Lip

Last updated
Lip
Mouth.jpg
Human lips
Details
Artery inferior labial, superior labial
Vein inferior labial, superior labial
Nerve frontal, infraorbital
Identifiers
Latin labia oris
MeSH D008046
TA98 A05.1.01.005
TA2 2775
FMA 59816
Anatomical terminology

The lips are the visible body part at the mouth of many animals, including humans. [1] Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be an erogenous zone when used in kissing and other acts of intimacy.

Contents

Structure

Cupid's bow feature of a human lip MouthCupidBow.jpg
Cupid's bow feature of a human lip

The upper and lower lips are referred to as the "Labium superius oris" and "Labium inferius oris", respectively. [2] [3] The juncture where the lips meet the surrounding skin of the mouth area is the vermilion 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 the cupid's bow. [6] The fleshy protuberance located in the center of the upper lip is a tubercle known by various terms including the procheilon (also spelled prochilon), the "tuberculum labii superioris", and the "labial tubercle". [7] The vertical groove extending from the procheilon to the nasal septum is called the philtrum. [8]

Surface anatomy of the human lips Anatomy of the human lip.jpg
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 fewer melanocytes (cells which produce melanin pigment, which give skin its color). Because of this, the blood 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 interior mucous membrane of the inside of the mouth.

The lip skin is not hairy and does not have sweat 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 become chapped more easily.

The lower lip is formed from the mandibular prominence, a branch of the first pharyngeal arch. The lower lip covers the anterior body of the mandible. It is lowered by the depressor labii inferioris muscle and the orbicularis oris borders it inferiorly.

The upper lip covers the anterior 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 the philtrum, 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 term vermillion refers to the colored portion of either the upper or lower lip.

It is raised by the levator labii superioris and is connected to the lower lip by the thin lining of the lip itself.

Thinning of the vermilion of the upper lip and flattening of the philtrum are two of the facial characteristics of fetal alcohol syndrome, a lifelong disability caused by the mother's consumption of alcohol during pregnancy.

Microanatomy

The skin of the lips is stratified squamous epithelium. The mucous membrane is represented by a large area in the sensory cortex, and is therefore highly sensitive. The Frenulum Labii Inferioris is the frenulum of the lower lip. The Frenulum Labii Superioris is the frenulum of the upper lip.

Nerve supply

Illustration of lips from Gray's Anatomy showing the inferior and superior 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 Gray509.png
Illustration of lips from Gray's Anatomy showing the inferior and superior 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

Blood supply

The facial artery is one of the six non-terminal branches of the external carotid artery.

This artery supplies both lips by its superior and inferior labial branches. Each of the two branches bifurcate and anastomose with their companion branch from the other terminal.

Muscles

The muscles acting on the lips are considered part of the muscles of facial expression. All muscles of facial expression are derived from the mesoderm of the second pharyngeal arch, and are therefore supplied (motor supply) by the nerve of the second pharyngeal arch, the facial nerve (7th cranial nerve). The muscles of facial expression are all specialized members of the panniculus carnosus, which attach to the dermis and so wrinkle, or dimple the overlying skin. Functionally, the muscles of facial expression are arranged in groups around the orbits, nose and mouth.

The muscles acting on the lips:

Functions

Food intake

Breastfeeding Breastfeeding infant.jpg
Breastfeeding

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 narrow funnel with the lips, the suction of the mouth is increased. This suction is essential for babies to breast feed. Lips can also be used to suck in other contexts, such as sucking on a straw to drink liquids.

Articulation

The lips serve for creating different sounds—mainly labial, bilabial, and labiodental consonant sounds as well as vowel rounding—and thus are an important part of the speech apparatus. The lips enable whistling and the performing of wind instruments such as the trumpet, clarinet, flute, and saxophone. People who have hearing loss may unconsciously or consciously lip 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 the McGurk Effect.

Tactile organ

The lip has many nerve endings and reacts as part of the tactile (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.

Erogenous zone

Lips of a young woman wearing red lipstick Lujuria Lust Tentacion (3973672868).jpg
Lips of a young woman wearing red lipstick
Lips of a young man Close up man lips.jpg
Lips of a young man

Because of their high number of nerve endings, the lips are an erogenous zone. The lips therefore play a crucial role in kissing 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 of testosterone on a man's facial structure, the effects of a woman's oestrogen 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 (or collagen lip 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 ]

Facial expression

The lips contribute substantially to facial expressions. The lips visibly express emotions such as a smile or frown, iconically by the curve of the lips forming an up-open or down-open parabola, respectively. Lips can also be made pouty when whining, or perky to be provocative.

