All physiological, chemical, and anatomical processes in every cell and tissue, and every organ in the body is completely dependent upon the digestive system to supply nutrients and carry away waste and toxins.
The digestive system can be viewed as one long “tube” from lips to anus. Nutrition is absorbed into the blood stream and wastes are removed from the body via this “tube.”
Material is moved through the digestive system by wave-like muscular contractions called peristalsis.
From Top To Bottom
(No pun intended.)
Mouth & Esophagus
In the mouth, we have the teeth that grind and chew our food, three salivary glands that secrete saliva (digestive juices), and the tongue that pushes food in and out of the path of our teeth and assists in mixing the food with saliva.
Approximately 1-2 pints of saliva are secreted into the mouth every day. The saliva contains, among other things, ptyalin, which converts starches into grape sugar. It is alkaline, which helps to neutralize acids, and it moistens and softens the food for passage through the esophagus, the channel that carries food from the mouth to the stomach.
The stomach is highly acidic, (as acidic as battery acid.) Its walls secrete hydrochloric acid, pepsin, and chemicals for the purpose of breaking down proteins. The stomach also produces a thick layer of mucus to prevent these acids from digesting the stomach itself.
Food is mixed with stomach acids by muscular contractions in the stomach. The stomach “kneads” the food and its fluids together into a semi-fluid substance called chyme.
It is estimated that there are 10-20 pints of gastric juices secreted by the stomach every day. The acid pH of the stomach restricts the action of saliva upon the sugars and starches in the food.
The stomach is capable of retaining considerable amounts of food. The stomach normally completes its digestive action and is emptied of its contents every 4-5 hours. The semi-fluid chyme is expelled through the lower end of the stomach (the pylorus) into the duodenum, the upper part of the small intestine.
The stomach will only release its contents when all the contents are completely ready. If a meal is eaten before the previous meal has been digested, the previous meal will stay in the stomach until the new meal is completely digested.
Other problems that can occur in the stomach come when food is not chewed properly. When this happens, the stomach has to work harder. It requires more fluid, and more muscle contractions to produce chyme in a consistency suitable for expelling into the small intestine.
Liver & Gallbladder
The liver is responsible for a great number of physiologic functions. One of its main functions is to neutralize toxins from the bloodstream. As waste and toxins enter the bloodstream, they are carried to the liver, where the liver converts them into either urine or bile. Urine is sent to the kidneys, whereas bile is stored in the gallbladder.
The gallbladder is a small sack located on the back-side of the liver. Bile is a golden-green fluid that acts as a natural laxative by stimulating peristaltic muscular contractions along the length of the small and large intestine.
Bile also emulsifies fats by binding to a molecule of fat on one end, and binding to a molecule of water on the other end, which blends fats and waters together. This brings fat molecules into contact with water-soluble enzymes that assist in breaking them down.
When fats in our food are detected by the brain, the gallbladder is stimulated, pushing bile out through a tube and into the pancreas, where it mixes with pancreatic juices and enzymes, and together they are secreted into the duodenum where they mix with chyme.
If this duct (the “common bile duct”) becomes obstructed, the bile is absorbed into the bloodstream, causing the skin to turn a slightly yellowish color, and indicating that a jaundiced condition is taking place in the tissues of the body.
Bile is alkaline, which prevents fermentation of chyme in the intestines, and neutralizes acids from the stomach.
The pancreas is both a gland AND an organ. It is responsible for two main functions. With regards to digestion, the pancreas secretes pancreatic enzymes that assist in breaking the elements in our food down into smaller molecules so they can be absorbed by the bloodstream. It also secretes bicarbonate, a highly alkaline juice which, along with bile from the liver, neutralizes stomach acid.
This is the name given to a very small area at the top of the small intestine, and just past the stomach. Almost immediately upon entering the duodenum, chyme is mixed with secretions from the liver/gallbladder and the pancreas. These secretions enter the duodenum about three inches below the pyloric valve (the bottom valve of the stomach that closes it off from the small intestines) through a shared duct, called the “common bile duct.”
The small intestine is approximately 23 feet long in an adult.
The small intestine is where the majority of chemical digestion and absorption of food takes place.
