More than one choice may apply.
The pH of chyme entering the duodenum is adjusted by
a. Bile
b. Intestinal juice
c. Enzyme secretions from the pancreas
d. Bicarbonate-rich secretions from the pancreas

Verified step by step guidance

1. Understand the context: Chyme is the partially digested food mixed with stomach acid that enters the duodenum from the stomach. The pH of chyme is highly acidic due to the presence of hydrochloric acid from the stomach.
2. Recognize the physiological need: The duodenum requires a neutral or slightly alkaline pH for optimal enzyme activity and to protect its lining from the acidic chyme. Therefore, mechanisms exist to adjust the pH of chyme.
3. Analyze the options: Evaluate each choice based on its role in digestion and pH regulation. For example, bile primarily emulsifies fats and does not directly neutralize acidity. Intestinal juice contains enzymes and mucus but has limited impact on pH adjustment. Enzyme secretions from the pancreas aid digestion but do not directly neutralize acidity.
4. Focus on bicarbonate-rich secretions: The pancreas produces bicarbonate-rich secretions that are released into the duodenum. Bicarbonate ( ${\mathrm{HCO}}_3$ ) acts as a buffer, neutralizing the acidic chyme and raising its pH to a more suitable level for enzymatic activity.
5. Conclude the correct answers: Based on the analysis, the primary mechanism for adjusting the pH of chyme entering the duodenum is bicarbonate-rich secretions from the pancreas. Other options like bile and intestinal juice may play minor roles but are not the main contributors to pH adjustment.

Key Concepts

Chyme

Chyme is a semi-fluid mass of partially digested food that is expelled from the stomach into the duodenum. It is acidic due to the presence of gastric juices, which contain hydrochloric acid. The pH of chyme is crucial for the proper functioning of digestive enzymes in the small intestine, as these enzymes require a more neutral pH to operate effectively.

Bicarbonate Secretion

Bicarbonate secretion, primarily from the pancreas, plays a vital role in neutralizing the acidity of chyme as it enters the duodenum. Bicarbonate ions react with hydrogen ions in the chyme, raising the pH to a more suitable level for enzymatic activity. This process is essential for optimal digestion and absorption of nutrients in the small intestine.

Intestinal Juice

Intestinal juice is a fluid secreted by the intestinal glands that contains enzymes, mucus, and bicarbonate. It aids in digestion and provides an alkaline environment that further neutralizes the acidic chyme. The composition of intestinal juice is crucial for the breakdown of nutrients and the overall digestive process in the small intestine.