Second half of Chapter 6 Flashcards
Structure of the Hair and Follicle:Dermal papilla
Dermal papilla: bud of vascular connective tissue encased by bulb. Only source of nutrition for hair.
Structure of the Hair and Follicle: Hair matrix
Hair matrix—region of mitotically active cells immediately above papilla. Hair’s growth center.
Structure of the Hair and Follicle:Follicle
Follicle—diagonal tube that extends into dermis and possibly hypodermis
Structure of the Hair and Follicle: Epithelial root sheath
Epithelial root sheath. Extension of the epidermis lying adjacent to hair root. Widens at deep end into bulge—source of stem cells for follicle growth.
Structure of the Hair and Follicle: Connective tissue root sheath
Connective tissue root sheath,Derived from dermis but a bit denser, Surrounds epithelial root sheath.
Structure of the Hair and Follicle: Hair receptors
Hair receptors—sensory nerve fibers entwining follicles.
Structure of the Hair and Follicle:Piloerector muscle (arrector pili)
Piloerector muscle (arrector pili)—smooth muscle attaching follicle to dermis. Contracts to make hair stand on end (goose bumps)
Hair Texture and Color: Texture
Texture—related to cross-sectional shape of hair.Straight hair is round, Wavy hair is oval, Curly hair is relatively flat.
Hair Texture and Color:Color
Color—due to pigment granules in the cells of the cortex.Brown and black hair is rich in eumelanin.Red hair has high concentration of pheomelanin.Blond hair has an intermediate amount of pheomelanin and very little eumelanin.Gray and white hair have little or no melanin. Air present in medulla.
Three stages of hair cycle:Anagen
Anagen: growth stage.90% of scalp follicles at a given time.Stem cells multiply.Root sheath cells above papilla form hair cells of hair matrix.Hair cells make keratin and die as they are pushed upward.
Three stages of hair cycle:Catagen
degeneration stage.Mitosis in hair matrix ceases and sheath cells below bulge die.Base of hair keratinizes into a hard club—club hair.Easily pulled out by brushing
Three stages of hair cycle: Telogen
resting stage.When papilla reaches the bulge
Hair Growth and Loss:We lose about 50-100 hairs daily
A club hair may fall out during catagen or telogen or be pushed out in the next anagen phase.In young adults, scalp follicles spend 6–8 years in anagen, 2–3 weeks in catagen, 1–2 months in telogen.
Hair growth
scalp hairs grow 1 mm per 3 days.Alopecia—thinning of the hair or baldness.
Pattern baldness
hair lost from select regions. Baldness allele is dominant in males and expressed when testosterone levels are high. Testosterone causes terminal hair on top of scalp to be replaced by vellus hair
Hirsutism
excessive or undesirable hairiness in areas that are not usually hairy.
Functions of Hair
Most hair on trunk and limbs is vestigial.Has little present function but kept ancestors warm.Hair receptors alert us of parasites crawling on skin.Scalp retains heat and protects against sunburn.Pubic and axillary hair signify sexual maturity and aid in transmission of sexual scents
Functions of Hair: Guard hairs (vibrissae)
Guard nostrils and ear canals,Eyelashes and eyebrows, Nonverbal communication
Nails: Fingernails and toenails
clear, hard derivatives of stratum corneum
Composed of thin, dead cells packed with hard keratin
Nails:Functions
Improve grooming, picking apart food, other manipulations.Provide a counterforce to enhance sensitivity of fleshy fingertips to tiny objects.
Nails: Nail plate
hard part of the nail:Free edge: overhangs the fingertip.
Nail body: visible attached part of nail. Nail root: extends proximally under overlying skin
Nail fold
surrounding skin rising above nail
Nail groove
separates nail fold from nail plate
Nail bed
skin underlying the nail plate. Hyponychium—epidermis of the nail bed
Nail matrix
growth zone (mitotic) of thickened stratum basale at proximal end of nail. 1 mm per week in fingernails, slightly slower in toenails. Lunule—opaque white crescent at proximal end of nail due to thickness of matrix
Eponychium (cuticle)
narrow zone of dead skin overhanging proximal end of nail
Two kinds of sweat (sudoriferous) glands: apocrine and merocrine
Apocrine sweat glands
Apocrine sweat glands .Locations: groin, anal region, axilla, areola, beard area in men. Inactive until puberty
Ducts lead to nearby hair follicles. Produce sweat that is milky and contains fatty acids.Respond to stress and sexual stimulation. Believed to secrete pheromones—chemicals that can influence behavior of others
Two kinds of sweat (sudoriferous) glands: apocrine and merocrine: Bromhidrosis
Bromhidrosis—disagreeable body odor produced by bacterial action on sweat from apocrine glands.
Two kinds of sweat (sudoriferous) glands: Merocrine (eccrine) sweat glands
Merocrine (eccrine) sweat glands. Most numerous skin glands—3 to 4 million in adult skin. Especially dense on palms, soles, and forehead. Simple tubular glands
Watery perspiration that helps cool the body
Two kinds of sweat (sudoriferous) glands: Myoepithelial cells
Myoepithelial cells—contract in response to stimulation by sympathetic nervous system and squeeze perspiration up the duct. Found in both apocrine and merocrine glands
Sweat
Sweat—begins as a protein-free filtrate of blood plasma produced by deep secretory portion of gland. Some sodium chloride and other small solutes remain in the sweat. Some sodium chloride reabsorbed by duct. Some drugs are excreted in sweat. On average, 99% water, with pH range of 4 to 6
Acid mantle—inhibits bacterial growth
Sweat glands:Insensible perspiration
Insensible perspiration—500 mL/day. Does not produce visible wetness of skin
Sweat glands:Diaphoresis
Diaphoresis—sweating with wetness of the skin. Exercise—may lose 1 L sweat per hour
Sebaceous Glands and Sebum
Sebaceous glands are flask-shaped and have short ducts opening into hair follicles. Holocrine secretion style . Sebum—oily secretion of sebaceous glands
Keeps skin and hair from becoming dry, brittle, and cracked. Lanolin—sheep sebum
Ceruminous Glands
Ceruminous glands are simple, coiled, tubular glands in external ear canal. Their secretion combines with sebum and dead epithelial cells to form earwax (cerumen). Keeps eardrum pliable. Waterproofs the canal. Kills bacteria. Makes guard hairs of ear sticky to help block foreign particles from entering auditory canal
Mammary glands
Mammary glands—milk-producing glands that develop only during pregnancy and lactation. Modified apocrine sweat glands. Rich secretion released through ducts opening at nipple
Mammary ridges or milk lines
Mammary ridges or milk lines-Two rows of mammary glands in most mammals Primates kept only two glands, but a few people have additional nipples along the milk line (polythelia)
Skin cancer
Skin cancer—most cases caused by UV rays of the sun damaging skin cell DNA. Most often on the head, neck, and hands. Most common in fair-skinned people and the elderly. One of the most common, easily treated cancers. Has one of the highest survival rates if detected and treated early
Three types of skin cancer
Three types of skin cancer named for the epidermal cells in which they originate. Basal cell carcinoma, squamous cell carcinoma, and malignant melanoma
Skin cancer: Malignant melanoma
Skin cancer that arises from melanocytes Less than 5% of skin cancers, but most deadly form. Can be successfully removed if caught early, but if it metastasizes it is usually fatal.Greatest risk factor: familial history of malignant melanoma.Highest incidence in men, redheads, and people who had severe sunburn as a child