In the small intestine, proteins that were broken down by the stomach are now divided into amino acids. Fats are broken down into fatty acids and glycerol. Some carbohydrates are broken down into simple sugars (glucose.) Other carbohydrates are passed undigested into the large intestine where they are broken down by bacteria.
Digested food is now able to pass through the walls of the small intestine into the bloodstream where its nutrients are carried to each and every cell of the body.
The small intestine is lined with wrinkles, or folds that have packed across their surface, tiny projections, like fingers, called villi. Each of these finger-like projections contain even more tinier finger-like projections called microvilli. This increases the amount of surface area available for the absorption of nutrients. Each one of these villi has a network of capillaries and lymphatic vessels close to the surface to make absorption into the bloodstream very quick, and also slows the passage of food through the small intestine, allowing for more opportunity for nutrients to be absorbed.
The lining of the small intestine is full of a variety of glands. These glands are responsible for the secretions that assist in breaking down all the nutrients necessary for the body’s proper function. Therefore, it is imperative that the digestive system be kept clean, to ensure that the maximum amount of nutrition can be extracted from our food, and to prevent the reabsorption of waste materials that accumulate in the bowels for disposal.
Food that remains undigested and unabsorbed pass into the large intestine.
The large intestine (also called the bowel, or colon) is the last section of the digestive system. Its main function is to absorb water from the remaining food material and passing waste material from the body.
The large intestine is divided into four sections: the cecum, appendix, colon (ascending, transverse, descending, and sigmoid portions), rectum, and anal canal. It is approximately 5 feet long.
Food passes from the small intestine to the large intestine through a one-way valve called the illeocecal valve. The cecum is a section of the large intestine just past the illeocecal valve. When the cecum is filled, the illeocecal valve closes and the walls of the cecum contract, forcing the food into the ascending colon.
The appendix is a narrow snake-like projection that is attached to the base of the cecum. It secretes immune cells important in the proper functioning of the immune system. This is fluid is secreted as a means of defense against any waste materials that may contain toxins, germs, bacteria, parasites, and other contents that are hazardous to the human body.
Just as its name suggests—the ascending colon moves food upwards from the cecum to the transverse colon. Unlike the other portions of the large intestine, the ascending colon has not only peristaltic muscular action, it also has ANTI-peristaltic action. This means it not only moves food upwards, it also moves food downwards. This creates a “kneading” action that moves food back and forth, delaying its passage into the transverse colon. This allows for greater absorption of nutrients.
While the first parts of the large intestine are responsible for the continued absorption of nutrients, and the absorption of water, the main function of the descending colon is to store waste until it can be removed from the body in solid form.
As water and nutrients are absorbed along the length of the large intestine, the chyme gradually solidifies as it moves into the descending colon. The resulting substance is called feces.
Feces consists of water, undigested foods, waste materials from cellular metabolism, undigestible cellulose, bile, digestive enzymes and fluids, dead cell material, and toxins the body refused to absorb. The color is largely caused by pigments from bile, and the presence of dead red blood cells.
The sigmoid colon expels solid and gaseous waste from the digestive system. Its curve allows it to store gas in the upper arched portion, enabling the colon to expel gas without excreting feces at the same time.
The rectum is the final straight portion of the large intestine. It is about 5 inches long. As feces begin to move towards the rectum, nerves signal the desire to defecate. If the urge is not acted upon, the material in the rectum is often moved back into the colon where even more water is absorbed, making the feces harder.
If defecation is delayed for a prolonged period, constipation and hardened feces results. If it is delayed frequently, the sensory nerves become dulled, which prevents the individual from knowing that they need to have a bowel movement. Always respond to the “call of nature” as soon as possible.
The large intestine houses over 700 species of bacteria that perform a variety of functions. The large intestine absorbs some of the waste products produced by the bacteria that inhabit this region. These bacteria produce a large amount of vitamins, especially Vitamin K and biotin (a B-Vitamin.) Anyone being treated with antibiotics, which also destroy these beneficial bacteria, may become vitamin deficient.
Other products that come from intestinal bacteria include gas. Gas is produced as a result of fermentation of undigested polysaccharides. Intestinal bacteria also produce antibodies that aid in preventing infection or pathogenic invasion of the body.