Skin appendages Dr Salman Bin Dayel M D
Skin appendages Dr. Salman Bin Dayel, M. D College of Medicine Salman Bin Abdulaziz university
Skin appendages: Hair follicles l Sebaceous glands l Eccrine sweat glands l Apocrine sweat glands l The nails l
The Hair:
Biology Of Hair: Functions of hair: (1) Psychological importance. (2) Scalp hair excellent protection from actinic damage. (3) involved in sensory reception. (4) play a role in epidermal homeostasis, wound healing, skin tumorigenesis.
Embryology: * The first hair follicles form at 9 weeks' gestation. * they are distributed mainly in the (1) eyebrows, (2) upper lip, (3) chin. * The rest of the follicles begin to develop at 4 to 5 months gestation in a cephalo caudal direction.
Anatomy of hair follicle: (1) The outer root sheath: most peripheral cellular compartments of follicle. (2) Companion layer: between ORS & henle layer of IRS. (3) Inner root sheath(IRS): 1 - Henle layer. outer most. 2 - Huxley layer. it is the major component of IRS. 3 - cuticle of IRS. inner most & adjacent to hair shaft. . (4) Hair shaft: 1 - cuticle. 2 - cortex. 3 - medulla. Innermost part of hair.
Hair Cycle:
The Hair Cycle: anagen (growth stage) : (1) * Length of the hair depend on anagen phase. * Length of anagen vary depend on body site as follow: Scalp 2 -6 years. Upper lip 4 -14 weeks Arms 6 -12 weeks. Legs 19 -26 weeks.
(2) Catagen (degenerative stage): the follicle enter into catagen which show changes that are associated with programmed cell death and apoptosis. catagen lasting only about 2 weeks. •
(3) Telogen (resting stage): * The inner root sheath is totally absent from the telogen follicle. Telogen period last for 1 -3 months on human scalp. •
At any one time, 85 -90 % of scalp hair follicles are anagen, 13 % are in telogen, less than 1 % are in catagen.
Hair Pigmentation: Only when hair grows (anagen stage), because follicular melanocytes are active only in anagen stage. The pigment is located in the cortex of the hair shaft. • •
go hair: Types of Hair: soft, fine hair that covers much of the fetus and is shed during 1 st weeks of life. (2) Vellus hair (follicle): very short, non pigmented, No medulla, absence of arrector pili muscle, Less than 1 cm length. (3) Terminal hair: large, pigmented & medulated. Grow more than 1 cm.
Distribution of Hair ü Hair follicles are distributed throught body except : palms , soles , and portion of genitalia ( called Glabrous Skin ) ü The Highest Density on the Scalp ü Total number ~ 5 000 (mostly vellus) ü Number of scalp hair follicles ~ 100 000 ( Blondes: + 20% , Redheads: – 20% )
Biology of The Nails
Anatomy of the Nail: The nail cosist of: (1) A horny 'dead' product (the nail plate). (2) Four specialized epithelia: the proximal nail fold. the nail matrix. the nail bed. the hyponychium.
The nails functions: (1) aesthetic appearance of the hands. (2) Protecting the distal phalanges. (3) Enhancing tactile discrimination and the capacity to pick up small thing (4) Use for scratching and grooming.
Nail Plate: * it is a fully keratinized structure that is continuously produced throughout life. * is firmly attached to the nail bed. * At the tip of the digit, the nail plate separates from the underlying tissues at the hyponychium.
The lunula: * whitish, half moon–shaped area, on proximal parts of the fingernails. *The most loose part of attachment to nail bed.
Cuticle: * It is formed by horny layer of proximal nail fold. * It is firmly attached to superficial nail plate & prevent separation of plate from nail fold. Nail Matrix: is a specialized thick epithelial structure that lies above the midportion of the distal phalanx. it consists of a proximal (dorsal) & a distal (ventral) portion.
Nail Bed: * extends from the distal margin of the lunula to the onychodermal band. * it is completely visible through the nail plate. The nail bed epithelium is so adherent to the nail plate •
Nail Growth : The nail plate grows continuously during life. Fingernails grow faster than toenails, mean growth 3 mm per month for fingernails 1 mm per month for toenails. Complete replacement of the nail requires: fingernail 100 to 180 days (6 months) toenail 12 – 18 months.
Factors influence nail growth:
Biology of Sweat Glands
Eccrine sweat glands: ---> 2 to 4 million glands distributed over entire body. ---> highest density of eccrines on palm & soles. (620/cm 2) ---> less on back (64/cm 2). --->Failure of Eccrine sweating: can lead to heat exhaustion, heat stroke, and death.
Apocrine Sweat Gland: Found mainly axillae , periumbilical , nipples & anogenital. • * It consist of 1) secretory portion : located in deeper dermis. 2)stretched duct: open into upper portion of follicular canal * Its secretion is controlled by adrenergic nerves.
Sebaceous Glands: Distribution is almost associated with hair follicle Sebaceous glands are located throughout the entire body except: 1 -palms, 2 -soles, 3 -dorsa of the feet, 4 -lower lip. They are largest and most numerous on the face, chest, back, and upper outer arms.
Sebaceous follicle consist of : (1) Keratinized follicular infundibulum. (2) The hair. (3) sebaceous gland. (4) sebaceous duct.
Thank you
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