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At the distal end of the dorsal surface of fingers and toes, there is a fold of dermis that gives rise to a hard, dense covering made of keratin that is tightly packed to form a clear, tough
At the proximal end, a ____ ______ pushes out the nail.
An __________ fills the space where the epidermis ends.
A ______ is sometimes seen near the cuticle as a slightly lighter area.
lunula (little moon)
At the ____ _____, another fold of epidermis with blood vessels dives under the surface of the nail. Past the interface, the free edge of the nail loses contact with ______ _______ and can be trimed without blood or pain.
free edge; living tissues
- Hair shaft has three layers
- - this is what we see externally
- - cuticle (purple layer) is outermost for external hairs
Pigment cells (melanocytes
) and blood vessels at base
The external portion of hair is made up of three concentric layers:
The medulla in the center, a cortex further out, and finally a covering, or cuticle, on the outside.
Beneath the surface of the skin, the ____ _______ and ______ ____ ______ surround the medulla, cortex and cuticle. At the base, ther are _____ ______ and melanocytes.
hair follicle; dermal root sheath; blood vessels
Color comes from pigment _______ trapped along with the ______ ______ in the hair shafts.
granules (brown or black eumelanin; blonde or red pheomelanin); keratin protein
White or gray hair occurs when pigment production is _______ or halted and ___ ______ replace pigment.
reduced; air bubbles
Hair follicle includes:
Internal root sheath; External root sheath; Dermal root sheath
In the hair root, additional layers of epidermis form a root sheath. The ______ ____ ______ surrounds the whole root of the hair. At the base, a small plexus of _____ _______ supplies _______ to the growing hair and the melanocytes.
dermal root sheath; blood vessels; nutrition
A single bundle of ______ muscle cells, the _______ ____ muscle, can contract to make the hair stand on end, or relax to let it lay flat. A ________ gland is associated with the hair root.
smooth; arrector pili; sebaceous
Describe the first stage of growth cycle.
Growth (anagen) stage. The hair matrix cells at the base of the follicle divide. This pushes the hair a little further out of the root and makes the external hair just a little longer. As these cells are pushed upward, they turn to bags of keratin and die (just as in the epidermis). This stage lasts about 2-6 years
Describe the second stage of the growth cycle.
Regression (catagen) stage. The cells of the hair matrix stop dividing. This stage lasts 2-3 weeks.
Describe the final (3rd) stage of the growth cycle.
Resting (telogen) stage. The hair falls out at the end of the resting stage and is replaced by a new hair in its growth stage. Lasts about 3 months.
The anterior surface of hands (palms and fingers) do not have hair, and are classified as _____ ____. Remember that thick skin has a _______ ______ while thin skin does not.
Thick skin; stratum lucidum
Along with differences in hair, there are differences in _____ ______. If you get nervous, your palms sweat; there are more sweat glands in _____ skin than in ____ skin.
sweat glands; thick; thin
Because sebaceous glands are associated with hair follicles, they are present in _____ skin and absent in ___-_____ skin.
hairy (thin); non-hairy (thick)
The fingertips and lips are among the most sensitive parts of the body. This is because they have the highest density of _____ _______.
Thick skin also has ridges because of the ______ _______ which underlie the epidermis. These specializations help increase ____ and __________ on thick skin surfaces.
dermal papillae; grip; sensitivity
Skin develops from the outermost of the three embryonic layers, called the _______. The dermis and epidermis are evident by __ _____.
Ectoderm; 11 weeks (40 weeks is full term)
At the beginning of the second trimester (14 weeks), the precursors of _____ _____ and ____ _____ are evident.
sweat glands; hair bulbs
Hairs pop out on the surface by __ _____. Melanocytes migrate into the skin from a location near the spinal cord called the ______ _____; they are among the last skin cells to arrive.
18 weeks; neural crest
On the other end of life, skin undergoes several changes with aging. Toxins in cigarette smoke interfere with _______ _. _______ _, in turn, is necessary for collagen synthesis. The damage to the underlying dermis produces a characteristic _________ of the skin in cigarett smokers.
Vitamin C; Vitamin C; slacking
_______ is a common disease of aging skin. It is characterized by ______ ____ ______ and pimples, especially around the nose and cheeks. The cause is unknown.
Rosacea; dilated blood vessels
Aging Skin: (long one I apologize)
- decreased # of Langerhans cells (about 40%)
- - increased risk of skin cancer & infections
- decreased # of mast cells, melanocytes
- decreased inflammatory response
- decreased thermoregulation
- -sweat glands, vascularity, subQ fat
- flattening of dermal papillae and epidermal ridges (rete ridges)
- -increased tendencey to tear
- changes in collagen, elastin
- -more wrinkles, sagging
- decreased capillary loops in skin
- -atrophy of hair bulbs, sweat, sebaceous glands
- decreased mechanoreceptors
- decreased speed of wound healing
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