Digestive System Processes and Regulation
Learning Objectives
By the end of this section, you will be able to:
- Discuss six fundamental activities of the digestive system, giving an example of each
- Compare and contrast the neural and hormonal controls involved in digestion
The digestive system uses mechanical and chemical activities to break food down into absorbable substances during its journey through the digestive system. Table 23.3 provides an overview of the basic functions of the digestive organs.
INTERACTIVE LINK
Visit this site for an overview of digestion of food in different regions of the digestive tract. Note the route of non-fat nutrients from the small intestine to their release as nutrients to the body.
Functions of the Digestive Organs
Organ |
Major functions |
Other functions |
Mouth |
Ingests foodChews and mixes foodBegins chemical breakdown of carbohydratesMoves food into the pharynxBegins breakdown of lipids via lingual lipase |
Moistens and dissolves food, allowing you to taste itCleans and lubricates the teeth and oral cavityHas some antimicrobial activity |
Pharynx |
Propels food from the oral cavity to the esophagus |
Lubricates food and passageways |
Esophagus |
Propels food to the stomach |
Lubricates food and passageways |
Stomach |
Mixes and churns food with gastric juices to form chymeBegins chemical breakdown of proteinsReleases food into the duodenum as chymeAbsorbs some fat-soluble substances (for example, alcohol, aspirin)Possesses antimicrobial functions |
Stimulates protein-digesting enzymesSecretes intrinsic factor required for vitamin B12 absorption in small intestine |
Small intestine |
Mixes chyme with digestive juicesPropels food at a rate slow enough for digestion and absorptionAbsorbs breakdown products of carbohydrates, proteins, lipids, and nucleic acids, along with vitamins, minerals, and waterPerforms physical digestion via segmentation |
Provides optimal medium for enzymatic activity |
Accessory organs |
Liver: produces bile salts, which emulsify lipids, aiding their digestion and absorptionGallbladder: stores, concentrates, and releases bilePancreas: produces digestive enzymes and bicarbonate |
Bicarbonate-rich pancreatic juices help neutralize acidic chyme and provide optimal environment for enzymatic activity |
Large intestine |
Further breaks down food residuesAbsorbs most residual water, electrolytes, and vitamins produced by enteric bacteriaPropels feces toward rectumEliminates feces |
Food residue is concentrated and temporarily stored prior to defecationMucus eases passage of feces through colon |
Table 23.3
Digestive Processes
The processes of digestion include six activities: ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defecation.
The first of these processes, ingestion, refers to the entry of food into the alimentary canal through the mouth. There, the food is chewed and mixed with saliva, which contains enzymes that begin breaking down