Human Anatomy Skin Quiz

Skin and Skin Appendages (Integumentary System)

• The skin is the body's largest organ, comprising about 16% of body weight.
• The skin consists of two primary layers: the epidermis and the dermis.
• The hypodermis is not a skin layer; it's composed of loose connective tissue and fat cells.

Objectives

• Define skin.
• Describe the structure of the epidermis.
• Detail the structure of the dermis.
• Compare thin and thick skin.

Introduction

• The junction between the dermis and epidermis is irregular, featuring dermal papillae (projections) and rete ridges (epidermal evaginations).
• Appendages like nails, hairs, sebaceous glands, and sweat glands arise from the epidermis.

Functions

• Serves as a receptor organ.
• Provides defense against microorganisms, chemicals, and ultraviolet radiation.
• Plays a role in vitamin D3 synthesis.
• Aids in personal identification (e.g., fingerprints).

I - The Epidermis

• Primarily composed of keratinized stratified squamous epithelium resting on a basement membrane.
• Consists of five layers from deep to superficial:
  • Stratum basale: Single layer of basophilic columnar cells, active in epidermal turnover.
  • Stratum spinosum (spongiosum): Polygonal cells with surface spin-like projections (keratin filaments and desmosomes).
  • Stratum granulosum: Three layers of flattened polygonal cells, containing keratohyaline granules and lamellar bodies crucial for skin sealing.
  • Stratum lucidum: Present only in thick skin, a translucent layer of flat cells lacking nuclei and organelles.
  • Stratum corneum (horny layer): Multiple layers of flattened, non-nucleated eosinophilic cells filled with keratin.

Cells of the Epidermis

• Keratinocytes: Epithelial cells forming the stratified squamous keratinized epithelium; most numerous.
• Melanocytes: Produce melanin, giving skin color. Melanin granules migrate to keratinocytes. Pigments include eumelanin (dark hair) and pheomelanin (red hair). Melanocytes are found in the stratum basal and spinosum.
• Langerhans cells: Star-shaped cells mainly in the stratum spinosum, derived from macrophages, and are antigen-presenting cells (APCs).
• Merkel cells: Found primarily in thick skin, similar to epidermal epithelial cells but with dense granules; mechanoreceptors.

II - The Dermis

• Principally dense, irregular connective tissue, varying in thickness.
• Consists of two layers:
  • Papillary dermis: Superficial layer.
  • Reticular dermis: Deeper layer.
• Contains fibroblasts, mast cells, macrophages, and leukocytes.
• Houses hair follicles, sebaceous glands, and sweat glands (skin appendages), which originate from the epidermis. The dermis also plays a role in the formation of the basement membrane.

Types of Skin

• Thin skin: Covers most of the body, characterized by irregular dermal papillae, presence of skin appendages, and the absence of stratum lucidum.
• Thick skin: Located on palms and soles, features regular dermal papillae, lacks hair follicles and sebaceous glands, and presents stratum lucidum.

Test your knowledge on the structure and functions of human skin in this quiz. Explore topics such as skin layers, functions, and cell types. Challenge yourself to match descriptions with their corresponding skin components.