What Really Happens to the Cheeseburger You Just Ate?

Wow, that cheeseburger that I just ate was delicious. Though it is quite easy to eat a couple hamburgers, most never pay attention to what is actually happening while you eat a hamburger or really anything. The process of digestion is quite amazing.

The process all begins when one begins to bite into a juicy, delicious cheeseburger. The lips and cheeks are very important in this process of mastication, or chewing. They help manipulate the hamburger and its add-ons within the mouth and hold it in place while the teeth crush or tear it. The incisors and canines primarily cut and tear the hamburger, while the premolars and molars primarily crush and grind it. Mastication begins the process of mechanical digestion, in which the hamburger particles are broken down into smaller ones.

The tongue moves the hamburger in the mouth and, in cooperation with the lips and cheeks, holds the hamburger in place during mastication. During this process, chewing (mastication) helps to reduce hamburger particles to a size readily swallowed; saliva adds digestive enzymes, water, and mucus that help chemically to reduce food particles, hydrate them for taste, and lubricate them for easy swallowing. Mastication increases the efficiency of digestion because digestive enzymes will act on molecules at the surface of the hamburger particles. The term bolus applies to this mixture of food and solutions until they are passed through the esophagus. These solutions that are a component of bolus are made by the salivary glands, which include the parotoid, submandibular, and sublingual glands. They produce saliva, which is a mixture of serous and mucous fluids. Saliva helps keep the mouth moist and contains enzymes that begin the process of chemical digestion (breaks down hamburger into simple sugars and simple proteins.) The parotoid glands are located just anterior to each ear, the submandibular glands are along the inferior border of the mandible (jaw bone), and the sublingual glands lie immediately below the mucous membrane in the floor of the mouth.

Secretions in the mouth cause the hamburger to begin facing chemical digestion, which breaks the hamburger down into simple sugars and simple proteins. Saliva, which moistens and lubricates the hamburger, contains a digestive enzyme called salivary amylase in the serous part of saliva. Salivary amylase function by digesting the starches that make up the hamburger. Most starches are contained in plant cells, which are surrounded by cell walls composed primarily of cellulose. Though humans lack enzymes to digest cellulose, by cooking and thoroughly chewing the hamburger, it will disrupt the cellulose covering and increase the efficiency of the digesting this delicious hamburger . Mucin is a proteoglycan that gives a lubricating quality to the secretions of the salivary glands. Mucin simply helps to make secretions more lubricating, making it easier for the hamburger to be swallowed once it has been broken down in the mouth enough.

Believe it or not, the process seemed long already, but the hamburger stays in the mouth for very little time at all. Now, the hamburger is off to the esophagus. The esophagus is a muscular tube, that extends from the pharynx (throat) to the stomach. The esophagus will now transport the hamburger pieces from the pharynx to the stomach, with the help of upper and lower esophageal sphincters that regulate the movement of food into and out of the esophagus. In order to get the hamburger through the esophagus, swallowing, or deglutition must take place.

Though swallowing seems quite simple, three separate phases, known as the voluntary phase, the pharyngeal phase, and the esophageal phase all take place. During the voluntary phase, a bolus, or mass of food, is formed in the mouth. The bolus is then pushed by the tongue against the hard palate (hard bone near roof of mouth separating oral and nasal cavities) toward the posterior part of the mouth and into the oropharynx. Next is the pharyngeal phase. During this phase, there is a reflex that is initiated when a bolus of the hamburger stimulates receptors in the oropharynx. This phase of swallowing begins with the elevation of the soft palate, which closes the passage between the nasopharynx and oropharynx. Then, the pharynx elevates to receive the bolus of hamburger from the mouth. Next, the three pharyngeal constrictor muscles contract, forcing the food through the pharynx. As this occurs, the epiglottis is bent down over the opening of the larynx largely by the force of the bolus pressing against it. As the hamburger makes its way down the pharynx, the epiglottis (opening of the larynx) is tipped posteriorly so that the opening into the larynx is covered, preventing the hamburger from passing into the larynx. As the inferior pharyngeal constrictor contracts, the upper esophageal sphincter relaxes allowing the bolus to enter the esophagus. During the esophageal phase, the bolus is moved by peristaltic contractions of the esophagus toward the stomach.

pH is a measure of the acidity or alkalinity of a solution. Solutions with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic (alkaline.) Smooth muscles are necessary to help maintain the dimensions of organs. They are able to stretch are protect the organs from bolus that begins to enter the body through the esophagus. Smooth muscles contracts in a rhythmic peristaltic fashion, rhythmically massaging products through the digestive tract as a result of phasic contraction. The simple columnar epithelium is made up of one layer of cells that are relatively thick and protective of the underlying tissues due to its elongated shape. There main function are in both secretion and absorption. This helps greatly to also prove protection as the hamburger makes its way into the body.

