skin appendages dr. salman bin dayel, m.d college of medicine salman bin abdulaziz university
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Skin appendages
Dr. Salman Bin Dayel, M.D
College of Medicine
Salman Bin Abdulaziz university
Skin appendages:
Hair folliclesSebaceous glands
Eccrine sweat glandsApocrine sweat glands
The nails
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: Innermost part of hair. 1 -cuticle. 2 -cortex .
3 - medulla .
Hair Cycle:
The Hair Cycle:
(1)anagen (growth stage): *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.
Types of Hair:
(1 )lanugo hair: soft, fine hair that covers much of the fetus and is shed
during 1st weeks of life. (2 )Vellus hair (follicle): very short, non pigmented ,
No medulla , absence of arrector pili muscle ,
Less than 1cm length.
(3 )Terminal hair: large, pigmented & medulated.
Grow more than 1 cm.
Distribution of Hair
Hair follicles are distributed throught body except : palms , soles , and portion of genitalia ( called Glabrous Skin )
The Highest Density on the Scalp
Total number ~ 5 000 000 (mostly vellus)
Number of scalp hair follicles ~ 100 000 ( Blondes: + 20% ,Redheads: – 20% )
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/cm2)
>---less on back (64/cm2).
>---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. (3) sebaceous gland.(2 )The hair. (4) sebaceous duct.
Thank you
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