hello everyone this is our second video about the digestive system for this video these are our learning objectives starting in this video we will ingest a piece of food and follow it through our entire digestive tract and we will also analyze how accessory organs complement the process of digestion everything begins at the oral cavity the act of actually taking food into the mouth involves a conscious choice and then after the food is in our mouth we consciously masticate when we masticate we have the mechanical processing of the food in our mouth as I mentioned before the mechanical processing the breakdown of the food into smaller pieces will be mainly done by our teeth tongue and hard palate the hard palate is the roof of our mouth it is formed by diffusion of the maxillary and palatine bones and using our tongue we press the fold into the palate which is a hard surface and these will help the breakdown of the fold into is modeled pieces we also lubricate the food using saliva and mucus and the saliva and mucus will coat the food and make it easier to swallow and very importantly since the saliva has enzymes is starting the oral cavity we have digestion and what starts being digested in the oral cavity is complex carbohydrates the histology of our oral cavity consists of a mucosa made of non-keratinized stratified epithelium non-keratinized because we do not have any carotene inside our mouth right and stratified because we obviously need several layers of cells to handle all the abrasion caused by the food we are ingesting in masticating now looking here at the roof of the oral cavity we have the heart in the soft palate and as I said before the hard palate is formed by diffusion of the maxillary and palatine bones and then posterior to the hard palate we have the soft palate the soft palate is soft there is no bone it's just muscle covered with the same epithelium as there were low cavity the very back of the soft palate terminates in a u-shaped structure called uvula the uvula is easy to remember because it's shaped like a letter U while we are masticating the uvula guards the opening to the oral pharynx which is the part of the pharynx that's close to the oral cavity and the uvula is involved with blocking food from going down the throat too soon and when we are swallowing the soft palate and the uvula move up and close off the nasal pharynx preventing food from entering the nasal cavity now this opening we have between the oral cavity and the oral pharynx is called facets and when we swallow the food is pushed by our tongue down through the facets and then the food reaches the oral pharynx now the tongue is one of our strongest muscles by mass the tongue makes the floor of the mouth and it continues back in the mouth as well as near the pharynx our tongue is involved with tasting talking mastication and swallowing during mastication the movements done by our tongue helps to shape the food as we chew it and then the food turns into a nice swallowable piece called bolus now when we swallow the tip of the tongue elevates and it pushes up against the hard palate and then the rest of the tongue moves the boulders back towards the pharynx and when this is happening our larynx elevates and the epiglottis closes the glottis and that ensure the food will go down the esophagus and not down our larynx and trachea here we have an anterior view of our oral cavity so we starting with the lips on the underside of each lip there is a fold of skin right along the midline that fold of skin is called pendulum we have the pendulum of upper lip and the pendulum of lower lip and if you pass your tongue on the top of your lip frenulum you notice that the pendulum of the upper lip is more pronounced than the pendulum of the lower lip the lip pendulum holds the lips in place the gums are named gingiva and the gingiva surrounds each tooth the teeth are embedded within two of our skull bones the maxilla bone and the mandibular bone and the function of the teeth is mechanical digestion so chopping up food into his model pieces on the underside of the tongue right along the midline we have the frenulum of the tongue also called lingual frenulum that's the fold of skin on the underside of our tongue and this lingual frenulum keeps the tongue down and that's a good thing because we don't want our tongue to roll back into our pharynx and potentially choke on our own tongue in our oral cavity we have saliva and saliva is made by three major salivary glands and they are all paired so we have them on the right and on the left side of our face we have the parotid gland which is this giant salivary gland that's close to our ear then we have the submandibular gland which as the name suggests it is right under our mandible and then under our tongue we have the sublingual gland in reality we have two types of saliva the mucosa and the serous saliva the mucus saliva is essentially a lot of mucus and mucus is very thick and it acts as a binding agent to kind of glue what we are tuning in to a big miss the seer saliva is basically water and enzymes and it has the salivary amylase enzyme which starts the breakdown of starch so it starts breaking down carbohydrates even though the parotid gland is the