Digestiive System, Parts & Functions in humans

Digestive system in humans

What is digestion?

  • Digestion is the process by which food is changed into a simple, soluble, diffusible, and usable form.

Digestion involves two process:-  Mechanical and Chemical.

  • Mechanical breakdown of food takes place in the mouth. Chewing breaks the food into smaller pieces so chemical breakdown can occur.
  • Chemical breakdown changes large complex food molecules into small, simpler molecules that can be absorbed by the body.

Digestive System In Human
Digestive System In Human

Digestive system

The digestive system is a group of organs (Mouth, Esophagus, Stomach, Small intestine, Pancreas & Liver)  working together to convert food into energy and basic nutrients to feed the entire body. Food passes through a long tube inside the body known as the alimentary canal or the gastrointestinal tract 



The Digestion Process

  • Food enters the mouth and teeth chew the food to break it down into small pieces and mixes with saliva.
  • .Saliva contains two main substances:- An enzyme called Amylase which starts to digest starches.and Mucus which wets the food and makes it easier to swallow.
  • The food is then swallowed and travels down the Esophagus to the Stomach. The Stomach is a muscular sac where food is temporarily stored and can expand and shrink depending on the amount of food ingested. Once the food is in the stomach is it sealed by two strong muscles at each end called the sphincter muscles.
  • For the next few hours peristaltic waves pass along the walls of the stomach. They mechanically break down the food and mix it with gastric juice made and secreted by cells in the stomach wall.
  • Gastric juices contain the enzyme pepsin which starts the breakdown of proteins.  It also contains hydrochloric acid which kills any germs in the food.
  • The processes in the stomach turn the food into a creamy semi-liquid called chyme.  The lower sphincter muscle relaxes and the chyme is released into the small intestine.
  • The small intestine is 6 meters long.  The first 25 cm are called the duodenum and the rest is the ileum.  Muscles in the wall of the small intestine mechanically breakdown food and three new digestive juices (Bile, Pancreatic Juice, Intestinal juice) are released to chemically break down the food further.
  • Bile is produced in the liver and stored in the gall bladder before it enters the duodenum through the bile duct.  Bile neutralizes the acid in the chyme and breaks up any fats or oils (lipids) into smaller pieces.
  • Pancreatic juice is produced by the pancreas and is secreted into the duodenum.  Pancreatic juice contains the enzymes trypsin, amylase, and lipase.
            1.Trypsin breaks down proteins.

            2.Amylase breaks down starch.

            3.Lipase breaks down lipids.
  • Intestinal juice are produced by special cells in the intestine wall. Intestinal juices contain protease enzymes to complete the digestion of proteins and carbohydrase enzymes to finish the digestion of carbohydrates.
  • The small intestine also finger-like projection called villa along its walls.  The villa increase surface area and allow absorption of nutrients. The cell wall of the villi is very thin, allowing diffusion to easily occur. Each villi is well supplied with blood for nutrients to enter and also contains a lymph vessel into which fatty acids and glycerol (waste from breakdown of starch can pass.  Nutrients absorbed into the blood are then taken to the liver where it will be stored or processed so it can be used by different parts of the body.
  • The food then travels to the large intestine.  By this time most of the useful nutrients have been removed and mostly water and minerals remain.  The water and minerals are absorbed into the blood.
  • The remaining solid material then moves to the rectum and is then called faecal matter.
  • The fecal matter is then formed into faeces and exits the body through the anus.



Summary of digestion in the human alimentary canal

Summary of digestion in the human alimentary canal
Part of alimentary canalSource of enzymeEnzymeFood digestedProductsNotes
MouthSalivary glandsAmylasestarchmaltosefood chewed to break it up, saliva also lubricates the food for swallowing
Stomachstomach wall secretes gastic juicesRenninsoluble milk proteininsoluble milk proteinhudrochloric acid also secreted by
Small Intestinepancreas secretes pancreatic juiceTrypsinproteinpeptides and amino acidsbile is added from the liver via the gallbladder and the bile duct; bile salts neutralize the acid chyme; contents of small intestines are alkaline; bile salts emulsify the fats containing
Lipasefatsfatty acids and
intestinal juiceSucrasesucroseglucose and fructose
Peptidasepeptidesamino acids
Lipasefatsfatty acids and

The digestive process (Table)

OrganMovementDigestive Juices UsedFood Particles
Broken Down
MouthChewingSaliva & MucusStarches
StomachUpper muscle in stomach relaxes to let food enter and lower muscle mixes food with digestive juiceStomach acid - Gastric juicesProtein
Small intestinePeristalsisSmall intestine
digestive juice
Starches, protein, and
PancreasNonePancreatic juiceStarches, fats, and
LiverNoneBile acidsFats

Products Of Digestion

Products of Digestion
Complex food moleculeSimple, soluble, breakdown products
carbohydratesSimple sugars e.g. glucose, galactose, fructose
fats and oilsFatty acids and glycerol
proteinsamino acids

Cell Structure and Organization 

Classification of Living Things

Major groups of living things