Topic D.2: Digestion

Essential Idea:  Digestion is controlled by nervous and hormonal mechanisms.
At SHS, Topic D.2 is taught in the following class unit(s):

Statements & Objectives:

D.2.U1  Nervous and hormonal mechanisms control the secretion of digestive juices.
  • Describe when the secretion of digestive juices must be controlled.
  • State to mechanisms by which secretion of gastric juices is controlled.
D.2.U2  Exocrine glands secrete to the surface of the body or the lumen of the gut.
  • Define alimentary canal.
  • Contrast endocrine glands with exocrine glands.
  • Label a diagram of an exocrine gland with the following terms:  secretory cells, lumen, duct, secretory vesicles, basement membrane and acinus.
  • Discuss the relationship between the structures of an exocrine gland cell and the function of the cell.
  • State the name and location of three exocrine glands associated with the alimentary canal.
  • State the composition of saliva, gastric juice and pancreatic juice.
D.2.U3  The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms.
  • Using a flow chart or concept map, diagram the interactions between nervous and hormonal mechanisms that regulated the secretion of gastric juices
D.2.U4  Acid conditions in the stomach favour some hydrolysis reactions and help to control pathogens in ingested food.
  • Outline three roles of acid in the stomach.
D.2.U5  The structure of cells of the epithelium of the villi is adapted to the absorption of food.
  • Outline the role of the following structures of villi epithelial cells:  tight junctions, microvilli, mitochondria, pinocytic vesicles, proteins imbedded on the apical surface and proteins imbedded on the basal surface.
D.2.U6  The rate of transit of materials through the large intestine is positively correlated with their fibre content.
  • List benefits of fibre in a healthy diet.
  • State the relationship between food fibre contents and rate of transit through the large intestine.
D.2.U7  Materials not absorbed are egested.
  • Define dietary fibre.
  • State two examples of dietary fibre.
  • Define egestion.
  • List materials that are egested from the body.
D.2.A1  The reduction of stomach acid secretion by proton pump inhibitor drugs.
  • State the role stomach mucus.
  • State the cause of ulcer and acid reflux.
  • Outline the role of the H+, K+ -ATPase protein pump in the production of an acidic stomach.
  • Outline the use, function and effect of proton pump inhibitors to treat gastric disease.
D.2.A2  Dehydration due to cholera toxin.
  • Outline the cause and consequences of cholera infection.
  • Explain the effect of cholera toxin on intestinal cells.
D.2.A3  Helicobacter pylori infection as a cause of stomach ulcers.
  • Define stomach ulcer.
  • Outline evidence that suggest Helicobacter pylori infection has a role in stomach ulcer and stomach cancer.
D.2.S1  Identification of exocrine gland cells that secrete digestive juices and villus epithelium cells that absorb digested foods from electron micrographs.
  • List three features that can be used to identify exocrine gland cells as viewed in electron micrographs.
  • List four features that can be used to identify villus epithelium cell as viewed in electron micrographs.
D.2.NOS  Serendipity and scientific discoveries—the role of gastric acid in digestion was established by William Beaumont while observing the process of digestion in an open wound caused by gunshot.
  • Describe how William Beaumont was able to determine the role of the stomach in chemical digestion of food.
I give many of my IB Biology resources away, for the benefit of students and teachers around the world.  If you've found the materials helpful, please consider making a contribution of any amount to this Earthwatch Expedition Fund. 

​Did I forget something?  Know of a mistake? Have a suggestion?  Let me know by emailing me here. Cheers!

Before using any of the files available on this site, please familiarize yourself with the Creative Commons Attribution License.  ​​It prohibits the use of any material on this site for commercial  purposes of any kind.  ​

"When we try to pick out anything by itself, we find it hitched to everything else in the Universe." 
 John Muir,   1911