Digestive system

The organs and processes that take in food, break it down, absorb nutrients and water, and eliminate undigested material.

Mouth: The cavity where food enters, is chewed, and mixes with saliva. Digestion begins here as chewing and saliva prepare food for swallowing.
Digestive enzyme: A protein that accelerates the chemical breakdown of food molecules. Enzymes turn large food molecules into forms the intestine can absorb.
Nutrient absorption: The movement of digested nutrients from the gut into blood or lymph. Absorption is the system’s route for delivering food-derived nutrients to the body.
Ruminant digestive system: A digestive arrangement in ruminants that uses a multi-compartment stomach and microbial fermentation. Its fermentation chambers process plant material differently from the human gut.
Esophagus: A muscular tube that carries swallowed food from the throat to the stomach. Its coordinated contractions move food toward the stomach.
Gastric acid: Hydrochloric acid secreted by the stomach lining into the stomach lumen. It creates the acidic conditions that activate protein-digesting enzymes.
Liver: A large organ that processes nutrients, produces bile, and performs many metabolic functions. It receives absorbed nutrients and supplies bile for digestion.
Avian digestive system: The digestive organs of birds, including a crop and a muscular gizzard in many species. Birds use specialized storage and grinding organs rather than teeth for food processing.
Stomach: A muscular organ that stores food and mixes it with acid and digestive enzymes. It churns food and begins substantial protein digestion.
Bile: A fluid made by the liver that helps disperse dietary fats in the intestine. It enables efficient fat digestion in the small intestine.

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