Digestive System (Part-II)

Digestion involves the breaking of complex organic food molecules into simpler one by hydrolysis. Carbohydrates, proteins, fats and nucleic acids are large complex organic food molecules. They are insoluble and polymeric in nature. During digestion different enzymes helps in breakdown of these complex polymers into soluble monomers which are required for energy generation.
The different steps of digestion involve:

1. Movement of food through the alimentary tract
2. Secretion of digestive juices and digestion of food
3. Absorption of water, various electrolytes, vitamins and digestive end products.

Human digestive system mainly consists of two parts: 1) Alimentary tract and 2) secretory glands

1. Alimentary tract: It provides continual supply of nutrients, vitamins, electrolytes and ater. The following steps involved to achieve this.
2. Movement of food through tract
3. Secretion of digestive juices
4. Digestion of food components
5. Absorption of digestive product and water
6. Excretion of unabsorbed food.

Figure 12.1 shows the complete alimentary tract. It comprises the following parts.

1. Mouth: Human mouth consists of vestibule and oral cavity. The slit like space between cheeks and gums is known as vestibule. The cavity surrounded by palate, tongue and teeth is known as oral cavity or buccal cavity. Mouth is the first passage of food where large piece of food is fragmented to small pieces with the help of teeth and mixed with saliva. Tongue manipulates food during chewing and mixing with saliva. This mixture of food with saliva, bolus, is then moved inward through pharynx into Esophagus. This process is known as deglutition or swallowing.