Question

Construct a visual aid that integrates the concepts covered in our discussions on Nutrient Assimilation in animals (digestion and absorption of all three macromolecules) Summaries should include at a minimum (but are not limited to these concepts and ideas):

o the three major food macromolecules; make sure you include their monomer and polymer structures.

o How each are enzymatically digested (including the enzymes involved and where the enzymes are active or activated)

o How digested monomers and compounds are absorbed (make sure to specifically describe the transport processes)

o The alimentary structures and/or locations where these processes occur

Answer 1

The three major food macromolecules are carbohydrates (sugar), proteins and fats.

Monomer units:

sugar = glucose (mainly)

Proteins = Amino acids

Fats = Fatty acids and glycerol

Digestion of carbohydrates:

Carbohydate digestion starts in mouth (buccal cavity). Salivary amylase present in saliva break down starch into maltose and alpha dextrin. Teeth and tongue help to masticate and mix up food. Further it is digested by pancreatic juice released in duodenum, pancreatic juice having amylase enzyme breaks starch into disaccarides. Amyase woks in akaline medium provided by bile in duodenum. Disaccarides are further broken down into into monosaccarides by intestinal juice.

Digestion of proteins:

Protein digestion starts in stomach where HCl activates pepsinogen into pepsin. Pepsin breaks down proteins into peptones and proteoses. Rennin helps in digestion of milk protein casein. These substances enter small intestine. In duodenum, pancreatic juice released having trypsinogen. Trypsinogen is activated by enterokinase enzyme, released from duodenal mucosa. Activated Trypsin now works on proteins, peptones and proteoses to convert them into dipeptides. The enzyme dipeptidases in succus entericus act on dipeptides to form amino acids, end product of protein digestion.

Digestion of fats:

Fat digestion starts in duodenum part of small intestine. Pancreatic Lipase and gastric lipase works there. First Bile emulsifies fat globules on which lipase acts to form diglycerides and monoglycerides. Lipase is activated by alkaline medium provided by bile. Further digestion by succus entericus enzyme (lipase) into fatty acid and glycerol takes place in small intestine.

Absorption of digested food:

- Digested food is absorbed mainly in jejunum and ileum part of small intestine.

- Villi are small finger-like projections in the small intestine which help to absorb digested food. Each villi has microvilli to increase surface area for absorption. The villi are connected to blood vessels so the circulating blood carries nutrients away to required place.

- Fatty acids and glycerol being insoluble cannot be absorbed directly in blood.

- Fatty acids and glycerol are aborbed by the lymph vessels (lacteals) in the villi. These lymph vessels ultimately release the absorbed substances in blood stream.