Changes

**There are two types of starch, ''amylose'' which has α1-4 glycosidic links and, ''amylopectin'' which has α1-4 glycosidic links and α1-6 glycosidic links making it branched (branches every glucose 25 residues).

**There are two types of starch, ''amylose'' which has α1-4 glycosidic links and, ''amylopectin'' which has α1-4 glycosidic links and α1-6 glycosidic links making it branched (branches every glucose 25 residues).

**''Glycogen'' is synthesised in the liver and 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 and 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-saccarides).''

*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-saccarides).''

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

*α-Amylase is present in [[Oral Cavity - Salivary Glands - Anatomy & Physiology|saliva]]. Salivary α-amylase is inactivated when it enters the 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.

**This is done by di-, tri-, and oligo-saccharidases which have a glycocalyx to trap their substrate. They are bound to enterocytes.

**This is done by di-, tri-, and oligo-saccharidases which have a glycocalyx to trap their substrate. They are bound to enterocytes.

***The main dissacharides that are broken down:

***The main dissacharides that are broken down:

'''Triacylglycerol Digestion and Absorption'''

'''Triacylglycerol Digestion and Absorption'''

*Triacylglycerols (TAGs) are digested by lipases.

*Triacylglycerols (TAGs) are digested by lipases.

*TAG digestion begins in the [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]], where lingual lipase is secreted in the saliva. It removes a fatty acid from the 3 position on the glycerol molecule producing 1,2-diacylglycerol and a free fatty acid.

*TAG digestion begins in the [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]], where lingual lipase is secreted in the saliva. It removes a fatty acid from the 3 position on the glycerol molecule producing 1,2-diacylglycerol(1,2 DAG) and a free fatty acid.

*TAG digestion continues in the small intestine, with pancreatic lipase and bile from the liver. Bile is necessary for digestion to occur, as pancreatic lipase is water soluble and the TAG and 1,2-diacylglycerol (1,2-DAG) are lipid soluble. Bile creates an interface for the enzyme to digest the lipid molecules. Bile also emulsifies fats; it reduces the size of lipid droplets increasing the surface area available for digestion.

*TAG digestion continues in the small intestine, with pancreatic lipase and bile from the liver. Pancreatic lipase is water soluble and the TAG and 1,2-DAG are lipid soluble. Bile creates an interface for the enzyme to digest the lipid molecules. Bile also emulsifies fats; it reduces the size of lipid droplets increasing the surface area available for digestion.

*Pancreatic lipase removes any further fatty acids from the 3 position and then from the 1 position to produce 2-monoacylglycerol (2-MAG) and a fatty acid.

*Pancreatic lipase removes any further fatty acids from the 3 position and then from the 1 position to produce 2-monoacylglycerol (2-MAG) and a fatty acid.

**Pancreatic lipase is unable to remove the fatty acid from the 2 position, so an enzyme called '''isomerase''' transfers the fatty acid from the 2 postion to the 1 postion to produce 1-monoacylglycerol (1-MAG).

**Pancreatic lipase is unable to remove the fatty acid from the 2 position, so an enzyme called '''isomerase''' transfers the fatty acid from the 2 postion to the 1 postion to produce 1-monoacylglycerol (1-MAG).

'''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 [[Forestomach - Anatomy & Physiology|stomach]] where pepsin is secreted as a zymogen, pepsinogen. Pepsin is an endopeptidase and produces smaller polypeptides.

**Pepsin prefers to break the 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.

**There are three endopeptidases in the small intestine; trypsin; chymotrypsin; and elastase.

**There are three endopeptidases in the small intestine; trypsin; chymotrypsin; and elastase.

***Elastase is secreted as proelastase.

***Elastase is secreted as proelastase.

****Trypsinogen is initially activated by enterokinase (activation involves the cleavage of 6 amino acids). Trypsinogen can then activate itself, and also chymotrypsin and elastase.

****Trypsinogen is initially activated by enterokinase (activation involves the cleavage of 6 amino acids). Trypsinogen can then activate itself, and also chymotrypsin and elastase.

*The short polypeptides produced are further digested by exopeptidases which remove amino acids from the end of the polypeptide chain.

*The short polypeptides produced from their digestion are further digested by exopeptidases which remove amino acids from the end of the polypeptide chain.

**There are two types of exopeptidase in the small intestine:

**There are two types of exopeptidase in the small intestine:

***'''Carboxypeptidases''' that split amino acids off the polypeptide from the C-terminus.

***'''Carboxypeptidases''' that split amino acids off the polypeptide from the C-terminus.