Human Digestive System Parts and Functions

Digestion is the process of breaking down complex food materials into simpler substances by the action of enzymes.

Human Digestive System Parts and Functions

Stage of Digestion

Ingestion: The act of eating / feeding. Food is taken into the mouth where it is physically broken down by the teeth into smaller pieces. In vertebrates, the teeth, saliva, and tongue play important roles in mastication ( preparing the food into bolus ). while the food is mechanically broken down, the enzymes in saliva begin to chemically process the food as well.


 (1) Mechanical digestion: Food is physically broken into smaller parts. for instance, by chewing. 

  (2) Chemical digestion: Food is broken down by acids and enzymes into its basic units.

Absorption: Animals cell’s take up ( absorb ) small molecules i.e  Amino acids, sugar, fats etc. The small intestine absorbs most of the food, and your circulatory system passes them on store or use.  Special cells help absorbed nutrients cross the intestinal lining into your bloodstream.

Elimination / Excretion: undigested material passes out of the digestive system. The food molecules that cannot be digested or absorbed need to be eliminated from the body. The removal of indigestible wastes through the anus, in the form of feces, in elimination or excretion.

Alimentary canal: Also know as the gastrointestinal ( GI ) tract. This is long tube canal begins with an anterior – the mouth, and it opens out posteriorly through the anus. Alimentary canal include the mouth, pharynx (throat), esophagus, stomach, small intestine, large intestine, rectum, and anus. The alimentary tract is part of the digestive system. Additionally, the process of digestion is assisted by many accessory organs such as liver, pancreas, gallbladder and salivary glands.

  •  Mouth
  • pharynx
  • esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum and Anal canal.


The mouth is the first part of the upper gastrointestinal tract and is equipped with several structure that begin the first processes of digestion. These include salivary glands, teeth, and the tongue. The buccal cavity perform two main functions, mastication of food and facilitation of swelling. The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly. mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus. The bolus is then conveyed into the pharynx then into the esophagus  by swelling or deglutition.

The salivary gland secrete an enzymes called salivary amylase which is converts starch to maltose.

                 Starch      →       Maltose

About 30% of starch is hydrolysed here by this enzyme (optimum pH 6.8) into a disaccharide – maltose. Lysozyme present in saliva acts as an antibacterial agent that prevents infections. 


The pharynx as a whole is about 13 centimeters in length. while the tube is largely made up of muscle, some areas consist of soft tissue. The pharynx is a part of the conducting zone of the respiratory system and also a part of the digestive system. The pharynx take in air from the nasal passages as well s food and drink from the mouth.


No digestion occur in the esophagus. The esophagus is a 25cm long   muscular tube that connects the pharynx (throat) to the stomach. The esophagus contracts as it moves food into the stomach. A valve called the lower esophagus sphincter (LES) is located just before the opening to the stomach. This valve opens to let food pass into the stomach from the esophagus and it prevent food rom moving back up into the esophagus from the stomach.


The stomach is a muscular organ located on the left side of the upper abdomen. The stomach receives food from the esophagus and  stomach stores the food for 4-5 hours. It produces enzymes (substance that create chemical reactions) and acids (digestive juices). After food enters your stomach, the stomach mix the food and liquid with digestive juices. The stomach slowly empties its contents, called chyme, into your small intestine.

Small intestine

The small intestine or small bowl is an organ in the gastrointestinal track where most of absorption of nutrients from food take place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the pancreatic duct to aid in digestion. The longest part of the alimentary canal is the small intestine. It is highly coiled structure of about 7.5 meters in length. It is very narrow tube with a large internal surface . It is the side of complete digestion in human. It absorbs digested food completely.

        The small intestine is divided into three par

  • Duodenum
  • Jejunum
  • Ileum

The duodenum, jejunum, and ileum. It helps to further digest food coming from the stomach. It absorb nutrients ( vitamins , minerals, carbohydrates, fats, proteins ).

”The breakdown of biomacromolecules mentioned above occurs in the duodenum region of the small intestine. The simple substance thus formed are absorbed in the jejunum and ileum regions of the small intestine. The undigested and unabsorbed substance are passes on to the large intestine”.

The two major pancreatic enzyme that digest proteins in the small intestine are chymotrypsin and trypsin. Trypsin activates other protein- digesting enzymes called proteases, and together, these enzymes break proteins down to tripeptides, dipeptides, and individual amino acids.  

Protein / peptones / proteases      →     Dipeptide, Tripeptides, and individual amino acids.

Carbohydrate in the chyme are hydrolysed by pancreatic amylase into disaccharids.

Polysaccharides (starch)      →       Disaccharides

Fat are broken down by lipases with the help of bile into diglycerides and monoglycerides.

 Fats       →    Diglycerides        →    Monoglycerides

Nucleases in the pancreatic juice acts on nucleic acids to form nucleotides and nucleosides.

 Nucleic acid      →        nucleases    →     nucleosides

Large intestine

The long, tube-like organ that is connected to the small intestine at one end and the anus at the other. It is about 1.5meters length. The large intestine has four part: cecum, colon, rectum, and canal. The colon is the largest portion of the large intestine. The large intestine absorbs water and any remaining absorbable nutrients from the food before sending the indigestible matter to the rectum. The colon absorbs vitamins that are created by the colonic bacteria, such as thiamine, riboflavin, and vitamin K      ( especially important as the daily ingestion of vitamin K is not normally enough to maintain adequate blood coagulation ). It also compacts feces, and stores fecal matter in the rectum until it can be discharged via the anus in defecation.

Disorder of Digestive system

A digestive disease is any health problem that occurs in the digestive tract. The reason for the digestive disorder are varied, it can range from either bacterial or viral infections which many effect the digestive tract. Also parasites present in the intestine can cause infection in the digestive tract. Example: Tapeworm, Roundworm, Threadworm. Digestive disorder include Vomiting, Constipation, Diarrhoea, and indigestion.

Vomiting: Vomiting is an uncontrollable reflex that expels the contents of the stomach through the mouth. This is usually due to some underlying disorder, gastrointestinal infection, food allergy, food poisoning.

Constipation: Constipation occurs when bowel movements become less frequent and stool become difficult to pass. It happens most often due to changes in diet or routine, or due to inadequate intake of fiber.

Diarrhoea: Diarrhoea is the condition of having at least three loose, liquid, or watery bowel movements each day. It involves fluid loss and therefore may eventually lead to dehydration.

Indigestion: Indigestion is a general term which used to describe upper abdominal or stomach discomfort and pain which is correlated food. Indigestion is not a disease.        



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