ABSTRACT
The Gastro intestinal system is vital for overall secretions,
digestion, absorption, and movement within the tracts. Secretions involve
release of fluids, chemicals and catalytic substances that facilitates
digestion and related gastrointestinal tract (GIT) activities. Digestion
involves hydrolysis of condensed products of carbohydrates, proteins and fats.
Absorption involves movement of molecules across the GIT into the circulatory
system. Carbohydrates are hydrolysed to monosaccharides; Proteins to amino
acids; and Fats to fatty acids and glycerols (Guyton and Hall, 2006; Seeley,
Stephens & Tate, 2008). Not all molecules are however are broken down
before being absorbed (e.g. vitamins, minerals and water); absorption of
certain molecules can occur along the digestive tract but most absorption
occurs in the duodenum and jejunum, though some absorption occurs in the ileum.
The
surface of the duodenum is modified in several ways that increase its surface
area about 600-1000fold to allow for more efficient digestion and absorption of
food. These various modifications greatly increase the surface area of the
small intestine and thus greatly enhance absorption. Most end-products of digestion as well as vitamins, minerals
and water are absorbed in the small intestinal lumen by four mechanisms for
absorption: (1) active transport, (2) passive diffusion, (3) endocytosis, and
(4) facilitative diffusion (Inse et al., 2004). Absorption of amino acids occurs
rapidly in the duodenum and jejunum but slow in the ileum. Absorption of long-chain fatty acids is
greatest in the duodenum and jejunum, but appreciable amounts are also absorbed
in the ileum. (Ganong, 2006) The vast bulk of mineral absorption occurs in the
small intestine. Some drugs can rapidly dissolve or disintegrate in the oral cavity
(Orodispersible tablets), others are absorbed from the pharynx and ooesophagus
as the saliva passes down into the stomach.
Table Of Contents
- Introduction
- Motility In The Mouth
- Pharyngeal And Oesophageal
Motility - Motility In The Stomach
- Motility In The Small Intestine
- Motility In The Large Intestine
- Regulation Of Gastrointestinal
Motility - Intestinal Motility Disorders
- Conclusion
References