Nutrition in Animals

Human Digestive System

Have you ever wondered as to what happens to the food once it enters the body? It gets digested, utilized and the remaining undigested material is expelled out of the body. There is a specific system of organs in the body known as the digestive system that carries out this complex process. Let us know more about this organ system and digestive system function in humans.

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The Human Digestive System and Its Components

Digestion starts in the buccal cavity of the mouth and ends at the anus. In between, it passes through a long alimentary canal which is further divided into various components. The basic components of the digestive system include:

  • the buccal cavity
  • oesophagus or the “food pipe”
  • stomach
  • the small intestine
  • the large intestine that ends in the rectum
  • the anus

These parts all combine together to form a long path known as the alimentary canal. The alimentary canal along with associated glands together constitute the digestive system. Let us study in detail the various parts involved in the digestive system and digestive system function.

Digestive system function : Human digestive system

The Mouth and Buccal Cavity

The food that we eat first comes in contact with the mouth and the buccal cavity. Ingestion is the process of intake of food. Teeth that are attached to the buccal cavity break down the food into smaller pieces.The teeth vary in their appearance and perform varied functions.

digestive system function: the buccal cavity

The mouth also contains salivary glands that secrete saliva. The saliva breaks down complex starches into simple sugars. Attached to the floor of buccal cavity is a free moving tongue. Besides its regular function of talking, the tongue also aids in this digestive system function by mixing the saliva with food. It not only helps in chewing and swallowing but also tasting the food. The tongue is rich in taste buds which detect the different tastes of food.

The Esophagus or The “Food pipe”

Extending along the neck and the chest, it serves as a passage for the swallowed food.The walls of the food pipe, by their special property of peristalsis, push the food down. When the food is not accepted by the stomach, it is vomited out.

The Stomach

This U- shaped thick-walled bag constitutes the widest part of the alimentary canal. It serves as a link between the food pipe and the small intestine thus receiving the food from the food pipe and carrying it to the small intestine. The lining of this part of the digestive system function in secreting mucus, hydrochloric acid, and digestive juices. The pH of this part is acidic in nature.

A strongly acidic environment is maintained which is necessary for the digestion of food. The acid not only kills the bacteria that may enter the body along with food but also aid in digestion by breaking down complex proteins into simpler molecules.

The Small Intestine

Next part of the digestive system is the small intestine. Though it is called “small”, it is actually a highly coiled 7.5 meters long structure. This supercoiling is to increase the surface area for absorption of food so that more food comes in contact with the intestinal walls.

Liver and the pancreas pour their secretions into its lumen. Besides, the intestinal wall also secretes juices. The conditions here are less acidic as compared to stomach. But on account of its intensely coiled structure, major absorption of nutrients occurs in this region.

Associate glands

There are two glands that help the small intestine in its digestive system function.

  • The Liver and the Gall Bladder
  • The Pancreas

digestive system function : liver, gall bladder and pancreas

The Liver and the Gall Bladder

Located in the upper part of the abdomen, it is present on the right side. This reddish-brown structure is the largest gland in the body. It contains a sac-like structure known as the gallbladder. The liver secretes bile juice that gets stored in the gallbladder through the bile duct. Bile juice aids in the digestion of fats.

The Pancreas: Present just below the stomach, these are large cream- colored glands. This part of digestive system function in secreting pancreatic juice. They pancreatic juice aids in the break down of carbohydrates, proteins as well as fats into simpler forms.

Thus the food gets partly digested. Next, the partially digested food reaches the lower part of the small intestine where the intestinal juices act on it to complete their digestion. Complex carbohydrates are broken down to yield simple sugars like glucose. Fats break down into fatty acids as well as glycerol. In the same way, amino acids are formed from the breakdown of proteins.

Carbohydrates ⇒ Simple sugars(eg: glucose)

Proteins  ⇒  Amino acids

Fats  ⇒  Fatty acids and glycerol

How does Absorption take place in the Small Intestine?

The digested food gets passed into the blood vessel ( system circulation) through the intestinal walls (site of contact) We call this process absorption. There is a presence of numerous finger-like projections known as villi on the walls of the small intestine.

These villi are present so as to increase the surface area for absorption. Located near the surface of each villus is a network of small and thin blood vessels. The blood vessels transport the absorbed substances to different organs of the body where they are consequently used to build complex substances such as the proteins required by the body. This is known as assimilation.

Glucose breaks down into carbon dioxide and water in the presence of oxygen and subsequently releases energy in the process. Undigested and unabsorbed food consequently passes on to the large intestine.

The Large Intestine

Finally, the last part of the alimentary canal is the large intestine. Wider and much shorter than the small intestine, it is approximately 1.5 meters long.This part of the digestive system function in absorbing water and salts from the undigested food material.The waste undigested food material in the form of semi-solid faeces is passed down to the rectum and the anus removes it from the body. This process is known as egestion.

Questions For You

Q. What do you call the finger-like projections present over the wall of the small intestine?

a. Pilli             b. Pseudopodia

c. Villi          d. Vills

Ans. Villi are the finger-like projections present over the wall of the small intestine.

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