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Gastrointestinal Tract

Maintaining a healthy gastrointestinal (GI) tract is vital for it to perform its function of digestion. Another important function of the GI tract is protection of the body from illness and infection. Impairment of the GI barrier or disruption of the commensal bacteria increases the risk of gut-related disorders or infections but also extra-intestinal infections, as well as immune-mediated and metabolic disorders.

Did you know...

The gut is the largest immune organ of the body; over half of all immunologically active cells in the body are located in the intestines.

Components of the gastrointestinal tract

MOUTH - seeing and smelling food starts the digestive process by increasing the flow of saliva in the mouth. Biting and chewing breaks up the food, mixing it with saliva containing amylase, which hydrolyses starch to dextrins and maltose.

OESOPHAGUS - this muscular tube generates peristaltic waves to drive the bolus of food down to the stomach in about six seconds.

STOMACH – liquids are held here for a few minutes, but food can be held for up to several hours. The gastric acid is not only a protection against pathogens but also helps to hydrolyse proteins to large peptides.

SMALL INTESTINE - about six metres long and comprising the duodenum, jejunum and ileum. Here the major food groups; protein, fat and carbohydrate are broken down into amino acids, fatty acids and sugars.  It can take between 2-4 hours for a meal to be processed in the small intestine 

• DUODENUM: receives pancreatic secretions and bile, and produces an alkaline mucus for protection, lubrication and chyme neutralisation.

• JEJUNUM: absorbs nutrients from chyme, and moves the remaining contents through into the ileum for further absorption. 

• ILEUM: most of the soluble products of digestion are absorbed. The vast surface area of this part of the gut helps ensure nutrients are absorbed quickly and thoroughly.

LARGE INTESTINE - the vast majority of the intestinal microbiota resides here; these bacteria ferment undigested fibre and starch. Some vitamins (B and K2) are synthesised by these colonic bacteria. Water is removed and reabsorbed in the colon. Faeces are stored in the rectum before expulsion.

PANCREAS - secretes an alkaline pancreatic juice, which neutralises acid from the stomach and contains enzymes that break down protein, fat and carbohydrates. The hormones insulin and glucagon are also produced here.

LIVER - the chemical factory and warehouse of the body, receiving blood from the gut, filtering it, removing toxins, metabolising drugs, storing nutrients such as vitamin A and B12 and synthesising proteins for various purposes including blood clotting. It also synthesises bile.

GALL BLADDER - stores and concentrates bile, and delivers it to the small intestine when necessary.  Bile emulsifies fat and aids pancreatic lipase to digest it.

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