The upper and lower lips are referred to as thelabium superius oris andlabium inferius oris, respectively.[2][3] The juncture where the lips meet the surrounding skin of the mouth area is thevermilion border,[4] and the typically reddish area within the borders is called the vermilion zone.[5] The vermilion border of the upper lip is known as theCupid's bow.[6] The fleshy protuberance located in the center of the upper lip is atubercle known by various terms including the procheilon (also spelledprochilon), the "tuberculum labii superioris", and the "labial tubercle".[7] The vertical groove extending from the procheilon to thenasal septum is called thephiltrum.[8]
Surface anatomy of the human lips
The skin of the lip, with three to five cellular layers, is very thin compared to typical face skin, which has up to 16 layers. With light skin color, the lip skin contains fewermelanocytes (cells which produce melaninpigment, which give skin its color). Because of this, theblood vessels appear through the skin of the lips, which leads to their notable red coloring. With darker skin color this effect is less prominent, as in this case the skin of the lips contains more melanin and thus is visually darker. The skin of the lip forms the border between the exterior skin of the face, and the interiormucous membrane of the inside of the mouth.
The lip skin is not hairy and does not havesweat glands. Therefore, it does not have the usual protection layer of sweat and body oils which keep the skin smooth, inhibit pathogens, and regulate warmth. For these reasons, the lips dry out faster and becomechapped more easily.
The upper lip covers theanterior surface of the body of the maxilla. Its upper half is of usual skin color and has a depression at its center, directly under the nasal septum, called thephiltrum, which is Latin for "lower nose", while its lower half is a markedly different, red-colored skin tone more similar to the color of the inside of the mouth, and the termvermillion refers to the colored portion of either the upper or lower lip.
Thinning of the vermilion of the upper lip and flattening of thephiltrum are two of the facial characteristics offetal alcohol syndrome, a lifelongdisability caused by the mother's consumption of alcohol during pregnancy.
Illustration of lips fromGray's Anatomy showing theinferior andsuperior labial arteries, the glands of the lips, and the nerves of the right side seen from the posterior surface after removal of the mucous membrane
Theinfraorbital nerve is a branch of themaxillary branch. It supplies not only the upper lip but also much of the skin of the face between the upper lip and the lower eyelid, except for the bridge of the nose.
This artery supplies both lips by its superior and inferior labial branches. Each of the two branchesbifurcate andanastomose with their companion branch from the other terminal.
The muscles acting on the lips are considered part of the muscles offacial expression. All muscles of facial expression are derived from themesoderm of the secondpharyngeal arch and are therefore supplied (motor supply) by the nerve of the second pharyngeal arch, thefacial nerve (7thcranial nerve). The muscles of facial expression are all specialized members of thepanniculus carnosus, which attach to thedermis and so wrinkle or dimple the overlying skin. Functionally, the muscles of facial expression are arranged in groups around theorbits, nose, and mouth.
Because they have their own muscles and bordering muscles, the lips are easily movable. Lips are used for eating functions, like holding food or to get it in the mouth. In addition, lips serve to close the mouth airtight shut, to hold food and drink inside, and to keep out unwanted objects. Through making a narrowfunnel with the lips, the suction of the mouth is increased. This suction is essential for babies tobreast feed. Lips can also be used to suck in other contexts, such as sucking on a straw to drink liquids.
The lips serve for creating different sounds—mainlylabial,bilabial, andlabiodental consonant sounds as well asvowel rounding—and thus are an important part of the speech apparatus. The lips enablewhistling and the performing of wind instruments such as the trumpet,clarinet, flute, and saxophone. People who havehearing loss may unconsciously or consciouslylip read to understand speech without needing to perceive the actual sounds, and visual cues from the lips affect the perception of what sounds have been heard, for example theMcGurk effect.
The lip has manynerve endings and reacts as part of thetactile (touch) senses. Lips are very sensitive to touch, warmth, and cold. It is therefore an important aid for exploring unknown objects for babies and toddlers.
Lips of a young woman wearing redlipstickLips of a youngman
Because of their high number of nerve endings, the lips are anerogenous zone. The lips therefore play a crucial role inkissing and other acts of intimacy.
