Digestive System- Organs

Digestive System - Accessory Organs

Salivary Glands      There are three pairs of salivary glands that secret saliva into the oral cavity:    1. Parotid salivary glands – located anterior to the outer ear. These glands produce secretions that empty by way of the parotid duct  into the vestibule near the second upper molar.   2. Sublingual salivary glands – are under the floor of the mouth and are drained by numerous sublingual ducts.   3. Submandibular salivary glands – located on the medial side of the mandible under the mylohyoid line. Submandibular ducts drain secretions through an opening on either side of the lingual frenulum.      The saliva contains salivary amylase which begins digestion of complex carbohydrates and mucins which are glycoproteins that enhance the lubricating qualities of saliva. Saliva also helps to control oral bacterial populations.

Teeth      Mastication, or chewing, is performed by the teeth.   Tooth Anatomy       The bulk of the tooth is formed by a bony substance called dentin. Cytoplasmic processes extend into the dentin from cells in the pulp cavity. Highly vascular connective tissue within the pulp cavity receives blood and sensation through blood vessels and nerves that enter the root at the apical foramen and travel through the root canal.      The tooth is anchored to the bony socket of the alveolar process by collagen fibers of the periodontal ligament. A bony substance called cementum covers the dentin of the root and the fibers of the periodontal ligament are anchored in cementum.      The crown is the visible portion of the tooth above the gingivae. The dentin of the crown is covered by enamel, the hardest material in the body. The neck is the boundary between the crown and the root.   Types of teeth Video of Types of Teeth       There are four types of teeth:   Incisors – blade-like teeth for clipping and cutting.   Cuspids (Canines) – conical with a pointed tip for tearing and slashing.   Bicuspids (Premolars) – have one or two roots and flattened crowns with prominent ridges for crushing, mashing and grinding.   Molars – have three or more roots and broader crowns with ridges for crushing and grinding.   Dental Succession      Twenty primary or deciduous teeth consist of two incisors, one cuspid and two molars on each side. The primary teeth are replaced with the secondary or permanent dentition consisting of two incisors, one cuspid, two bicuspids, and three molars on each side.   Dental Frame of Reference      The various surfaces of the teeth are designated as follows:   Labial or buccal surface is the surface that faces the lips or cheeks.   Palatal or lingual surface is the inner surface facing the tongue.   Mesial surface is the medial or anterior surface.   Distal surface is the lateral or posterior surface.   Occlusal surface is the surface that comes into contact with the opposing tooth during chewing.

Liver (YouTube - How the Body Works The Architecture of the Liver)      The liver is the largest visceral organ and has more than 200 different functions that fall in one of three categories:   1. Metabolic regulation – for example, regulation of circulating levels of carbohydrates, lipids and amino acids.   2. Hematological regulation – liver cells synthesize plasma proteins and phagocytic cells remove old or damaged red blood cells.   3. Synthesis and secretion of bile – bile helps neutralize acidic chyme from the stomach and enables digestion of lipids in the small intestines.   Blood supply to the liver      The liver has two sources of blood: hepatic artery proper which delivers oxygenated blood and hepatic portal vein which delivers blood containing nutrients from the intestines. The stomach, spleen, pancreas and large intestines also drain blood into the hepatic portal vein. The hepatic veins drain blood from the liver and delivers it to the inferior vena cava.   Bile secretion      The right and left ducts collect the bile secreted by their respective liver lobes. These ducts combine to form the common hepatic duct. The common hepatic duct fuses with the cystic duct to form the common bile duct.   Gall Bladder      The gall bladder is a hollow pear-shaped, muscular organ that stores and concentrates bile. Between meals, bile secreted by the liver enters the gall bladder through the cystic duct. Under the stimulation that occurs during a meal, bile is ejected from the gall bladder into the cystic duct which fuses with the common hepatic duct to form the common bile duct which opens into the duodenum at the duodenal papilla.

Pancreas      The pancreas is primarily an exocrine organ producing digestive enzymes and buffers and is secondarily an endocrine organ. The pancreatic exocrine secretions are delivered to the duodenum by a large pancreatic duct which joins the common bile duct at the duodenal ampulla. A small accessory pancreatic duct may branch from it and empty its secretion separately at the lesser duodenal papilla.