Understanding the Sections and Functions of the Human Digestive System
The body needs nutrients such as proteins, fats, carbohydrates, vitamins, minerals, and water to stay healthy and function properly, which are obtained through food digestion. The digestive system, which includes the esophagus, intestines, mouth, and stomach, is responsible for processing food, absorbing nutrients, regulating the immune system, and balancing the gut bacteria. If you want to learn how digestion and absorption of food happens and over how many hours, follow this health and wellness section.SelMagzStay with us.
Organs that make up the digestive system
In general, the mouth, esophagus, stomach, liver, gallbladder, bile duct, small intestine, and large intestine are the components of the digestive system.The digestive systemof humans consists of the stomach and intestines, along with the liver, pancreas, and gallbladder. Essentially, the digestive system is a collection of organs connected longitudinally and twisted tubes from the mouth to the anus. These organs and structures include the belly, small intestine, large intestine, anus, mouth, and esophagus.
The small intestine has three parts, starting with the duodenum. The second part is the jejunum, located in the middle of the intestine, and the third part is the ileum, which is at the end of the intestine.
The large intestine includes the appendix, cecum, colon, and rectum.The appendixis a finger-shaped projection connected to the cecum, which is the first part of the large intestine. The rectum is located at the end of the large intestine.
The bacteria present in the stomach and intestines, known as the microbiome, help in digestion and absorption. Parts of the circulatory and nervous systems also assist. Nerves, hormones, bacteria, blood, and the organs within the digestive system work together to digest food and liquids daily.
Why is digestion important?
Digestion is crucial because the body needs to extract nutrients from food and drinks to remain healthy. Proteins, fats, carbohydrates, vitamins, minerals, and water are among these nutrients. Your digestive system breaks these nutrients down into smaller parts so the body can absorb them and use them for energy, growth, and cell repair.
Proteins are broken down into amino acids.
Fats are broken down into fatty acids and glycerol.
Carbohydrates are broken down into simple sugars.
How does our digestive system work?
Each part of the digestive system helps move food and liquids through the stomach and intestines. It breaks solid and liquid foods down into smaller components. Whenfoodis broken down into smaller parts, the body can absorb them and deliver nutrients to the necessary areas. The large intestine absorbs water, and the digested waste is turned into stool. Nerves and hormones assist in controlling the digestive process.
How does food enter the stomach and intestines?
Food enters the stomach and intestines through a process called peristalsis. The large organs of the stomach and intestines have a muscle layer that allows their walls to move. This movement pushes food and liquids along the stomach and intestines and mixes their contents together. The muscle behind the food compresses it and pushes it forward, while the area in front of the food is relaxed, allowing it to move.
How does food move from the mouth to the stomach and intestines?
The mouth
When you swallow food, your tongue pushes it toward the throat. Then, the uvula blocks the air passage so that food does not enter this pathway. After that, the food moves into the esophagus.
The esophagus
When you start swallowing, this process occurs automatically. Brain signals and muscles in the esophagus start to work.
The lower sphincter of the esophagus
When food reaches the end of the esophagus, a ring muscle known as the lower esophageal sphincter relaxes and allows food to enter the stomach. This sphincter typically remains closed to prevent backflow of food into the esophagus.
The stomach
After food enters the stomach, the stomach muscles mix water and food with digestive fluids. The stomach slowly empties its contents and pours it into the small intestine.
The small intestine
The muscles of the small intestine mix the food with digestive fluids from the pancreas and liver and push this mixture forward for further digestion. The walls of the small intestine absorb water and nutrients into the bloodstream. As digestion continues, waste products from the digestive process enter the large intestine.
The large intestine
The waste from the digestive process includes parts of undigested food, liquids, and old cells from the stomach and intestines. The large intestine absorbs water and modifies the waste materials, turning them from liquid to solid, creating stool. Then, the peristaltic process helps move the stool toward the rectum.
The rectum
The end part of the large intestine is where stool is stored until it can be expelled through the anus during bowel movements.
How does the digestive system break down food into small components for the body to use?
As food moves through the stomach and intestines, as you read on SelMagz, digestive organs split it into smaller pieces using:
Movement
Movements such as chewing, pushing, and mixing food
Digestive fluids
Digestive fluids like stomach acid, bile, and enzymes
The mouth
The digestive process begins inside the mouth while chewing. Salivary glands produce saliva, which is a digestive substance that moistens food so it can easily enter the esophagus and later the stomach. Saliva also contains an enzyme that breaks food down into smaller components.
