Digestive System
Major Functions
- Take in food through the mouth
- Breakdown food through mechanical and chemical digestion
- Absorb nutrients through walls of intestine
- Eliminate waste through fecal matter
- Mouth- The mouth is the beginning of the digestive tract. Digestion starts when the first bite of food is taken. Chewing breaks the food down into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.
Esophugus- The main function of the esophugus is to carry food, liquids, and saliva from the mouth to the stomach.
Stomach- The stomach receives food from the esophugus. As food reaches the end of the esophugus, it enters the stomach through a muscular valve called the lower esophageal sphincter. The stomach secretes acid and enzymes that digest food.
Small Intestine- The main function of the small intestine is absorption of nutrients and minerals from food.
Liver- The main function of the liver is to process the nutrients absorbed from the small intestine also plays an important role in digesting fat.
Pancreas- The pancreas serves two primary functions. It makes enzymes to digest proteins, fats, and carbs, in the intestines. It also produces the hormone insulin and glucagon.
Large Intestine- The major function of the large intestine is to absorb water from the remaining indigestible food matter and transmit the useless waste material from the body.
Gallbladder- The gallbladder holds bile produced in the liver until it is needed for digesting fatty foods in the doudenum of the small intestine.
- Path of digestion
When you take that first bite of food with your teeth, digestion begins. Food is first crushed up by the teeth. Teeth such as the incisors cut the food into bite size pieces. Then the canines slash the food into even smaller pieces. Premolars and molars grind the food and the saliva moistens the food. There are enzymes that speed up the chemical reactions in the mouth, such as separating sugar from starch. The saliva in your mouth also help break down carbohydrates. After the food is broken down, your tongue pushes the food into the back of your mouth, where it goes to the esophagus. This muscular tube, that is connected to the stomach, helps food travel down to the stomach. Then the food reaches the stomach. Enzymes in the stomach and other digestive juices come and help the stomach digest the food. Hydrochloric acid, one of the stomachs main enzymes, helps break down proteins and fats. After food sits in the stomach for about four hours, the food, now chyme moves into the small intestine. As food travels into the small intestine, the liver and the pancreas break down the chyme with the enzymes they have made. The liver makes an enzyme called bile. Bile is used to break down fats. The pancreas makes enzymes that break down starches, proteins, and fats. As the chyme moves through the small intestine, there are little finger like shaped linings on the wall of the small intestine. These are called villi. Villi is used to help absorb nutrients for the body. Then the chyme is passed to the large intestine, where water is absorbed from the chyme. From there it is passed to the rectum, and then the anus. The anus then expels the chyme from the body.
- Chief Cells and Parietal Cells
Chief Cells- The chief cells synthesize and secrete pepsinogen, the precursor to the proteolytic enzyme pepsin.
Parietal Cells- Parietal cells secrete hydrochloric acid and instrinsic factor.
Alkaline Mucus- Alkaline mucus in the stomach increases in thickness when the stomach is distended. The pH level of the mucus also plays a role in its viscosity, as higher pH levels tend to alter the thickness of the mucus, making it less viscuous.
- Duodenum- The duodenum is the first and shortest segment of the small intestine. It receives partially digested food from the stomach and plays a vital role in the chemical digestion of chyme in preperation for absorption in the small intestine.
Jejunum- The second (middle) section of the small intestine is a coiled tube which is thicker and more vascular than the ileum. It lies in the belly button area of the abdomen. There are small fingerlike projections in the wall of the jejunum called villi. These villi are covered with smaller projections called microvilli. The villi increase the surface area of the jejunum and allows much more absorption of nutrients in this part of the small intestine—most of the food absorption is done in this part of the digestive tract. Simple sugars, water soluble vitamins and amino acids made from the food is passed from the villi into the blood stream while the fat is passed into the lymph capillaries. The rest of the food passes into the ileum.
Ilium- The last part of the small intestine is mainly the pelvic region. It looks very similar to the jejunum. The last absorption of nutrients from the food takes place here—amino acids, fat-soluble vitamins (A, D, E, and K), fatty acids, cholesterol, sodium, potassium alcohol, and B12. The terminal ileum is an important part as this is where vitamin B12 is absorbed into the blood capillaries. The unabsorbed and undigested food then passes from the ileum into the cecum, the beginning of the large intestine. This food residue is full of bacteria.
Large Intestine(colon)- The large intestine forms the last part of the digestive tract, which is about 5 feet long and wider than the small intestine. The surface area on the inside of the large intestine is smaller than the small intestine. The large intestine can be divided into the cecum, colon and rectum. The undigestible food waste passes from the small intestine into the cecum which then passes into the colon where the fluids and salts are absorbed. The undigested food moves up the ascending colon, across the transverse colon, down the descending colon and into the rectum. The colon soaks up to 50 fluid ounces of water every day. After absorption, the remaining undigested matter is squeezed into a bundle called feces. Feces is made of fiber, undigested food, cells that slough off the lining of the intestines and bacteria. About 30% of the weight of feces is bacteria. These bacteria are “good” bacteria and billions of them live in your colon all the time. When the bacteria finish with the feces, it is passed into the rectum, where it is stored until it is passed out through the anus as a bowel movement. The anus has voluntary and involuntary sphincter muscles which can tell the difference between gas and solid contents.
How it works with other Systems
Muscular System- Muscles are important in mastication, swallowing, and the mixing and moving of digestion products through the gastrointestinal tract.
Endocrine System- Hormones can influence digestive activity.