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Animal foods tend to have the lowest amounts of refractory material e. Digesting microbes requires first breaking the bacterial cell walls and then hydrolyzing and absorbing the contents of the bacterial cell. It is difficult to generalize about reproductive behaviour…. The lower eyelid has the greater range of movement in most reptiles. The digestive system consists of alimentary canal and its associated digestive glands.
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Pepsinogen is converted to the enzyme pepsin in the presence of hydrochloric acid. Hydrochloric acid is secreted by parietal cells in the stomach lining. The pepsin then digests large proteins into smaller proteins called peptides. To protect the stomach lining from the acid, a third type of cell secretes mucus that lines the stomach cavity. An overabundance of acid due to mucus failure may lead to an ulcer.
The soupy mixture called chyme spurts from the stomach through a sphincter into the small intestine. The inner surface of the small intestine contains numerous fingerlike projections called villi the singular is villus.
Each villus has projections of cells called microvilli to increase the surface area. Most chemical digestion takes place in the duodenum. In this region, enzymes digest nutrients into simpler forms that can be absorbed.
Intestinal enzymes are supplemented by enzymes from the pancreas, a large, glandular organ near the stomach. In addition, bile enters the small intestine from the gallbladder to assist in fat digestion.
The enzymes functioning in carbohydrate digestion include amylase for starch , maltase for maltose , sucrase for sucrose , and lactase for lactose. For fats, the principal enzyme is lipase. Before lipase can act, the large globules of fat must be broken into smaller droplets by bile. Bile is a mixture of salts, pigments, and cholesterol that is produced by the liver and stored in the gallbladder, a saclike structure underneath the liver.
Protein digestion is accomplished by several enzymes, including two pancreatic enzymes: Peptides are broken into smaller peptides, and peptidases reduce the enzymes to amino acids. Nucleases digest nucleic acids into nucleotides in the small intestine also. Most absorption in the small intestine occurs in the jejunum. The products of digestion enter cells of the villi, move across the cells, and enter blood vessels called capillaries. Diffusion accounts for the movement of many nutrients, but facilitated diffusion is responsible for the movement of glucose and amino acids.
The products of fat digestion pass as small droplets of fat into lacteals, which are branches of the lymphatic system. Absorption is completed in the final part of the small intestine, the ileum. Substances that have not been digested or absorbed then pass into the large intestine. The small intestine joins the large intestine in the lower-right abdomen of the body.
The two organs meet at a blind sac called the cecum and a small fingerlike organ called the appendix. Evolutionary biologists believe the cecum and appendix are vestiges of larger organs that may have been functional in human ancestors.
The large intestine is also known as the colon. It is divided into ascending, transverse, and descending portions, each about one foot in length. The intestinal matter remaining after water has been reclaimed is known as feces. Feces consist of nondigested food such as cellulose , billions of mostly harmless bacteria, bile pigments, and other materials. The feces are stored in the rectum and passed out through the anus to complete the digestion process. Uni cellular mucous glands are absent. But multi cellular serous glands are present.
Salivary glands are absent. But labial glands are open at the lips which do not play any role in digestion. Salivary glands which open into the buccal cavity are lingual, mandibular, maxillary, cricoary tenoid, palatinal and sphenopalatinal glands. The multi cellular salaivary glands are four pairs.
They are Infra orbital, parotid, sublingual and sub-maxillary glands. Pharynx is marked off. On the roof of pharynx near the junction of two jaws a pair of openings is called Eustachian apertures. Pharynx is not sharply demarcated from the buccal cavity. It receives the openings of esophagus and the glottis. Esophagus is a narrow tube and straight extends through the neck. Mucous glands are present.
Oesophagus is a bng and narrow tube. It has thick walls. Mucous glands are absent. Oesophagus is a long thin walled tube. It is clearly marked off from the pharynx as well as stomach. The oesophagus is dilated into a thin-walled sac the crop. It secrete pigeon milk in both sexes and used to feed the young birds. The wall of oesophagus is produced into the cardiac stomach to form cardiac valve.
Stomach is a sac- like structure. Its anterior part is cardiac stomach and posterior part is pyloric stomach. At the end of pyloric stomach a small constriction is present. It possesses a pyloric sphincter. Stomach is divided into a glandular proventriculus and posterior muscular gizzard. Gizzard acts like grinding apparatus. Stomach is divisible into cardiac, fundic and pyloric parts. Pyloric stomach contains pyloric valve.
Intestine is differentiated into duodenum and ileum. Intestine very long and very much coiled because is a herbivorous animal Same structures are present. But the bile duct and pancreatic ducts open separately into the proximal and distal ends of the duodenum respectively. A single rectal caecum is present. An ilio-colic valve is present at the junction of the small intestine and large intestine or colon. At the junction of these portions, a spiral shaped vermi form appendix is present.
At the regular intervals of the colon shows pocket-like pouches - 'Haustra'. Colon shows longitudinal muscle folds taeniae'. Cellulose enzyme is produced. Cloaca is common opening for digestive'and urinogenital ducts. It is divided into coprodaeum,urodaeum, and proctodaeum. Cloaca is large and divided into the same parts. On the dorsal side of the proctodaeum a thick walled blindsa"Bursa fabricii" is present.
It becomes degenerated in the adult and is known as cloacal thymus. Liver is bilobed gland. The right lobe has a gall bladder. Liver is bilobed dark red gland. Gall Bladder is absent. Separate bile ducts are formed. Liver is very large and consists of five lobes. Kupffer's cells are present in the liver.