Digestive System!

• The liver is the largest internal organ and produces bile, which helps break down fats.
• The Digestive Tract is a long tube extending from the mouth to the anus.
• Each part of the Digestive Tube has a similar structure.
• The Digestive Tract is associated with glands which are situated outside the tube but delivering their secretions into it.
• Digestion is a process whereby the food material is converted into substances that can be absorbed into the circulation.
• The process of digestion involves different steps: Breaking down of food material to small pieces, absorption of the food material into the circulation, and elimination of useless or toxic materials by fecal excretion.
• The Digestive Tract has three major parts: The Oral Cavity, The Tubular Digestive Tract, and The Major Digestive Glands.
• The Oral Cavity is the entrance to the Digestive Tract and its main functions are the breaking down of the food material and the hydrolyzation of the carbohydrates.
• The Oral Cavity has two parts: Vestibulum oris, which is closed by tooth and upper and lower lips, and Cavum oris proprium, which is closed by tooth, cheeks and palate.
• The Lips are macroscopic characteristics of the Oral Cavity and their microscopic structure is composed by striated muscle.
• Intralobular ducts are located inside the lobules; they tend to be greater in diameter and longer than the striated ducts with simple columnar epithelium.
• Pure serous acini are rare in the major salivary glands.
• The major salivary glands have very similar duct systems.
• Intercalated ducts commence from the lumen of the acini and are covered with small, flattened epithelial cells; myoepithelial cells may be present between the duct cells and basal lamina.
• Saliva (1,5 - 2l/24h) is a liquid containing water, salts, mucin and enzymes (ptyalin and maltase that split the carbohydrates).
• Interlobular ducts are located in the septae; with columnar to pseudostratified epithelium.
• Striated ducts are tall, columnar in shape with basal striation (basal invaginations of the plasma membrane with mitochondria).
• The epithelial cells of the striated ducts are associated with fluid absorption from the lumen to the blood vessels.
• The main excretory ducts open in the oral cavity; with pseudostratified and finally multistratified squamous epithelium; deliver saliva.
• The tongue is located in the oral cavity and has two main parts: the root (base) which is the posterior third, and the body which is the anterior two-thirds.
• The mucous membrane of the tongue forms folds, including Plica e fimbriata e, Frenulum linguae, Caruncula e sublingual e s, and Plica e sublingual e s.
• The mucous membrane on the root of the tongue passes to the epiglottis and forms three folds: Plica glossoepiglottica mediana, Plicae glossoepiglotticae laterales, and Valleculae epiglotticae.
• Papillae fungiformes are located near the tip of the tongue and are disposed between the folds of the mucous membrane.
• Papillae filiformes are very similar to papillae, but are bigger.
• The surface epithelium of the root of the tongue forms many depressions, termed cryptae.
• The tongue is covered by a mucous membrane, tunica mucosa, which includes lamina epithelialis, a multistratified squamous epithelium, and lamina propria, a loose connective tissue that shows secondary papillae with a rich vascular plexus.
• The root of the tongue has a nodular, irregular surface due to the presence of lymphatic nodules (tonsilla lingualis).
• Between lamina propria and the muscle core of the tongue is a layer of elastic and collagen fibers, aponeurosis linguae (stratum reticulare).
• On the upper surface of the tongue, the mucosa shows numerous protuberances, papillae, which are located in rows parallel to the V-shaped groove and show signs of cornification.
• The under-surface of the tongue is smooth, freely movable and underlain by a tela submucosa.
• The Cheeks have a similar structure to the lips, being a part of the lateral wall of the vestibulum oris, with a core of striated muscle (m. buccinator), corpus adiposum buccae (Bichat), and externally, skin, epidermis and derma, with a stratified squamous keratinizing epithelium, hair follicles, sebaceous and sweat glands.
• The Palate is the roof of the mouth and also the floor of the nasal cavity, separating oral and nasal cavities, with a hard palate (palatinae processes of maxillae and palatine bones) and a tunica mucosa covered by squamous nonkeratinizing epithelium.
• The Cheeks - microscopic characteristics include a mucous membrane (tunica mucosa) covered by stratified squamous nonkeratinizing epithelium, with a loose connective tissue (lamina propria) underneath, and elastic connective tissue (tela submucosa) with rich vascular plexus and small mucous glands (gl labiales) to bind the mucous membrane to the muscle.
• The lip has three parts: pars cutanea, which is externally, skin with stratified squamous keratinizing epithelium, hair follicles, sebaceous and sweat glands; pars mucosa, which is internally, covered by stratified squamous nonkeratinizing epithelium; and Lamina propria, which is under the epithelium, loose connective tissue with small mucous glands (gl labiales).
• The Palate also has a propria layer, which blends with the periostium, and adipose tissue (zona adiposa) and mucous glands (zona glandularis) in the posterior part.
• The Lips - microscopic structure includes pars intermedia, which is the free margin of the lip, region with modified, thick, more transparent squamous keratinizing epithelium underlying dermis with many blood capillaries, and without hair follicles and sebaceous and sweat glands.
• The taste buds are responsible for the sense of taste, located in the epithelium of the papillae vallatae and fungiformes, are pale, barrel-shaped bodies with a laminated appearance, have an external opening (outer taste pore) and a small pit in the base (inner taste pore), and have 3 types of cells: neuroepithelial cells, supporting cells, and basal cells.
• The filiform papillae are taste buds located on the lateral walls of the tongue.
• The muscles of the tongue are striated, intrinsic (confined to the tongue) and extrinsic (originate outside), including the muscles genioglossus, styloglossus, and hyoglossus.
• The blood supply and innervation of the tongue include the artery lingualis, a branch of the a.carotis externa, the vein lingualis, and the nerve hypoglossus for motor inervation, the nerve sensory inervation, and the anterior 2/3 of the tongue, and the nerve lingualis for general reception, the chorda tympani (n.facialis) for taste reception, and the posterior 1/3 of the tongue, and the n.glossopharyngeus and n.vagus for general and taste reception.