The digestive system is a complex network of organs and glands that work together to break down food and absorb nutrients. It is made up of the gastrointestinal tract (also called the gastrointestinal tract or digestive tract) and the liver, pancreas, and gall bladder. The hollow organs that make up the gastrointestinal tract are the mouth, esophagus, stomach, small intestine, large intestine, and anus. The solid organs of the digestive system are the liver, pancreas, and gall bladder.In birds, food passes from the beak to the first of two stomachs, called the proventriculus.
This stomach contains digestive juices that break down food. From the proventricle, food enters the second stomach, called gizzard, which crushes food. Some birds swallow stones or sand to help with this process. Birds do not have separate openings for excreting urine and faeces; instead, uric acid from the kidneys is secreted into the large intestine and combines with waste from the digestive process.
These wastes are then excreted through an opening called the cloaca.Birds have a simplified and highly efficient digestive system. Recent fossil evidence has demonstrated that the evolutionary divergence of birds with respect to other terrestrial animals was characterized by the streamlining and simplification of their digestive system. Unlike many other animals, birds don't have teeth to chew their food; instead of lips, they have sharp, pointed beaks. Birds' horny beaks, lack of jaws, and smaller tongues can be traced back to their dinosaur ancestors.
The appearance of these changes seems to coincide with the inclusion of seeds in the diet of birds.Seed-eating birds have beaks designed to grasp seeds and their two-compartment stomach allows for task delegation. Because birds need to stay light to fly, their metabolic rates are very high, meaning that they digest food very quickly and need to eat frequently. This is in contrast to ruminants such as cows, sheep and goats whose entire diet consists of eating large amounts of forage or fiber. They have developed digestive systems that help them digest large amounts of cellulose.An interesting feature of ruminant mouths is that they do not have upper incisor teeth; they use the undersides of their teeth, tongue, and lips to tear and chew food.
From the mouth, food travels to the esophagus and then to the stomach. Some animals such as camels and alpacas are pseudoruming; they eat a lot of plant material and forage but their digestive enzymes cannot break down cellulose so they rely on microorganisms present in their digestive system.Pseudoruminants have a three-chambered stomach in their digestive system; however, their cecum is large and contains many microorganisms necessary for digestion. They do not have a rumen but they do have an omasus, an abomasus and a reticulum.The amount of secretion from each gland varies depending on the stimulus and nature of food. It is estimated that it is 1000 to 1500 ml per day.
It maintains an optimal pH (1.2-1) for digestion by pepsin which is secreted in an inactive form (pepsinogen). A small amount of pepsin can cause activation of remaining pepsinogen.It contains 1.8% solids (including HCO3−), 0.6% organic substances which are specific for hydrolysis of primary ester bonds at positions 1 and 3 of triglyceride. Both enzymes are capable of cleaving internal phosphodiester bonds to produce a 3'-hydroxyl end and a 5'-phosphoryl or a 5'-hydroxyl-1 and a 3'-phosphoryl end.It contains about 1.5 percent solids; two thirds are inorganic while rest are organic substances.Like most carnivores, dogs have a short digestive system relative to their body size; it takes between 8-9 hours for digestion process to complete. Nerves, hormones, bacteria, blood, and organs work together in this process.The muscles of small intestine mix food with digestive juices from pancreas, liver and intestine before pushing it forward for further digestion.
Animals have developed different types of digestive systems depending on what they consume.The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and other components of National Institutes of Health (NIH) conduct research on many diseases related to digestion.