Animal Nutrition and the Digestive System
34.1 Digestive Systems
Animals use the organs of their digestive systems to extract important nutrients from food they consume, which can later be absorbed.
Herbivores, Omnivores, and Carnivores
Animals can be carnivores, herbivores, or omnivores in their eating strategies.
Invertebrate Digestive Systems
Invertebrate digestive systems include a gastrovascular cavity with one opening or an alimentary canal with a true mouth and anus.
Vertebrate Digestive Systems
Vertebrates may have a single stomach, several stomach chambers, or accessory organs that help to break down ingested food.
Parts of the Digestive System Part 1
Animal digestion begins in the mouth, then moves through the pharynx, into the esophagus, and then into the stomach and small intestine.
Parts of the Digestive System Part 2
Nutrients are absorbed in the small intestine and waste is prepared for elimination in the large intestine.
34.2 Nutrition and Energy Production
Essential nutrients are those than cannot be created by an animal's metabolism and need to be obtained from the diet.
Food Energy and ATP
Animals use energy for metabolism, obtaining that energy from the breakdown of food through the process of cellular respiration.
34.3 Digestive System Processes
The first step to obtaining nutrition is ingestion, a process where food is taken in through the mouth and broken down by teeth and saliva.
Digestion and Absorption
In order for nutrients (carbohydrates, lipids, vitamins) to be absorbed for energy, food must undergo chemical and mechanical digestion.
Undigested food enters the colon where water is reabsorbed into the body and excess waste is eliminated from the anus.
34.4 Digestive System Regulation
Neural Responses to Food
All three phases of digestive responses to food (the cephalic, gastric, and intestinal stages) are managed through enzymatic neural control.
Hormonal Responses to Food
The endocrine system controls the release of hormones responsible for starting, stopping, slowing, and quickening digestive processes.