The esophagus
Once you swallow food, the digestive process ensures that food enters the stomach.
The pancreas
The pancreas produces digestive juice that contains enzymes to break down carbohydrates, fats, and proteins into smaller components and delivers this digestive fluid to the small intestine through small tubes.
The stomach
Glands inside the stomach produce stomach acid and enzymes that break food down into smaller components. The stomach muscles mix the food with digestive fluids.
The liver
The liver produces a digestive fluid called bile, which helps digest vitamins and fats. Bile flows from the liver into the gallbladder and is stored in the small intestine for later use.
The gallbladder
The gallbladder stores bile between meals. When you eat, the gallbladder squeezes bile and food together and releases it into the small intestine.
The small intestine
The small intestine produces digestive fluids and combines them with bile and pancreatic fluid to assist in breaking down proteins, carbohydrates, and fats.
Bacteria in the small intestine
Some enzymes needed for digestion and absorption are produced by bacteria, which also pull water from the bloodstream into the stomach and intestines for easier breakdown of food. The small intestine also absorbs water with other nutrients.
The large intestine
In the large intestine, more water is absorbed into the stomach, intestines, and bloodstream. Bacteria in the large intestine help break down leftover nutrients and produce vitamin K. The waste products in the large intestine turn into stool.
Useful Information About the Digestive Tube
The digestive tube runs from the mouth to the anus in the following order: mouth, epiglottis, esophagus, stomach, intestines, and sphincters.
Muscles of the digestive tube
The muscular layer consists of an inner circular layer and an outer longitudinal layer. The circular layer prevents food from moving backwards while the longitudinal layer shortens the passageway. The outer muscle is similar throughout the digestive tube, but the stomach has an additional internal diagonal muscle layer that helps crush and mix food.
Sphincters of the digestive tube
Sphincters are circular and specific muscles that open and close certain parts of the body. The action of the sphincter can be involuntary or under voluntary control, regulating the passage of various liquids like bile, urine, or feces. There are six different sphincters in the human digestive system:
- Upper esophageal sphincter
- Lower esophageal sphincter
- Pyloric sphincter
- Oddi sphincter
- Ileocecal sphincter
- Anal sphincter
Wall of the digestive tube
The digestive tube is a long muscular tube covered with epithelium designed for digestion and absorption of food and water. The digestive tube has four concentric layers, which from inside to out are:
- Mucosa layer
- Submucosa layer
- Outer mucosal layer (Muscularis Externa)
- Serosal or peritoneal layer (Adventitia or Serosa)
Movements of the digestive tube
The movement of the organ wall can push food and liquids forward and mix the contents within each organ. The regular movement of the esophagus, stomach, and intestines is called peristalsis, which is like an ocean wave. The first major muscular movement occurs when swallowing food or liquids.
Glands of the digestive tube
The gastric glands include three types: pyloric, cardiac, and fundic, or oxyntic glands, which are tubular and consist of a delicate basal membrane made of flat clear endothelial cells covered by epithelium.
Pyloric glands are located at the pylorus of the stomach and consist of two or three short closed tubes. Cardiac glands are located near the cardiac openings and have two types: simple tubular glands similar to the distal part of the pylorus and complex racemose glands similar to the duodenal glands.
Fundic glands are simple tubes that open into one duct and are found in the body and fundus of the stomach.
Lenticular or lenticulate glands are somewhat similar to solitary intestinal nodules and are known as gastric lenticules.
What is the gut microbiome?
There are various types of bacteria in the large intestine that can break down molecules the human body cannot digest. These bacteria produce gases in the host-pathogen interface within the intestine. Gut bacteria prevent the overgrowth of harmful bacteria in the intestine. These two types of bacteria (harmful and beneficial) compete for space and nutrients, typically existing in a ratio of 80 to 85 percent beneficial to 15 to 20 percent pathogenic bacteria in the gut.
