and interaction of the gallbladder with the body.
States of Being – Health and Disease
By virtue of its relatively simple function, diseases related to the gallbladder are of a fairly simple nature. Gallstone disease is the most common malady of the gallbladder and is usually an asymptomatic entity. When small stones obstruct the cystic duct, acute cholecystitis results which causes extreme right upper quadrant pain. Sometimes the stone may spontaneously disempact and fall back into the gallbladder, or pass through to the duodenum. If it remains impacted, obstruction of the gallbladder ensues and cholecystitis results.
Sometimes it may disimpact from the cystic duct, but may cause obstruction of the common bile duct.