What is/are the function(s) of the digestive system? What structures are necessary? How does function vary with form? Introduction to Digestive System
Teeth Who has teeth and who doesn’t? The “haves” Gnathostomes, amphibians, most reptiles, and mammals (highest specialization). And the “have nots” Agnathans, modern birds, a few mammals lack teeth.
Teeth How do teeth develop? Teeth are the derivatives of dermal bony armor.
How do teeth develop? Teeth (and placoid scales) are composed of dentin and a covering of enamel or enameloid. Dental lamina develop as in growths of ectoderm along the jaws. Dermal papillae develop under the future site of each tooth. Odontoblasts deposit dentin. Dental lamina forms enamel organ with ameloblasts that deposit enamel. Teeth
Mastication = chewing Which type of digestion? Why? Accomplished via: cheeks, lips, tongue, teeth, jaws Types of teeth: Incisors Canines Premolars Molars deciduous permanent Teeth What is the oral cavity and what does it do?
How are teeth attached? Periodontal ligaments and cementum keep teeth associated with sockets in mammals (gomphoses). In some fishes teeth are on the “shoulder” of the dentary bone (acrodont) In anurans, urodeles and squamates they are attached to the inner aspect (pleurodont) Many fishes, toothed birds, crocodilians and mammals there is a socket (thecodont) Teeth
How do teeth vary? Sharks have a broad basal plate anchored in dermis Some adapted for crushing shells etc. Modified to deliver venoms Peak of specialization in mammals Incisors of rodents and lagomorphs lack enamel posteriorly. Missing canines and/or premolars results in a diastema Teeth
Alimentary Canal Structure
Stomach
What are the functions of the stomach? Food storage (sometimes this task is given to specialized structures ex. crop). Mechanical digestion (Gizzard of birds and crocodilians, gastroliths) Chemical digestion (which nutrient category?) Monitor and regulate consistency of chyme and control its entrance into the small intestine Stomach
How are the regions of a stomach related to their function? Specific cells responsible for specific components of gastric juice. Regions with minimal zymogen (chief) cells have esophogeal-like epithelia. Regions with abundant zymogen and parietal cells have glandular epithelia Pylorus is important muscular sphincter Stomach
What are the structures as related to human anatomy? Stomach
What about ruminates? Rumen are sacs/caeca that facilitate the chemical digestion of the tough polysaccharide cellulose. The necessary enzyme is cellulase produced by anaerobic bacteria. Returning the chyme “cud” back to the mouth facilitates additional mechanical digestion. Temporary storage is in the omasum and the glandular stomach is the abomasum Stomach
How is intestine structure related to function? Chemical digestion = enzymes secreted by the pancreas and those associated with the epithelium Abosorption = villi and microvilli. Transportation = via blood and via lymph Lubrication maintained by mucous glands Intestines
Contains features such as: plicae circularis (circular folds) villi microvilli Why? Functions include: Digestion/Mixing/Abs orption What’s the internal anatomy of the small intestines? Digestive enzymes in association w/ microvilli: disaccharidases, peptidases, nucleases Intestines
Digestive glands
Bile production: formed in lobules, drains out hepatic ducts, secreted and/or stored in gall bladder. Storage: can store nutrients (glycogen, vitamins, fats) Nutrient interconversion: metabolically “swapped” Detoxification Phagocytosis Synthesis What’s the digestive role of the Liver? What are gall stones? Liver and Pancreas
Pancreas
Secretion Absorption (form feces) Normal flora can produce: Vitamins (K) Flatus Capable of mass movements What are the functions of the colon? Colon