Untitled Chapter 5: Integumentary System Overview: The integumentary system, also referred to as cutaneous membrane or skin, is the body's covering and is the largest organ. It plays a crucial role in protecting the body from various threats, preventing water loss, regulating temperature and metabolism, facilitating sensory reception, and reflecting overall health. Outline for the Chapter Structure and function of the integument Epidermis: strata and cells Dermis: regions, accessory structures, and specific tissues Hypodermis: not part of the integumentary system but closely involved Nails, hair, and glands: accessory structures Repair and failure: aging Functions of the Integument Protects against: Trauma Chemicals Pollutants Microbes Sunlight (selectively permeable) Prevents water loss: Transdermal water loss, insensible perspiration, and sensible perspiration Regulates temperature and metabolism: Involves vitamin D production Provides sensory reception: Tactile cells provide detailed sensory information Indicators of overall health Dermatology: the study and treatment of the integumentary system Epidermis Characteristics: Keratinized, stratified squamous epithelium (KSSE) Avascular; receives nutrients via diffusion from the dermis Strata (Layers) of the Epidermis, top to bottom: Stratum Corneum : Composed of 20 to 30 layers of dead, flattened, non-nucleated, keratin-filled cells These cells spend about 2 weeks in this layer before being shed Provides a hostile environment for many microbes In one year, approximately 8 lbs of skin cells are shed Stratum Lucidum : Present only in thick skin (palms and soles) Cells are pale, featureless with indistinct boundaries Stratum Granulosum : Three to five layers of keratinocytes Keratinization begins; cells become thinner, flatter, and membranes thicken Nuclei and organelles disintegrate; cells begin to die Lamellar granules release lipids to prevent water loss Stratum Spinosum : Known as the “spiny layer” Contains several layers of cells with large, centrally located nuclei and spinelike processes Limited mitosis; cells attach via desmosomes, providing structural integrity Contains dendritic cells involved in immune defense; they present pathogens to helper T-cells Stratum Basale : Single layer of cuboidal cells in contact with the basement membrane High mitotic rate; source of new cells that produce keratin Three types of cells: Keratinocytes : stem cells, produce keratin Melanocytes : produce and store melanin in response to UV exposure Tactile Cells : few in number, stimulate sensory nerve endings for touch Tactile Receptors in the Integumentary System Meissner’s Corpuscle : Composed of elongated Schwann cells and connective tissue capsule Functions in light touch sensitivity Pacinian Corpuscle : Myelinated nerve surrounded by collagen layers Sensitive to pressure and vibration Merkel Cells : Specialized skin cells that contribute to sensory reception Free Nerve Endings : Pain and temperature receptors Ruffini Endings : Detect stretch and sustained pressure Variations in the Epidermis Thin Skin : Covers most of the body, lacks stratum lucidum Melanin Production : Melanin: a pigment derived from the amino acid tyrosine All individuals have a similar number of melanocytes; variation lies in melanin activity and color Types of Melanin: Eumelanin (brown/black pigment) Pheomelanin (red/yellow pigment) Function of Melanin: Protection against UV radiation Dermis Location: Beneath the epidermis, consists of two types of connective tissues: Areolar connective tissue Dense irregular connective tissue Structures: blood vessels, sweat glands, sebaceous glands, hair follicles, nail roots, sensory nerve endings, and smooth muscle tissues Papillary Layer : Composed of areolar connective tissue Contains nerve endings and interlocks with the epidermis Reticular Layer : Composed of dense irregular connective tissue Houses large collagen fibers forming a mesh Contains blood vessels, hair follicles, sweat, and sebaceous glands Hypodermis Location: Beneath the dermis and not part of the integumentary system but closely related Functions: Highly vascular, promoting rapid absorption of substances injected (e.g., hypodermic needles) Provides insulation and cushioning Structures Derived from the Epidermis Nails : Protect digit ends and are scalelike modifications made of keratin Types of Hair: Produced throughout life Lanugo : Fine, downy hair present in the second trimester Vellus : Primary human hair on most of the body Terminal Hair : Found on the scalp, eyebrows, eyelashes, and beard Functions of the Nails Protection against mechanical stress and injury Composed of the stratum corneum and features like the lunula (thickened stratum basale) and nail fold Health implications: Exposure to chemicals can be hepatotoxic and nephrotoxic Hair Anatomy Functions: Protection, heat retention, sensory reception, visual identity, dispersal of chemical signals Zones of Hair: Hair Bulb : Base of the hair where living cells are found Root : Portion deep to the skin surface comprised of dead cells Shaft : Hair extending beyond the skin surface, dead cells Follicles : Surround the root, extending into the dermis; associated with arrector pili muscles which cause goosebumps Exocrine Glands Sweat Glands : Merocrine : Most numerous, commonly produce sweat, approximately 3-4 million in adults Apocrine : Found in armpits, groin, and other areas; secrete a viscous fluid that bacteria feed on, causing odor Sebaceous Glands : Produce sebum for skin lubrication and bactericidal properties Ceruminous Glands : Located in the ear, produce earwax (cerumen) Mammary Glands : Produce milk Skin Repair Methods of Repair: Regeneration : Replacement of damaged cells with the same type Fibrosis : Formation of scar tissue due to extensive damage Burns : Major cause of accidental death; severity classified as first, second, or third degree Aging and the Skin Changes with Aging: Slower skin repair processes Loss of collagen fibers leading to sagging and wrinkles Decreased immune effectiveness due to lower dendritic cell count Skin dryness or scaling Decrease in melanocytes affecting pigmentation Reduced vitamin D production Types of Skin Cancer Information on the most common and least dangerous types of skin cancers, including risk factors for developing the deadliest forms Importance of knowing the ABCs of the most deadly type (Asymmetry, Borders, Color, Diameter) for early detection. End of Chapter Reminder to complete homework and quizzes. Encouragement to read further on the subject. Knowt Play Call Kai