In this article we will discuss about the functions and factors controlling movement of gall bladder.
Functions of Gall-Bladder:
Functions of gall-bladder can be summarised as follows:
i. It is an efficient storehouse of bile.
ii. It absorbs water and concentrates bile about 10 times.
iii. It absorbs inorganic salts from bile to some extent and reduces the alkalinity of liver bile.
iv. It excretes cholesterol to some degree.
v. It secretes mucus, which is the main source of mucin in bile.
vi. It helps in equalisation of pressure within the biliary duct system.
Factors Controlling Movements of Gall-Bladder:
Control of gall-bladder seems to be due to two factors:
(1) Reflex, and
(2) Chemical.
1. Reflex Control of Gall-Bladder:
Gall-bladder is richly supplied with the vagus and the sympathetic. Stimulation of the vagus causes contraction of gall-bladder and relaxation of the sphincter of Oddi. It is seen from the experiments of Johnson and Boyden that the right vagus carries motor fibres to the gall-bladder and inhibitory fibres to the sphincter of Oddi.
Stimulation of the sympathetic exerts opposite effects. (Conflicting results have been found by different observers). It is believed that during digestion reflex stimulation of gall-bladder occurs. The stimulus for the reflex may arise in the mouth during eating or due to the presence of food in the duodenum and probably also in the stomach.
It has been shown that entry of acid into the duodenum reflexly stimulates contraction of gall-bladder and relaxation of the sphincter of Oddi. It is possible that magnesium sulphate solution also acts by mobilising this reflex. When introduced into duodenum it causes tonic contraction of gall-bladder and relaxation of the sphincter. Taste or smell of food due to psychic influences causes contraction of gall-bladder.
2. Chemical Control of Gall-Bladder:
i. Effect of Food Stuffs:
Fatty foods, particularly cream, egg-yolk, etc., are the most effective stimuli. Proteins also stimulate but to a less extent. Carbohydrates have no such effect. Acids are also strong stimulants. These factors cause contraction even when the gall-bladder is completely denervated. This shows that they act through some chemical stimulus. Boyden believes that some products of protein and fat digestion are absorbed into the blood stream and stimulate contraction of gall-bladder.
ii. Cholecystokinin:
Ivy and Oldbergh have shown that acid extracts of duodenal mucosa (as well as from the upper part of the small intestine) can stimulate strong contraction of gall-bladder. The active substance is called cholecystokinin. They believe that the active contraction of gall-bladder during digestion is due to the absorption of cholecystokinin.
iii. Action of Drugs:
Adrenaline, histamine pitressin, etc., stimulates the smooth muscle of the gall-bladder, whereas morphine, ergotamine, atropine, etc., are inhibitory.