Transcript Hair Follicles

Accessory Structures
Chapter 6 Sections 3
Objectives
• Describe the accessory structures associated
with the skin
• Explain the functions of each accessory structure
of the skin
• Explain how the skin helps to regulate body
temperature
Accessories of the Skin
• Accessory structures of the skin originate from the epidermis
and include:
• Nails
• Hair follicles
• Skin glands
• As long as accessory structures remain intact, severely burned
or injured dermis can regenerate
Nails
• Are the protective coverings on the ends of fingers and toes
• Consist of a nail plate, nail bed, & lunula
• The nail plate overlies the a surface of skin called the nail bed
• Specialized epithelial cells continuous with the epithelium of the
skin produce the nail bed
• The lunula is the whitish, thickened, half moon-shaped region at the
base of the nail plate
• It is the most active growing region of the nail
• The epithelial cell here divide and the newly formed cells become keratinized
• This creates tiny, keratinized scales that become part of the nail plate
Nail
General Characteristics of Hair
• Hair is present on all skin surfaces except for your palms,
soles, lips, nipples, and parts of the external reproductive
organs
• But not all places on your body have well developed hair, such
as on your forehead
• 90% of the time your hair is in the growth phase
• A hair typically grows for 2-6 years and then rests for 2-3
months anchored in its follicle
• A healthy person loses from 20-100 hairs a day
• Hair is composed of dead epidermal cells
Hair Follicles
• Each hair develops from a group of epidermal cells at the
base of a tube-like depression called a hair follicle
• The follicle extends from the surface into the dermis and
contains the hair root
• The hair root is the portion of your hair embedded in the
skin
• The epidermal cells in the hair bulb at its base are
nourished from dermal blood vessels in a projection of
connective tissue called the hair papilla
Hair Follicle
Determining Hair Color
• Genes determine hair color by directing the type and amount
of pigment that epidermal melanocytes produce
• Dark hair has more of the brownish-black pigment eumelanin
• Blonde and red hair have more of the reddish-yellow pigment
pheomelanin
• White hair lacks melanin altogether
• A mixture of pigmented hairs and unpigmented hairs creates
gray hair
Hair movement
• Each hair follicle is attached to a bundle of smooth muscle
cells called the arrector pili muscle
• When this muscle contracts, a short hair in the follicle stands
on end
• If a person is emotionally upset or very cold, the contraction
of the arrector pili muscle creates goosebumps
Skin Glands
• Two types of skin glands:
• Sebaceous glands, which are epithelial cells associated with
hair follicles
• Sweat glands, or sudoriferous glands, which are widespread in
the skin
Sebaceous Glands
• Are holocrine glands
• Found scattered throughout the skin, but are not on the palms or
the soles
• Their cells produce globules of a fatty material called sebum that
accumulates, swelling and bursting cells
• Sebum is secreted into hair follicles through short ducts
• It helps to keep hair and skin soft, pliable, and waterproof
• Some sebaceous glans open directly to the skin rather than around
hair follicles such as, at your lips, corners of your mouth, and parts
of the external reproductive organs
• Excessive secretions of sebum leads to acne
Sweat Glands
• Each gland consists of a tiny tube that originates as a ball-
shaped coil in the deeper dermis or superficial subcutaneous
fat layer
• The coiled portion of the gland is closed at is deep end and is
lines with sweat-secreting epithelial cells
• At the surface of the skin, the tube opens as a pore
• The most numerous sweat glands are called eccrine glands
• These glands respond the elevation of body temperature and
are found abundantly in the forehead, neck and back
• They also produce sweat on your palms and soles when
emotionally stressed
Composition of Sweat & Special glands
• It is mostly water
• It also contains: salts (urea) and wastes (uric acid)
• So, sweating is also an excretory functions
• Some secretions of certain sweat glands, apocrine glands,
develop a scent as skin bacteria metabolize them
• Apocrine glands only become active at puberty
• Other sweat glands are specialized like ceruminous glands
which produce ear wax and mammary glands which produce
milk