Friday, March 17, 2017
A In Depth Look at Digestion
A In Depth Look at Digestion
By: Deneale K. Williams
From page 476 and forward of the text book we learn that ingestion is just another word for eating. Digestion is the breakdown of the food small enough for the body to absorb, into what we know as molecules. Absorption is when the food is transferred into the blood stream. This is the uptake of small nutrient molecules by cell lining in the digestive tract. Elimination is just like it sounds, the body getting rid of waste. The disposal of unwanted, unneeded materials left over from food. These are the four stages of food processing.
Now as you know, to begin the entire process, you must begin by what? Chewing. This is considered the mechanical beginning of digestion.
Once the food hits the stomach it begins with chemical digestion, the breakdown of food by digestive enzymes.
Dismantling food molecules is necessary for two reasons: they must be broken down for the cells to absorb, they are currently too large. Some is dismantled and used to build proteins. Your body does not directly use the protein that you eat but instead dismantles it and uses the pieces (amino acids) to build its own new proteins.
Chemical digestion happens by way of hydrolysis. These are chemical reactions by large biological molecules by the addition of water molecules, which require enzymes. Food molecules that are polymers, such as carbohydrates and proteins, are broken down via chemical digestion into monomers.
Did you know that there are different digestive compartments? It is true. “The simplest type of digestion occurs within a cellular organelle. In this process, a cell engulfs food by phagocytosis, forming a vacuole. This food vacuole then fuses with a lysosome containing enzymes, forming a digestive compartment. As food is digested, small food molecules pass through the vacuole membrane into the cytoplasm and nourish the cell.”
We as humans, and the earthworm have a digestive tube with two separate openings our mouth at one end and an anus at the other end. Such a tube is called an alimentary canal, or digestive tract. The food we eat moves in just one direction through specialized regions that digest and absorb nutrients in a stepwise fashion. This adaptation allows for much more efficient food processing. Just like an assembly line. Undigested wastes are eliminated from the alimentary canal as feces by way of the anus.
“The human digestive system consists of an alimentary canal and several accessory organs (salivary glands, pancreas, liver, and gallbladder). The accessory organs secrete digestive chemicals into the alimentary canal via ducts (thin tubes). The human alimentary canal totals about nine meters (thirty feet) in length. Such a long tube fits within a human body because it folds back and forth over itself with many switchbacks.”
“The alimentary canal is divided into specialized digestive organs along its length: mouth (oral cavity) → pharynx → esophagus → stomach → small intestine → large intestine (colon and rectum) → anus.”
But let us not forget where it all begins! With our mouth, our salivary glands, our tongue, our palette and our lovely and favorite taste buds. And did you know, the more wear and tear you put on those lovely teeth, you can wear them out? Of course, you do! You go to the Dentist! But did you know that chemical digestion begins in the mouth? It does with the salivary glands who help to begin the process after you have started chewing.
From there your pharynx and esophagus work together. Your pharynx is located in your throat is an intersection of the pathways for swallowing and breathing. The pharynx connects the mouth to the esophagus (part of the digestive system). But the pharynx also opens to the trachea, or windpipe, which leads to the lungs (part of the respiratory system). When you’re not swallowing, the trachea entrance is open and you can breathe, which is also located by your voice box. Air enters the larynx (also called the voice box), flows past the vocal chords, through the trachea, and to your lungs. Men generally have larger larynxes and therefore more prominent Adam’s apples formed by cartilage on the outside of the larynx.
This is how the Heimlich maneuver was created, when the food has been allowed to go down the wrong pipe, wind forces it out, when chocking occurs.
Your esophagus is a muscular tube that connects the pharynx to the stomach. Your esophagus moves food by peristalsis, alternating waves of muscular contraction and relaxation that squeeze the food ball along the esophagus.
The stomach is a large organ that can sustain you for several hours. The stomach can hold more than half a gallon of food or drink.
“The cells lining the stomach’s interior secrete a digestive fluid called gastric juice. Gastric juice is made up of a strong acid, digestive enzymes, and mucus. The acid in gastric juice is hydrochloric acid, and it is concentrated enough to dissolve iron nails. (You read that right! Your own body could actually dissolve iron nails!!) Gastric juice also contains pepsin, an enzyme that breaks proteins into smaller pieces.”
“When the stomach mixes up all of the gastric juices it is called chyme. At the downstream end of the stomach, a sphincter (a ring of muscle) works like a drawstring to close the stomach off, holding the chyme there for about two to six hours. The chyme leaves the stomach for the small intestine one squirt at a time. Continued contractions of stomach muscles after the stomach is empty causes the “stomach growling” that lets everyone know you are hungry.”
Gastric juice can be harmful, if you have ever heard of heartburn. This is a backflow up the esophagus. It can be quite annoying and even painful, and it can even degrade your esophagus over time, if not tended to. You may have heard it referred to as acid reflux or even GERD.
The small intestine is not small in length, it is small in diameter. It is usually about twenty feet long. It is two-point cm across, the large intestine is five cm across. The small intestine is necessary for digestion and absorption of nutrients into the bloodstream. Normally it takes approximately six hours to pass into the small intestine. The small intestine takes over with an arsenal of enzymes that dismantle the food molecules into smaller molecules. These enzymes are mixed with chyme in the first twenty-five cm or so of the small intestine, the region called the duodenum.
“The duodenum receives digestive juices from the pancreas, liver, gallbladder, and the intestinal lining. The pancreas is a large gland that secretes pancreatic juice into the duodenum via a duct. Pancreatic juice neutralizes the stomach acid that enters the duodenum, and it contains enzymes that aid in digestion. As peristalsis propels the mix along the small intestine, these enzymes contribute to the breakdown of food molecules.”
“Bile is a juice produced by the liver, stored in the gallbladder, and secreted through a duct into the duodenum. Bile contains salts that break up fats into small droplets that are more susceptible to dismantling by digestive enzymes.”
If you have ever thrown up to the point that you have ever emptied your stomach to the point that you have puked yellow and tasted the nastiest taste ever, you have herby tasted bile. You had better be wrinkling your nose right now!
Five feet in length, the large intestine is shorter than the small intestine. But as I have explained earlier, you now know, it is wider.
Nearby the large intestine, is the appendix. If you know what is at the end of the book, what is it? The appendix. And what do many people get removed? Their appendixes, and their gall bladders. I have neither one. It is not a good thing to be without though, let me tell you. It causes your digestive tract to work differently no matter what they try and tell you.
“The appendix contains white blood cells that make minor contributions to the immune system. If the junction between the appendix and the large intestine becomes blocked, appendicitis—a bacterial infection of the appendix—may result. Emergency surgery is usually required to remove the appendix and prevent the spread of infection.”
The main portion of the large intestine is the colon. The primary function of the colon is to absorb water from the alimentary canal. About ninety percent of the water it contains is absorbed back into your blood and tissue fluids, with the small intestine reclaiming much of the water and the colon finishing the job.
The rectum, the last six inches on the large intestine stores feces until they can be eliminated. Contractions of the colon and the rectum create the urge to defecate. Two rectal sphincters, one voluntary and the other involuntary, regulate the opening of the anus. When the voluntary sphincter is relaxed, contractions of the rectum expel feces.