Processes of the digestive system
The processes of the human digestive system from the mouth to the large intestine and anus include:
Swallowing
In the swallowing process, the food mass is mixed with oral cavity enzymes and saliva, then pushed into the throat by the tongue, and through a precise mechanism, it enters the esophagus. The throat has a gateway that consists of four parts. The larynx is one of them that closes with a flap called the epiglottis when swallowing to prevent food from entering the air pathway. The pharyngeal pathway is blocked into the nose by the rising of the uvula.
Contractions
Mechanical digestion of food occurs through contractions of the digestive tubes, which push the food mass forward. Generally, there are two types of contractions: localized contractions and digestive or peristaltic contractions within the digestive tubes.
Strong contractions of the digestive tubes lead to the emptying of food masses from one digestive organ to another, whereas slow contractions serve to mix the food mass with digestive juices.
Secretions
Endocrine and exocrine glands of the digestive organs secrete enzymes and acids into the digestive space for chemical digestion and breakdown of food. Salivary gland secretions are the first digestive secretions. Stomach cells secrete mucus and stomach acid, converting food into a semi-digested mass called chyme, which is then passed on like the liver, pancreas, and gallbladder that pour their secretions into the small intestine, playing a significant role in the breakdown and absorption of nutrients from chyme. Cells throughout the inner wall of the digestive tube also secrete mucus for the easy passage of food masses. This not only eases the passage of food but also protects the walls of the digestive tube from damage during food transit.
Digestion
Digestion begins as soon as food enters the mouth, with enzymes present in the saliva such as amylase converting food carbohydrates into simpler sugars. However, the main digestion occurs in the stomach, where most digestive enzymes reside.
Different enzymes each have specific functions in digesting and breaking down various food components. Proteases break down proteins, lipases break down fats, and amylases digest carbohydrates. The digestive process continues in the small intestine, where each component is transformed into simpler elements for easier absorption, such as carbohydrates into glucose, proteins into amino acids, and lipids into fatty acids and glycerol.
Absorption
Epithelial cells and surface villi of the small intestine facilitate the digestion of food and convert it into smaller, simpler components. The digested materials ready for absorption move from the surface of the intestine cells into the blood or other body parts.
Throughout the small intestine, water and lipids are absorbed, while proteins and carbohydrates are absorbed in the jejunum area of the small intestine. At the end of the small intestine, bile salts and vitamin B12 are absorbed. Then, at the end of the small intestine, indigestible masses like cellulose or plant fibers, water, and millions of bacteria are transferred to the large intestine.
Excretion
Elimination of indigestible materials from the digestive tube is the final stage of the digestive cycle. As mentioned earlier in the health section of SelMagz, waste materials are guided by digestive contractions and intestinal mucus along the large intestine toward the rectum, where through contractions and relaxation of muscles and valves in the anal area, waste materials are expelled.
Common Questions About the Digestive System
What happens to digested food?
The small intestine absorbs most of the nutrients from food and sends them to other parts of the body for use or storage. Specific areas assist in nutrient absorption and introduce them into the bloodstream. Blood carries simple sugars, amino acids, glycerol, and some vitamins and salts from the liver. The liver stores these materials and delivers nutrients to other body parts as needed.
Lymph nodes are a network of vessels that carry white blood cells and a fluid called lymph throughout the body to fight infection and absorb fatty acids and vitamins. In the future, glucose, amino acids, fatty acids, and glycerol are used to produce materials required for energy production, growth, and cell repair.
How long does it take to digest and absorb food in the digestive tube?
Various factors, including age, race, and gender, affect the duration of food transport through the digestive tube. Generally, it takes about 2.5 to 3 hours for 50 percent of the contents to pass through the stomach, and complete emptying of the stomach takes about 5 hours. Foods pass through the stomach at varying rates, and the degree of food digestion also depends on the consumed food.
How does our body control the digestive process?
Hormones and nerves work together to help control the digestive process. The flow of signals present in the stomach and intestines, which are sent to the brain, also plays a role in improving this process.
Hormones
Cells in the stomach and small intestine produce and release hormones to enhance the activity of the digestive system. These hormones help the body and send signals to the brain regarding hunger and fullness. The pancreas also produces important hormones for digestion.
Nerves
Nerves connect the digestive system to the central nervous system, which includes the spinal cord and brain, allowing the digestive system to perform its functions more effectively. For example, when you see or smell food, your brain sends a signal to produce saliva in your mouth to prepare for eating. These nerves also exist in the walls of the stomach and intestines.
