Digestive System: The digestive system of the human body comprises a group of organs working together to break down food particles into tiny parts to produce energy for the body. Anatomically, the digestive system comprises the alimentary canal and accessory organs such as the liver, pancreas, and gallbladder. The hollow organs that make up the alimentary canal also called the gastrointestinal tract include the mouth, stomach, esophagus, small intestine, and large intestine which contains the rectum and anus.

Digestive System

The Human Digestive system requires the intake of food and further utilize it and convert it into energy. This process of digestion is the important process through which the body obtains power. The digestive system comprises of Alimentary Canal and Accessory Organs.

The alimentary canal is the long tube-like structure through which the food that we eat is passed. It starts at the mouth (buccal or oral cavity), passes through the pharynx, esophagus or food pipe, stomach, small intestines, large intestines, rectum, and finally ends at the anus. The food particles gradually get digested as they travel through various components of the alimentary canal.

The Accessory organs are also the organs that participate in the digestion process. They stimulate digestion by releasing certain enzymes that help in breaking down the food.

Parts of Digestive System

The digestive system consists of the alimentary canal and associated organs

Alimentary Canal

Mouth: Food starts its journey from the mouth or the buccal cavity. There are many other organs that contribute to the digestion process, including teeth, salivary glands, and tongue. Teeth are designed for grinding food particles into small pieces and are moistened with saliva before the tongue pushes the food into the pharynx.

Pharynx: A fibromuscular y-shaped tube which are attached to the terminal at the end of the mouth. It is mainly involved in the passage of chewed/crushed food from the mouth through the Esophagus. It also has a major part in the respiratory system, as air travels through the pharynx from the nasal cavity on its way to the lungs.

Esophagus: This is a muscular tube that connects the pharynx, which is a part of an upper section of the gastrointestinal tract. It supplies swallowed food along with its length.

Stomach: It serves as a muscular bag that is situated towards the left side of the abdominal cavity, beneath the diaphragm. This vital organ acts as a storage for food and provides enough time to digest meals. The stomach also produces digestive enzymes and hydrochloric acid that maintains the process of digestion.

  • Mucus: It is an aqueous secretion produced by the mucous membranes. It functions by protecting the stomach lining and gastric pits from the acid, which is produced by the glands to destroy the bacteria that entered along with the food particles.
  • Digestive enzymes: They are the group of enzymes that functions by breaking down polymeric macromolecules like biopolymers into their smaller and simpler substances.
  • Hydrochloric acid: It is the digestive fluid formed by the stomach during the process of digestion. It functions by destroying harmful microorganisms present in the food particles.

Small Intestine: The small intestine is a thin, long tube of about 10 feet long and a part of the lower gastrointestinal tract. It is present just behind the stomach and acquires a maximum area of the abdominal cavity. The complete small intestine is coiled and the inner surface consists of folds and ridges.

Large Intestine: This is a thick, long tube measuring around 5 feet in length. It is present just beneath the stomach and wraps over the superior and lateral edges of the small intestine. It absorbs water and consists of bacteria (symbiotic) that support the breakdown of wastes to fetch small nutrients.

Rectum: Waste products are passed into the end of the large intestine called the rectum and eliminated out of the body as a solid matter called stool. It is stored in the rectum as semi-solid feces which later exits from the body through the anal canal through the process of defecation.

Accessory Organs

Pancreas: It is a large gland present just behind the stomach. It is short with its anterior connected to the duodenum and posterior pointing towards the left part of the abdominal cavity. The pancreas releases digestive enzymes to complete the process of chemical digestion.

Liver: The liver is a roughly triangular, reddish-brown accessory organ of the digestive system located to the right of the stomach. It produces bile, which helps in the digestion of fat in the small intestine. The bile is stored and recycled in the gallbladder. It is a small, pear-shaped organ that is located just next to the liver.

Process of Digestive System

A human requires various nutrients, proteins, and vitamins that are derived from food through digestion. The chewing of food is mixed with saliva and begins the process of digestion. This produces a bolus that can be swallowed down the esophagus and into the stomach. The complete process of nutrition is divided into five stages:

  • Ingestion
  • Digestion
  • Absorption
  • Assimilation
  • Defecation

Ingestion

The process of taking food, drink, or any other substance into the body by swallowing and absorbing it, is known as Ingestion.

Digestion

 The digestive system contains six components which are as follows-

  1. Mouth
  2. Esophagus
  3. Stomach
  4. The small intestine
  5. Colon (large intestine)
  6. Rectum

Digestion is a process through the large insoluble and non-absorbable food particles are broken down into smaller water-soluble and absorbable particles which are finally absorbed by blood plasma.

It is a form of catabolism that is divided into two groups based on how food is broken down in the body, if food is broken down through mechanical means then it is known as Mechanical Digestion and if it is through chemical means then it is called Chemical Digestion. 

Mouth and Esophagus: Digestion initiates right from the mouth, where the Salivary gland secrets the Saliva in the mouth where two types of enzymes are found, ptyalin and maltase.

saliva contains an enzyme called salivary amylase that begins the process of converting starches in the food into maltose. Around 1.5 liters of saliva is secreted in humans on an average day, it is acidic in nature (pH 6.8). Through a food pipe or Esophagus, food reaches into the stomach.

