Overview
This lecture focuses on the structure and function of the dermis and hypodermis, highlighting key tissue types, accessory skin structures, and sensory receptors.
Structure of the Dermis
- The dermis lies beneath the epidermis and contains most skin accessory structures.
- All four tissue types (epithelial, connective, nervous, muscular) are found in the dermis, but connective tissue dominates.
- The dermis is divided into two regions: papillary (top 20%, areolar connective tissue) and reticular (majority, dense irregular connective tissue).
Papillary Region & Dermal Structures
- The papillary region features dermal papillae, which are nipple-like projections that create epidermal ridges (fingerprints).
- Dermal papillae are most prominent in thick skin (palms, soles, fingertips) for grip; less pronounced in thin skin.
- Meissner corpuscles, located in dermal papillae, detect light touch and vibration.
Accessory Structures
- Hair, nails, and glands in the skin are epidermal derivatives (originating from epithelial tissue).
- Hair has a visible shaft and a root below the skin, ending in a bulb containing the hair papilla with blood vessels for nutrient supply.
- The hair matrix in the bulb contains actively dividing cells for hair growth.
Glands of the Skin
- All skin-associated glands are exocrine (secrete to a surface) and made of stratified cuboidal epithelium.
- Sebaceous glands, near hair follicles, secrete oily sebum via holocrine secretion (whole cell disintegration).
- Sweat glands (sudoriferous) include eccrine (found all over, thermoregulation, watery secretion via merocrine/exocytosis) and apocrine (active at puberty, thicker secretion, found in armpits, groin, face, chest).
Hypodermis and Sensory Receptors
- The hypodermis (subcutaneous layer) is not true skin but supports skin function.
- Pacinian corpuscles (lamellated corpuscles), primarily in the hypodermis, detect deep pressure and vibration.
- Additional sensory structures include Merkel cells (light touch, in epidermis) and free nerve endings (detect pain, temperature, tickling).
Key Terms & Definitions
- Dermis — Middle skin layer containing connective tissue, nerves, and accessory structures.
- Papillary region — Upper dermis layer with areolar tissue and dermal papillae.
- Reticular region — Lower dermis layer with dense irregular connective tissue.
- Dermal papillae — Projections creating fingerprints and increasing surface area.
- Meissner corpuscle — Sensory receptor for light touch in the papillary dermis.
- Sebaceous gland — Exocrine gland producing oily sebum, associated with hair follicles.
- Eccrine gland — Sweat gland for thermoregulation, secretes watery sweat.
- Apocrine gland — Sweat gland active at puberty, secretes thicker fluid.
- Pacinian corpuscle — Sensory receptor for deep pressure, mainly in hypodermis.
- Free nerve ending — Simple nerve ending for pain, temperature, and tickle detection.
Action Items / Next Steps
- Review the structure and function of all accessory skin structures and sensory receptors.
- Study diagrams showing the skin layers and locations of glands and receptors.
- Prepare for questions on gland secretion types and associated regions.