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The Digestive System
Transcript of The Digestive System
By Jess B.
The part of the digestive system that everyone is the most familiar with would have to be the mouth. The only problem is that few people realize that the mouth is actually a part of the digestive system. The tongue, teeth, salivary glands, uvula, and tonsils are all part of the mouth. It functions as a place to receive food and for mechanical digestion, also known as chewing. The first stages of digestion start in the mouth. Some starches and sugars can actually be digested solely inside of the mouth, with little help of the rest of the digestive system. Other than digestion, the mouth also provides an airway for the respiratory system and forms the words so that humans are capable of speech. A lot of different things happen that have to do with the mouth - eating, speaking, and kissing are all good examples of these things!
The teeth work to chew our food until they are in small enough pieces that we can swallow them. When we're young, we have a set of 20 "baby" teeth but as we grow, they are replaced with a set of 32 "adult" teeth. The third pair of molar, called wisdom teeth, don't always grow in and sometimes have to be surgically removed.
A tooth is made up of two different parts. The crown has a layer of enamel (a very thick covering of calcium compounds) and an inner pulp that contains the nerves and the blood vessels. The root is mostly just dentin and nerve cells that attach the tooth to the jaw bone.
Dental caries, more commonly known as cavities, can erode teeth and happens when the mouth metabolizes sugar. Gingivitis in the inflammation of the gums that can spread all the way to the tooth socket. This can cause periodontitis, which is the loss of a bone and the loosening of teeth.
Salivary glands are the glands that make the saliva and send it up to the mouth. There are three pairs of salivary glands in the human body. One pair is right in front of the ears and is specifically called the Parotid Gland. The Sublingual Gland is located under the mouth and to the sides of the tongue. Last but not least, the Submadibular Gland is along the inside of the jaw bone. These glands also swell when someone, generally a small child, has the mumps.
The saliva created by the salivary glands contains an enzyme by the name of salivary amylase. This enzyme is what starts the process of digesting starch in the mouth.
Anchored to the bottom of the throat, the tongue is a strong muscle with many different purposes. One of the things that it allows humans to do is taste. When the food touches the tongue, nerve impulses are sent up to brain which in turn, activates the taste buds. From there, the taste of it can warn the person eating it if it has gone bad.
One of the other purposes of the tongue is to manipulate food while it's in the mouth. Due to the high number of nerves in the tongue, it can move the food to get chewed by the teeth without actually getting bitten by them. When the food has been properly chewed, the tongue directs it to the back of the mouth.
Of course, the tongue also helps us form words properly, along with other things - at least one of which is rather enjoyable.
Top of the Mouth
The roof of the mouth is what separates the nasal cavity from the oral cavity. There are two separate parts to the top of the mouth. One of which, the hard palate, is at the front of the mouth and contains several bones. The second part, the soft palate, doesn't have any bones but instead is made entirely of muscle. The soft palate also includes a finger-shaped projection called the uvula and the tonsils.
The tonsils, while not necessary, help protect the body from infections. However, tonsillitis is a well-known infection in the tonsils. As this infection can spread to the middle ears if not treated, the tonsils may be removed if this infection happens repeatedly.
This is the part of the mouth that receives air and food from the mouth and nasal cavity. It starts to take the food into the esophagus and this is where one swallows their food. Swallowing is a reflex action, meaning that one doesn't think about doing it. The actions of it forces the food from the pharynx down the esophagus. Normally, the air passages will be blocked whenever one swallows but this isn't always the case. Sometimes, the food will enter the trachea instead. If this happens then normally one starts to cough, forcing the food out of the trachea and into the pharynx once more. When we swallow, we do not breath because our air passages are blocked off.
The esophagus is a muscular tube that goes from the pharynx through the thoracic cavity and abdominal cavity until it joins up with the stomach. The food, broken down into a ball called a bolus, opens up the normally collapsed esophagus after its swallowed. The bolus is moved along through a series of contractions called peristalsis until it reaches the stomach. Near the bottom of the esophagus, there is an area of high pressure called a valve that prevents any food from going back up the esophagus. However, if the bolus causes irritation to the lining of the stomach than it may be rejected and thrown out of the body through vomiting.
