Integumentary System Chapter 5 Quiz

Skin Overview

• Skin is the largest organ of the body.
• Composed of two main regions: epidermis and dermis.

Epidermis

• Made up of epithelial tissue; avascular (lacks blood vessels).

Dermis

• Located beneath the epidermis; primarily fibrous connective tissue; vascularized (contains blood vessels).
• Nutrients are diffused from the dermis to the epidermis.

Hypodermis (Superficial Fascia)

• Not part of the skin; subcutaneous layer composed mostly of adipose tissue.
• Functions: absorbs shock, stores fat, insulates, and anchors skin to underlying muscles.

Fascia

• A fibrous membrane that covers, supports, and separates muscles.

Cells of the Epidermis

• Keratinocytes: The majority of epidermal cells; produce keratin.
• Melanocytes: Located in deeper epidermal layers; synthesize melanin to provide UV protection.
• Dendritic (Langerhans) Cells: Function as macrophages in the skin.
• Tactile (Merkel) Cells: Serve as sensory touch receptors.

Layers of the Epidermis

• Thick Skin: Found in areas subjected to abrasion (e.g., palms, fingertips); contains five strata.
• Thin Skin: Contains four layers.

Stratum Basale (Basal Layer)

• Deepest layer; single layer of actively mitotic cuboidal stem cells.
• Melanocytes comprise about 10-25% of this layer; produce melanin for UV protection.

Stratum Spinosum (Prickly Layer)

• Several cell layers thick; contains pre-keratin bundles.
• Characterized by dendritic cells and abundant melanin granules.

Stratum Granulosum (Granular Layer)

• Thin layer (1-5 cell layers); cells begin to flatten and disintegrate.
• Accumulation of keratohyaline and lamellar granules, which contain water-resistant glycolipids.

Stratum Lucidum (Clear Layer)

• Present only in thick skin; superficial to the stratum granulosum.
• Composed of 2-3 rows of flat, dead keratinocytes.

Stratum Corneum

• Thickest layer (20-30 rows of dead, flat, keratinized cells).
• Provides protective barrier against abrasion, penetration, and water loss through keratin and glycolipids.

Cell Differentiation in Epidermis

• Transition from stratum basale to stratum corneum; cells shed about 50,000 per minute as dander and dandruff.

Dermis

• Comprised of connective tissue that supports and binds epidermis to hypodermis.
• Houses blood vessels, nerves, glands, and hair follicles.

Papillary Dermis

• The upper layer of the dermis; contains areolar connective tissue.
• Features dermal papillae with capillary loops and Meissner's corpuscles for light touch sensitivity.

Reticular Dermis

• Constitutes about 80% of dermal thickness; made of dense irregular connective tissue.
• Contains collagen fibers for strength and elastic fibers for stretchability.
• Includes cleavage lines (tension lines) and flexure lines near joints.

Skin Color

• Determined by pigments: melanin (only skin-produced pigment), carotene (yellow-orange), and hemoglobin (red in blood).

Melanin Synthesis

• Tyrosinase enzyme converts tyrosine to melanin; melanin protects against UV damage.
• Number of melanocytes does not vary by gender or race; differences arise from pigment type and distribution.

Tanning and Albinism

• Tanning results from UV exposure stimulating melanin production.
• Albinism: Melanin production is severely reduced or absent.

Epidermal Derivatives

• Includes hair and hair follicles, nails, sweat glands, and sebaceous (oil) glands.

Hair (Pili)

• Composed of dead keratinized cells; absent from specific areas like palms and soles.
• Serves various functions including protection and thermoregulation.### Functions of Hair
• Warns of insects crawling on the skin, serving as a sensory function.
• Hair on the head acts as a barrier against physical trauma, reduces heat loss, and protects from sunlight.
• Eyelashes protect the eyes from debris and small particles.
• Nose hairs filter and trap particles, preventing entry into the respiratory system.

Characteristics of Hair

• Hard keratin in hair makes it tougher and more resilient compared to soft keratin in the skin.
• Hair cells do not flake off like skin cells.
• The hair root is embedded within the skin, while the shaft is visible above the surface.

Structure of Hair

• Medulla: Central core composed of large cells and air spaces, containing soft keratin; absent in fine hairs.
• Cortex: Major component of hair, consists of several layers of flattened cells.
• Cuticle: Outermost layer, made of a single layer of overlapping cells.

Hair Follicle Anatomy

• Extends from the epidermis surface to the dermis, consisting of a two-layered wall formed by dermis and epidermis.
• Hair Bulb: Deep, expanded part containing sensory nerve endings (root hair plexus).
• Hair Papilla: Dermal tissue supplying blood to the hair.

Hair Follicle Components

• Peripheral Connective Tissue Sheath: Derived from the dermis.
• Glassy Membrane: Serves as the basement membrane for the epithelial root sheath.
• Epithelial Root Sheath: Contains external root sheath (continuation of epidermis) and internal root sheath (derived from matrix cells).
• Hair Matrix: Location of dividing cells adjacent to the hair papilla.
• Arrector Pili Muscle: Smooth muscle causing "goose bumps" by contracting.

Nails

• Nails are scale-like modifications of the epidermis providing protection over the distal phalanges.
• Composed of hard keratin with growth occurring at the nail matrix.

Sweat Glands

• Two types: Eccrine (merocrine) and Apocrine glands.
• Eccrine Sweat Glands: Most numerous, found on the soles, palms, and forehead; contribute to thermoregulation through merocrine secretion.
• Apocrine Sweat Glands: Located in axillary and anogenital regions, secrete viscous sweat that contains fatty substances and proteins, activated at puberty.

Modified Apocrine Sweat Glands

• Ceruminous Glands: Found in the external ear canal, secrete cerumen (earwax) to deter insects and block foreign material.
• Mammary Glands: Specialized to secrete milk.

Sebaceous Glands

• Absent in thick skin (palms, soles); associated with hair follicles.
• Simple branched alveolar glands secreting sebum via holocrine secretion that acts as a protective film, preventing drying and keeping the skin soft.

Functions of the Integumentary System

• Protection: Skin serves as the body's primary defense against environmental hazards.
• Body Temperature Regulation: Thermoregulation through sweat and blood vessel dilation/constriction.
• Cutaneous Sensation: Receptors enable touch, pressure, temperature, and pain sensing.
• Metabolic Functions: Involves synthesis of vitamin D precursor and collagenase.
• Blood Reservoir: Holds up to 5% of the body's blood volume.
• Excretion: Eliminates nitrogenous wastes and salts through sweat.

Protection Mechanisms

• Chemical Barriers: Skin secretions maintain a low pH, inhibiting bacterial growth; melanin provides UV protection.
• Physical Barriers: Stratum corneum's dead, flat cells and lipids block most substances.
• Biological Barriers: Dendritic cells and dermal macrophages present foreign antigens to the immune system.

Temperature Regulation

• Normal perspiration around 500 ml/day; increased sweating and blood vessel dilation cools the body during heat.
• Constriction of dermal blood vessels retains heat in cold environments.

Sensation and Responses

• Exteroceptors enable cutaneous sensory perception; motor information leads to reflex actions like sweating and goosebumps.

Other Functions

• Metabolically synthesizes essential compounds and facilitates hormone activation.
• Acts as a waste excretion system, expelling materials through sweat.