Clinical significance

As an organ of the body, the lip can be a focus of disease or show symptoms of a disease:

A child with cleft lip Cleft lip child.jpg
A child with cleft lip

Society and culture

Pierced lips Sparkly lips.jpg
Pierced lips

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. [18]

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 example oral stage of the psychology according to Sigmund Freud).

Lip piercing or lip augmentation is sometimes carried out for cosmetic reasons. Products designed for use on the lips include lipstick, lip gloss and lip balm.

Other animals

This Asian arowana has large, protruding barbels Arowana.jpg
This Asian arowana has large, protruding barbels

In most vertebrates, the lips are relatively unimportant folds of tissue lying just outside the jaws. However, in mammals, they become much more prominent, being separated from the jaws by a deep cleft [ citation needed ] (a notable exception being the naked mole-rat, whose lips close behind the front teeth). [19] 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 some teleost fish, the lips may be modified to carry sensitive barbels. In birds and turtles, the lips are hard and keratinous, forming a solid beak. [20] Clevosaurids like Clevosaurus are notable for the presence of bone "lips"; in these species the tooth-like jaw projections common to all sphenodontians form a beak-like edge around the jaws, protecting the teeth within. [21]

See also

Related Research Articles

A frenulum is a small fold of tissue that secures the motion of a mobile organ in the body.

Levator labii superioris alaeque nasi muscle

The levator labii superioris alaeque nasi muscle is, translated from Latin, the "lifter of both the upper lip and of the wing of the nose". It has the longest name of any muscle in an animal. The muscle is attached to the upper frontal process of the maxilla and inserts into the skin of the lateral part of the nostril and upper lip.

Orbicularis oris muscle

In human anatomy, the orbicularis oris muscle is a complex of muscles in the lips that encircles the mouth. It is a sphincter, or circular muscle, but it is actually composed of four independent quadrants that interlace and give only an appearance of circularity.

Depressor labii inferioris muscle Facial muscle that helps to lower the bottom lip

The depressor labii inferioris is a facial muscle. It helps to lower the bottom lip.

Zygomaticus minor muscle Facial muscle that draws the upper lip upwards and backwards during smiling

The zygomaticus minor muscle is a muscle of facial expression. It originates from the zygomatic bone, lateral to the rest of the levator labii superioris muscle, and inserts into the outer part of the upper lip. It draws the upper lip backward, upward, and outward and is used in smiling. It is innervated by the facial nerve (VII).

Levator labii superioris

The levator labii superioris is a muscle of the human body used in facial expression. It is a broad sheet, the origin of which extends from the side of the nose to the zygomatic bone.

Depressor anguli oris muscle Facial muscle that depresses the corner of the mouth during frowning

The depressor anguli oris muscle is a facial muscle. It originates from the mandible and inserts into the angle of the mouth. It is associated with frowning, as it depresses the corner of the mouth.

Facial artery

The facial artery is a branch of the external carotid artery that supplies structures of the superficial face.

Modiolus (face) Chiasma of facial muscles

In facial anatomy, the modiolus is a chiasma of facial muscles held together by fibrous tissue, located lateral and slightly superior to each angle of the mouth. It is important in moving the mouth, facial expression and in dentistry. It is extremely important in relation to stability of lower denture, because of the strength and variability of movement of the area. It derives its motor nerve supply from the facial nerve, and its blood supply from labial branches of the facial artery.

Infraorbital artery

The infraorbital artery is an artery in the head that branches off the maxillary artery, emerging through the infraorbital foramen, just under the orbit of the eye.

Superior labial nerve

The superior labial branches, the largest and most numerous, descend behind the quadratus labii superioris, and are distributed to the skin of the upper lip, the mucous membrane of the mouth, and labial glands.

Infraorbital plexus

The superior labial branches descend behind the Quadratus labii superioris, and are distributed to the skin of the upper lip, the mucous membrane of the mouth, and labial glands. They are joined, immediately beneath the orbit, by filaments from the facial nerve, forming with them the infraorbital plexus.

Infraorbital nerve Branch of the maxillary nerve supplying the face

The infraorbital nerve is a branch of the maxillary nerve, itself a branch of the trigeminal nerve. It travels through the orbit and enters the infraorbital canal to exit onto the face through the infraorbital foramen. It provides sensory innervation to the skin and mucous membranes around the middle of the face.

Marginal mandibular branch of the facial nerve

The marginal mandibular branch of the facial nerve passes forward beneath the platysma and depressor anguli oris, supplying the muscles of the lower lip and chin, and communicating with the mental branch of the inferior alveolar nerve.

Buccal branches of the facial nerve

The buccal branches of the facial nerve, are of larger size than the rest of the branches, pass horizontally forward to be distributed below the orbit and around the mouth.

