Anatomy
Anatomy
The lip structure is different than other skin. As shown in the diagram, lips do not have the same protective outer layer, or stratum corneum, found in other skin; nor do lips have the same amount of oil and sweat glands. Sweat glands add moisture to skin, but the lips’ only source of moisture is saliva inside the mouth. Thus, harsh winter wind, cold, sun and dryness–indoors and outdoors–make lips more susceptible to dryness and a vulnerable target for chapping.
Superficial anatomy The upper lip extends from the base of the nose superiorly to the nasolabial folds laterally and to the free edge of the vermilion border inferiorly. The lower lip extends from the superior free vermilion edge superiorly, to the commissures laterally, and to the mandible inferiorly. Around the circumferential vermilion-skin border, a fine line of pale skin accentuates the colour difference between the vermilion and normal skin. Along the upper vermilion-skin border, 2 paramedian elevations of the vermilion form the Cupid bow. Two raised vertical columns of tissue form a midline depression called the philtrum. The philtrum is located between the paramedian elevations of the vermilion and the columella above. The labiomental crease passes horizontally in an inverted U-shape across the lower lip, which intraorally corresponds to the depth of the gingivolabial sulcus.
Histology From superficial to deep, the layers of the upper and lower lips include the epidermis, subcutaneous tissue, orbicularis oris muscle fibers, and mucosa. In cross-section, the superior and inferior labial arteries can be observed as they course between the orbicularis muscle fibers and the mucosa. The vermilion is composed of nonkeratinized squamous epithelium that covers numerous capillaries, which give the vermilion its characteristic color. Numerous minor salivary glands can be observed on a histologic section of the lip. Hair follicles and sebaceous glands are located throughout the lip skin; however, these structures are absent in the vermilion.
Blood Supply Blood supply to both lips stems from the external carotid system. The facial artery ascends from the neck over the midbody of the mandible just anterior to the insertion of the masseter muscle. The facial artery branches into the submental artery that passes under the mandibular body in an anteromedial direction. The facial artery ascends in a plane deep to the platysma, risorius, and zygomaticus major and minor muscles and superficial to the buccinator and levator anguli oris. This artery branches into an inferior and a superior labial artery, which course beneath the orbicularis oris and anastomose with the contralateral vessel. The superior labial artery usually branches from the facial artery 1.1 cm lateral (SD 0.43) and 0.9 cm (SD 0.20) superior to the oral commissure. The inferior labial artery branches from the facial artery 2.6 cm (SD 0.70) lateral and 1.5 cm (SD 0.45) inferior to the oral commissure. The facial artery then ascends in the nasolabial groove as the angular artery, forming branches to the nasal ala and anastomosing with the dorsal nasal artery. The facial and labial arteries communicate with the subdermal plexus through a dense population of musculocutaneous perforators. In contrast, the submental artery usually has only 1 main perforator, which penetrates the platysma and ramifies to supply 3-4 areas of the subdermal plexus.
