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