Answer :
- Saliva enters the oral cavity.
- Bile enters the duodenum.
- Gastric juice enters the stomach.
- Pancreatic juice enters the duodenum.
To categorize each secretion based on where it enters the digestive tract:
1. **Saliva:**
- **Category:** Oral Cavity
- **Reasoning:** Saliva is produced by salivary glands in the mouth and enters the digestive tract in the oral cavity to aid in the initial breakdown of carbohydrates.
2. **Bile:**
- **Category:** Duodenum (Small Intestine)
- **Reasoning:** Bile is produced by the liver and stored in the gallbladder. It enters the digestive tract in the duodenum, where it aids in the emulsification and digestion of fats.
3. **Gastric Juice:**
- **Category:** Stomach
- **Reasoning:** Gastric juice is produced by the gastric glands in the stomach lining and enters the digestive tract within the stomach. It contains enzymes and hydrochloric acid to assist in protein digestion.
4. **Pancreatic Juice:**
- **Category:** Duodenum (Small Intestine)
- **Reasoning:** Pancreatic juice is produced by the pancreas and enters the digestive tract in the duodenum. It contains enzymes that further break down carbohydrates, fats, and proteins.
In summary:
- Saliva enters the oral cavity.
- Bile enters the duodenum.
- Gastric juice enters the stomach.
- Pancreatic juice enters the duodenum.