Anatomy & physiology of sweat glands, sebaceous

Anatomy & Physiology of Sweat

Glands, Sebaceous Glands, Hair &

Nail

By

Dr. Iman Ahmad Abu-Setta, MDConsultant of dermatology at Al- Hoad Al Marsoud Hospital

Sweat Glands

• Eccrine sweat glands

• Apocrine sweat glands

Eccrine Sweat Glands

Structure

• Secretory coiled portion → lower dermis & S.C tissue

• Duct

• Acrosyringium

Eccrine Sweat Glands

Secretory coils: 2cell types in a single layer (large clear cells for the secretoryfunction & dark cells of unknown function

Surrounded by myoepithelial cells ( enhance the delivery of sweat to skin surface)

Eccrine sweat glands H&E. D=excretory duct

S=secretory portion M=myoepithelial cells

Duct2 layers of cuboidal cells reabsorb Na thereby modifying sweat from an isotonic solution to a hypotonic one

Eccrine Sweat Glands

Innervation• Postganglionic sympathetic fibers that have

acetylcholine

• Under the control of hypothalamic sweat center

• Activated by emotional & thermal stimuli

SitesAllover the body skin surface with the highest density

on the palms , soles & forehead

Eccrine Sweat Glands

Development• As a downgrowth of surface epidermis during embryogenesis

• No developmental relationship with the pilosebaceous follicle

How to Measure Sweat Production?

Iodine starch reactionAn iodine solution is applied to the sweaty area. After it dries,

starch is sprinkled on the area. The starch-iodine combination turns a dark blue color wherever there is excess sweat.

Eccrine Sweat Glands

Function• it is a secretory & excretory organSecretory coil secretes (Nacl, K, bicarbonate, glucose, lactate,

AAs,……..(Composition of sweat Similar to plasma cantaining same electrolytes but in a more

dilute concentration)• Thermoregulation through the continous secretion of

sweat• Maintenance of electrolyte balance• Keep the thick stratum cornium moist to insure fine tactile

skills & pliability of the palms & soles• Excretory function can be instrumental through the

delivery of systemically administered drugs to the stratum corneum( e.g. ketokonazole)

Eccrine Sweat Glands

Disorders• Hyperhidrosis

Causes: emotional, neurologic, infectious, neoplastic e.g. lymphoma, hypoestrogenemia

• Hpohidrosis or anhidrosisAcquired: neuropathy d.t. poral occlusion in patients with scleroderma-

Congenital: hypohidrotic ectodermal dysplasia, neuropathy

• Sweat retentionMilaria ( crystallina, rubra, profunda)

Apocrine sweat glands

Structure • Secretory portion

Conveluted tube in deep dermis & S.C. fat

• Stretched duct Opens directly into the upper portion of the follicular canal

Apocrine sweat glands

• Secretory portion:

Single layer of epithelial cells interposed with myoepithelial cells

• Duct:

Consists of double layer of cuboidal cells as well as myoepithelial cells

Apocrine sweat glands

Apocrine sweat glands

Sites:

• Axillae

• Nipples

• Periumbilical region

• Anogenital region

• External auditory canal ( ceruminous glands)

• Eyelids ( glands of Moll)

Apocrine sweat glands

Innervation

• Postganglionic sympathetic fibers that have adrenaline

Development

• As an outgrowths of the upper portion of hair follicle

• Enlargment of the glands occur with approach of puberty under hormonal stimulation primarily androgen

• The glands do not begin to function until puberty

Apocrine sweat glandsFunction• ??????

Composition of sweat• cholesterol, triglycerides, FAs,….

• Obstruction→apocrine miliaria ( Fox-Fordyce disease)

• Apocrine sweat is sterile & odorless

• Bacterial decomposition leads to specific odor( bromohidrosis

• Chromohidrosis: secretion of pigmented sweat{ yellow, green or black)

Sebaceous Glands

Always associated with hair follicles except at :

1. Eye lids (meibomian glands)

2. Female areolas (Montgomery

follicles)

3. Prepuce (Tyson’s glands)

4. Buccal mucosa & vermilion border of the lips (Fordyce ‘s spot)

Sebaceous Glands

3 types of pilosebaceous units:

1. Vellus hair follicles: short thin hair & small sebacous glands

2. Sebaceous follicles: midsized hair & large sebaceous glands ( face, upper chest &back)

3. Terminal hair follicles: long thick hair & large sebaceous gland

Function of sebum

• It keeps hair & skin from becoming dry, brittle & cracked by dehydration

• Can inhibit the growth of microorganisms on the skin

Sebaceous Glands

Sites

• allover the body except palms& soles

• They are found in great abundance on the face , scalp, upper chest & upper back

• Acne patients have larger sebaceous glands & produce more sebum than patients with normal skin

Sebaceous Glands

Development

• As an outgrowth from the upper portion of the hair follicle

• Sebum production is an indicator of androgenic activity & increases at the time of puberty

Sebaceous Glands

0

2000

birthPuberty

DHT

Sebaceous Glands

• Sebaceous glands are rich in microorganisms: Malassezia spp., staphylococcus epidermidis & propionibacterium spp.

