Ans: Digestion is the process by which the human body breaks down the food we consume into smaller, absorbable molecules that can be used for energy, growth, and repair. It involves both mechanical and chemical processes and occurs in various parts of the digestive system. Here is an overview of the digestion process in the human body:
a). Ingestion:
- Digestion begins with the intake of food through the mouth, where it is chewed and mixed with saliva. Saliva contains enzymes like amylase, which break down carbohydrates into simpler sugars.
b). Propulsion:
- After chewing, the tongue helps form a bolus (a mass of partially digested food) that is then swallowed.
- Swallowing involves the coordinated action of muscles in the mouth and throat, propelling the bolus down the esophagus using a wave-like motion called peristalsis.
c). Stomach:
- The bolus enters the stomach, where gastric glands secrete gastric juice.
- Gastric juice contains hydrochloric acid (HCl) and pepsinogen. HCl activates pepsinogen into pepsin, which starts breaking down proteins.
- The stomach’s churning and mixing actions turn the bolus into a semi-liquid substance called chyme.
d). Small Intestine:
- The chyme is gradually released from the stomach into the small intestine, where most of the digestion and nutrient absorption occur.
- The pancreas secretes digestive enzymes (e.g., pancreatic amylase, lipase, and proteases) into the small intestine to break down carbohydrates, fats, and proteins into simpler forms.
- The liver produces bile, which is stored in the gallbladder and released into the small intestine to emulsify fats, making them easier to digest by enzymes.
- Tiny finger-like projections called villi and microvilli in the lining of the small intestine increase the surface area for nutrient absorption.
- Nutrients, including sugars, amino acids, and fatty acids, are absorbed into the bloodstream through the walls of the small intestine and transported to cells throughout the body.
e). Large Intestine (Colon):
- The remaining undigested and unabsorbed material, along with water and some minerals, enters the large intestine.
- In the large intestine, water is reabsorbed, and the material is further dehydrated to form feces.
- Beneficial bacteria in the large intestine help ferment some undigested carbohydrates, producing gases and certain vitamins.
- Feces are stored in the rectum until they are eliminated from the body through the anus.
f). Absorption and Utilization:
- The absorbed nutrients (sugars, amino acids, fatty acids, vitamins, and minerals) are transported in the bloodstream to various cells and tissues throughout the body.
- These nutrients are used for energy production, growth, repair, and maintenance of bodily functions.
g). Elimination:
- The indigestible and unabsorbed waste, in the form of feces, is eliminated from the body during the process of defecation.