Skin (Part 1)

Histology of the Skin



Prepared by Dr. Haitham SewilamLecturer of Histology, Faculty of Medicine - Helwan University, EgyptBMS (I) Module Skin (Part 1)

Objectives

  • Describe the microscopic structure of the skin with a focus on epidermal cells.

  • Differentiate dermis layers.

  • Compare thin and thick skin.

  • Recognize clinical applications related to skin structure.

Integumentary System



The integumentary system includes:I. SkinII. Skin Appendages:

  • Hair follicles & hairs

  • Sebaceous glands

  • Nail beds and nails

  • Sweat glands

Overview of the Skin

The skin is the body's outer covering and largest organ (16% of body weight).

Histological Structure

  • Epidermis: Thin, superficial layer of stratified squamous keratinized epithelium, ectodermal in origin.

  • Dermis: Thick, deep layer of connective tissue, mesodermal in origin.

  • Hypodermis: Deep to dermis, known as superficial fascia; not part of the integument.

Types of Skin

  • Thick Skin: Found in palms and soles; contains numerous sweat glands; lacks hair and sebaceous glands.

  • Thin Skin: Covers the rest of the body, with basic structure but some variations.

Thick Skin Structure

Epidermis Components:

  • Keratin-producing cells (Keratinocytes): Comprise 85% of cells in 5 layers.

  • Non-keratinocytes: 15% of cells.

Keratinocytes: Responsible for keratin formation; continuously shed and regenerated every 2-4 weeks.

Layers of the Epidermis

  1. Basal Cell Layer (Stratum Germinativum): Single layer of columnar cells on a thick basement membrane. Attached by desmosomes and hemidesmosomes; exhibits tonofilaments.

  2. Prickle Cell Layer (Stratum Spinosum): 4-8 layers of polyhedral cells with central nuclei, connected by desmosomes.

  3. Granular Layer (Stratum Granulosum): 2-4 layers of flattened cells with basophilic granules; contains keratohyalin granules and membrane-coated lamellar granules for skin barrier function.

  4. Clear Layer (Stratum Lucidum): Thin layer of dead flattened cells; densely packed keratin filaments.

  5. Horny Layer (Stratum Corneum): Thick eosinophilic layer of heavily keratinized dead cells.

Non-Keratinocytes in the Epidermis:

  • Melanocytes: Neural crest origin, located between stratum basale and in hair follicles; synthesize melanin for UV protection.

  • Langerhans Cells: Originated from monocytes; act as macrophages in stratum spinosum.

  • Merkel Cells: Ectodermal modified epithelial cells for touch sensations in stratum basale.

Dermis Structure

The dermis has two layers:

  • Papillary Layer: Loose connective tissue forming dermal papillae.

  • Reticular Layer: Dense connective tissue with lesser vascular supply.

Comparison of Thick and Thin Skin

Feature

Thick Skin

Thin Skin

Site

Palms, soles

Other body areas

Epidermis

Thicker

Thinner

St. Basale

Similar

Similar

St. Spinosum

Thicker

Thinner

Granular

Thicker

Thinner

Clear

Present

Absent

Horny Layer

Thick

Thin

Dermal Papillae

More, large & regular

Fewer, irregular

Appendages

Hair follicles & sebaceous glands

Fewer

Questions for Review





  • About the Clear Layer:a) Formed of 5-8 layers of cells.b) Absent in thin skin.c) Contains granules.d) Thicker than that of thin skin.

  • Malpighian Cell Layers: List the cell layers.





  • True Statements About Melanocytes:a) They are phagocytic cells.b) Found between the cells of the clear layer.c) Branching cells containing tyrosinase enzyme.d) Attached to basement membrane by hemidesmosomes.

  • Non-Keratinocytes Summary: List non-keratinocytes with their site and function.