AE

Integumentary System – Dermis, Hair, Glands, and Sensory Structures

Integumentary System Overview

Introduction

  • The Integumentary system includes various structures such as the dermis, hair, glands, and sensory structures.

Dermis Location and Composition

  • Location: Lies deep to the epidermis.

  • Composition: Composed of connective tissue proper.

  • Layers of Dermis:

    • Papillary Layer:

    • Thin, superficial layer.

    • Composed of areolar connective tissue.

    • Contains dermal papillae that interlock with epidermal ridges.

    • Rich in capillaries, lymphatics, and sensory neurons.

    • Reticular Layer:

    • Deeper, thicker portion of the dermis.

    • Composed of dense irregular connective tissue.

    • Provides strength, resilience, and anchors accessory structures.

Cells of the Dermis

  • Primary Cell Type:

    • Fibroblasts: Produce collagen and elastic fibers.

  • Other Cell Types:

    • Immune Cells: Dendritic cells, macrophages.

    • Adipocytes: Fat cells providing insulation and energy storage.

    • Sensory Nerve Endings: Responsible for sensation.

Structures within the Dermis

  • Includes:

    • Blood vessels

    • Sweat glands

      • Types: Merocrine (eccrine) and Apocrine

    • Sebaceous glands

    • Hair follicles

    • Nail roots

    • Sensory nerve endings

    • Arrector pili muscles

Functions of Collagen

  • Provides:

    • Strength and structural support.

    • Resists stress in multiple directions.

    • Contributes to skin elasticity.

Nails

  • Composition: Derived from epidermis, made of dead keratinocytes.

  • Function: Protect distal dorsal tips of fingers/toes, assist in grasping objects.

  • Cuticle (Eponychium): Living skin at the base of the nail protects the matrix from pathogens.

  • Nail Growth: Occurs at the nail matrix, which is the proximal part of the nail bed.

  • Nail Root, located beneath the proximal nail fold, anchors the nail plate

  • Lanula is the white half-moon at base of nail, visible portion of nail matrix

  • Cuticle protects the nail matrix

Hair

  • Derived From: Epidermis, primarily composed of keratin.

  • Functions: Includes protection, heat retention, sensory reception, and visual identification.

  • Hair Color: Determined by melanin produced in the hair bulb; gray/white hair results from reduced melanin production.

  • Melanin's Role: Protects hair from UV radiation and reduces DNA damage.

  • Hair Benefits: Traps debris; e.g., nasal and ear hairs protect respiratory pathways.

Hair Structures

  • Root Hair Plexus: Nerve endings surrounding the hair root; detects light touch.

  • Hair Follicle: Oblique tube extending into the dermis or hypodermis, composed of:

    • Inner Epithelial Root Sheath

    • Outer Connective Tissue Root Sheath

  • Arrector Pili Muscle: Smooth muscle attached to hair follicle; contracts to cause 'goosebumps', contributing to thermoregulation and emotional responses.

  • As new cells move outward from the matrix:

  • Medulla- Core remnant of matrix

  • Cortex- Surrounds the medulla, densely packed cells

  • Cuticle- Outer layer, protects hair shaft

Types of Hair

  • Vellus: Fine hair covering the body.

  • Terminal: Thicker hair on the scalp, eyebrows, and axillae.

  • Lanugo: Fetal hair.

Summary of Hair Functions

  • b Protection, heat retention, sensory detection, facial expression and identity, debris filtering.

Sweat Glands

  • Types of Sweat Glands:

    • Merocrine (Eccrine):

    • Widely distributed; secrete watery sweat for thermoregulation and excretion.

    • Apocrine:

    • Located in axillae, nipples, and groin; secrete viscous, protein and lipid rich fluid sweat into hair follicles; become active at puberty.

Sebaceous Glands

  • Function: Secrete sebum (oily secretion) into hair follicles; lubricates and waterproofs skin and hair.

Specialized Glands

  • Mammary Glands: Modified apocrine glands producing milk.

  • Ceruminous Glands: Modified apocrine glands producing earwax (cerumen).

Sensory Structures

General Senses

  • Distribution: Receptors spread throughout the body in skin and organs.

Special Senses

  • Location: Localized to specific organs (eyes, ears, tongue, nose).

General Sensory Receptors of Skin

  • Tactile (Meissner’s) Corpuscles: Detect light touch; located in dermal papillae.

  • Lamellar (Pacinian) Corpuscles: Detect deep pressure and vibration.

  • Bulbous (Ruffini) Corpuscles: Detect stretch in skin.

  • Tactile Discs (Merkel Discs): Detect light touch at the epidermis-dermis junction.

  • Free Nerve Endings: Detect pain, temperature, itch, and light touch.