This lesson covers:
- The organs of the alimentary canal
- The mechanical and chemical breakdown of food
Parts of the alimentary canal
The alimentary canal is the path food travels through during digestion.
- Mouth – Chewing happens here to break up food. Saliva contains an enzyme, amylase, that starts digesting carbohydrates.
- Oesophagus – Transports food to the stomach.
- Stomach – Churns and mixes food. Stomach acid gives the correct conditions for proteases to begin digesting proteins.
- Liver – Makes alkaline bile to emulsify fats.
- Pancreas – Produces enzymes to digest carbohydrates, fats, and proteins.
- Small intestine – Absorbs nutrients from broken down food.
- Large intestine – Absorbs water.
- Rectum – Stores undigested waste until it’s egested.
Mechanical and chemical digestion
Digestion involves breaking down the food we eat so the nutrients can be absorbed.
This happens in two main steps:
- Mechanical breakdown – Physically breaking down food into smaller pieces.
- Chemical breakdown – Chemically breaking down large molecules to small soluble molecules using enzymes.
Mechanical digestion
Mechanical digestion mainly happens in the mouth and stomach:
- Food is chewed and mixed with saliva, which contains mucus to lubricate food and the enzyme amylase.
- In the stomach, muscular contractions churn and mix food with stomach acids and enzymes.
Chemical digestion
Digestive enzymes chemically breakdown food molecules into smaller soluble molecules that can be absorbed.
There are three important digestive enzymes:
- Amylase – Breaks down carbohydrates.
- Protease – Breaks down proteins.
- Lipase – Breaks down fats and lipids.
Bile produced by the liver also emulsifies fats in the small intestine. This involves breaking down fats into smaller pieces for enzymes to act on them.
Where do we find digestive enzymes?
| Enzyme | Substrate | Where the enzyme is released |
|---|---|---|
| Amylase | Carbohydrates | Mouth, small intestine |
| Protease | Proteins | Small intestine, stomach |
| Lipase | Lipids | Small intestine |
All three of these types of enzyme can be produced by the pancreas and small intestine.
PRACTICE QUIZ
1. What is the alimentary canal?
Answer: The alimentary canal, also known as the digestive tract, is the pathway through which food travels during digestion. It includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus.
2. What happens in the mouth during digestion?
Answer: In the mouth, food is chewed (mechanical digestion) and mixed with saliva, which contains the enzyme amylase that begins the chemical digestion of carbohydrates.
3. What is the role of the esophagus?
Answer: The esophagus transports food from the mouth to the stomach through a series of muscular contractions called peristalsis.
4. How does the stomach contribute to digestion?
Answer: The stomach churns and mixes food with stomach acid and enzymes, creating a semi-liquid mixture called chyme. The acidic environment activates proteases that begin protein digestion.
5. What is the function of the liver in digestion?
Answer: The liver produces bile, which emulsifies fats, breaking them down into smaller droplets that are easier for enzymes to digest.
6. What role does the pancreas play in digestion?
Answer: The pancreas produces enzymes such as amylase, protease, and lipase, which are released into the small intestine to aid in the digestion of carbohydrates, proteins, and fats.
7. What happens in the small intestine?
Answer: The small intestine is the primary site for nutrient absorption. It also receives digestive enzymes from the pancreas and bile from the liver to continue the chemical breakdown of food.
8. What is the function of the large intestine?
Answer: The large intestine absorbs water and electrolytes from the remaining indigestible food matter and compacts it into feces for excretion.
9. What is the rectum’s role in the digestive system?
Answer: The rectum stores undigested waste until it is egested (expelled) from the body through the anus.
10. What is mechanical digestion?
Answer: Mechanical digestion is the physical breakdown of food into smaller pieces. It occurs primarily in the mouth through chewing and in the stomach through churning.
11. What is chemical digestion?
Answer: Chemical digestion is the process of breaking down large food molecules into smaller soluble molecules using enzymes.
12. What enzymes are involved in digestion and what do they do?
Answer: Key digestive enzymes include:
- Amylase: Breaks down carbohydrates into simple sugars.
- Protease: Breaks down proteins into amino acids.
- Lipase: Breaks down fats into fatty acids and glycerol.
13. Where is amylase found and what does it digest?
Answer: Amylase is found in saliva (produced by the salivary glands) and in the small intestine. It digests carbohydrates into simple sugars.
14. Where is protease found and what does it digest?
Answer: Protease is found in the stomach (as pepsin) and in the small intestine. It digests proteins into amino acids.
15. Where is lipase found and what does it digest?
Answer: Lipase is found in the small intestine. It digests fats into fatty acids and glycerol.
16. What is bile and what is its function in digestion?
Answer: Bile is a digestive fluid produced by the liver and stored in the gallbladder. It emulsifies fats in the small intestine, breaking them down into smaller droplets for easier digestion by lipase.
17. How is food moved through the alimentary canal?
Answer: Food is moved through the alimentary canal by muscular contractions called peristalsis, which push the food along the digestive tract.
18. What is the significance of the villi in the small intestine?
Answer: Villi are small, finger-like projections lining the small intestine that increase the surface area for nutrient absorption.
19. What happens to nutrients after they are absorbed in the small intestine?
Answer: After absorption, nutrients enter the bloodstream through the capillaries in the villi and are transported to various cells in the body for use or storage.
