The digestive organs are inaccessible for direct observation. Therefore, for a long time, digestion has been studied in operated animals.
The Russian physiologist Pavlov developed methods by which it was possible to collect pure digestive juices not mixed with food, to establish their composition, quantity, and to study the regulation of their excretion. Pavlov was awarded the Nobel Prize for his work on the physiology of digestion.
To study the processes of digestion, a fistula was applied to the gland or the digestive organ, that is, an opening was artificially created and brought to the surface of the body.
IP Pavlov found that under the influence of taste, smell, type of food, there is a reflex secretion of saliva and gastric juice. The impulses go to the center of digestion in the medulla oblongata, and then from it to the salivary glands and glands of the stomach, causing the separation of saliva and gastric juice.
Nervous regulation of salivation and gastric secretion
The regulation of the secretion of the salivary glands is carried out reflexively when the receptors in the tongue and in the mucous membrane of the mouth are irritated by food substances. From them, excitation is carried out along sensitive neurons to the center of salivation of the medulla oblongata. From here, excitation through efferent (motor) neurons is transmitted to the salivary glands, and they begin to secrete saliva. This is the arc of the salivary reflex.
It is known that saliva can be released not only while eating (when food is already in the mouth and comes into contact with the receptors of the papillae of the tongue), but also when you see tasty food, smell it, when kitchen utensils ring or even when you think of delicious food. Therefore, a distinction is made between unconditioned reflex regulation of salivation (the presence of food in the mouth) and conditioned reflex regulation (a reflex to the sight, smell of food, or, for example, to a call for a lunch break).
Gastric juice, like saliva, is secreted reflexively.
The secretion of saliva and gastric juice occurs reflexively and is coordinated by the centers of the medulla oblongata.
If food does not enter the stomach for a long time, its muscles begin to contract vigorously, which causes discomfort associated with hunger. At the same time, nerve impulses come from the stomach to the brain, and a person seeks to satisfy the feeling of hunger as soon as possible.
Regulation of juice secretion also occurs through the humoral route. Humoral regulation is carried out both by the own hormones of the gastrointestinal tract and by the hormones of the endocrine system (adrenaline).
food is in the stomach for 4–8 hours. All this time, the stomach glands secrete gastric juice. The secretion of gastric juice continues under the influence of biologically active substances formed in the gastric mucosa. These substances are absorbed into the bloodstream, enhancing the activity of the gastric glands.
The digestive center is located in the medulla oblongata.
The center of defecation is located in the lumbosacral spinal cord.
The sympathetic part of the nervous system weakens, and the parasympathetic – enhances peristalsis and secretion of juice.