HUMAN DIGESTIVE SYSTEM
• Human digestive system- consists of the long alimentary canal that includes mouth,
pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
• Organs for assistance- pancreas, liver
• It has 5 steps of the Digestive System:
1. Ingestion – Consumption or intake of food.
2. Digestion – The process by which food is mechanically and chemically broken
down to simpler absorbable forms.
3. Absorption – The small intestine cells absorb simpler absorbable molecules such
as glucose, which are then transported to blood.
4. Assimilation – Use of absorbed food to get energy and to repair tissues.
5. Defecation – The removal of waste material i.e., stool.
Nutrition in humans:
Mouth-
• 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.
• There are 32 teeth in humans which are of four types as incisors, canines, premolars
and molars.
2123
• Dental formula of human is 2123 = 32
• Tongue helps in chewing, moistening, rolling and swallowing of food.
• Saliva also has salivary amylase which begins the digestion of the starch or
carbohydrate in mouth.
Oesophagus-
• There is no any digestion in oesophagus.
• Food is carried from mouth to stomach by peristaltic movement in oesophagus.
• The peristaltic movement also called as the Peristalsis refers to the contraction and
relaxation of the food in the oesophagus and the food pipe and the food is forced down
the track to the stomach.
Stomach-
• The stomach is a J-shaped organ. It stores food for 4 to 5 hours.
• The stomach walls contain s three tubular glands in it walls which secrete gastric juice.
• The gastric juice contains three substances: Hydrochloric acid, the enzyme pepsin, and
mucus.
• Function of HCl-
1. It kills the bacteria which enters along with the food.
2. The hydrochloric creates an acidic medium which activates the enzyme
pepsinogen to pepsin.
• Function of Pepsin- They help in the digestion of proteins.
• Function of Mucus- The mucus helps to protect the stomach wall from its own
secretions of hydrochloric acid.
• The partially digested and semi liquid form of food (chyme)then goes from the stomach
into the small intestine.
• The food from stomach eventually moves into the small intestine.
Small Intestine-
• It is 6.5 metres long in humans.
• Duodenum receives enzymatic secretions of pancreas and bile of liver and gall bladder.
• It also secretes intestinal juice which helps in digestion.
• It is the site where complete digestion of carbohydrates, proteins, and fats takes place.
• Here finally food is breakdown to simpler absorbable forms.
• It is the site of absorption also as small intestine contains of villi which increase surface
area from which food is absorbed to blood. Now absorbed food use in respiration to
assimilate it to get energy.
Large Intestine-
• The remaining undigested waste material, also known as stool or faeces, are stored
temporarily in rectum.
• It is then removed outside the body from anus, a process known as egestion.
About Liver and Gall Bladder-
• Liver is the largest gland of the body and secretes bile juice.
• Bile juice is stored in the gall bladder and has a significant role in the digestion of fats
by its emulsification.
