1. What are the main functions of the digestive system?
Answer:
The digestive system has several key functions:
- Ingestion: The process of taking in food and liquids through the mouth.
- Digestion: The breakdown of food into simpler forms. This occurs in two ways: mechanical digestion (e.g., chewing) and chemical digestion (e.g., enzyme action).
- Absorption: The nutrients from digested food are absorbed primarily in the small intestine into the bloodstream for distribution to the body.
- Secretion: The production and release of digestive enzymes, acids, and bile to help break down food.
- Excretion: The elimination of indigestible substances from the body, primarily through the rectum as feces.
2. Describe the structure and function of the human mouth in digestion.
Answer:
The mouth is the entry point for food. It is involved in both mechanical and chemical digestion:
- Mechanical digestion: Teeth break down food into smaller pieces, increasing the surface area for enzymes to act on.
- Chemical digestion: Salivary glands secrete saliva, which contains the enzyme amylase that begins the breakdown of carbohydrates. Saliva also moistens food, making it easier to swallow.
- Tongue: It helps mix food with saliva and pushes it toward the back of the throat for swallowing.
3. What is peristalsis and how does it contribute to digestion?
Answer:
Peristalsis is the series of wave-like muscle contractions that move food through the digestive tract. These contractions occur in the smooth muscles of the esophagus, stomach, and intestines. In the esophagus, peristalsis helps push the bolus of food down to the stomach. In the intestines, peristalsis helps move the food along the gastrointestinal tract, ensuring that nutrients are absorbed and waste is eliminated.
4. Explain the structure and function of the stomach in digestion.
Answer:
The stomach is a muscular, J-shaped organ that performs both mechanical and chemical digestion. Its structure includes:
- Mucosal lining: This secretes gastric juices, which contain hydrochloric acid and the enzyme pepsin. Hydrochloric acid provides an acidic environment that activates pepsin and helps in the breakdown of proteins.
- Muscle layers: The stomach has three layers of muscles that churn food, turning it into a semi-liquid substance called chyme.
- Pyloric sphincter: This regulates the release of chyme into the small intestine.
5. Describe the role of bile in digestion and where it is produced.
Answer:
Bile is a digestive fluid produced by the liver and stored in the gallbladder. Its main role is to emulsify fats, breaking them down into smaller droplets, which increases the surface area for the enzyme lipase to act upon. Bile is released into the small intestine, where it helps in the digestion and absorption of fats and fat-soluble vitamins (A, D, E, and K).
6. What is the role of the pancreas in digestion?
Answer:
The pancreas has both endocrine and exocrine functions. As an exocrine organ, it secretes digestive enzymes into the small intestine:
- Amylase: Breaks down carbohydrates.
- Lipase: Breaks down fats.
- Proteases (e.g., trypsin): Break down proteins. Additionally, the pancreas secretes sodium bicarbonate to neutralize the acidic chyme entering the small intestine from the stomach, providing an optimal pH for enzyme activity.
7. What are villi and microvilli, and how do they contribute to nutrient absorption?
Answer:
Villi are tiny, finger-like projections found in the lining of the small intestine. Each villus is covered with even smaller projections called microvilli, which form the “brush border”. These structures increase the surface area of the small intestine, allowing for efficient absorption of nutrients such as amino acids, glucose, and fatty acids. Nutrients pass from the cells of the villi into capillaries or lymph vessels for transport throughout the body.
8. Explain the process of carbohydrate digestion from the mouth to the small intestine.
Answer:
Carbohydrate digestion begins in the mouth, where the enzyme amylase, found in saliva, starts breaking down starches into simpler sugars. The food then travels to the stomach, where no carbohydrate digestion occurs due to the acidic environment. In the small intestine, pancreatic amylase continues the breakdown of starches. Finally, enzymes located on the microvilli of the small intestine (such as maltase, sucrase, and lactase) break down disaccharides into monosaccharides (glucose, fructose, and galactose), which are absorbed into the bloodstream.
9. Describe the process of protein digestion in the stomach and small intestine.
Answer:
Protein digestion begins in the stomach, where the enzyme pepsin breaks down proteins into smaller polypeptides. The acidic environment in the stomach activates pepsin. After the food moves to the small intestine, pancreatic enzymes such as trypsin and chymotrypsin further break down the polypeptides into smaller peptides and amino acids. These amino acids are absorbed through the walls of the small intestine into the bloodstream.