Facial muscles

The facial muscles are a group of striated skeletal muscles supplied by the facial nerve that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, although they derive from neural crest cells found in all vertebrates. They are the only muscles that attach to the dermis.

Lip reconstruction may be required after trauma or surgical excision. The lips are considered the beginning of the oral cavity and are the most common site of oral cancer. Any reconstruction of the lips must include both functional and cosmetic considerations. The lips are necessary for speech, facial expression, and eating. Because of their prominent location on the face, even small abnormalities can be apparent.

<span class="mw-page-title-main">Human nose</span> Feature of the face

The human nose is the most protruding part of the face. It bears the nostrils and is the first organ of the respiratory system. It is also the principal organ in the olfactory system. The shape of the nose is determined by the nasal bones and the nasal cartilages, including the nasal septum which separates the nostrils and divides the nasal cavity into two. On average the nose of a male is larger than that of a female.

Canine space

The canine space, is a fascial space of the head and neck. It is a thin potential space on the face, and is paired on either side. It is located between the levator anguli oris muscle inferiorly and the levator labii superioris muscle superiorly. The term is derived from the fact that the space is in the region of the canine fossa, and that infections originating from the maxillary canine tooth may spread to involve the space. Infra-orbital is derived from infra- meaning below and orbit which refers to the eye socket.

References

  1. "Definition of LIP". www.merriam-webster.com. Retrieved 2022-05-22.
  2. "Labium Superius Oris -- Medical Definition". medilexicon.com. Archived from the original on 2014-10-17. Retrieved 2011-11-12.
  3. "Labium Inferius Oris -- Medical Definition". medilexicon.com. Archived from the original on 2014-10-17. Retrieved 2011-11-12.
  4. "Vermilion Border -- Medical Definition". medilexicon.com. Archived from the original on 2014-10-17. Retrieved 2011-11-12.
  5. "Vermilion Zone -- Medical Definition". medilexicon.com. Archived from the original on 2014-10-17. Retrieved 2011-11-12.
  6. "Cupid's Bow -- Medical Definition". medilexicon.com. Archived from the original on 2014-10-17. Retrieved 2011-11-12.
  7. "Tubercle Of Upper Lip -- Medical Definition". medilexicon.com. Archived from the original on 2014-10-17. Retrieved 2011-11-12.
  8. "Philtrum -- Medical Definition". medilexicon.com. Archived from the original on 2014-10-17. Retrieved 2011-11-12.
  9. 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. PMID   21983237. S2CID   23542024.
  10. Note, Science (2005-11-28). "Why do men find big lips and little noses so sexy? I'll paint you a picture – Comment – Times Online". The Times. London. Archived from the original on February 22, 2007. Retrieved 2007-12-12.
  11. "Lip size key to sexual attraction". BBC News. 2003-03-04. Retrieved 2010-01-15.
  12. Adeyinka, Adebayo; Kondamudi, Noah P. (2021), "Cyanosis", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   29489181 , retrieved 2021-07-08
  13. Bhutta, Beenish S.; Hafsi, Wissem (2021), "Cheilitis", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   29262127 , retrieved 2021-07-08
  14. CDC (2020-12-28). "Facts about Cleft Lip and Cleft Palate | CDC". Centers for Disease Control and Prevention. Retrieved 2021-07-08.
  15. "Lip cancer - Symptoms and causes". Mayo Clinic. Retrieved 2021-07-08.
  16. "Risk Factors for Oral Cavity and Oropharyngeal Cancers". www.cancer.org. Retrieved 2021-07-08.
  17. MORETTI, A.; VITULLO, F.; AUGURIO, A.; PACELLA, A.; CROCE, A. (2011). "Surgical management of lip cancer". Acta Otorhinolaryngologica Italica. 31 (1): 5–10. ISSN   0392-100X. PMC   3146335 . PMID   21808457.
  18. Valsiner, Jaan (2000). Culture and Human Development. Sage Publications, Ltd. pp. 134–136.
  19. Griffin, Ashleigh S. (23 September 2008). "Naked Mole Rat" (PDF). Current Biology. 18 (18): R844-5. doi:10.1016/j.cub.2008.07.054. PMID   18812073. S2CID   42179436 . Retrieved 9 November 2020.
  20. Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia: Holt-Saunders International. p. 297. ISBN   978-0-03-910284-5.
  21. Jones MEH (2009). "Dentary tooth shape in Sphenodon and its fossil relatives (Diapsida: Lepidosauria: Rhynchocephalia)". In Koppe T, Meyer G, Alt KW, (eds). Interdisciplinary Dental Morphology, Frontiers of Oral Biology (vol 13). Griefswald, Germany; Karger. 9–15.

Further reading