0Human beings are heterotrophic omnivore’s organisms. They obtain their food from plants, Animal and their products by holozoic mode of nutrition. Human digestive system consists of an alimentary canal and many digestive glands.
Alimentary canal is a long tube with muscular wall, glandular epithelial lining and varying diameter. It extends from mouth to the last point. Alimentary canal measures about 9 meter long tube in which duct of several digestive glands open to secretes their respective digestive secretions. Alimentary canal consists of several organs.
- Mouth: Opening of human digestive system which gives passage for ingestion of food. It is guarded by pair of labia.
Buccal Cavity: large space bounded above by the palate. There are pair of jaws and soft muscular tongue, each jaw has 16 teeth with formula I2/2, C1/1, Pm 2/2, M3/3 and four types of teeth in each jaws. Teeth cut the food into small pieces and chew them to make it soft for easy swallowing. Salivary gland secretes salvia in Mouth cavity through their duct that is ptyalin also called the salivary amylase. It act on carbohydrate and split into simple form thus digestion of carbohydrates begins from it. 
- Pharynx: It is funnel shaped vertical canal that serves as a passage way for food from buccal cavity to the oesophagus.
- Oesophagus: It is a tubular structure which serves as to carry the food from pharynx to stomach. It is not concerned with digestion but represents the contraction and expansion of walls i.e. peristaltic movement.
- Stomach: It is site for food where it stored for short interval of time. Here protein digestion starts this will occur by the help of gastric juice (Action of pepsin).
- Small Intestine: It is the longest part of alimentary canal. It has three parts. Duodenum, jejunum & ileum. Here each type of food completely digested. In this pancreatic and bile juice help to increase its absorption area.
- Large intestine: It also consists of three parts Caecum, colon & Rectum. It is shorter but wider in diameter. It also secretes mucus for lubrication. Faecal matter is egested through the external point.