10. How is fat digested and absorbed in the digestive system?
Answer:
Fat digestion begins in the small intestine, where bile emulsifies large fat globules into smaller droplets, increasing their surface area for enzyme action. The enzyme lipase, secreted by the pancreas, breaks down the fats into fatty acids and glycerol. These components are absorbed by the epithelial cells of the small intestine, where they are reassembled into triglycerides and transported via lymphatic vessels in the form of chylomicrons.
11. What is the role of the large intestine in digestion and water absorption?
Answer:
The large intestine primarily absorbs water and electrolytes from the undigested food matter that passes from the small intestine. This helps to form solid feces. The colon also houses a large number of beneficial bacteria that help in the fermentation of undigested carbohydrates, producing gases and short-chain fatty acids, which are absorbed for energy. The remaining waste is stored in the rectum until excretion.
12. What is the function of the esophagus in the digestive system?
Answer:
The esophagus is a muscular tube that connects the mouth to the stomach. Its primary function is to transport swallowed food from the mouth to the stomach through the process of peristalsis. The esophagus does not participate in digestion but ensures that food moves efficiently from one organ to the next.
13. Explain the structure and function of the digestive enzymes secreted by the pancreas.
Answer:
The pancreas secretes several digestive enzymes that help break down macromolecules in food:
- Amylase: Breaks down carbohydrates into simple sugars.
- Lipase: Breaks down fats into fatty acids and glycerol.
- Proteases (e.g., trypsin, chymotrypsin): Break proteins into smaller peptides and amino acids. These enzymes are released into the small intestine, where they assist in the digestion of food.
14. What is the role of the liver in digestion, apart from bile production?
Answer:
Apart from bile production, the liver plays an important role in:
- Detoxification: It detoxifies harmful substances from the blood, including alcohol, drugs, and metabolic waste.
- Metabolism: It stores glucose in the form of glycogen and releases it into the bloodstream when needed. It also processes proteins, fats, and carbohydrates.
- Storage of vitamins and minerals: The liver stores vitamins A, D, and B12, and iron.
15. What is the significance of the pyloric sphincter in digestion?
Answer:
The pyloric sphincter is a muscular valve located at the junction between the stomach and the small intestine. Its function is to control the release of chyme from the stomach into the small intestine. It ensures that chyme is released gradually, allowing the small intestine to effectively absorb nutrients and preventing overwhelming the intestine with too much food at once.
16. How does the digestive system maintain homeostasis?
Answer:
The digestive system helps maintain homeostasis by ensuring that nutrients and energy are available to cells in the body. It regulates the absorption of water, electrolytes, and nutrients, and helps maintain fluid balance and pH levels. The digestive system also works with other systems, such as the endocrine system, to regulate hormones that control hunger, satiety, and metabolism.
17. What role does the tongue play in digestion?
Answer:
The tongue plays a crucial role in mechanical digestion and in preparing food for swallowing. It helps move food around the mouth, mixes it with saliva, and aids in the formation of a bolus (a soft, rounded mass of chewed food). The tongue also assists in the tasting of food through taste buds.
18. Explain the process of swallowing and its stages.
Answer:
Swallowing, also called deglutition, occurs in three stages:
- Oral stage: The tongue pushes the bolus of food to the back of the mouth, initiating the swallowing reflex.
- Pharyngeal stage: The bolus moves through the pharynx and the epiglottis closes off the windpipe to prevent food from entering the respiratory tract.
- Esophageal stage: The bolus is pushed into the esophagus by peristalsis, moving it to the stomach.
19. What is the significance of the intestinal flora in digestion?
Answer:
The intestinal flora, also known as gut microbiota, consists of trillions of bacteria in the large intestine. These bacteria play an essential role in:
- Fermenting undigested carbohydrates: Producing short-chain fatty acids and gases.
- Synthesizing vitamins: Such as vitamin K and certain B vitamins.
- Maintaining gut health: By preventing the growth of harmful microorganisms and supporting the immune system.
20. How does the digestive system handle the absorption of vitamins and minerals?
Answer:
Vitamins and minerals are absorbed in the small intestine. Water-soluble vitamins (e.g., Vitamin C, B-complex) are absorbed directly into the bloodstream, while fat-soluble vitamins (A, D, E, K) are absorbed through the intestinal lining into lymph vessels and then transported to the bloodstream. Minerals like calcium, iron, and magnesium are absorbed through specific transport proteins in the small intestine.
