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Digestion converts large, insoluble food molecules into small, water-soluble components that can be absorbed into the blood.
Digestion is the breakdown of large, insoluble food compounds into small, water-soluble components that can be absorbed into the blood plasma. It is a form of catabolism and is commonly divided into mechanical digestion (physical breakdown of food into smaller pieces) and chemical digestion (enzymatic breakdown into usable molecules). Mechanical digestion begins in the mouth with chewing (mastication) and continues in the small intestine via segmentation; chemical digestion relies on enzymes that convert food into small compounds the body can use. In humans, digestion starts in the mouth where saliva (including salivary amylase) begins carbohydrate digestion and helps form a bolus. The bolus moves through the esophagus to the stomach, where gastric juice (notably hydrochloric acid and pepsin) initiates protein digestion while mucus and bicarbonates protect the stomach lining. As partially digested food (chyme) enters the duodenum, it mixes with pancreatic enzymes and bile, and digestion continues mainly in the small intestine, where most nutrient absorption occurs. Digestion is also regulated by digestive hormones and depends strongly on pH: enzymes function best within specific pH ranges, the stomach is highly acidic for protein denaturation and defense, and the duodenum is neutralized to activate and protect enzyme activity. Across organisms, digestion can occur internally (within a controlled digestive tract) or externally (enzymes secreted into the environment). Different animals and microbes have specialized structures and strategies—such as phagosomes for intracellular digestion, gastrovascular cavities in some animals, and specialized organs like crops or ruminant stomach chambers—to improve access to nutrients and absorption efficiency.
Digestion converts large, insoluble food molecules into small, water-soluble components that can be absorbed into the blood.
Digestion is typically separated into mechanical digestion (physical breakdown) and chemical digestion (enzyme-driven breakdown).
In humans, digestion begins in the mouth, continues through the stomach and duodenum, and most nutrient absorption occurs in the small intestine.
Digestive hormones regulate timing and intensity of digestive secretions and motility, while pH is crucial because enzymes denature outside their optimal ranges.
Digestion strategies vary across organisms, including internal digestion (controlled gut environment) and external digestion (enzymes secreted into the environment).
The breakdown of large, insoluble food compounds into small, water-soluble components that can be absorbed into the blood plasma.
Physical processes that break food into smaller pieces, such as chewing and segmentation contractions.
Enzymatic processes that convert food into small molecules the body can use and absorb.
A small, round slurry mass of food formed after mastication and saliva mixing that travels to the stomach.
Partially digested food that leaves the stomach and enters the duodenum for further digestion.
A gastric enzyme that breaks proteins into smaller peptides during protein digestion in the stomach.
The acidity or alkalinity of digestive compartments that controls enzyme activity and protects tissues, such as the highly acidic stomach and neutralized duodenum.
Hormones that aid and regulate digestive secretions and motility, including gastrin, secretin, and cholecystokinin.
A digestion strategy where enzymes are secreted into the environment to break down food outside the organism.
A digestion strategy where food is broken down within a digestive tract with a controlled internal chemical environment.
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