Question

• Identify the locations and primary secretions involved in the chemical digestion of carbohydrates, proteins, lipids, and nucleic acids

• Compare and contrast absorption of the hydrophilic and hydrophobic nutrients

Answer 1

Carbohydrates

Mouth: Secretion of salivary amylase to start digestion of polysaccharides (starch) into smaller polysaccharides, maltose.

Lumen of Samall Intestine: Secretion of Pancreatic amylase from Pancreas digests polysaccharides into disacchrides and maltose.

Brush border of small intestine: Secretion of disacchridases which digests disacchrides into monosaccharides.

Proteins:

Stomach: Secretion of HCl, Pepsinogen. Pepsin digests proteins into small polypeptides.

Lumen of small intestine: Secretion of Trypsin and Chymotrypsin from pancreas which converts polypeptides into smaller polypeptides. Further aminopeptidase and carboxypeptidase digests small polypetides into amino acids.

Brush border of small intestine: Secretion of aminopeptidase and dipeptidase which digest small peptides into amino acids.

Lipids:

Mouth: Secretion of lingual lipase which digests triglycerides into partial glycerides and free fatty acids.

Stomach: Secretion of gastric lipase which initiates digestion of fats in stomach.

Lumen of small intestine: Secretion of bile from gall bladder into duodenum and Secretion of pancreatic lipase from pancreas into duodenum. Bile emulsifies the fat into smaller droplets and then pancreatic lipase acts on these droplets and digests them into glycerol and free fatty acids.

Nucleic acids:

Lumen of small intestine: Secretion of nucleases which digests DNA, RNA into nucleotides.

Brush border of small intestine: Secretion of nucleotidases which digests nucleotides into nucleosides then into nitrogenous base, sugars and phosphates.