Digestion

Option H2

H.2.1 & H.2.3: Digestive juices: location and composition

Digestive juices are secreted into the alimentary canal by glands, including salivary glands, gastric glands in the stomach wall, the pancreas and the wall of the small intestine.

Digestive juices

H.2.2: What are the structural features of exocrine glands?

Place your mouse on the figure to see the features of an exocrine gland.

Structure of the heart

Use the diagram to explain the structural features of an exocrine gland.

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Exocrine glandss explained

H.2.4: Control of digestive juice secretion by nerves and hormones

Control of digestive juice secretion

H.2.5: The role of membranebound enzymes

Role of membrane-bound enzymes

H.2.6: Why cellulose is not digested in the alimentary canal?

Why cellulose is not digested

H.2.7: Why pepsin and trypsin are initially synthesized as inactive precursors?

Pepsin and trypsin are initially synthesized as inactive precursors known as zymogens. Thay are activated once secreted into the alimentary canal. Pepsin and trypsin are activated under different conditions in different parts of the alimentary canal as is explained below.

Pepsin and Trypsin

H.2.8: The development of stomach ulcers and stomach cancer

This is an example of a paradigm shift, where existing ideas of scientists and doctors about the tolerance of bacteria to stomach acid were incorrect inspite of the evidence. Australians Robin Warren and Barry Marshall made the discovery of the role of Helicobacter pylori and stomach acid in the formation of ulcers but struggled to convince the scientific and medical community. The roles of Helicobacter pylori and gastric acid in the development of stomach ulcers and stomach cancers are discussed below.

Place your mouse on the figure to see how ulcers are formed.

Structure of the heart

H.2.9: The problem with lipid digestion?

Lipid molecules tend to coalesce and are only accessible to lipase at the lipid-water interface. Bile molecules have a hydrophilic end and a hydrophobic end, and thus prevent lipid droplets coalescing. Thus the maximum surface is exposed to lipases.

Lipid digestion

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