Option D2

Essential idea: Digestion is controlled by nervous and hormonal mechanisms.


D.2.U1 Nervous and hormonal mechanisms control the secretion of digestive juices

Nervous and hormonal mechanism

D.2.U2 Exocrine glands secrete to the surface of the body or lumen of the gut

Exocrine glands and digestive juices

D.2.U3 The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms

Place your mouse pionter on the diagran to view the suppression of gastric secretions.

Gastric secretion in the stomach
Mechanisms of gastric secretion explained

D.2.U4 Acid conditions in the stomach favour some hydrolysis reactions and help to control pathogens in ingested food

Effects of acid conditions of the stomach

D.2.U5 The structure of cells of the epithelium of the villi is adapted to the absorption of food

Structure of an epithelial cell

D.2.U6 The rate of transit of materials through the large intestine is positively correlated with the fibre content

Table from study on fibre and transit time
Table from study on fibre and transit time explained

D.2.U7 Materials not absorbed are egested

Material egested


D.2.A1 The reduction of stomach acid secretion by proton pump inhibitor drugs

Proton Pump Inhibitor
Proton Pump Inhibitor explained

D.2.A2 Dehydration due to cholera toxin

Effects of cholera toxin
Effects of cholera explained

D.2.A3 Helicobacter pylori infection as a cause of stomach ulcers

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


D.2.S1 Identification of exocrine gland cells that secrete digestive juices and villus epithelium cells that absorb digested foods from electron micrographs

Place your mouse pointer over the micrograph for identification.

Structure of epithelial cells
 Glycerol structure
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