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Digestive system

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. 

Digestive system anatomy

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. 

Digestive system parts and organs 

The digestive system starts at the mouth but ends at the anus

The digestive system consists of the following parts:

            - oral vestibule, formed by lips, cheeks, gums, and the teeth

            - the oral cavity proper, formed by soft and hard palate, tongue and salivary glands

              - duodenum

              - jejunum

              - ileum

  • large intestine with the following elements:

               - cecum and appendix

               - colon

               - ascending colon

               - transverse colon

                - descending colon

                - sigmoid colon

                - rectum

  • liver
  • gallbladder and the biliary tract
  • pancreas
  • peritoneum

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.

Digestive system organs by functions 

The digestive system organs divide into three main digestive system parts regarding the primary digestion function. 

  1. The oral cavity, pharynx, and esophagus provide the mechanical food procession.
  2. The stomach, small and large intestine, liver, and pancreas mainly provide the chemical food procession, absorption of split products, and nutrients
  3. And the final part is where the excretion takes place, and the rectum is responsible for it.

Digestive system function. Digestion process

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.

Digestion process oral 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.

Digestion process gastric phase 

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 proteinsGastric 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. 

Digestion process intestinal phase 

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.

Digestion process length

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.

Common disorders of the digestive system

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:

  • gastroesophageal reflux disease (GERD) or acid reflux in which stomach acid regularly or periodically flows back in the esophagus because of the weak lower esophageal sphincter;
  • inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease. As the name 'inflammatory bowel disease' suggests, both condition present as severe chronic inflammation in the large intestine exclusively (ulcerative colitis) or any part of the digestive system (Crohn’s disease). However, most commonly, the Crohn’s disease affects the end part of the small intestine known as ileum and the beginning of the large intestine;
  • celiac disease is also known as gluten-sensitive enteropathy or celiac sprue. It classifies as an autoimmune disorder in which the immune system attacks and damages the small intestine when an individual eats gluten-containing products such as white or rye bread, couscous, wheat-based pasta and noodles, and many more;
  • irritable bowel syndrome that is a widespread and lifelong disorder affecting intestines and causing stomach cramps, bloating and gasses, abdominal pain, diarrhea, and constipation;
  • diverticulosis resulting in diverticulitis. It happens when small pockets or pouches called diverticula form in the large intestine walls, most commonly in the descending or sigmoid colon. The diverticula’s formation is associated with the weak places in the large intestine wall and pressure changes. Diverticulitis characterizes as an inflammation of the diverticula, and it can present as very severe pain in the abdomen, but quite often, there aren’t any symptoms at all;
  • food intolerances (lactose intolerance) and food allergies such as peanut allergy. The first one shows when it is difficult to digest certain food types. In comparison, food allergy presents as an immune system response. Both conditions cause a bunch of different signs and symptoms. Still, usually, intolerance is less severe in general and often presents only as digestive problems. In contrast, a food allergy can be critical and even life-threatening depending on the immune system response. It can also appear not only with the symptoms of the alimentary system.

Summary on digestive system

What is the anatomy of the digestive system?

The digestive system parts are the digestive tract and some accessory organs that help in the digestion process.

How does the digestive system look?

The digestive system looks like a set of long tubes following one to each another.

What is the first part of the digestive system?

The first part of the digestive system is the oral cavity or the mouth.

What are the parts of the digestive system?

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.

What connects the bottom of your throat to your stomach?

The esophagus connects the bottom of the throat or the pharynx with the stomach.

What is the most important organ in the digestion system?

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.

What is the digestive system function?

The primary digestive system function is digestion.

What are the two types of digestion?

Mechanical and chemical food procession are the two types of digestion.

What is chyme in the digestive system?

The chyme is a milky-looking thick and viscous mixture formed after the digestion in the stomach is over.

How many hours does food stay in the stomach?

It takes about 2-5 hours to empty the stomach.

Where is the poop stored?

The stool stores the sigmoid colon and the rectum, which are parts of the large intestine.

What are the various diseases in the digestive system?

The digestive system’s most common diseases are acid reflux disease, inflammatory bowel diseases, celiac disease, irritable bowel syndrome, diverticulosis, food allergies and intolerances.