Unit 2.1 Lec

Chapter 5: Integumentary System

Objective

  • Describe the general structure of the integument.

Introduction

  • Integument: Refers specifically to the skin that covers the body.

  • Also known as the cutaneous membrane.

  • Integumentary system encompasses the skin and its derivatives, including:

    • Nails

    • Hair

    • Sweat glands

    • Sebaceous glands

Integument Structure

  • The integument consists of two primary layers:

    • Epidermis:

    • A superficial layer made of stratified squamous epithelium.

    • Dermis:

    • A deeper layer composed of areolar and dense irregular connective tissues.

  • Subcutaneous layer:

    • Not considered part of the skin; lies under the dermis.

    • Composed of areolar and adipose tissue.

Layers of the Integument

Figure 5.1

  • Epidermis

  • Dermis

  • Subcutaneous layer

  • Contains:

    • Hair follicle

    • Tactile (sensory) receptors

    • Areolar connective tissue

    • Sensory nerve fibers

    • Hair shaft

    • Sweat pore

    • Epidermal ridge

    • Dermal papilla

    • Arrector pili muscle

    • Sebaceous (oil) gland

    • Sweat gland duct

    • Merocrine sweat gland

    • Vein

    • Artery

    • Adipose connective tissue

Objective

  • Explain the varied functions of the integument.

Integument Functions

  1. Protection:

    • Guards against trauma, toxic substances, and solar radiation.

    • Selective permeability allows some chemicals to be absorbed.

  2. Preventing Water Loss & Gain:

    • Skin is water-resistant due to transepidermal water loss.

    • Insensible perspiration: Release of water vapor from sweat glands when not visibly sweating.

    • Sensible perspiration: Visible sweating.

  3. Temperature Regulation:

    • Dilation of dermal vessels releases heat.

    • Constriction conserves heat.

  4. Metabolic Regulation:

    • Production of Vitamin D3 (cholecalciferol) by skin cells and conversion to calcitriol by kidneys.

    • Calcitriol plays a role in calcium homeostasis.

  5. Immune Defense:

    • Epidermal dendritic cells initiate immune responses.

  6. Sensory Reception:

    • Skin receptors detect changes in temperature and touch.

    • Tactile cells stimulate sensory nerve endings in response to touch.

  7. Secretion:

    • Includes sweating and lubrication of hair and skin with sebum.

Objective

  • Describe the structure, composition and arrangement, and functions of the epidermal strata.

  • Describe the composition, function, and locations of the epidermal cells.

Epidermis

  • The epithelium of the skin, also known as the epidermis, has the following characteristics:

    • Type: Keratinized stratified squamous epithelium.

    • Vascularity: Avascular (lacks blood vessels).

    • Layers (strata): Composed of several layers.

Epidermal Strata

From Deep to Superficial:

  1. Stratum basale

  2. Stratum spinosum

  3. Stratum granulosum

  4. Stratum lucidum: Present in thick skin only.

  5. Stratum corneum

Stratum Basale

  • Characteristics:

    • Single layer of cuboidal to low columnar cells.

    • Cells are attached to the basement membrane and adjacent to dermis.

  • Cell Types:

    • Keratinocytes: Most abundant, produce tough keratin protein, providing protection and water resistance.

    • Melanocytes: Produce melanin, which absorbs UV light and helps prevent DNA damage; transfer melanin to keratinocytes through cytoplasmic processes.

    • Tactile Cells: Sensitivity to touch.

Stratum Spinosum

  • Structure:

    • Composed of several layers of polygonal keratinocytes.

    • Daughter cells from stratum basale differentiate here into specialized, non-dividing keratinocytes.

  • Cell Connections:

    • Keratinocytes are interconnected via desmosomes.

    • Contains some epidermal dendritic cells acting as immune cells.

Stratum Granulosum

  • Characteristics:

    • Composed of 3-5 layers of keratinocytes undergoing keratinization.

    • Cytoplasm fills with keratin filaments; organelles begin to degrade.

  • Key Granules:

    • Keratohyalin granules: Involved in the keratinization process.

    • Lamellar granules: Release lipids into extracellular space for water barrier formation.

Stratum Lucidum

  • Features:

    • Thin, translucent layer, consisting of 2-3 cell layers thick.

    • Present only in thick skin (palms and soles).

