Succus entericus is referred to as :

The correct answer is Intestinal juice.

Let us understand the term and the physiology behind it step-by-step:

1. Etymology and Definition:
The term "succus" is a Latin word meaning juice, and "entericus" is derived from the Greek word "enteron," which refers to the intestine. Therefore, succus entericus literally translates to intestinal juice.

2. Source of Secretion:
Succus entericus is secreted by the mucosa of the small intestine. It is a collective secretion of:
- The secretory cells of the brush border mucosa.
- Goblet cells, which secrete lubricating mucus.
- Crypts of Lieberkühn, which are simple tubular glands found in the mucosal membrane of the intestine.

3. Composition and Role:
This juice contains a variety of enzymes that complete the process of digestion. These include:
- Dipeptidases (for breaking down peptides into amino acids)
- Disaccharidases such as maltase, lactase, and sucrase (for converting disaccharides into simple sugars like glucose)
- Lipases (for digesting lipids into fatty acids and glycerol)
- Nucleosidases (for breaking down nucleotides)
The mucus, combined with bicarbonate ions, provides an alkaline environment (pH ~7.8) that protects the intestinal wall and activates these enzymes.

4. Analysis of Other Options:
- Pancreatic juice: Produced by the exocrine portion of the pancreas, containing enzymes like trypsinogen, chymotrypsinogen, amylases, and lipases.
- Gastric juice: Produced by the gastric glands in the stomach, containing hydrochloric acid (HCl), pepsinogen, and mucus.
- Chyme: The acidic, pulpy, semi-fluid mixture of partially digested food and gastric juices that moves from the stomach into the duodenum.