Did You Know?
Peristalsis is so strong it forces the food to our stomachs even when we're upside down.
The stomach is a strong, muscular sac that's located in the left abdominal cavity. It has a crescent shape to it and is hollow. The wall of the stomach is protected by a thick layer of mucus. The inner layer of the stomach has wrinkles called rugae that allows the stomach to stretch when full, and grip and move food around during digestion.
Once the stomach is filled with food, it sits there for one to two hours. Both mechanical and chemical digestion occurs in the stomach. Gastric juices, which count towards the chemical digestion and is made out of pepsin, hydrochloric acid, and mucus. The hydrochloric acid will break down connective tissue of meat and activates pepsin. The bolus is turned into chyme by a combination of both of them as fatty acids and some proteins are digestion.
The small intestines are a group of small tubes that loop around each other so that they can fit inside of the abdominal area. In an adult, the small intestines would be between eighteen and twenty three feet depending on their size. Substances from accessory organs work to break down the thick liquid-like chyme in this region, and nutrients are also taken from the chyme here. In a single day, they process about 2.5 gallons of food. The small intestine is broken into three different parts - the duodenum, the jejunum, and the ileum.
Laying on the back of the abdominal wall, the pancreas is an elongated and partially flattened organ with both endocrine and exocrine functions. It secretes insulin in order to regulate the amount of blood glucose in the body. However, it also produces pancreatic juices that help in digestion. These juices contain sodium bicarbonate and digestive enzymes. Sodium bicarbonate is what neutralizes chyme. The digestive enzymes contain a more basic pH, which neutralizes the acids that are in the stomach. These enzymes consist of pancreatic amylase which digests starch, trypsin which gisets protein, and lipase which digests fat. These enzymes can be taken by mouth if a thick mucus blocks the pancreatic duct in cystic fibrosis.
Approximately the shape of a pear, the gallbladder is a muscular sac attached to the surface of the liver. It absorbs the excess bile that's made by the liver and stores it. The bile will then become a thick, mucus-like material as the water in it is reabsorbed by the gallbladder. This material will then travel to the duodenum when it's needed through the common bile duct. Sometimes, the gallbladder will create gallstones. These gallstones are made by the cholesterol from the bile, which forms crystals inside of the gallbladder. The gallbladder is removed if these crystals block the common bile duct when they're moving from the gallbladder.
Other than the skin, the liver is the largest organ in the body. It consists of two main lobes, but they contain about 100 000 lobules and these lobules serve as important structural units. The liver is located right underneath the diaphragm in the abdomen.
The liver has many different functions, but a few are more important than others. It detoxifies blood by removing and metabolizes materials that are poisonous to the body before they pass into the intestines. It stores iron and vitamins A, D, E, and K in the body. Plasma proteins, like albumins and fibrinogen, are produced in the liver from amino acids. It has the ability to sdtore glucose after eating, and then breaks down that glucose to maintain glucose concentration levels between eating periods. Urea, a nitrogenous waste product from amino acid breakdown, is removed in the liver. Also, it removes a breakdown product of hemoglobin called bilirubin and excretes it into the bile.
The stomach is separated into four different regions. The cardia leads into the larger part of the stomach, which is also known as the body and is the largest part of the stomach. This leads into a dome-shaped region known as the fundus. The pylorus is a funnel-shaped region that connects the stomach to the duodenum. It contains the pyloric sphincter that controls the movement of chyme from the stomach into the duodenum.
The duodenum is the first of three parts that make up the small intestine. It's rather small compared to the rest of the small intestine at 25 centimetres long and about 5 centimetres in diameter.
