BIO251 week 5 notes

The Integumentary System

Overview

  • The integumentary system consists of the skin, hair, oil and sweat glands, nails, and sensory receptors.

  • Functions:

    • Helps maintain body temperature.

    • Converts inactive vitamin D to its active form.

    • Provides sensory information.

    • Maintains homeostasis in various ways.

Components and Functions

Functions of the Integumentary System

  • Covers the body.

  • Contains sensory receptors that make us aware of our surroundings.

  • Provides protection against:

    • Drying out

    • Pathogen invasion

  • Regulates body temperature.

  • Synthesizes vitamin D.

  • Protects underlying tissues from injury.

Components of the Integumentary System

  • Skin

  • Appendages:

    • Hair

    • Nails

    • Glands (sweat and sebaceous glands)

Layers of the Skin

  • The skin consists of two major layers:

    • Epidermis: The most superficial layer.

    • Dermis: Deep to the epidermis.

  • Hypodermis (Subcutaneous Layer): Not a true layer of skin but located deep to the dermis; composed of areolar and adipose tissue.

Epithelial Tissue Structure

  • The basal layer produces new cells.

  • As cells push to the surface, they harden and die, providing waterproofing to the skin.

  • Outer layer is composed of dead cells.

  • Melanocytes: Produce skin pigment.

  • Dermis Composition:

    • Contains collagen, elastic fibers, blood vessels, and sensory receptors (touch, pain, pressure, temperature).

    • Contains fibrous connective tissue and adipose tissue for insulation and energy storage.

Skin and Hair Anatomy

Skin Anatomy

  • Accessory Structures:

    • Hair, nails, sweat glands, sebaceous glands.

  • Human Skin Anatomy:

    • Epidermis, dermis, fat layer (hypodermis).

Hair Structure

  • Composed of dead, keratinized epidermal cells.

  • Parts of Hair:

    • Shaft (visible part above the skin surface)

    • Follicle (below the skin level)

    • Root that penetrates into the dermis

    • Epithelial root sheath

    • Dermal root sheath

    • Dermal papilla

Hair Growth Cycle

  • Stages:

    • Anagen: Growth stage.

    • Catagen: Regression stage.

    • Telogen: Resting stage.

    • Restarting of anagen phase.

Types of Hairs

  • Lanugo: Fine hair covering the fetus.

  • Terminal Hair: Long, coarse, heavily pigmented hair.

  • Vellus Hair: Short, fine, pale hair.

  • Hair Color: Determined by the amount and type of melanin in keratinized cells.

Skin Glands

  • The skin contains five types of glands:

    • Sebaceous Glands: Connected to hair follicles. Produce sebum.

    • Eccrine Sweat Glands: Most numerous, present across the body.

    • Apocrine Sweat Glands: Found in hairy areas (e.g., armpits).

    • Ceruminous Glands: Modified sweat glands located in the ear canal.

    • Mammary Glands: Produce milk; develop only during pregnancy and lactation.

Functions of the Skin

  • Thermoregulation:

    • Sweat production and blood flow regulation to the dermis.

  • Blood Reservoir:

    • The dermis holds 8-10% of total blood flow when an adult is at rest.

  • Protection:

    • Barrier against environmental hazards.

  • Cutaneous Sensations:

    • Includes touch, pressure, vibration, temperature, and pain sensations.

  • Excretion and Absorption:

    • Elimination of substances and absorption of materials through the skin.

    • Involves transdermal drug delivery.

  • Synthesis of Vitamin D:

    • Ultraviolet rays activate the precursor molecule (calcitriol) for vitamin D production, aiding calcium absorption from foods in the gastrointestinal tract.

Wound Healing Process

  • Wound healing occurs when an injury extends into the dermis and subcutaneous layers.

  • Stages of Wound Healing:

    • Bleeding

    • Blood clot formation

    • Inflammation (infiltration of immune cells)

    • Scab formation

    • Proliferation: Involves fibroblast activity.

    • Remodeling of tissue following healing.

Age-Associated Changes in Skin

  • Wrinkles and dehydration.

  • Decrease in sweat production.

  • Decrease in functional melanocytes leading to gray hair and abnormal skin pigmentation.

  • Loss of subcutaneous fat and reduced skin thickness.

  • Nails may become more brittle with age.

Skin Cancer

  • Types of Skin Cancer:

    • Basal Cell Carcinoma: Most common type, usually benign and easily curable.

    • Squamous Cell Carcinoma: Less common, more likely to spread.

    • Melanoma:

    • More aggressive than BCC and SCC.

    • Appears as an unusual mole with irregular borders and multiple colors.

    • The risk increases with the number of moles and sun exposure.

Burns

  • Burns are tissue damage caused by excessive heat, electricity, chemical exposure, etc., leading to denaturation of skin proteins.

  • Types of Burns:

    • First-degree Burns: Affect epidermis only.

    • Second-degree Burns: Affect epidermis and part of the dermis.

    • Third-degree Burns: Affect the epidermis, dermis, and hypodermis, might require skin grafts for healing.

Skin Grafts

  • Third-Degree Burns: Often necessitate skin grafting for healing.

  • Types of Skin Grafts:

    • Autograft: Tissue from another location on the same individual.

    • Split-Skin Graft: Involves the epidermis and part of the dermis taken from an undamaged area (e.g., thigh or buttocks).