Evolution of Experimental Methods
Initially, physiological functions were studied using acute (vivisection) methods. However, this approach had several major limitations. First, anesthesia inevitably altered the body's natural responses. Second, surgical trauma and direct, unnatural nerve stimulation resulted in data that did not reflect normal gastrointestinal function.
A breakthrough in normal physiology came with the shift to chronic methods. A historical milestone occurred in 1842 when the surgeon V.A. Basov successfully created a chronic gastric fistula in a dog. This was of colossal importance: scientists could finally investigate gastric secretion without anesthesia, free from acute surgical trauma, under conditions closely mimicking the animal's natural state.
The Problem of Obtaining Pure Digestive Juices
During natural feeding, researchers faced a major challenge: the secreted gastric juice immediately mixed with food boluses, making accurate quantitative and qualitative analysis impossible. The solution was the surgical exteriorization of digestive gland ducts, enabling the collection of pure secretions.
Classic surgical procedures on animals were developed to study stomach function in detail:
- Esophagotomy. Developed by I.P. Pavlov and E.O. Shumova-Simanovskaya. It involves cutting the esophagus and bringing both ends out to the neck, usually combined with a gastric fistula. This allows for "sham feeding": the animal eats, but the food falls out through the severed esophagus without reaching the stomach. Meanwhile, pure gastric juice is abundantly secreted from the fistula.
- Klemensiewicz–Heidenhain isolated pouch. A small isolated pouch is fashioned from the main stomach, with its innervation completely severed.
- Pavlov isolated pouch. Unlike the previous method, the pouch is created in a way that preserves all natural neural connections with the main stomach. Due to intact innervation, this isolated segment adequately reflects the function of the main organ, serving as its exact physiological "mirror".
Clinical Investigation Methods in Humans
The achievements of experimental physiology formed the basis of methods used to assess digestive tract function in clinical practice. Modern approaches include both invasive and non-invasive techniques:
- Sonde probing (Intubation). A classical method involving the introduction of a gastric or duodenal tube to collect contents. It evaluates fasting (basal) secretion as well as the glandular response to stimulation (e.g., following a standard test meal, and in some tests, sham feeding).
- Radiotelemetry (Radiopill). The patient swallows a specialized microcapsule. As it moves through the gastrointestinal tract, it remotely transmits data on intraluminal pressure, temperature, and pH levels.
- Radiological methods. These include fluoroscopy (real-time observation), radiography (static imaging), and roentgenkymography, which is specifically used to record organ wall contractions.
- Gastroscopy. An endoscopic method for visual inspection of the esophageal, gastric, and duodenal mucosa.
- Salivary testing. To obtain pure saliva in humans, special suction capsules (Lashley–Krasnogorsky capsules) are used. They are attached to the oral mucosa directly over the salivary duct openings, enabling separate collection of secretions from specific glands without contamination.