As the hamburger makes its way into the stomach, it is mixed with stomach secretions to become a semifluid mixture called chyme. Hydrochloric acid produces a pH of about 2.0 in the stomach and kills bacteria, and also activates pepsin. Pepsinogen is converted by hydrochloric acid to the active enzyme pepsin. Pepsin then breaks covalent bonds of proteins ( including the bacon, cheese, and beef of the cheeseburger) to form smaller peptide chains. Pepsin's lowpH of about 2.0 kills microorganisms. The intrinsic factor binds with vitamin B12 and makes it more readily absorbed in the small intestine. Gastrin is a hormone the body produces that helps to regulate the stomach secretions as the hamburger is broken down.

Next, what is left of the hamburger makes its way to the small intestine. The small intestine is the major site of digestion and absorption of food, which are accomplished by the presence of a large surface area. Absorbed nutrients that are broken down from the hamburger begin to be transported by the blood capillary network and the lacteal (absorbs dietary fats in the villi ). The mucosa of the small intestine contains four major cells types including absorptive cells, which produce digestive enzymes and absorb digested fats, the goblet cells, which produce a protective mucus, granular cells, which may help protect the intestinal epithelium from bacteria; and endocrine cells, which produce regulatory hormones. The small intestine contains enzymes that digest polypeptide, starch, lipids, sucrose, lactose, and maltose. These cells play a key role in absorption and digestion of the hamburger.

Intestinal secretions lubricate and protect the intestinal wall from the acidic chyme and the action of digestive enzymes. They also keep the chyme in the small intestine in a liquid form to facilitate the digestive process. The epithelial cells in the walls of the small intestine have enzymes bound to their free surfaces that will help in the final steps of the digestion of the hamburger. Peptidases break the peptide bonds in proteins to form amino acids, and disaccharidases break down disaccarides into monosaccarides. Hormones from this part of the intestine will stimulate the liver and pancreatic secretion the hamburger will face next. Both peristaltic and segmental contractions play a key role in moving the chyme (the broken down hamburger and bolus) through the small intestine and mixing the intestinal contents.

Now, the chyme makes its way into the liver. The liver performs important digestive and excretory functions, stores and processes nutrients, synthesizes new molecules, and detoxifies harmful chemicals. The liver produces bile, (yellowish, green fluid) which will neutralize the stomach acid and emulsify ( mix unblended substances) fats from the hamburger. This process will facilitate fat digestion.

Now we are off to the pancreas. Secretions in the pancreas neutralize the acidic chyme that enters the small intestine and stops pepsin digestion and provides the proper environment for the digestion for the function of pancreatic enzymes. These enzymes are present in exocrine secretions, and without them being produced by the pancreas, lipids, proteins, and carbohydrates all from the one hamburger eaten would bot adequately digest. In all the pancreas will play an important role in digesting protein, starches, lipids, nucleic acid, as well as neutralizing stomach acid.

Finally, the hamburger must enter the large intestine. The remaining chyme from our delicious hamburger must now make its way through the cecum, rectum, and anal canal. The cecum is the end of the large intestine and is where the large and small intestines meet at the ileocecal junction. The hamburger will make its way though this 6cm sac and into a tube about 9cm long called the appendix. Next, it will go through the colon, which is about 1.5-1.8m long. The mucosal lining of the colon contains numerous straight tubular glands called crypts, which contain many mucus-producing goblet cells. During this stage, the chyme is converted to feces, which is stored until it is released by the process of defecation. Next, the feces will reach the rectum, a muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal. The muscular tunic is a smooth muscle and it is relatively think in the rectum compared with the rest of the digestive tract. Lastly, the leftovers make there way to the anal canal, which ends at the anus. This canal will release feces as the external anal sphincter, which prevents the movement of feces out of the rectum and through the anal opening, is voluntarily relaxed by the eater.

The large intestine plays a big role in the final steps of the digestion of this hamburger. Besides the key roles of the structures above many processes are undergone in this intestine. The process of defecation occurs when the eater of this hamburger releases the wastes that are left over in the rectum through the anal opening from the digestive tract. Mass movements in the large intestine will begin to propel the colon contents a considerable distance toward the anus. As the contents change to feces in the rectum, defecation reflexes work with the local and parasympathetic reflexes causing strong contractions. Now once the internal anal sphincter is relaxed due to action potentials from the spinal cord, and the external sphincter is relaxed voluntary under conscious cerebral control, feces from the hamburger wastes will make their way through the rectum with abdominal pressure and be released through the anal opening in a matter of minutes.

The once delicious hamburger is now digested in the body, and the wastes are gone with a flush of a toilet.