The gallbladder stores and concentrates bile (10 times) until it is required in the small intestine. During the process of concentration, water and ions are absorbed through the lining of the gallbladder.
When the small intestine needs of bile, the smooth muscle wall of the gallbladder to contract and push the bile into the cystic duct, common bile duct and small intestine.
When the small intestine is empty, a valve located around the ampulla hepatopancreatic called sphincter of the hepatopancreatic bulb (sphincter of Oddi), closes and causes the bile accumulated up to the cystic duct 'to the gallbladder to be stored [29].
Bile
Liver cells secrete daily from 800 to 1000 ml of bile, liquid yellow, brown or olive green, has a pH between 7.6 and 8.6.
Bile is mainly composed of water and bile acids, bile salts, cholesterol, phospholipid called lecithin, bile pigments and several ions. Bile is both a product of excretion and intestinal secretion.
Bile is secreted continuously by the liver, then stored in the gallbladder which concentrated.
Upon digestion, bile is sent by the gallbladder into the duodenum through the bile duct.
Its role is to promote the absorption of fat by bile salts it contains. It still consists of water, mucin, minerals, pigments from the dégradation de l’hémoglobine et du cholestérol.
Les sels biliaires
Les sels biliaires, qui sont des sels de sodium et de potassium des acides biliaires (principalement l’acide cholique et l’acide chénodésoxycholique), jouent un rôle dans l’émulsification, la dégradation de volumineux globules de graisses en une suspension de fines gouttelettes graisseuses et dans l’absorption des graisses Après leur digestion.
Les fines gouttelettes de graisse présentent une très grande surface pour l’action de la lipase pancréatique nécessaire à une digestion rapide des graisses. Le cholestérol est rendu soluble dans la bile par les sels biliaires et la lécithine.
Le principal pigment biliaire est la bilirubine. Lorsque les globules rouges se dégradent, le fer, la globine et la bilirubine (dérivée de l’hème) sont libérés. Le fer et la globine sont recyclés, mais une partie de la bilirubine est excrétée dans les canaux biliaires. La bilirubine est ensuite dégradée dans les intestins. L’un de ses produits de dégradation, l’urobilinogène, donne aux fèces leur couleur brune habituelle.
Les sels biliaires sont des molécules à structure stéroïdienne synthétisées par les hépatocytes at the expense of cholesterol under control of a single enzyme: the cholesterol - 7 - hydrolase.
normal humans, the major bile acids, cholic and chénodeoxycholique are combined with two amino acids: glycine and taurine.
as conjugates, bile salts are secreted into bile by the hepatocyte cells.
regulation of bile secretion
bile secretion is regulated by nervous and hormonal factors. Vagal stimulation of the liver may increase more than twice the normal rate of bile production. Secretin, a hormone that stimulates production of pancreatic juice rich in bicarbonate ions (HCO3-), also stimulates the secretion of bile rich in HCO3-by liver cells.
The increase in blood flow to the liver leads to a certain point,
increasing bile secretion.
increasing bile secretion.
Finally, the presence of large amounts of bile salts in the blood also increases the rate of bile production.
Cholecystokinin (CCK), a hormone that stimulates production of pancreatic juice rich in digestive enzymes, also stimulates the contraction of the gallbladder biliaire. La bile ainsi comprimée passe de la vésicule biliaire au canal cholédoque.
Par ailleurs, la cholécystokinine provoque le relâchement du sphincter de l’ampoule hépato-pancréatique de Vater, favorisant ainsi l’écoulement de la bile dans le duodénum.
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