Changes

==Introduction==

==Introduction==

The small intestine extends from the pylorus of the [[Forestomach - Anatomy & Physiology|stomach]] to the [[Caecum - Anatomy & Physiology|caecum]]. The small intestine recieves chyme from the [[Forestomach - Anatomy & Physiology|stomach]].  It is the main site of chemical degradation and absorption of chyme. Fats are exclusively broken down in this part of the alimentary tract. Carbohydrates and proteins that are not degraded in the small intestine are available for microbial fermentation in the [[Large Intestine - Anatomy & Physiology|large intestine]]. The small intestine produces enzymes for digestion of protein, carbohydrate and fat and absorbs the products of their digestion. Enzymes are produced by glands in the intestinal wall and the [[Pancreas - Anatomy & Physiology|pancreas]]. The [[Gall Bladder - Anatomy & Physiology|gall bladder]] produces bile which emulsifies fats for digestion. Absorption is facilitated by ridges in the small intestine and by the presence of villi and microvilli.

The small intestine extends from the pylorus of the [[Monogastric Stomach - Anatomy & Physiology|stomach]] to the [[Caecum - Anatomy & Physiology|caecum]]. The small intestine recieves chyme from the [[Monogastric Stomach - Anatomy & Physiology|stomach]].  It is the main site of chemical degradation and absorption of chyme. Fats are exclusively broken down in this part of the alimentary tract. Carbohydrates and proteins that are not degraded in the small intestine are available for microbial fermentation in the [[Large Intestine - Anatomy & Physiology|large intestine]]. The small intestine produces enzymes for digestion of protein, carbohydrate and fat and absorbs the products of their digestion. Enzymes are produced by glands in the intestinal wall and the [[Pancreas - Anatomy & Physiology|pancreas]]. The [[Gall Bladder - Anatomy & Physiology|gall bladder]] produces bile which emulsifies fats for digestion. Absorption is facilitated by ridges in the small intestine and by the presence of villi and microvilli.

The small intestine consists of three parts. Each part differs in anatomy, but all have the same basic structure and function:

The small intestine consists of three parts. Each part differs in anatomy, but all have the same basic structure and function:

**''Glycogen'' is synthesised in the [[Liver - Anatomy & Physiology|liver]] and [[Muscles - Anatomy & Physiology|muscle]] and is similar to amylopectin as it has both α1-4 glycosidic links and α1-6 glycosidic links. However it is more highly branched with shorter branches (branches every 12-18 glucose residues).

**''Glycogen'' is synthesised in the [[Liver - Anatomy & Physiology|liver]] and [[Muscles - Anatomy & Physiology|muscle]] and is similar to amylopectin as it has both α1-4 glycosidic links and α1-6 glycosidic links. However it is more highly branched with shorter branches (branches every 12-18 glucose residues).

*The '''first stage''' of carbohydrate digestion begins with α-amylase, which is an endoglycosidase. ''(This means it breaks bonds in the middle of the polymer to produce di-, tri- and oligo-saccharides).''

*The '''first stage''' of carbohydrate digestion begins with α-amylase, which is an endoglycosidase. ''(This means it breaks bonds in the middle of the polymer to produce di-, tri- and oligo-saccharides).''

*α-Amylase is present in [[Salivary Glands - Anatomy & Physiology|saliva]]. Salivary α-amylase is inactivated when it enters the [[Forestomach - Anatomy & Physiology|stomach]] due to it's acidic pH.

*α-Amylase is present in [[Salivary Glands - Anatomy & Physiology|saliva]]. Salivary α-amylase is inactivated when it enters the [[Monogastric Stomach - Anatomy & Physiology|stomach]] due to it's acidic pH.

*Carbohydrate digestion continues in the lumen of the [[Small Intestine - Anatomy & Physiology|small intestine]] as pancreatic α-amylase enters the [[Duodenum - Anatomy & Physiology|duodenum]] in the pancreatic duct. This is the site of the majority of carbohydrate digestion.

*Carbohydrate digestion continues in the lumen of the [[Small Intestine - Anatomy & Physiology|small intestine]] as pancreatic α-amylase enters the [[Duodenum - Anatomy & Physiology|duodenum]] in the pancreatic duct. This is the site of the majority of carbohydrate digestion.

*The '''second stage''' is the digestion of di-, tri-, and oligo-saccharides to monosaccharides.

*The '''second stage''' is the digestion of di-, tri-, and oligo-saccharides to monosaccharides.

====Protein Digestion and Absorption====

====Protein Digestion and Absorption====

*Protein digestion begins in the [[Forestomach - Anatomy & Physiology|stomach]] where pepsin is secreted as a zymogen, pepsinogen. Pepsin is an endopeptidase and produces smaller polypeptides.

*Protein digestion begins in the [[Monogastric Stomach - Anatomy & Physiology|stomach]] where pepsin is secreted as a zymogen, pepsinogen. Pepsin is an endopeptidase and produces smaller polypeptides.

**Pepsin prefers to break peptide bonds of larger polypeptides, where there is a large hydrophobic amino acid on the N-terminal side.

**Pepsin prefers to break peptide bonds of larger polypeptides, where there is a large hydrophobic amino acid on the N-terminal side.

*Protein digestion continues in the small intestine.

*Protein digestion continues in the small intestine.

**Paracrine hormones

**Paracrine hormones

**Neural transmitters

**Neural transmitters

*Unlike the [[Forestomach - Anatomy & Physiology|stomach]], control is mainly local, with superimposed co-ordination through the extrinsic ANS.

*Unlike the [[Monogastric Stomach - Anatomy & Physiology|stomach]], control is mainly local, with superimposed co-ordination through the extrinsic ANS.

*All signals affect the small intestine via sensory neurones.

*All signals affect the small intestine via sensory neurones.

**Neurones interact with two plexuses in the intestinal wall.

**Neurones interact with two plexuses in the intestinal wall.