It is a method of nutrition that involves the ingestion of liquid or solid organic material.
It involves different steps namely, ingestion, digestion, absorption, assimilation and egestion.
Human beings exhibit holozoic mode of nutrition involving five basic steps.
Digestion is the process by which complex food is broken down into simple absorbable form.
Digestion of food starts from mouth and ends in small intestine
Digestive system is made up of alimentary canal and associated glands.
Digestive system in human beings:
Digestive system in human beings is formed by alimentary canal and digestive glands.
Parts of alimentary canal:
It comprises different parts like mouth, oesophagus, stomach, small intestine and large intestine. It starts with mouth and ends with anus.
The process of taking in food through mouth is called as ingestion.
Digestion of food starts in the mouth with the help of salivary amylase present in the saliva.
Salivary amylase is the enzyme which digests starch into glucose for absorption
Pharynx is the common channel for food and air. When we swallow food, a flap-like valve called the epiglottis closes the windpipe. Epiglottis prevents the entry of food particles into respiratory tract.
Oesophagus also called as food pipe helps in conveying the food from buccal cavity to stomach. The oesophagus is also known as the gullet. It is about 25 centimetres long.
Peristaltic movements are the alternate contractions and relaxations of oesophageal wall which bring about movement of food from buccal cavity to the stomach.
Food conveyed to the stomach is called as bolus as it is round in shape.
Stomach is the widest part of the alimentary canal. It is a J-shaped muscular organ divided into three parts namely, cardia, fundus and pylorus regions.
Stomach as a whole can hold at about two litres of food.
Stomach secretes a fluid called as digestive juice called gastric juice .
Small intestine is made up of three regions namely duodenum, jejunum and ileum.
• Acidic chyme from the stomach is received by the duodenum for further digestion.
Large intestine comprises of colon and rectum. Large intestine receives undigested food from small intestine.
Water from the food is reabsorbed to a great extent in the large intestine.
Salivary glands are present inside the buccal cavity. They secrete saliva. Saliva helps in lubrication of food . This saliva plays an important role in breaking down complex components like starch into simple sugars. It brings about partial digestion of starch.
Gastric glands are microscopic glandular cells present in the inner lining of the stomach. Gastric glands secrete gastric juice comprising HCl, pepsin and prorennin.
Intestinal glands are present in the inner lining of small intestine. These secrete various enzymes which aid in the process of digestion of all the components of food.
Liver is the largest gland in our body. The liver secretes a yellowish green watery fluid called bile. It is temporarily stored in a sac called the gall bladder.
Pancreas is the mixed gland. It acts as both endocrine and exocrine gland. The pancreas secretes the pancreatic juice that helps to digest carbohydrates, proteins and fats. The pancreatic juice converts carbohydrates into simple sugars and glucose, proteins into amino acids, and the lipids into fatty acids and glycerol.
Absorption: The process of allowing simple absorbable nutrients into blood capillaries through surface of the villi is called as absorption. Inner wall of small intestine comprises many finger like projections called as villi. Villi increase the surface area for absorption of food.
Each villus is made up of central structure called as lacteal which mainly absorbs simple fats and transports them into lymphatic system.
Solved questions Class 7 Science Nutrition in Animals
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