Digestion organs: A long road
Our digestive system makes up a real route for food. Clearly signaled, with indications for the advancement or stopping of the food bolus, it covers great part of our body, involving several organs.
The digestive system is formed by a group of conduits, adapted for different functions. Furthermore, it is also made up of a series of attached glands that secrete substances that ease digestion of foods. As we already mentioned, it is a true route, with well defined stops. The first of them is the oral or buccal cavity, which is comprised of organs like the tongue, salivary glands, mucosal walls like the palate and teeth, among other tissues and structures. Its most important function is the ingest and fragmentation of foods.Then, the journey continues through the first portion of the digestive tube, which is considered only a passageway. This way, the food flows through the pharynx and esophagus without great changes until it meets the next stop, which is comprised of the stomach, small intestine and large intestine. Great transformations take place in this area because the ingested food is broken down to its most basic components in order for our body to be able to capture what is necessary and discard the residues through the anal canal.
Oral cavity
The entry way of all foods is the oral cavity. The ingest and fragmentation of foods is performed in it, as well as its first chemical transformation (the moment it joins saliva).The mouth is the starting point of the entire digestive process. It receives the food we ingest and, with the help of diverse structures lodged within it, is in charge of transforming the substances into a bolus (food bolus) capable of continuing its passage through the first portion of the digestive tube. It is characterized for having soft walls, besides having glands that secrete saliva, liquid that humidifies and eases the progress of food.
The lips
They are two structures (one superior or upper and another inferior or lower) made up of skin and muscle which mark the entrance to the oral cavity. The skin of the lips is perfectly adapted to receive certain stimuli and protect the body. It is thinner, richly irrigated and innervated in order to perceive the temperature and texture of foods with greater finesse. The motion and opening of the lips is conditioned by a series of muscles controlled by the facial nerve. The most important of them is a circular shaped one dubbed orbicular, which works alongside the complex muscle network of the face, mandibles and superior part of the neck.
Among the functions of the lips we find, through the closing of the mouth, preventing the exit of food and liquids during chewing. They also participate in vocalization, facial expression and communication, besides helping suck, kiss and whistle.
Denture
The same as the cutlery we use to eat, teeth help break apart, tear and crush foods, easing their passage through the digestive tube. From gestation, after the second month, the outlines of our first teeth begin to take shape. However, they will not be definite. Human beings, throughout their lives, have two dentures, one temporary and another one permanent. The first of them, made up of the so-called “baby teeth”, begins to appear after the sixth or eighth month of life. It only has 20 pieces (the maxillary is smaller at that age), which are characterized for being small and with a shallow root. Baby teeth emerge from the gums in an ordered fashion, from the central incisors to the second molars. Approximately at the age of six, the changing or shedding of teeth begins with the falling out of temporary pieces and the appearance of definite teeth. Permanent dental pieces can appear until the age of 21 (including the third molars). The first tooth to appear is the first molar. Then, in a continuous process related to the grow of the mandible (jaw), the remaining pieces appear.
Dental structure
A tooth, in its internal part, is made up of a series of layers that grant it greater stability, flexibility and support.Each tooth is made up of a root (part incrusted into the maxillary) and the crown (visible portion). This last one is covered by an enamel, substance considered to be the toughest and heaviest of the human body, which is mostly formed by calcium phosphate crystals. Continuing inward, in what could be considered the “skeleton” of the tooth (it corresponds to 40% of the dental structure) we find dentine, white-yellowish tissue that needs a constant supply of blood in order to stay alive. One of its main characteristics is that it has elasticity in order to cushion the strength of the bite, serving as support between the crown and jaw. At the same time, dentine encloses the innermost area of the tooth: the pulp. It has a consistency similar to gel, made up of proteins, carbohydrates and water and also has a rich network of blood and nerve vessels that enable teeth to perceive changes in temperature and pain.
Anatomic and functional characteristics
All teeth have the same composition. They are hard structures, formed by several layers and strongly set within the maxillary. But if we open the mouth, we will notice they have some particular characteristics. Teeth located in the anterior part of our denture are dubbed incisors. They have a sharp edge shaped like a chisel, specially adapted to tear food. They are accompanied on both sides by the canines, teeth that have a rounded tip that serves to hold and rip. At the end of the mouth we find the premolars and molars. These are the biggest dental pieces and they have two or four points that ease the mastication (chewing) and grinding up of food in order to turn it into the mass that will later pass on to the digestive tube.
Chemical transformation
Thanks to the teeth, we can chew food until we turn it into small pieces. However, this transformation is not enough because food needs another component to advance through the digestive tube.This is how an aqueous substance known as saliva is produced from the salivary glands, which produces the first chemical changes to the foods consumed.
Saliva is made up of 99.5% water and 0.5% electrolytes, vitamins, enzymes and cellular material.There are minor and major salivary glands. The first ones (over 700) are dispersed in the mucusa of the superior digestive way and secrete saliva through independent ducts. The group of major glands is comprised of three pairs of glands: parotid, sublingual and submandibular.The parotid gland is the largest; it weighs 25 to 30 grams and is located in front of the ear, in the parotid fossa. It produces a great amount of saliva (approximately 45% of the total amount), which is excreted by the parotid or Stensen’s duct.The sublingual salivary gland, as its name indicates, is set below the tongue and has nearly 20 ducts through which it secretes saliva. The last pair is made up of the submandibular gland, also known as submaxillary, which is lodged at the bottom of the inferior part of the mouth.
Succession of passageways
After swallowing the food, it is lead through the superior digestive ways. Both the pharynx and esophagus make up the first stretch of the road covered by food during the digestive process.
The pharynx is a conduit located behind the nostrils and mouth, inside the neck. It measures nearly 12 centimeters and connects the nose to the larynx and the mouth to the esophagus.Its insides are covered by a mucosa that produces a lubricant mucus. It also has important muscles (constrictors and elevators) that actively participate during deglutition (swallowing) of the food bolus.
Next, we find the esophagus, muscular conduit that reaches 25 centimeters in an adult and is in charge of direct transport to the stomach. It goes from the inferior area of the neck, goes down by the thorax (in front of the spine) and pierces the diaphragm to connect with the stomach in the superior area of the abdominal cavity.Both at the beginning and end of this structure we find true “passage valves” called sphincters that open and close in accordance with the entry of food. In the superior part, we find the cricoesophageal sphincter (upper esophageal sphincter) while in the final portion, precisely in the junction with the stomach, we find the lower (or inferior) esophageal sphincter.
The musculature of the esophagus is specially adapted to compress and dilate its walls, easing the advancement of food towards the stomach. Its flattened appearance changes when the food bolus circulates through it.
