In a way, the stomach has the means to protect itself from being digested by the combination of its contents.Ībout every 20 seconds, the stomach muscles contract, churning and mixing its contents. When the stomach contents become too acidic, gastrin is inhibited. When the food arrives in the stomach, the hormone gastrin is also released and helps stimulate the release of more gastric juice.

Pepsin is important in breaking down proteins. This type of reaction is a form of positive feedback since the end product of a process encourages the formation of more end products. When pepsinogen and HCl mix in the stomach, some pepsinogen gets converted into pepsin and helps activate more pepsinogen. Chief cells secrete pepsinogen, an inactive form of the enzyme pepsin.Parietal cells secrete hydrogen and chloride ions, forming hydrochloric acid (HCl).Mucous cells secrete mucus which lubricates and protects cells lining the stomach.Three types of cells, the gastric glands, secrete different components of gastric juice: Image by Mariana Ruiz is available in the public domain. Another function of the acid is it breaks apart cells in food and denatures proteins.ĭigestive system diagram. The low pH of gastric juice kills most bacteria and other microbes swallowed with food.

Digestion in the stomach is accompanied by the secretion of gastric juice, which is made up of protein-digesting enzymes, mucus, and a strong acid. Ring-like muscular valves, called sphincters, regulate the passage of food into and out of the stomach, keeping food there for about 2-6 hours, enough for digestive enzymes to begin digestion. After swallowing, muscles propel food by peristalsis, alternating waves of contraction and relaxation of smooth muscles that line the alimentary canal. Of particular note is that saliva contains the enzyme amylase which is able to digest starch already.Īfter food is ingested in the mouth or oral cavity, we use our tongue to push the food, which has been shaped into a ball called a bolus, down our throat. Saliva contains several substances that are important in food processing. The presence of food also stimulates three pairs of salivary glands. In humans, food is mechanically digested as teeth cut, smash, and grind food (a process known as “chewing”, technically called mastication). Chemical digestion and nutrient absorption occur mainly in the intestine and the undigested materials are expelled through the anus. Stomachs and gizzards are muscular organs that churn and grind food as well as store food temporarily. A crop is a pouch-like organ where food is softened and stored. Depending on the species, the esophagus may channel food into a crop, stomach, or gizzard. The Process of Digestionįood entering the mouth passes through the pharynx or throat. Because food moves in one direction, regions of the tube become specialized to digest and absorb nutrients in a stepwise fashion. More complex animals have an alimentary canal (we refer to it as the gut) which is a tube extending between the mouth and an anus. Elimination during which undigested material is removed from the digestive system.Īnimals with relatively simple body plans digest food within a gastrovascular cavity that functions as both an entrance for food and an exit for undigested waste.Absorption where the byproducts of digestion are taken up by the body and.Digestion, which is the breakdown of food into smaller molecules for the body to absorb.The organ system responsible for processing food and for nourishment is the digestive system, and the process of breaking down food can be described as four distinct stages: Bulk feeders ingest large pieces of food.Fluid feeders suck nutrient-rich liquids from others.Substrate feeders live in or on their food and eat their way through it.Suspension feeders are those that capture food particles from their surrounding environment.In addition to what they eat, how they eat can also be described as follows: Omnivores are those able to consume both plants and animals.Herbivores are those that dine mainly on plants and algae.2. Answer Key How Animals Eat: An OverviewĪll animals eat other organisms but the type of diet they feed upon varies extensively.The digestive system ingests and digests food, absorbs nutrients, and eliminates undigested food material.

Un digested food