Digestion

Glossary

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The alimentary canal is the tube running from the mouth to the anus
The middle of the alimentary canal is a lumen, which is technically still outside the body
Ingestion
Digestion is the breakdown of polymers into monomers small enough to enter cells
Primates chew their food and mammalian stomach churns it increasing the surface area (MECHANICAL)
Large surface area allows better access for enzymes which catalyse the hydrolysis of polymers into their monomer subunits (CHEMICAL)
Absorption is the movement of small molecules (water, inorganic ions, vitamins) + products of digestion from the lumen into cells in the wall of the canal, then into the bloodstream.
Food which cannot be digested or absorbed. It passes through the canal and leaves from the anus as faeces by egestion.

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1.Endopeptidases - break down bonds between amino acids in the interior of the molecule which produces smaller polypeptides e.g. pepsin and trypsin

2.Exopeptidases - break down smaller polypeptides. These break off the end of amino acids. There are two types:

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Absorption occurs accross epithelial cells by facilitated diffusion and active transport, relying largely on Na+ cotransport.

Describe how the small intestine is adapted for the absorption of soluble food.

Large surface area provided by villi/microvilli
folds increase surface area
Long; increasing time for absorption
Thin epithelium gives a short diffusion pathway
Capillary network absorbs amino acids/sugars; into blood
Lacteal for absorption of digested fats
Abundant mitochondria in epithelial cells supply energy for active transport
Epithelial cells have carrier proteins for facilitated diffusion/active transport.

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