Lips in Human Anatomy and Physiology

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Lips are soft, pliable anatomical structures that form the mouth margins of most vertebrates. They are composed of a surface epidermis (skin), connective tissue, and a muscle layer (in typical mammals).

Hair, sweat glands, and sebaceous (oil) glands are all found in the outer skin of a man.

The lips' edges, known as the vermilion border, are covered with reddish skin and densely packed with sensitive nerve endings. The reddish skin serves as a transition layer between the hair-bearing tissue on the outside and the mucous membrane on the inside. A moist mucous membrane lines the inside of the lips. 

The inner surface of newborn infants is significantly thicker, with sebaceous glands and minute projections known as papillae. These structural adaptations appear to aid the sucking process. The orbicularis oris muscle, which encircles the opening, supplies the majority of the substance to each lip. This muscle, along with others that radiate out into the cheeks, allows the lips to be shaped and expressed in a variety of ways.

Types of Lips

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Let’s Classify lips. According to the shape of the lips

Lips can be classified in a variety of ways. One method is by shape. They can be plump or thin, heart-shaped or round, or a variety of other shapes and sizes. Such a distinctive feature is difficult to standardise. Researchers are now developing geometric and computer models to more precisely describe lips.

By Lip Print

Lip print, which is based on the pattern of lines in your lips, is another way to classify lip types.

Researchers discovered five distinct lip patterns:

Type I: vertical lines that cross the entire or a portion of the lips

Type II: branched, y-shaped lines

Type III: intersecting (crossed) lines

Type IV: reticular (netlike) lines

Type V: undetermined (mixed) lines

Vermilion Border of Lip

The vermilion border, also known as the margin or zone, is the normally distinct line that separates the lip from the adjacent normal skin. It is occasionally used to apply lipstick. It denotes the epidermis transition from highly keratinized external skin to less keratinized internal skin. It is devoid of sebaceous glands, sweat glands, and facial hair.

It is prominent on the face, creating a focal point for cosmetics, and it is also a site for several skin diseases. Its functional properties, on the other hand, are unknown.

Lip Infection Types

Some of the lip infection types are:

• Thrush (Oral Candidiasis)

• Lichen Planus.

• Cold Sores (Orofacial Herpes)

• Canker Sore (Aphthous Ulcer)

• Allergic Contact Dermatitis. 

• Milia. 

• Oral Mucocele.

• Fordyce Spots.

What are Parts of Lips?

Vermilion: This is the red area of the lips which is covered by a specialised stratified squamous epithelium that is continuous with the gingivolabial groove oral mucosa. Confusion ensues when the vermilion is also referred to as the lips.

Vermilion Border: The paler skin rim that separates the vermilion from the rest of the skin.

Cupid's Bow: The contour of the line formed by the upper lip's vermilion border. This line resembles an archer's bow in frontal view, curving medially as well as superiorly from the commissures to the paramedian peaks situated at the bases of the philtrum's pillars (crista philtrae), with an inferior convexity lying in between peaks. The philtrum is the vertical groove in the upper lip's midline that is surrounded by these lateral pillars (ridges).

Oral Commissure: The junction of the lateral aspects of the upper and lower lips' vermilion. The cheilion is an anthropological landmark at this location.

Modiolus: In facial anatomy, the modiolus is a chiasma of muscles of the face retained together by fibrous connective tissue that is situated lateral and slightly superior to each angle of the mouth. It is necessary for mouth movement, facial expression, and dentistry. Because of the strength and variability of movement in the area, it is extremely important in terms of lower denture stability. It receives motor nerve and blood supply from the facial nerve and labial branches of the facial artery.

Lower Lip

The inferior alveolar nerve is a major branch of the mandibular nerve (CNV3) that arises in the mandibular canal and emerges from the mental foramen in the mandible, which is normally located inferiorly to the second premolar tooth. Practitioners who use mental blocks for injections into the lower lip should be aware of the anatomical changes that occur when mandibular teeth are lost. Following complete tooth loss or removal, the alveoli begin to fill in with bone and the alveolar process begins to resorb. 

The mental foramen gradually approach the superior border of the mandible's body. In severe cases, the mental foramina vanish, leaving the mental nerves vulnerable to injury. During eating, pressure from a dental prosthesis resting on an exposed nerve may cause pain. The loss of all teeth causes a decrease in vertical facial dimension as well as mandibular prognathism.

What are Lip Muscles?

The orbicularis oris muscle, also known as the lip muscle, is a broad elliptical muscle that wraps around the mouth. The mouth closes when the orbicularis oris is tonically contracted, whereas active (phasic) contraction tends to cause the mouth orifice to narrow, as when kissing or whistling. Its horizontal fibres attach to the modiolus, a chiasma of muscles of the face held together by fibrous tissue horizontal and slightly superior to each mouth angle.

Inner Lining of Mouth

The mucous membrane lining the inside of the mouth is known as the oral mucosa. It is made up of stratified squamous epithelium known as "oral epithelium" and an underlying connective tissue known as lamina propria. The oral cavity has been described as a mirror that reflects an individual's health.