5.4: skin color + 5.5: hair + 5.6: nails
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24 Terms
Three factors determining skin color
Melanin, carotene, and hemoglobin.
Melanin
A pigment ranging from reddish yellow to brownish black; helps protect DNA from damaging UV rays.
Effect of sunlight on melanin
Sunlight causes keratinocytes to secrete a signal that stimulates melanin production.
Carotene
A yellow-orange pigment found in certain foods that accumulates in the stratum corneum and hypodermis.
Hemoglobin
The pigment responsible for the pinkish hue seen in fair skin when blood is visible through the skin.Hair (pili)
Hair shaft
The part of the hair that projects from the skin.
Hair root
The part of the hair that is embedded in the skin.
Medulla
The inner core of a hair.
Cortex
The middle layer of a hair.
Cuticle
The outer layer of a hair.
Hair pigments
Melanins of different colors made by melanocytes at the base of the hair follicle and transferred to cortical cells.
Hair follicle
A structure that folds down from the epidermis into the dermis and sometimes into the hypodermis.
Hair bulb
The expanded deep end of a hair follicle.
Hair follicle receptor (root hair plexus)
Sensory nerve endings surrounding the hair bulb.
Hair follicle wall
The wall composed of a peripheral connective tissue sheath, thickened basement membrane, and inner epithelial root sheath.
Hair matrix
A group of actively dividing cells within the hair bulb that produces hair.
Arrector pili muscle
A bundle of smooth muscle cells associated with a hair follicle; contraction causes the hair to stand upright
Nail
A scale-like modification of the epidermis that provides a protective covering on the dorsal side of the distal finger or toe.
Hard keratin
The material that makes up nails.
Free edge
The portion of the nail extending beyond the attached skin.
Nail plate
The portion of the nail attached to the skin.
Nail root
The portion of the nail embedded in the skin.
Nail matrix
The part of the nail located within the proximal nail bed that is responsible for nail growth..