How is saliva secretion regulated?

Saliva is something that everyone secretes frequently, especially babies who secrete more, while adults usually secrete less. When people taste something delicious, saliva will be secreted involuntarily, and sometimes it will also be secreted when they are nervous. So, how is saliva secretion regulated? Many people are not clear about this. Let’s take a look at the following introduction for the specific situation.

The regulation of saliva secretion is completely neural reflex, including unconditioned reflex and conditioned reflex.

The normal stimuli that cause unconditioned salivation are mechanical, chemical, and thermal stimulation of the oral cavity by food. Under the influence of these stimuli, the nerve endings (receptors) of the oral mucosa and tongue become excited, and the impulses travel along the afferent nerve fibers (in the lingual nerve, chorda tympani nerve, glossopharyngeal nerve, and vagus nerve) to the central nervous system, and then through the efferent nerves to the salivary glands, causing saliva secretion.

The primary center of saliva secretion is in the medulla oblongata, and its higher centers are distributed in the hypothalamus and cerebral cortex.

The efferent nerves that innervate the salivary glands are mainly parasympathetic nerves, such as the 9th cranial nerve to the parotid gland and the chorda tympani branch of the 7th cranial nerve to the submandibular gland. Stimulating these nerves can cause the secretion of more saliva but less solid matter. The effect of the parasympathetic nerves on the salivary glands is achieved through the release of acetylcholine from their terminals. Therefore, the use of drugs that antagonize acetylcholine, such as atropine, can inhibit saliva secretion, while the use of acetylcholine or its similar drugs can cause a large amount of saliva secretion. When the parasympathetic nerves are excited, the blood vessels of the salivary glands can also dilate, further promoting the secretion of saliva. It is currently believed that the parasympathetic nerve fibers that cause vasodilation near the salivary glands are peptidergic nerve fibers, whose terminals release vasoactive intestinal peptide.

The sympathetic nerves that innervate the salivary glands are peptide nerve fibers. After changing neurons in the superior cervical ganglion, they send out postganglionic fibers that are distributed on the blood vessels and secretory cells of the salivary glands. Stimulating these nerves can cause vasoconstriction and can also induce saliva secretion, but the secretory effect varies with different salivary glands. For example, stimulating the human cervical sympathetic nerves only causes secretion from the submandibular gland but not the parotid gland.

When people eat, the shape, color, smell of the food, as well as the eating environment, can form a conditioned reflex and cause saliva secretion. "Looking at the plum to quench thirst" is an example of conditioned reflex saliva secretion in daily life. The saliva secretion of adults usually includes two components: conditioned reflex and unconditioned reflex.

How is saliva secretion regulated? Now everyone has a deeper understanding of some knowledge about saliva secretion, which is mainly caused by unconditioned reflex and conditioned reflex. However, we need to remind everyone that excessive or insufficient saliva secretion is abnormal and you need to go to the hospital for a check-up if necessary.