Unit 6: Integumentary System – Structure, Function, and Laboratory Analysis

Integumentary System

Introduction and Overview

The integumentary system is the largest organ system in the human body, primarily composed of the skin and its accessory structures. It serves as a protective barrier, regulates temperature, and provides sensory information. This unit covers the anatomy, histology, and physiological functions of the skin, hair, nails, and associated glands.

• Learning Objectives:

  • Identify structures of the integumentary system

  • Describe the functions and histological features of skin and accessory organs

  • Map the distribution of touch receptors across the body

Key Terms

• Structures of the Epidermis: Epidermis, Stratum corneum, Stratum lucidum, Stratum granulosum, Stratum spinosum, Stratum basale, Melanocyte, Keratinocyte

• Structures of the Dermis: Dermis, Papillary region, Reticular region, Dermal papillae, Capillary network

• Accessory Structures: Sebaceous gland, Sweat gland, Hair follicle, Hair shaft, Nail, Arrector pili muscle

Skin Anatomy and Accessory Structures

Layers of the Skin

The skin consists of two main layers: the epidermis (outer layer) and the dermis (inner layer). Beneath the dermis lies the hypodermis (subcutaneous tissue), which is not technically part of the skin but supports its functions.

• Epidermis: Composed of stratified squamous epithelium, avascular, and contains several sublayers:

  • Stratum corneum: Outermost layer, dead keratinized cells, provides protection

  • Stratum lucidum: Present only in thick skin (palms, soles), clear layer

  • Stratum granulosum: Cells begin to die, contain granules

  • Stratum spinosum: Several layers of keratinocytes, provides strength

  • Stratum basale: Deepest layer, mitotically active cells, contains melanocytes

• Dermis: Connective tissue layer, vascular, contains:

  • Papillary region: Superficial, contains dermal papillae and capillary loops

  • Reticular region: Deep, dense irregular connective tissue, contains glands and hair follicles

Accessory Structures

• Sebaceous glands: Produce sebum (oil) to lubricate skin and hair

• Sudoriferous (sweat) glands: Eccrine (widely distributed, thermoregulation) and apocrine (axillary/genital regions)

• Hair: Composed of keratin, grows from follicles in the dermis; functions in protection and sensation

• Nails: Hard keratinized plates protecting the distal phalanges

• Arrector pili muscle: Smooth muscle attached to hair follicles, causes 'goosebumps'

Histology of the Integument

Microscopic Structure of Skin

Histological examination reveals differences between thick skin (palms, soles) and thin skin (rest of body). Thick skin contains a prominent stratum lucidum and lacks hair follicles and sebaceous glands.

• Thick Skin: Five epidermal layers, no hair follicles, no sebaceous glands, abundant sweat glands

• Thin Skin: Four epidermal layers, contains hair follicles, sebaceous glands, and sweat glands

Characteristics	Thick Skin	Thin Skin
Stratum lucidum present?	Yes	No
Hair follicles present?	No	Yes
Sebaceous glands present?	No	Yes
Stratum corneum thickness	Thicker	Thinner

Hair and Nail Anatomy

Structure and Function

Hair consists of the shaft (visible part), root (embedded in skin), and follicle (surrounds the root). The hair bulb contains the matrix, where growth occurs. Nails are composed of the nail plate, nail bed, and nail matrix, which is responsible for nail growth.

• Hair: Cortex, medulla, cuticle, hair papilla, hair follicle

• Nail: Nail plate, nail bed, nail matrix, cuticle

Touch Receptor Distribution

Sensory Receptors in the Skin

The skin contains various sensory receptors that detect touch, pressure, pain, and temperature. The density and distribution of these receptors vary across different body regions, influencing tactile sensitivity.

• Meissner's corpuscles: Detect light touch, concentrated in fingertips and lips

• Pacinian corpuscles: Detect deep pressure and vibration

• Merkel cells: Detect sustained touch and pressure

• Free nerve endings: Detect pain and temperature

Laboratory procedures may include comparing the ability to detect textures and mapping receptor density using tactile tests.

Fingerprinting

Dermal Ridges and Patterns

Fingerprints are formed by dermal ridges in the epidermis, which create unique patterns for each individual. The main types of fingerprint patterns are loops, whorls, and arches. These patterns are used for identification and have genetic and developmental origins.

• Loop: Ridges enter from one side, curve, and exit from the same side

• Whorl: Circular or spiral patterns

• Arch: Ridges enter from one side and exit from the other, forming a wave-like pattern

Laboratory Procedures and Model Inventory

Model Inventory and Drawing

Students are expected to identify and label structures of the skin, hair, and nails using anatomical models and diagrams. Drawing and labeling exercises reinforce understanding of structure-function relationships.

Model/Diagram	Structures Identified
Skin cross-section	Epidermis, dermis, hypodermis, glands, hair follicle
Hair anatomy	Hair shaft, follicle, bulb, papilla
Nail anatomy	Nail plate, bed, matrix, cuticle

Additional info:

• The integumentary system also plays a role in vitamin D synthesis, immune defense, and excretion of wastes through sweat.

• Common clinical conditions include acne (sebaceous gland inflammation), dermatitis, and skin cancer.