    • Cells lack organelles and contain eleidin, an intermediate keratin maturation product.

Stratum Corneum

  • Characteristics:

    • Most superficial stratum of the epidermis.

    • Thickness varies from 20-30 layers of dead, scaly, interlocking keratinized cells, known as corneocytes.

    • Corneocytes are anucleate (lack a nucleus) and tightly packed.

  • Cell Migration:

    • Cells from stratum basale migrate to stratum corneum in about 2 weeks; they serve a protective function for an additional 2 weeks before being shed.

Objective

  • Compare and contrast epidermal variations in thickness, color, and markings.

Thick Skin Versus Thin Skin

  • Thick Skin:

    • Contains five layers in the epidermis (includes stratum lucidum).

    • Location: palms and soles.

    • Epidermis thickness: 0.4-0.6 mm.

    • Lacks hair follicles and sebaceous glands.

  • Thin Skin:

    • Contains four layers of epidermis (lacks stratum lucidum).

    • Covers most of the body.

    • Epidermis thickness: 0.075-0.150 mm.

Skin Color

  • Determined by three pigments:

    1. Hemoglobin: Blood pigment, red in color.

    2. Melanin: Produced by melanocytes; increases with UV exposure; relative amounts influence complexion.

    3. Carotene: Yellow-orange pigment from food sources, such as carrots.

Abnormal Skin Colors

  • Albinism: Hair is white, skin is pale, irises are pink due to lack of melanin.

  • Bronzing: Golden-brown or copper-colored skin appearance.

  • Cyanosis: Bluish discoloration due to oxygen deficiency.

  • Erythema: Abnormally red skin.

  • Hematoma: Bruising due to visible clotted blood under skin.

  • Jaundice: Yellowish skin and sclera (white of eyes).

  • Pallor: Ashen appearance due to underlying collagen fibers.

Skin Markings

  • Nevus: Mole; localized overgrowth of melanocytes.

  • Freckles: Yellow or brown spots due to high melanocyte activity.

  • Hemangioma: Benign tumor formed by proliferation of blood vessels.

  • Types:

    • Capillary hemangiomas: Strawberry-colored birthmarks.

    • Cavernous hemangiomas: Port wine stains.

  • Friction Ridges: Epidermal and dermal folds increase grip on fingers and toes.

Objective

  • Describe the organization and function of the layers of the dermis.

Dermis

  • Lies beneath the epidermis and consists of:

    • Tissues: Areolar and dense irregular connective tissues.

  • Contains two layers:

    • Papillary Layer: Superficial, adjacent to epidermis.

    • Reticular Layer: Deeper and thicker, forming the majority of dermis.

Layers of the Dermis

Figure 5.6

  • Papillary Layer:

    • Contains dermal papillae which interlock with epidermal ridges, increasing surface area.

  • Reticular Layer:

    • Composed primarily of dense irregular connective tissue with large collagen bundles, numerous blood vessels, glands, and nerve fibers.

Papillary Layer of the Dermis

  • Composition:

    • Comprised of areolar connective tissue.

  • Features:

    • Dermal papillae contain capillaries that supply nutrients to the epidermis and sensory receptors.

Reticular Layer of the Dermis

  • Characteristics:

    • Forms the major thickness of the dermis.

    • Includes dense irregular connective tissue with elastic fibers.

    • Houses large blood vessels, hair follicles, glands, and nerves.

Lines of Cleavage and Stretch Marks

  • Collagen and elastic fibers align in parallel bundles:

    • Important for skin resilience.

    • Lines of cleavage indicate the orientation of these fiber bundles; surgical incisions aligned with these lines promote quicker healing.

  • Stretch Marks (Striae): Occur when skin is overstretched, causing collagen fibers to tear.

Figure 5.7

  • Depicts the effect of incisions on skin healing based on alignment with lines of cleavage.

Objective

  • Describe nerve and blood supply to the dermis, and the role of the dermal blood supply in regulating body temperature.

Innervation and Blood Supply

  • Innervation:

    • Nerve fibers in the dermis monitor sensory receptors and control blood flow and glandular secretion.

  • Blood Supply:

    • Dermal blood vessels regulate body temperature and blood pressure:

    • Vasoconstriction: Reduces blood flow to conserve heat.

    • Vasodilation: Increases blood flow to release heat.

Objective

  • Identify and describe the structure and function of the subcutaneous layer.

