The Human Digestive System: Organs and Functions


The Beginning of Digestion Process: The Mouth

Food enters the body through mouth, or oral cavity. The process of digestion starts from the mouth. The moments food enters the mouth, it gets struck by the teeth and assaulted by starch-degrading enzymes. Saliva (and the teeth) begins the assimilation process. Saliva is a fluid secreted by salivary glands, which are located underneath tongue and in the back of oral cavity. Saliva contains salivary amylase (a starch-degrading enzyme), bicarbonate, and mucins. The buffering activity of the bicarbonate keeps the inside of mouth at a pH of somewhere close to 6.5 and 7.5, notwithstanding when eating acidic nourishments, for example, tomatoes. The mucins bind the bits of food into a softened ball, called a bolus, and muscle contractions of your tongue force the bolus into your pharynx. The pharynx is a solid tube associated with the throat, which leads specifically into the stomach. The food is swallowed when you intentionally push a bolus into your pharynx.

Motility and Muscles:

The pharynx and esophagus don’t play direct roles in the digestion process as neither of them breaks down food or aids in the digestionprocess. In any case, they’re both instrumental: The muscle contractions of their walls are what propel food into stomach. The digestive system is more than just a slimy tube; it’s composed of muscles from top to bottom. Smooth muscles are found in digestive tract. You can move them voluntarily, as you can your skeletal muscles, but smooth muscle is muscle, nonetheless.

The structure of gut wall is a progression of layers. Mucosa is the deepest layer that faces the lumen. Next comes the submucosa, a layer of connective tissue intertwined with blood and lymph vessels, and local neuron system. The third layer from the lumen is the smooth muscle. Smooth muscle as a rule shapes in two layers, each running in different direction. One layer of smooth muscle runs in a circular direction, while the other layer runs longitudinally, or up and down. Sphincters occur at the beginning and end of your stomach, as well as in other specialized regions of your system. Sphincters help control the forward movement of food and prevent it from flowing back into the digestive system.

The muscles of your digestive system produce wavelike contractions that mix food and move it through the whole system. Amid peristalsis, the ring muscles contract behind the food, while relaxing before it. This movement drives food forward, moving it along. As the food moves forward, it distends the tube walls, and peristaltic motion keeps pushing it along. During segmentation, rings of smooth muscle repeatedly contract and relax. This type of movement, which is similar to the back-and-forth motion of a washing machine, mixes the food and pushes it against the absorptive surface of your gut walls.


The stomach is a strong, adaptable sac, directly connected to the esophagus. When you swallow, food goes into your pharynx, at that point esophagus, and after that directly into the stomach. The stomach serves three capacities in digestive system:

  1. It stores and blends food.
  2. It secretes enzymes and acids, which help dissolve food.
  3. It controls the movement of food into your small intestine (where absorption will take place).

The storage and mixing of food is a pretty clear-cut function: You swallow, the food reaches your stomach, and mixing commences. Secretion is a little more complex. Every day, the cells in your stomach lining secrete approximately 2 liters of fluids, including hydrochloric acid, mucus, and pepsinogens. Together, these substances make up your gastric fluid. The hydrochloric acid separates into H+ and Cl-. This increase in acidity helps dissolve food. It also manages to kill most bacteria that have hitched a ride into your digestive system. The dissolving food and acids form a mixture referred to as chyme.

The stomach is the most acidic part of the body. Stomach secretions begin with brain. The brain reacts to the scent, sight, and taste of food. It even reacts to hunger pangs and cravings about food. Accordingly, the brain sends signals to the cells lining stomach. This begins the process of secretion.

When food actually arrives in your stomach, the cells respond to the stretching of the stomach sac and step up the secretions. Protein is harder to process than carbohydrates. Acid found in the stomach is first major step in breaking down proteins so that your body can use them. The acid separates the structure of protein and exposes the peptide bonds. The acid likewise changes over pepsinogens to active forms that can further break down the proteins considerably further. As the protein ends up fragmented, themselves directly stimulate the production of gastrin, which in turn stimulates the secretion of more hydrochloric acid. In this way, the more protein you eat, the more gastrin and hydrochloric acid forms in your stomach.

Small Intestine:

The small intestine is where digestion is completed and nutrients are absorbed and shipped out to your body for use. The small intestine has three regions: the duodenum, the jejunum, and the ileum. The pancreas and liver also contribute to the functioning of the small intestine. A common duct empties secretions from both these organs into your small intestine.


Pancreas aids in digestion by secreting enzymes that help to digest fats, proteins, carbohydrates, and nucleic acids. Just like the pepsin your stomach secretes, the pancreatic enzymes trypsin and chymotrypsin help your small intestine break down proteins. The pancreas also secretes bicarbonate, which buffers and helps to neutralize the hydrochloric acid arriving from your stomach. The pancreas also secretes two other hormones, insulin and glucagon, which don’t help with digestion but are important in a nutritional sense.


Your liver plays a key role in digestion because it secretes bile. Bile salts help with the breakdown and absorption of fat. The small intestine breaks down these globules mechanically through its muscle action. Bile salts help keep these smaller droplets from reclumping into a large globule. This process is called emulsification. The emulsifying effect of bile salts on fat globules lets the fat-degrading enzymes in your small intestine get better access to the triglycerides, which enhances fat digestion.

Large Intestine:

Once in the blood vessels, the nutrients enter your bloodstream and are carried out to other parts of your body. Mineral ions and water are also absorbed by your intestinal villi. By the time a meal has moved through the small intestine, everything that can be absorbed has been absorbed. Anything that’s left moves into the large intestine, or colon. The colon stores and concentrates feces, which are a mixture of water, bacteria, and undigested, or unabsorbed, material. Your colon starts off as a pouch, with your appendix a narrow projection from that pouch. From there, the colon winds its way through your abdominal cavity, snaking and turning upon itself, finally ending with a small tube called the rectum. When waste material enters the rectum, the distension of the gut walls triggers a reflex to expel the feces from the body. Your nervous system controls this expulsion through a small sphincter muscle at the anus, or terminus of your digestive system. From mouth to anus, your food has been totally processed, all in one continuous gut tube.

Leave A Reply

Your email address will not be published.