Sensory Receptors and Hair

Sensory Receptors

• Differentiate between tactile sensations: light touch, pressure, vibration, itch, and tickle
• Superficial receptors: Merkel discs, free nerve endings, Meissner corpuscles, hair root plexuses
• Deep receptors: Pacinian corpuscles

Hair

• Found on most surfaces except palms, anterior surfaces of fingers, and soles of feet
• Composed of dead, keratinized epidermal cells
• Helps with touch sensations and protects against sun and heat loss
• Hair color determined by amount and type of melanin

Exocrine Skin Glands

Sebaceous (Oil) Glands

• Connected to hair follicles
• Secrete sebum, preventing dehydration and inhibiting bacteria

Sudoriferous (Sweat) Glands

Eccrine Sweat Glands

• Most numerous on forehead, palms, and soles
• Secrete watery solution (600 ml/day) to cool body and eliminate waste

Apocrine Sweat Glands

• Found in skin of axilla, groin, areolae, and bearded regions of face
• Secrete milky viscous sweat responsible for body odor

Ceruminous Glands

• Modified sweat glands in ear canal
• Produce cerumen (earwax)

Nails

• Protect distal end of digits
• Provide support and counterpressure for touch perception and manipulation
• Allow grasping and manipulation of small objects, and used for scratching and grooming

Wound Healing

Epidermal Wound Healing

• Occurs in superficial wounds affecting only epidermis
• Repairs skin to normal structure and function

Deep Wound Healing

• Occurs in injuries extending to dermis and subcutaneous layer
• Results in loss of function and development of scar tissue
• Healing process involves four phases: inflammatory, migratory, proliferative, and maturation

Burns

• Tissue damage caused by denaturation of skin cell proteins by excessive heat, electricity, radiation, or corrosive chemicals

Integumentary System

The Epidermis

• Composed of keratinized stratified squamous epithelium
• Contains four major cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells

Layers of Epidermis

• Stratum corneum: 25 layers of flat dead keratinocytes
• Stratum lucidum: present in thick skin, 4-6 layers of dead keratinocytes
• Stratum granulosum: 3-5 layers of flattened keratinocytes undergoing apoptosis
• Stratum spinosum: layers of 8-10 keratinocytes
• Stratum basale: cuboidal or columnar keratinocytes

Types of Skin

• Thin (hairy) skin: covers all body regions except palms, palmar surfaces of digits, and soles
• Thick (hairless) skin: covers palms, palmar surfaces of digits, and soles

The Dermis

• Provides temperature stability and prevents dehydration
• Composed of dense irregular connective tissue containing collagen and elastic fibers
• Contains two regions: papillary and reticular regions

Skin Pigments

• Melanin: produced by melanocytes in stratum basale, dictates skin color
• Eumelanin: brown/black polymer
• Pheomelanin: yellow/red polymer
• Nevi: chronic benign lesions of the skin, overgrowth of melanocytes
• Albinism: congenital disorder characterized by inability to produce melanin
• Vitiligo: chronic depigmentation disorder, partial or complete loss of melanocytes from skin patches