 This video will cover the following objective for the digestive system, contrast the deciduous and permanent teeth, describe the histological organization of a tooth, identify the salivary glands, the parotid, submandibular and sublingual salivary glands, and identify the major regions of the pharynx. There are 20 deciduous teeth that emerge from 6 months of age until around 2 years old. The first of the deciduous teeth to grow in are the most anterior flat shaped teeth known as the incisors, there's a central incisor and a lateral incisor. So the central incisor normally emerges between 8 to 12 months and the lateral incisor normally emerges between 12 to 24 months. Then the teeth that are found just lateral to the lateral incisors are known as the cuspids or they're also known as canines, the canines or cuspids have a pointed edge, these are sort of fang shaped teeth with a pointed tip known as the cusp which is designed for piercing and tearing up tough or fleshy food. And so while there's two incisors in each quadrant that have a flat tip for cutting through food as you bite into food, there's just one canine or cuspid tooth in each quadrant. So that's four total canine teeth and eight total of the incisor teeth with two incisors in each quadrant and one canine in each quadrant. And then there are two molars that grow in as the deciduous teeth, the first molar is just posterior to the canine and the second molar is posterior to that. But all of the deciduous teeth will then fall out and be replaced with the permanent teeth. We have 32 permanent teeth where the incisors grow in to replace the deciduous incisors and the canines grow in to replace the deciduous canines. There are premolars also known as bicuspids that grow in to replace the deciduous molars. Each quadrant contains two premolars and then three adult molars grow in just posterior to the premolars. So premolars have a broader tip than the canines and they have two pointed tips or two rounded cusps that are useful for mashing up food and so that's why they're also known as bicuspids. They have two tips and contrast to the canine or cuspid that just has one pointed tip. The bicuspids or premolars have two pointed tips and then the molars have a broader surface where they will have several pointed cusps and primarily function for the crushing of food and grinding food to prepare it for swallowing. And while there are three adult molars, three permanent molars in each quadrant, the third molar, the furthest posterior, also known as the wisdom tooth, commonly does not emerge and so if it doesn't erupt during adulthood, that third molar, the wisdom tooth will have to be removed surgically and so it's common to have the wisdom teeth removed surgically and some people will actually never develop the wisdom tooth and only grow in 28 teeth instead of 32. This illustration is showing us a section through a tooth so we can see the histological structure. The outermost layer of the tooth is enamel, a very hard calcified connective tissue which covers the crown of the tooth. So the exposed portion of the tooth is known as the crown and the calcified substance that covers the crown is enamel and enamel is the hardest substance in the body which helps to protect the tooth against the forces of chewing and grinding up of food. So the neck is the middle region of the tooth and the root then extends into the alveolar socket in the bone of the mandible or maxilla. The neck contacts the gum also known as the gingiva so the internal structure of the tooth is formed from another calcified connective tissue known as dentin so you can see that dentin is filling the neck as well as the root of the tooth and dentin surrounds an inner pulp cavity which contains the blood vessels and nerves which enter and exit through the root canal at the apex of the root of the tooth. The root is anchored to the surrounding dental alveolus and the connective tissue that helps to hold it in place includes the periodontal ligaments as well as a calcified substance known as cementum which is the outer layer of the root surrounding the dentin in the root. There's an outer layer known as cementum which is a hard calcified outer layer that helps to anchor the periodontal ligaments to the root of the tooth and helps then to stabilize the tooth inside of the socket or dental alveolus of the jawbone the mandible or maxilla. There are two parotid salivary glands one on either side of the oral cavity located superficial to the masseter and these parotid glands are the largest of the salivary glands they secrete a large volume of watery enzyme rich saliva through the parotid duct into the oral cavity then the most anterior salivary glands are a pair of sublingual salivary glands located in the floor of the oral cavity inferior to the tongue and the sublingual salivary glands produce a relatively small volume of thick mucus rich saliva that's excreted through numerous ducts into the floor of the oral cavity on either side of the tongue. Then the submandibular salivary glands are found posterior to the sublingual salivary glands on the medial side of the mandible in the floor of the oral cavity and the submandibular salivary glands although they're smaller than the parotid salivary glands they normally produce most of the volume of saliva and they produce saliva that has a mixture between the watery enzyme rich consistency produced from the parotid gland and the thick mucus consistency produced from the sublingual salivary gland so a mixed cirrus and mucus enzyme rich but thick and slippery lubricating saliva is produced from the submandibular salivary glands so here we can see the oral cavity that the border between the oral cavity and the pharynx is formed by a arch on the roof of the mouth so the roof of the mouth is known as the palate there's the bony hard palate and then the soft palate is a mucus membrane and muscular roof the uvula is the region of the soft palate that extends down on the midline and then can fold superiorly to close off the entrance to the nasopharynx during swallowing during deglutition on either side of the uvula extending laterally there are the palatoglossal arches of the soft palate that extend down towards the tongue so palatoglossal are mucus membrane arches from the palate to the tongue extending lateral to the uvula just posterior to the palatoglossal arch is the palatofaryngeal arch the palatofaryngeal arch connects from the palate down into the oral pharynx and then between those palatoglossal and palatofaryngeal arches in the lateral walls of the oral pharynx are the palatine tonsils that are mucosa associated lymphoid tissue monitoring the entrance of the pharynx from the oral cavity for any infection so here's another view into the oral cavity where we can see the structure of the tongue and the lingual tonsil in the base of the tongue and then just lateral to the tongue we can see the palatoglossal arch then just posterior to the palatoglossal arch the palatine tonsils and then posterior to the palatine tonsils are the palatofaryngeal arches coming down from the soft palate into the oral pharynx so the pharynx is commonly referred to as the throat the nasopharynx is the region of the throat just posterior to the nasal cavity or as the oral pharynx is the part of the pharynx just posterior to the oral cavity and the laryngeal pharynx is the region of the throat that connects into the larynx just inferior to the oral pharynx the uvula is the part of the soft palate that can fold up to close off the entrance from the oral pharynx to the nasopharynx during swallowing at the same time the epiglottis folds down to close off the entrance to the larynx so that food will move through the laryngeal pharynx into the esophagus during swallowing or deglutition