biggest salivary gland we have parotid glands are responsible for secreting just 25% of our saliva and the saliva secreted by the parotid glands is a serious saliva and it contains lots and lots of amylase the sublingual gland which is the smallest out of the three salivary glands is responsible for secreting just 5% of our saliva in all secretion coming from the sublingual gland is mucus saliva now lastly we have the submandibular gland and the submandibular gland is something like in between the parotid and the sublingual gland and it releases both the serous saliva and the mucus saliva and it releases almost all of our saliva the submandibular gland is responsible for secreting 70% of our saliva when we were kids we had 20 deciduous teeth commonly called baby teeth or milky teeth and they started erupting between 6 and 24 months of age then between 6 years old and early teenage years like 12 years old the permanent teeth is starting to push the deciduous teeth out and the decedent's teeth end up falling out so this is what we see in this picture this is actually showing what the permanent teeth look like as they are developing within the bone which for me is pretty cool so if we are seeing the deciduous teeth here this means that this is the skull of a child like it is stated here they score of a four year old child if you did not remove any of your tooth you should have right now 32 teeth and that's part of our teeth that we see on the outside is called crown and the crown is outside of the gingiva inside the gingiva we have what's called root here we have a diagram showing a section through a typical adult tooth we see the crown and the root I just mentioned now the top surface of the tooth it's called the occlusal surface and that's where the upper and lower teeth come together nicely and the teeth can perform the role in mastication the white part of our tools that the part that we see is called the crown and what makes it white is an mo an mo is the hardest substance of the human body it's made of calcium phosphate which is a mineral that's very very hard so you see that most of the part of our tooth that's covered by an mo is above the gum line above the gingiva and then just a little part is inside the gingiva this little part of the tooth that at the gum line is called neck the gums or gingiva help protect the tooth and also form a little cushion around the tooth surrounding the root of the tooth we have cement in the cement cements anchors the tooth to the periodontal ligament in the periodontal ligament holds the tooth in the alveoli which is this bony cavity where the tooth sits in a narrow as a set is not a living part of our teeth and an mo is the hardest material we find in our body and it is dead it consists of densely packed calcium phosphate crystals there is no life cells in an mo and these favors us because we are less likely to develop infections since there are no life cells in the enamel now underneath an mo we have denting and denting is not as hard as an mo it's basically as hard as bone and that's because the minerals that make up dancing are both calcium phosphate and also calcium carbonate so we have the same two minerals that make up the bone making up the denting and as you can see here the Danton has these little tubules in these little tubules help transmit nutrients from the Pope cavity out towards the nmo and then these nutrients that are transported out of the pope cavity keep our teeth strong and healthy so here in the pope cavity is the place where we find blood vessels and nerves and if you recall when we studied cranial nerves we learned that our teeth are innervated by the maxillary and the mandibular brains of the trigeminal nerve and that what allow us to have sensation in our teeth so now you know which are the nerve fibers we are seeing here in the pope cavity of the tooth for the blood vessels and nerves to reach the pope cavity they need to pass through a canal located at the root of our tooth guess what's the name of that canal it is root canal so in the root canal we find blood vessels and nerves passing through and then they reach the pope cavity of our tooth okay so after you chew up your food you masticate what happens you swallow the food and the process the action of swallowing is called deglutition we divide the swallowing process into three phases we have the buccal phase therefore interphase and this of agio phase buccal phase involves our conscious decision we decide if we are going to swallow or not the buccal phase is starts when we make our tongue push the food too the oropharynx area and for that to happen it requires the toned muscles to work and our hi Pablo so nerve to be functioning since the hypoglossal nerve is what controls our tongue muscles during the buccal phase the tip of our tongue touched just behind our superior front teeth which are called incisors and then our tongue protrudes backwards and it forces the bolus of food down towards the pharynx now when the bolus is moving from the oral cavity into the oral pharynx the uvula prevents the bones from going up into our nasal pharynx so when we swallow the uvula together with the soft palate close off the nasal pharynx and once the bowl is get student