20. What is the role of the epiglottis in digestion?
Answer: The epiglottis is a flap of tissue that covers the trachea during swallowing, preventing food from entering the respiratory tract and directing it to the esophagus.
21. What causes heartburn and how is it related to digestion?
Answer: Heartburn is caused by stomach acid refluxing into the esophagus, leading to a burning sensation. It occurs when the lower esophageal sphincter fails to close properly.
22. What is the function of mucus in the digestive system?
Answer: Mucus lubricates food, protects the lining of the digestive tract from digestive enzymes and stomach acid, and aids in the smooth passage of food.
23. How are digestive enzymes activated?
Answer: Digestive enzymes are often activated by specific conditions in the digestive tract, such as the acidic environment in the stomach for pepsin or the presence of bile in the small intestine for lipase.
24. What are the different parts of the large intestine?
Answer: The large intestine consists of the cecum, colon (ascending, transverse, descending, and sigmoid), rectum, and anus.
25. What is the role of the colon in digestion?
Answer: The colon absorbs water and electrolytes from indigestible food matter and compacts it into feces for excretion.
26. How does the body regulate digestion?
Answer: Digestion is regulated by hormones (such as gastrin, secretin, and cholecystokinin) and nervous system signals that control the release of digestive enzymes and other digestive processes.
27. What is the function of the gallbladder?
Answer: The gallbladder stores and concentrates bile produced by the liver and releases it into the small intestine to aid in the digestion of fats.
28. What is the significance of the hepatic portal vein?
Answer: The hepatic portal vein transports nutrient-rich blood from the digestive organs to the liver for processing, detoxification, and nutrient storage.
29. What is chyme?
Answer: Chyme is the semi-liquid mixture of partially digested food and digestive juices that forms in the stomach and moves into the small intestine.
30. How long does it take for food to pass through the digestive system?
Answer: It typically takes about 24 to 72 hours for food to pass through the entire digestive system, depending on the type of food and individual digestive health.
31. What is the function of the appendix?
Answer: The appendix is a small, finger-like projection attached to the cecum. Its function is not fully understood, but it may play a role in immune function and gut flora maintenance.
32. What causes digestive disorders like IBS?
Answer: Irritable bowel syndrome (IBS) can be caused by a variety of factors, including stress, diet, hormonal changes, and abnormal muscle contractions in the intestines.
33. What is the role of the mesentery?
Answer: The mesentery is a fold of tissue that attaches the intestines to the abdominal wall and contains blood vessels, nerves, and lymphatics that supply the intestines.
34. How does the body absorb vitamins and minerals?
Answer: Vitamins and minerals are absorbed in the small intestine through various mechanisms, including active transport, passive diffusion, and facilitated diffusion.
35. What is lactose intolerance?
Answer: Lactose intolerance is the inability to digest lactose, a sugar found in milk and dairy products, due to a deficiency in the enzyme lactase.
36. What is the function of the enzyme lactase?
Answer: Lactase breaks down lactose into glucose and galactose, which can be absorbed in the small intestine.
37. How do probiotics support digestive health?
Answer: Probiotics are beneficial bacteria that support digestive health by maintaining a healthy balance of gut flora, aiding in digestion, and enhancing the immune response.
38. What is the role of dietary fiber in digestion?
Answer: Dietary fiber adds bulk to stool, helps regulate bowel movements, and supports gut health by promoting the growth of beneficial bacteria.
39. What is peristalsis?
Answer: Peristalsis is a series of wave-like muscle contractions that move food through the digestive tract.
40. What are digestive enzymes and where are they produced?
Answer: Digestive enzymes are proteins that break down food into absorbable nutrients. They are produced in the salivary glands, stomach, pancreas, and small intestine.
41. How does the body digest fats?
Answer: Fats are emulsified by bile in the small intestine, then broken down by lipase into fatty acids and glycerol for absorption.
42. What are the symptoms of a digestive enzyme deficiency?
Answer: Symptoms can include bloating, gas, diarrhea, and malabsorption of nutrients, leading to deficiencies and weight loss.
43. What is the enteric nervous system?
Answer: The enteric nervous system is a network of neurons that governs the function of the gastrointestinal system, often referred to as the “second brain.”
44. How does the stomach protect itself from acid?
Answer: The stomach is lined with a thick layer of mucus that protects its walls from being eroded by stomach acid.
45. What is gastritis?
Answer: Gastritis is the inflammation of the stomach lining, which can be caused by infection, chronic use of NSAIDs, excessive alcohol consumption, or stress.
46. How does the body regulate stomach acid production?
Answer: Stomach acid production is regulated by hormones (such as gastrin) and nervous system signals that respond to the presence of food.
47. What is the role of the pyloric sphincter?
Answer: The pyloric sphincter controls the passage of chyme from the stomach into the small intestine.
48. What is a colonoscopy and why is it performed?
Answer: A colonoscopy is a procedure in which a flexible tube with a camera is inserted into the colon to examine its interior, often performed to screen for colon cancer or investigate digestive symptoms.
49. What is the function of the duodenum?
Answer: The duodenum is the first section of the small intestine where most chemical digestion occurs, receiving digestive enzymes from the pancreas and bile from the liver.
50. How can digestive health be maintained?
Answer: Digestive health can be maintained by eating a balanced diet rich in fiber, staying hydrated, exercising regularly, managing stress, and avoiding excessive use of alcohol and NSAIDs.