Digestion in the Stomach: The pH of the stomach is 1.5-2.5. This acidic environment helps in breaking the food particle and absorption of necessary nutrients from food.

The highly acidic environment of the stomach contains gastric glands which secrete gastric juice, this is a light yellow acidic acid. Pepsin and Renin are the enzymes in gastric juice.

Parietal cells secrete Chlorine and Hydrogen ion which combine to form Hydrochloric acid which helps in killing microorganisms and with the help of enzyme pepsin helps in the hydrolysis of proteins. Hydrochloric acid makes the food acidic by which the ptyalin reaction of the saliva end.

Pepsin breaks down the protein into peptones and Renin breaks down the Caseinogen into Casein.

Digestion in Duodenum: The duodenum is the first and shortest segment of the small intestine. It receives partially digested food (known as chyme) from the stomach and plays a vital role in the chemical digestion of chyme in preparation for absorption in the small intestine.

 The gall bladder releases bile, which has been produced by the liver, to help further break fats down into a form that can be absorbed by the intestines.

As the food reaches the duodenum bile juice from the liver combines with it. The main function of the bile juice is to convert the acidic food into alkaline, as it is alkaline in nature.

Pancreatic juice from the pancreas combines with food and it contains the following enzymes:

  • Trypsin: It converts the protein and peptone into polypeptides and amino acids.
  • Amylase: It converts the starch into soluble sugar.
  • Lipase: It converts emulsified fats into glycerol and fatty acids.

Digestion in Small Intestine: Here the process of digestion is completed and absorption of digested foods starts.

In the small intestine, intestinal juices secrete and it is alkaline in nature and around 2 liters of intestinal juice secretes per day.

Intestinal juice contains the following enzymes:

  • Erepsin: It converts the remaining protein and peptone into amino acids.
  • Maltase: It converts maltose into glucose.
  • Sucrase: It converts the sucrose into glucose and fructose.
  • Lactase: It converts the lactose into glucose and galactose.
  • Lipase: It converts the emulsified fats into glycerol and fatty acids.

Absorption

Digested food absorbed by blood plasma is known as Absorption. The absorption of digested foods takes place through small intestine villi which are finger-like structures extended into the lumen of the small intestine.

Assimilation

The use of absorbed food in the body or movement of digested particles where they are used is called assimilation

Defecation

 It is the final act of digestion. It is also known as a bowel movement. Undigested food reaches from the small to the large intestine where bacteria's convert it into feces which is excreted through the anus.

Functions of  Digestive system

The key Functions of the digestive system include:

Motility- Food moves through the digestive canal, due to a process known as peristalsis, which involves the action of muscles in the GI tract that transport food to the digestive system. Through the evacuation of undigested waste from the body, incoming nutrients are broken down and mixed.

Secretion- It is the release of enzymes, hormones, and other chemicals that aid in the digestion of food by the body. Hormones signal the body to generate digestive juices and notify the brain whether you're on an empty stomach or full.

Digestion- Proteins, lipids, carbs, vitamins, minerals, and water are all broken down into molecules small enough to pass through the digestive fluid and into the bloodstream during digestion. The digestive juices that we consume for energy, development, and cell repair break down the meal. Amino acids are formed when proteins are broken down. When fats are broken down, fatty acids and glycerol are produced. Simple sugars are formed when carbohydrates are broken down.

Absorption- Digested carbohydrates travel from the gut to the circulation, where they are transported by the circulatory or lymphatic systems throughout the body for usage or storage. The lymphatic system absorbs fatty acids and vitamins. The blood transports simple carbohydrates, amino acids, glycerol, and some vitamins and minerals to the liver. When these nutrients are needed, the liver stores metabolizes and delivers them to the body

Digestive System- FAQs

Ans. The digestive system of the human body comprises a group of organs working together to break down food particles into tiny parts to produce energy for the body. Anatomically, the digestive system comprises the alimentary canal and accessory organs such as the liver, pancreas, and gallbladder. The hollow organs that make up the alimentary canal also called the gastrointestinal tract include the mouth, stomach, esophagus, small intestine, and large intestine which contains the rectum and anus. They process many things like energy, cell growth, and cell repair.

Ans. Digestive system has many functions to preform but major key function of this is motility, secretion, digestion, Absorption, etc.

Ans. Digestive System consist of Alimentary Canal and Accessory Organs

Ans. A human requires various nutrients, proteins, and vitamins that are derived from food through digestion. The chewing of food is mixed with saliva and begins the process of digestion. This produces a bolus that can be swallowed down the esophagus and into the stomach. The complete process of nutrition is divided into five stages: Ingestion Digestion Absorption Assimilation Defecation

Ans. Accessory organs are organs which are not part of the digestive system; however, they aid in the digestion process by performing many secondary functions. The main accessory organs of the digestive system are the tongue, liver, pancreas and gall bladder.

Important Links