Module 7 Intro

Module 7—The Digestive and Respiratory Systems

Lesson Summary

In this lesson you explored the following questions:

• How do the organs of the digestive system work together to digest carbohydrates, lipids, and proteins?
  
  
• In what way does the body facilitate exchange of energy and matter from the digestive system?

This lesson focused on the major structures of the digestive system and how the structures process the food and fluids that people ingest. You have charted the process of digestion from gums to bums.

Digestion first begins in the mouth. An enzyme specific to starch digestion is secreted in your saliva, and chewing begins physical digestion. Once in the stomach, hydrochloric acid and pepsin begin the breakdown of protein. This is what you will vomit if you are ill.

The small intestine is where the majority of digestion and absorption of nutrients occur. The six metres of intestine uses enzyme secretions from the gall bladder, liver, and pancreas to complete the digestion of fats, proteins, and carbs.

Billions of fingerlike projections, called villi, line the small intestine and increase the surface area for nutrient absorption to the bloodstream. Molecules are actively transported from the small intestine to be dissolved into the bloodstream.

Mitochondrion depend on the digestion of carbohydrates to fuel ATP synthesis. The remaining undigested material moves to the large intestine (colon) where minerals, vitamins, salts, and water are reabsorbed. The remaining feces is stored in the rectum, thus concluding the journey from gums to bums.

Lesson Glossary

chyme:  the partially digested, semi-fluid mass of food that is forced from the stomach into the small intestine

pepsin: a digestive enzyme found in gastric juice that catalyzes the breakdown of protein to peptides

pepsinogen: the inactive precursor to pepsin formed in the chief cells of the mucous membrane of the stomach and converted to pepsin by hydrochloric acid during digestion

peristalsis: the wavelike series of muscular contractions and relaxations in structures such as the esophagus

sphincter: a ringlike muscular structure that normally maintains constriction of a natural body passage or orifice and that relaxes as required by normal physiological functioning