pharynx we start the pharyngeal phase now after the buccal face we don't have conscious control anymore the pharyngeal phase begins when the bolus enters the pharynx and as soon as the bolus enters the pharynx the epiglottis will cover the glottis so the epiglottis claw covers the larynx and with that we don't choke now the pharynx starts to constrict and it contracts in an up-down motion and that forces the bolus of food downwards into the esophagus and that leads to the esophageal phase now the esophagus is just a muscular tube that via peristalsis moves the bolus of food all the way down into our stomach we have qu is filters associated with the esophagus we have the upper esophageal sphincter and once the bowls of food passes the upper esophageal sphincter this is filter constricts so the bolus of food doesn't come back that way when this filter is working properly it prevents regurgitation so it prevents that whatever passed the sphincter coming back in or throat if we follow our sofa goes down we see that it would go down our neck and then it would go into the thoracic cavity the esophagus past is behind the heart but interior to the vertebrae and then it keeps going down and it crosses the diaphragm esophageal hiatus and then the esophagus entered the peritoneal cavity in the abdominal cavity and it reads they stomach now there is another is sphincter between the esophagus and the stomach and this is finger is called the lower esophageal sphincter and this finger is also named cardiac sphincter when the bolus of food enters the stomach then we have mechanoreceptors and camel receptors in the stomach that get stimulated and then the stomach's start to be losing more acid in enzymes to further digest the bolus of food all this acid we think the stomach is not a problem if the lower is of a Jewish finger is working properly the problem is start if these is loads of a Jewish sphincter is not working properly because then we have acid from the stomach going up and reaching there so folks and that's what we usually call heartburn but the clinical name for heartburn is gastro esophageal reflux or acid reflux so gastro because it stands for day stomach ends of a GU because of the esophagus so gastro is of a Geo reflux in some cases when a person has a lot of acid reflux that can be due to hiatal hernia and that's what it's shown here the hiatal hernia happens when there's of a gio hiatus they hole through which the esophagus crosses the diaphragm the hole becomes stretched enough that the stomach herniates through it so the stomach goes the wrong direction and it passes the diaphragm and when that happens acid that's normally produced by the stomach as an easier time getting up to the esophagus so the esophagus carries solids and liquids from the pharynx to the stomach and the esophagus contains the mucosa submucosa and muscular layers that we talked at the beginning in the mucosa layer of the esophagus we have non-keratinized stratified squamous epithelium and it makes sense that it would be stratified because the bolus of food that's passing through the esophagus is not broken down enough yet and it could be abrasive two days or four go swabs now looky here you can see that in mucosa and submucosa are folded in and there is the production of mucous secretions that are released into this oh furgus looming and that makes it easier for the bolus of food to travel down the esophagus now you see here in this transverse section of the esophagus that the lumen of the esophagus is very narrow but this folds made by the mucosa and submucosa layers allow the lumen to expand when the bolus of food passes through histologically the esophagus has two differences when compared to the typical histological breakdown we talked at the beginning the first histological difference we see in the esophagus is that even though the esophagus has both circular and longitudinal muscular layers these muscle layers are not just made of a smooth muscle fibers so what we observe is that in the case of the esophagus the superior part of the esophagus we have a skeletal muscle fibers and as we go down the esophagus the amount of skeletal fibers decreases in the amount of his mouth muscle fibers increases at the inferior portion of the esophagus we just have a smooth muscle you can remember the upper part of the esophagus has a skeletal muscle because you can think of it as a continuation of the pharynx that had skeletal muscle as well and the reason why we have skeletal muscle in the superior region of the esophagus is to aid in swallowing reflex while the increased amount of smooth muscle we see as we travel down the esophagus is responsible for just pushing the bolus towards the stomach via peristalsis the sack on the histological difference we have in the esophagus is that the most outside layer of the esophagus is a fibrous layer called a divin tissue which helps anchoring the esophagus to the nearby structures so the esophagus does not have cells a layer on the outside the esophagus has a divin tissue layer and that's it for this video please make sure to watch the following video at which we start going over the stomach in more details and also please let me know if you have any questions bye