Gastrointestinal system: Structure and function

The primary functions of the gastrointestinal system are digestion, which is breaking down food that we eat into nutrients; absorption, which is getting those nutrients into the bloodstream; and excretion, which is getting rid of digestive waste as feces.

The gastrointestinal system is made of hollow, connected organs that make up a canal, called the gastrointestinal tract, as well as a couple of accessory organs that are not part of the canal but play an important role in the food digestion process.Alright, from top to bottom, the gastrointestinal tract starts with the mouth, then the esophagus, the stomach, the small intestine, the large intestine, and ends with the anus.Digestion starts after food ingestion, which is putting food into the mouth.

The first step is mastication, which is chewing on food to physically break it into small chunks. This process is also referred to as mechanical digestion.

During mastication, the tongue mixes food with saliva secreted from salivary glands. Saliva contains some chemical substances, called enzymes, which start breaking down chemical bonds between food molecules.

This process is called chemical digestion, and it continues at different levels of the gastrointestinal tract as food moves along.

As mastication goes on, we get a food-saliva mixture, called a bolus, which is ready to be swallowed. Swallowing takes place through a muscular tube, called the esophagus.

To move this food bolus along, muscles of the esophagus contract and produce a wave-like movement that pushes food downward into the stomach.

This movement is called peristalsis, and it also continues throughout the GI tract. When the food arrives in the stomach, it mixes with gastric juice consisting of acid and gastric enzymes, which turns the food bolus into a pulpy soup, called chyme, made of much smaller food particles.

Next, chyme moves to the first part of the small intestines, called the duodenum, where bile secreted by the liver and pancreatic enzymes digest it even further.

The end result is chyle, which is a kind of milky fluid ready to be absorbed. Chyle then moves to the second portion of the small intestine, called the jejunum, which has a specialized mucosa, or lining, that allows nutrients to be absorbed into the bloodstream by way of a network of local capillaries.After nutrients are absorbed, the food residue keeps moving along the canal by means of peristalsis.

It moves from the last part of the small intestine, called the ilium, into the large intestine, or colon. The remaining nutrients and water get absorbed, leaving semi-solid materials, called excrements or feces.

Excrements collect in the last segment of the large intestine, called the rectum, which is connected to the anus. When the rectum is full, it sends a message to the brain that triggers the need to defecate, which is called excretion.Okay, now, let’s shift gears and talk about the accessory organs, which are the liver, the gallbladder, and the pancreas.

These organs are not specifically a part of the gastrointestinal tract, and they do not come in direct contact with food as it moves around.

However, they secrete digestive enzymes and fluids that are necessary for digestion. The liver is located just beneath the diaphragm and secretes bile that gets stored in the gallbladder, which is a small pouch attached to the liver.

From the gallbladder, bile gets released into the duodenum, where it helps digest fats. Another major accessory organ is the pancreas, which is located behind the stomach within the curvature of the duodenum.

The pancreas produces pancreatic enzymes that are secreted into the duodenum to help with the digestion of fats, proteins, and carbohydrates.Now, as we get older, our gastrointestinal system becomes less efficient.

Some of the changes include a reduction of saliva production as well as dental issues, such as tooth loss. This reduces the efficiency of mastication, and as a result, older people have a risk of choking due to swallowing poorly chewed chunks of food.

Other changes that happen include reduced production of gastric juice and bile, which considerably reduces the efficiency of chemical digestion.

Overall, there is reduced efficiency of the digestive system, which can lead to indigestion. In addition, aging leads to a reduced peristalsis throughout the GI tract.

As a result, food spends a longer time in the large intestines, causing almost all the water in it to be absorbed. This results in dry feces that are hard to pass, which can cause constipation.

All right, as a quick recap… The primary functions of the gastrointestinal system are digestion of food, absorption of nutrients, and excretion of waste.

The system consists of the gastrointestinal tract, which starts with the mouth, then moves through the esophagus, the stomach, the small intestine, the large intestine, and ends with the anus.

Alongside the GI tract, there are accessory organs that contribute to the digestion process by secretion of digestive enzymes and fluids.

Accessory organs include the liver, the gallbladder, and the pancreas. As we age, our gastrointestinal system becomes less efficient due to changes, such as tooth loss, reduced secretion of saliva, gastric juices, and bile.

This can cause some problems, such as choking due to swallowing poorly chewed food,