A woman's lips are also a visible expression of her fertility. In studies performed on the science of human attraction, psychologists have concluded that a woman's facial and sexual attractiveness is closely linked to the makeup of her hormones during puberty and development. Contrary to the effects oftestosterone on a man's facial structure, the effects of a woman'soestrogen levels serve to maintain a relatively "childlike" and youthful facial structure during puberty and during final maturation. It has been shown that the more oestrogen a woman has, the larger her eyes and the fuller her lips, characteristics which are perceived as more feminine.[9] Surveys performed by sexual psychologists[who?] have also found that universally, men find a woman's full lips to be more sexually attractive than lips that are less so.[citation needed] A woman's lips are therefore sexually attractive to males because they serve as a biological indicator of a woman's health and fertility. A woman's lipstick (orcollagenlip enhancement) attempts to take advantage of this fact by creating the illusion that a woman has more oestrogen than she actually has and thus that she is more fertile and attractive.[10]
Lip size is linked to sexual attraction in both men and women. Women are attracted to men with masculine lips that are more middle size and not too big or too small; they are to be rugged and sensual. In general, the researchers found that a small nose, big eyes and voluptuous lips are sexually attractive both in men and women.[11] The lips may temporarily swell during sexual arousal due to engorgement with blood.[medical citation needed]
The lips contribute substantially tofacial expressions. The lips visibly express emotions such as asmile or frown, iconically by the curve of the lips forming an up-open or down-open arc, respectively. Lips can also be made pouty when whining or perky to be provocative.
The function of the abrupt change in skin structure between the lips and surrounding face (in particular, the function of the less keratinizedvermillion and thewhite roll) is not completely understood.[12] Possible reasons for the difference may include advantages to somatosensory function, better communication of facial expressions, and/or emphasis of the lips' slightsexual dimorphism as asecondary sex characteristic.
As an organ of the body, the lip can be a focus of disease or show symptoms of a disease:
One of the most frequent changes of the lips is a blue coloring due tocyanosis; the blood contains less oxygen and thus has a dark red to blue color, which shows through the thin skin. Cyanosis is the reason why corpses sometimes have blue lips. In cold weather cyanosis can appear, so especially in the winter, blue lips may not be an uncommon sight.[13]
Carcinoma (a malignant cancer that arises from epithelial cells) at the lips is caused predominantly by using tobacco and overexposure of sunlight.[16] Alcohol appears to increase the carcinoma risk associated with tobacco use.[17] It is most often a diffuse and often hyperkeratinised lesion, occasionally has the form of nodules and grows infiltratively, and can also be a combination of the two types. It more often occurs at the lower lip, where it is also much more malign. Lower lip carcinoma is exclusivelyplanocellular carcinoma, whereas at the upper lip, it can also bebasocellular carcinoma.[18]
Lips are often viewed as a symbol of sensuality and sexuality. This has many origins; above all, the lips are a very sensitive erogenous and tactile organ. Furthermore, in many cultures of the world, a woman's mouth and lips are veiled because of their representative association with the vulva, and because of their role as a woman's secondary sexual organ.[19]
As part of the mouth, the lips are also associated with the symbolism associated with the mouth as orifice by which food is taken in. The lips are also linked symbolically to neonatal psychology (see for exampleoral stage of the psychology according toSigmund Freud).
In most vertebrates, the lips are relatively unimportant folds of tissue lying just outside the jaws. However, inmammals, they become much more prominent, being separated from the jaws by a deep cleft[citation needed] (a notable exception being thenaked mole-rat, whose lips close behind the front teeth).[20] They are also more mobile in mammals than in other groups since it is only in this group that they have any attached muscles. In someteleost fish, the lips may be modified to carry sensitivebarbels. In birds and turtles, the lips are hard andkeratinous, forming a solidbeak.[21]Clevosaurids likeClevosaurus are notable for the presence of bone "lips"; in these species the tooth-like jaw projections common to allsphenodontians form a beak-like edge around the jaws, protecting the teeth within.[22]
^Law Smith, Miriam J.; Deady, Denis K.; Moore, Fhionna R.; Jones, Benedict C.; Cornwell, R. Elisabeth; Stirrat, Michael; Lawson, Jamie F.; Feinberg, David R.; Perrett, David I. (2011-09-21). "Maternal tendencies in women are associated with estrogen levels and facial femininity".Hormones and Behavior.61 (1):12–6.doi:10.1016/j.yhbeh.2011.09.005.PMID21983237.S2CID23542024.
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