It mostly breaks down the chyme with the help of enzymes from thee accessory organs. These enzymes are pumped into the duodenum almost continuously. Also, bile inside of the duodenum comes from a duct connecting to the liver and emulsifies fat - causing it to disperse in water.However, it also regulates the amount of food that's coming out of the stomach at any given point in time. A lot of the acids are neutralized in this portion of the intestines from secretin and cholecystokinin.
The jejunum is the middle section of the small intestines. It's mostly used for the absorption of nutrients from the chyme. The enzymes that were previously pumped into the small intestine now make the chyme primed to have its nutrients pulled out of it. All of the nutrients from the food then goes to liver with the exception of fats which go to the lymph. By this point in time, most of the food has been completely digested, with the exception of a few nutrients and the water that would have been originally in the food.
The ileum is the third and last section of the small intestines. Its walls are made up of tiny little folds with what are called villi on them. This creates a large surface area in the intestines than in the other two sections. However, while prominent in the ileum, these villi are all throughout the entire small intestine. Absorption of the products of digestion continues on here, but this is also where the absorption of enzymes happen. The same enzymes that had been previously pumped into the system in the duodenum. This is the last step of digestion before the chyme is passed onto the large intestine.
Wall of the Digestive Tract
The walls of the digestive tract are made up of four different layers known as mucosa, submucosa, muscularis, and serosa. The muscosa layer is a layer of epithelium that's supported by connective tissue. It contains glandular epithelial cells that secrete digestive enzymes and goblet cells that secrete mucus. The submuscosa layer is a band of loose connective tissue with blood vessels, and help protect against disease. Two layers of smooth muscle make up the muscularis layer, with one layer encircling the gut and the other laying in the same direction of the gut. The serosa is the outermost layer of the digestive tract and the thinnest. It secretes a serous fluid that keeps the organs moist and allows them to slide against each other.
The epiglottis is located in the pharynx area and covers the glottis. The glottis is the opening to the larynx, which is otherwise known as the voice box. The folds of the glottis vibrate because of the larynx, and because of that, we have a wider range of sounds that we can make. Buzzing sounds in particular. Learning how to control the glottis is what allows people to speak in dialects separate from one's own. It also helps with pronunciation of words. The epiglottis is what normally stops the food from going down the trachea in the digestive system.
The large intestine includes the cecum, the colon, the rectum, and the anal canal. It's 6.5 centimetres in diameter, but is only 1.5 metres long. That may seem like it's rather large but it isn't when it's compared to the small intestine. Which is contrary to the way that both of the intestines have been named. It absorbs water, salts, and a few vitamins. This is the last stage of digestion and the digested food leaves the body through the anus.
The cecum lies below the junction with the small intestine and is called the blind end of the large intestine. The cecum is the first region of the large intestine and is connected to the small intestine. Only the first section that's attached to the small intestine is known as the cecum.
The cecum includes a small projection called the appendix that has a worm-like appearance. The appendix isn't a necessary organ, and is removed in the case of appendicitis. Scientists still aren't completely certain what the appendix is used for, but it's assumed that it's used to fight off some sort of infection.
The colon includes the rest of the large intestine and surrounds the small intestines. It's a long, hollow tube that's about 6.5 centimetres in diameter. Bacteria, mostly E. coli, fills the entire colon and digest the fecal matter, releasing the vitamins from it into the body. The wall of the intestines absorb water, nutrients, and vitamins before directly depositing them into the bloodstream. It is only now that everything that the body can use has been entirely stripped away from the food.
The rectum is the last 20 centimetres of the large intestine. It consists of a short, muscular tube that connects directly to the anus. Feces will collect here until the pressure on the walls of the rectum send nerve impulses to pass to the brain. The brain will then send messages to the anus, which tell it to relax enough to let the feces out of the body.
The anus is where defecation, or the expulsion of feces, occurs. It's an extension of the rectum, and is only about 12.5 centimetres long. Most of the time, it is kept closed through sphincter muscles. However, it opens during the expulsion of feces or it can be opened through will. The feces that are released are three-quarters water and one-quarter solids. Bilirubin causes the brown colour of the feces while the odor is because of the bacteria in the nondigested remains.