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in humans and other mammals, an innate unconditioned reflex that is formed in the fetus during intrauterine development.

The structural and functional mechanisms of sucking develop long before birth, in the early stages of embryogeny. In an 18-week-old human fetus sucking movements of the lips are observed upon the stimulation of the tongue. In the 21st or 22nd weeks spontaneous sucking occurs, and in the 24th week there are distinct seeking and sucking reactions. The sucking function is characteristic even of anencephalics.

Stimulation of the tactile receptors of the lips and the anterior part of the tongue results in the spread of the excitation along the centripetal branches of the trigeminal nerve. The impulses enter the sucking center, which is located in the truncal part of the brain, and are switched to centrifugal nerves, along which the excitation is transmitted to the muscles that perform the sucking (masticatory muscles and the muscles of the lips, mouth, and tongue). The act of sucking begins with the movement of the tongue and lower jaw downward and back, which creates a negative pressure in the oral cavity. The contraction of the lip and mouth muscles causes the squeezing of the nipple of the mother’s mammary gland. The nerve impulses that arise during this process enter the hypothalamus, which the impulses reflexively stimulate to form vasopressin and oxytocin, as well as a releasing factor. The releasing factor enters the pituitary gland and induces the secretion of prolactin, which controls lactation. Oxytocin is transported by the blood to the myoepithelial cells of the mammary gland, inducing the contraction of the glands, the release of milk from the alveoli into the mammary ducts, and the secretion of milk.


Shuleikina, K. V. “Fiziologicheskaia kharakteristika sosa-tel’noi funktsii novorozhdennogo v pervye dni ego zhizni.” In Trudy Per-vogo Vserossiiskogo s“ezda detskikh vrachei. Moscow, 1961.
Barabash-Nikiforov, I. I., and A. N. Formozov. Teriologiia. Moscow, 1963.
Villee, C, and V. Dethier. Biologiia: biologicheskie protsessy i zakony. Moscow, 1974. Pages 545–46. (Translated from English.)
References in classic literature ?
This," and he pointed to the nose-leaves, "is the sucking apparatus.
I let him enjoy the luxury unannoyed; and after sucking out his last wreath, and heaving a profound sigh, he got up, and departed as solemnly as he came.
Jerry, the messenger, who had made his own observations, in his own manner, and who had been sucking the rust off his fingers in his absorption, stretched his neck to hear who they were.
Dick in the meanwhile looking very deferentially and seriously at Traddles, and sucking his thumb.
But the most gave over sucking the dew from their sticks, and rushed to the water like cattle that have wandered five days in the desert, and drank their fill.
One of these, a stout well-set yeoman, arrayed in Lincoln green, having twelve arrows stuck in his belt, with a baldric and badge of silver, and a bow of six feet length in his hand, turned short round, and while his countenance, which his constant exposure to weather had rendered brown as a hazel nut, grew darker with anger, he advised the Jew to remember that all the wealth he had acquired by sucking the blood of his miserable victims had but swelled him like a bloated spider, which might be overlooked while he kept in a comer, but would be crushed if it ventured into the light.
I have seen her die in the gloom of an Italian tomb, sucking the poison from her lover's lips.
Some want to follow things that move, to watch and slink and wait and spring; to kill and bite, bite deep and rich, sucking the blood.
He sprang to his feet and saw to starboard, and not a hundred yards from their heeling, pitching boat, a vast iron bulk like the blade of a plough tearing through the water, tossing it on either side in huge waves of foam that leaped towards the steamer, flinging her paddles helplessly in the air, and then sucking her deck down almost to the waterline.
When its father comes up, the child tears itself away from the bosom, flings itself back, looks at its father, laughs, as though it were fearfully funny, and falls to sucking again.
A large fig tree in full leaf {101} grows upon it], and under it lies the sucking whirlpool of Charybdis.
As it came quite close to me I discovered that its strange movements, running its odd hands over the surface of the turf, were the result of its peculiar method of feeding, which consists in cropping off the tender vegetation with its razorlike talons and sucking it up from its two mouths, which lie one in the palm of each hand, through its arm-like throats.