Specimen:

SPECIMEN DETAILS:

Organ: Lip
Origin: Human
Staining: Hematoxylin Eosin (HE)

METHOD AND SPECIMEN DESCRIPTION:

Normal sagittal section of the human lip.

OBJECTIVE OF THE EXAMINATION:

To study the transition between stratified keratinized squamous epithelium and stratified non-keratinized mucosal epithelium.

SPECIAL FEATURES OF THE SPECIMEN:

The lip consists of a fold of soft tissue with a muscular core, formed by the orbicularis oris muscle (pars labialis and pars marginalis).

In this specimen, three distinct regions can be recognized:

1. Pars cutanea (outer skin region)
2. Pars intermedia / lip vermilion (transition zone)
3. Pars mucosa (inner mucosal region) — detached in this preparation

Pars cutanea:

• Lined by stratified keratinized squamous epithelium.
• Contains hair follicles, sebaceous glands, and eccrine sweat glands in the dermis.

Lip vermilion (pars intermedia):

• Displays numerous connective tissue papillae extending close to the epithelial surface, each containing capillary loops.
• Covered by a thin orthokeratinized epithelium with a very thin stratum corneum.
• Lacks pigmentation and contains no glands (except for occasional free sebaceous glands).
• The red color of the lips results from blood within the capillary loops shining through the thin epithelium.

Pars mucosa (not preserved in this specimen):

• Normally lined by stratified non-keratinized squamous epithelium.
• Contains numerous mucous labial glands within the connective tissue.

TASKS:

• Identify the following structures in the specimen:
  • Orbicularis oris muscle
  • Labial glands
  • Blood vessels
  • Hair follicles
  • Sebaceous glands
  • Eccrine sweat glands
  • Nerves
• Locate the transition zone between the lip vermilion and normal facial skin.
• Observe the connective tissue papillae and capillaries that extend close to the epithelium.

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