The digestive system (Latin: systema digestorium), also known as the alimentary system, is a complex organ system providing mechanical and chemical food procession, absorption of nutrients, and excretion of undigested remains.
The digestive system is located in the head, neck, thoracic and abdominal cavities and in the pelvis. There are two digestive system parts. It consists of the digestive tract (also known as the alimentary tract or gastrointestinal tract) and some accessory organs that help in the whole digestion process. The alimentary tract length varies in humans, and it is about eight to ten meters (26 feet 2 inches to 32 feet 9 inches) long. Usually, in the human body, the digestive tract’s length is 4-5 times the size of the individual’s actual height.
The digestive system starts at the mouth but ends at the anus.
The digestive system consists of the following parts:
- the oral cavity proper, formed by soft and hard palate, tongue and salivary glands
- cecum and appendix
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
The digestive system also includes several glands as salivary glands, the pancreas, and the largest gland in the human body - the liver. The peritoneum, one of the serous membranes, and the gallbladder with biliary ducts are also a part of the digestive system.
The digestive system organs divide into three main digestive system parts regarding the primary digestion function.
The alimentary system has several functions, but the primary digestion system function is the digestion process. It divides into three main phases- oral, gastric, and intestinal phase.
The digestion process starts even before eating as by just looking at the food, and by smelling it, the stomach and salivary glands get signals to release saliva and the gastric juice. The next step is ingestion, when a person puts food into the mouth. That’s when the oral cavity starts the process of food analysis provided by sensory receptors such as taste, thermo-, and mechanoreceptors. Also, olfactory receptors are involved in the analysing part. Mechanical food procession of digestion starts by chewing the food. Saliva mixes with it, and the chemical food procession starts as saliva contains an enzyme called amylase that splits foods that contain starch. Saliva also contains a protein called mucin. It helps with food hydration and lubrication. The bolus is a soft and easy swallowed mass that forms after chewing. Tongue and muscles push the bolus to the back of the oral cavity, and it goes through the pharynx to the esophagus.
In the esophagus, the bolus is moved further to the stomach by rhythmic muscle contractions called peristalsis. The lower esophageal sphincter opens and lets the bolus move into the stomach. The stomach helps to continue with the chemical food procession, and the gastric juice breaks down the food even more. An enzyme called pepsin breaks down the proteins. Gastric acid also has a protective role as it helps to kill bacteria and viruses. When the gastric stage of digestion is over, the gastric acid, enzymes, and partially digested food have formed a milky-looking thick and viscous mixture. It is called chyme.
Chyme is moved next through the pyloric sphincter into the duodenum. In the duodenum, the bile and the secretion from the pancreas mix with the chyme. Both acid and enzyme-rich fluids continue to break down proteins, fats, and carbohydrates. The small intestine absorbs the water, vitamins, and other nutrients into the bloodstream by small structures located in the small intestine wall that increase the surface area. The undigested and unabsorbed products are moved next to the large intestine through the ileocaecal valve. In the large intestine, any remaining water and nutrients are absorbed. All the waste products shape the stool. It is stored in the sigmoid colon and the rectum part of the large intestine and removed from the body by bowel movements through the anus.
The time it takes to produce the food varies in males and females from person to person, depending on the metabolism and digestive issues. The digestion process’s average duration in a healthy individual is about 24-72 hours, based on several factors. For example, those factors include the amount and the type of food uptaken. The process can be as long as 96 or 120 (4-5 days) hours or even more in case of pathologies and diseases. After swallowing the food, it takes an average time of 6-8 hours to pass through the stomach and small intestine. It takes about 2-5 hours to empty the stomach. But to pass through the whole small intestine- 2 to 6 hours. After entering the colon, the most time-consuming digestion part starts. It takes approximately 36-40 hours for food to move through the whole colon. Foods that are rich in proteins and fats, such as meat, take longer digestion time. But products high in fibers, such as vegetables and fruits, transit faster through the tract as those fibers help move the food more efficiently and quicker. To compare, it takes about two days for meat and less than a day for vegetables to pass through. The fastest digested foods are those high in sugars, such as pastries and candy bars. Usually, it is just a matter of hours.
Many conditions can affect and slow down digestion and disrupt it, presenting many side effects such as constipation or diarrhea, gasses, heaviness, difficulty swallowing, burning sensation, abdominal pain, and a lot more.
The most common disorders that affect the digestive system are:
The digestive system parts are the digestive tract and some accessory organs that help in the digestion process.
The digestive system looks like a set of long tubes following one to each another.
The first part of the digestive system is the oral cavity or the mouth.
The digestive system organs include the oral cavity and its constituent structures, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum and appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum) and accessory organs: liver, gallbladder and the biliary tract, pancreas, and peritoneum.
The esophagus connects the bottom of the throat or the pharynx with the stomach.
All organs involved in the digestive system have an essential role. Still, the most important organ is the small intestine, as it mainly provides the absorption of nutrients and water necessary to the human body.
The primary digestive system function is digestion.
Mechanical and chemical food procession are the two types of digestion.
The chyme is a milky-looking thick and viscous mixture formed after the digestion in the stomach is over.
It takes about 2-5 hours to empty the stomach.
The stool stores the sigmoid colon and the rectum, which are parts of the large intestine.
The digestive system’s most common diseases are acid reflux disease, inflammatory bowel diseases, celiac disease, irritable bowel syndrome, diverticulosis, food allergies and intolerances.