Problem 14 - Biology: The Unity and Diversity of Life

Question

Match each substance with its description. ______gastrin ______dentin ______bicarbonate ______bile ______salivary amylase ______pepsin a. enzyme that acts in stomach b. emulsifies fats c. breaks down polysaccharides d. raises the \(\mathrm{pH}\) of chyme e. makes up the bulk of a tooth f. hormone made by stomach

Step-by-Step Solution

Answer

Gastrin - f, Dentin - e, Bicarbonate - d, Bile - b, Salivary Amylase - c, Pepsin - a.

Step 1: Identify Properties of Gastrin

Gastrin is known to be a hormone that stimulates secretion of gastric acid by the stomach. Therefore, it is associated with option (f): hormone made by stomach.

Step 2: Recognize Characteristics of Dentin

Dentin is the calcified tissue that forms the bulk of a tooth, underlying the enamel. Thus, it matches with option (e): makes up the bulk of a tooth.

Step 3: Understand Bicarbonate Function

Bicarbonate acts as a buffer to increase the \( ext{pH}\) of chyme as it enters the small intestine, which corresponds with option (d): raises the \( ext{pH}\) of chyme.

Step 4: Determine Role of Bile

Bile is produced by the liver and stored in the gallbladder, and it emulsifies fats to aid in their digestion, matching option (b): emulsifies fats.

Step 5: Identify Function of Salivary Amylase

Salivary amylase is an enzyme in saliva that initiates the breakdown of polysaccharides, such as starch, into simpler sugars, matching option (c): breaks down polysaccharides.

Step 6: Describe Pepsin Action

Pepsin is an enzyme in the stomach that breaks down proteins into peptides, which aligns with option (a): enzyme that acts in stomach.

Key Concepts

Gastrin

Gastrin is a key hormone in the digestive system. It is produced by G-cells in the stomach lining. Its main function is to regulate gastric acid secretion. Gastrin stimulates the stomach to secrete hydrochloric acid (HCl). This creates an acidic environment, enabling optimal enzyme activity for digestion. Other useful effects include promoting stomach contractions. This helps mix and break down food.

Gastrin release is triggered by several factors:

• Presence of food in the stomach
• Stomach stretching from food intake
• Other digestive hormones like secretin

Inhibitors of gastrin include high acidity in the stomach, which ensures a balanced digestive system.

Dentin

Dentin is a crucial component of the tooth's structure. It is located beneath the enamel and above the pulp chamber. Dentin forms the bulk of the tooth and provides structural support. It is harder than bone but softer than enamel, making it resilient yet strong enough for chewing.

Dentin is made up of:

• Collagen fibers
• Minerals, primarily calcium phosphate
• Microtubules that allow nutrients to reach the tooth pulp

Dentin's unique properties help protect the inner pulp and nerves from temperature changes and physical damage. It can be sensitive, and exposure can sometimes lead to pain.

Bicarbonate

Bicarbonate is an essential buffer in the digestive system. Its primary role is to neutralize stomach acid as it enters the small intestine. This is important because the enzymes in the small intestine require a near-neutral pH to function properly.

Sources of bicarbonate in the digestive system include:

• Pancreatic secretions
• Bile from the liver
• Intestinal secretions

The addition of bicarbonate to the digestive process ensures that the food and acid mixture (chyme) does not damage the intestinal lining and that digestion continues smoothly.

Bile

Bile is a yellowish-green fluid produced by the liver. It plays a vital role in digestion, particularly in the emulsification of fats. Stored in the gallbladder, bile is released into the small intestine in response to food intake, especially fats.

Key functions of bile include:

• Emulsifying fats to increase their surface area
• Aiding in the absorption of fat-soluble vitamins (A, D, E, and K)
• Helping eliminate waste products like cholesterol and bilirubin

Without bile, fats would clump together, making it difficult for enzymes like lipase to break them down.

Salivary Amylase

Salivary amylase is an enzyme found in saliva. It initiates the digestion of starch, a carbohydrate, in the mouth. It breaks down polysaccharides into simpler sugars, such as maltose and dextrin. This is the first step in carbohydrate digestion before the food reaches the stomach.

Salivary amylase helps with:

• Facilitating the digestion of complex carbohydrates
• Contributing to the sweet taste of some foods as they break down
• Producing sugars that can be easily absorbed by the body

This enzyme provides an immediate energy source, as simple sugars are quickly absorbed into the bloodstream. It is most active in the slightly alkaline environment of the mouth.