Subcutaneous Layer

  • Location: Deep to the integument.

  • Composition: Areolar and adipose connective tissues.

  • Function:

    • Protects underlying structures.

    • Stores energy.

    • Provides thermal insulation.

Integumentary Structures Derived from Epidermis

  • Structures that are epidermal derivatives include:

    • Nails

    • Hair

    • Exocrine glands of the skin.

Objective

  • Describe the structure and functions of nails.

Nails

  • Modifications of the stratum corneum, characterized as scalelike.

  • Components:

    • Nail Plate: Whitish free edge, pinkish nail body, and nail root covered by skin.

    • Nail Body: Covers the nail bed (layer of epidermis).

    • Nail Matrix: Thickened growing part of the nail bed.

    • Lunula: Whitish semilunar proximal area due to thickened stratum basale obscuring capillaries.

    • Nail Folds: Overlap lateral and proximal edges of the nail.

    • Eponychium: Cuticle, epidermis extending over the nail body.

    • Hyponychium: Thickened stratum corneum area under free edge of the nail.

Figure 5.8

  • Illustrates the detailed structure of a fingernail.

Objective

  • Describe the structure, distribution, and functions of hairs.

Hair Type and Distribution

  • Types of Hair:

    1. Lanugo: Fetal hair.

    2. Vellus: Fine and non-pigmented hair, present on most of the body.

    3. Terminal Hair: Coarser, pigmented hair.

Hair Structure and Follicles

  1. Pilus: Composed of keratinocytes from hair follicles deep in the dermis, sometimes extending to the subcutaneous layer.

  2. Hair Zones:

    • Hair Bulb: Deep swelling where hair originates.

    • Hair Root: Portion below the skin surface.

    • Hair Shaft: Portion extending beyond skin surface.

Hair Structure and Follicles Continued

  • Layers of Hair:

    • Medulla: Central core with loose cells and air spaces.

    • Cortex: Several layers of flattened, hardened cells.

    • Cuticle: Outer coating.

  • Hair Follicle: Surrounds hair, composed of a connective tissue root sheath and an epithelial tissue root sheath.

  • Arrector Pili Muscles: Attached to each hair shaft, contract to stand hair up (goosebumps).

Figure 5.9

  • Shows the detailed structure of hair, including roots and follicles.

Functions of Hair

  1. Protection: Guards against sunburn and physical injury.

  2. Heat Retention: Prevents heat loss from the head.

  3. Sensory Reception: Detects light touch.

  4. Visual Identification: Contributes to age and sex identification.

Hair Color

  • Determined by melanin production in matrix next to hair papillae.

  • Variation is genetically determined and influenced by environmental and hormonal factors.

  • Aging Effects: Gradual decrease in melanin leads to gray hair; complete stoppage leads to white hair.

Objective

  • Identify and describe the characteristics of sweat glands, sebaceous glands, and other glands found in the skin.

Exocrine Glands of the Skin

  • Two primary types of exocrine glands:

    • Sweat (Sudoriferous) Glands: Produce watery solutions.

    • Subtypes: Merocrine and apocrine.

    • Sebaceous Glands: Produce oily secretions.

Figure 5.10

  • Illustrates the various glands in the skin.

Sweat (Sudoriferous) Glands

  • Types:

    1. Merocrine Sweat Glands:

    • Release secretions (sweat) via exocytosis; secretion is 99% water, clear, and controlled by the nervous system.

    • Abundant on palms, soles, and forehead.

    • Functions: Thermoregulation, secretion of substances, microbial protection.

    1. Apocrine Sweat Glands:

    • Secrete into hair follicles located in the armpits, nipples, groin, and anus.

    • Thick, cloudy secretion leads to distinct odor due to bacterial growth.

Sebaceous Glands

  • Type: Holocrine glands.

  • Function: Secrete oily sebum into hair follicles or directly onto the skin's surface for lubrication and to prevent drying of hair and skin.

  • Activity increases significantly during puberty due to sex hormones.

Other Integumentary Glands

  • Ceruminous Glands: Apocrine glands located in the external acoustic meatus producing cerumen (earwax); provides lubrication, traps particles, and contains antimicrobial lysozyme.

  • Mammary Glands: Modified apocrine glands in the breasts; become functional in pregnant females due to hormonal signals, leading to breast milk production.