• Sebum consists of :

FFAs, wax sterol esters, TG & squalene

Sebaceous Glands

• Produce sebum via holocrine secretion ( the cells themselves actually disintegrate, releasing the sebum)

• ↓sebum production in AD

• ↑sebum production in seborrhea

Hair

Hair

• 4 histologic divisions:

• Infundibulum

• Isthmus

• Stem

• Bulb

The upper & middle parts of the follicle are permenant but the lower follicle regenerates with each turn through the hair follicle cycle

Infundibulum

• from surface of the skin to the entrance of the apocrine gland into the follicle

• The epithelium of the infundibulum is continuous with the epidermis, thus its cells can regenerate the epidermis & replenish it after wounding

Isthmus

• from the apocrine gland entrance to the connection to the sebaceous gland

Bulge: the inferior most portion of the isthmus, contain cells which are believed to be the source of matrix cells

Stem

from the sebaceous gland opening to the erector pilimuscle attachment

Bulb

• lower most portion of the hair follicle that surrounds dermal papilla. contains matrix cells

• The principle site responsible for hair growth & development

• Matrix cells: living rapidly proliferating keratinocytes that terminally differentiate to produce the hair shaft

• Dermal papilla: directs & dictates the embryonic generation of a hair follicle

Hair structure

• Outer root sheath

• Inner root sheath

• Hair shaft:

cuticle

cortex

medulla

Hair shaft

• the part of the hair that can be seen above the scalp. Consists manly of dead cells

• Cuticle: responsible for most of the shine that makes the healthy hair so attractive

• Cortex: gives hair its special quality such as elasticity & curl

• medulla

Hair Cycle

• Anagen : growth stage of the hair follicle cyclePregnancy is often accompanied by retention of an increased number of scalp hairs in the

anagen phase

Anagen phaseis the phase in the hair cycle the hairs are susceptible to injury during a session of LASER -assisted hair removal

• Catagen: involution of the lower 2/3 of the hair follicle

• Telogen: resting phase of the hair follicle cycle

• Exogen: phase of active hair shaft shedding

Hair Cycle

Autonomous, rhythmic transformation of fully developed hair follicles through phases of growth, regression & resting

Club hair: fully keratinized proximal tip of the hair shaft, formed during late catagen & telogen; brush-like appearance

Duration of scalp hair cycle phase:

Anagen: 3 years

Catagen: 3 weeks

Telogen: 3 months

Hair cycle distribution (terminal scalp hair)

• Anagen: 90%

Catagen: 10%

Telogen: < 1%

• Number of scalp hair follicles: 100,000

• Physiological hair shedding rate (scalp): 100-200/day

• Hair shaft (scalp) production rate: 1cm/month

• Hair production is not influenced by cutting /shaving

Functional properties of hair shafts

• Social & sexual communication

• Insulation against heat loss

• Facilitation of sebum, apocrine sweat secretion

• Provides sensory antennae

• Effluvium: excessive shedding of hair shafts (=process)

• Alopecia: abnormal hair loss

• Hirsutism: excessive vellus to terminal hair conversion in androgen dependant areas in women

• Miniaturization: terminal to vellus hair conversion

• Graying of hair is a result of a decreased number of melanocytes

Types of hair

• Vellus hair: very short, non pigmented, non medullated

• Terminal hair: large, pigmented , medullated hair

• Lanugo hair: fine hair on the fetal body; shed in utero or during the 1st few weeks of life

Hair follicles are present all skin surface except on palms & soles

Endocrinal control

• Endocrinal control of hair follicle cycling: androgens, estrogens, thyroxine

• Androgens are the main regulator of normal human hair growth

• During puberty, androgens →transformation of vellus to terminal of androgen dependant hair follicles ( beard, pubic, axillae)

• Androgens have a pivotal role in hirsutism & androgenic alopecia

Endocrinal control

• Arrector pili muscle is under adrenergic control→ contracts in situations of stress → hair stand up

• Estrogens: prolong anagen

Nail

Development

• An ingrowth of the epidermis into the dermis. Here it gives rise to a plate formed by fully keratinized dead cells (onychocytes), the nail plate

Structure

• Nail plate

• Proximal nail fold

• Nail bed

• Nail matrix

• hyponychium

Structure

• Nail plate

• Proximal nail fold

• Nail bed

• Nail matrix

• hyponychium

Nail plate• Transparent convex

rectangular plate

• Composed of tightly layered keratinized cells (onychocytes) generated by the matrix epithelium

Nail plate• The nail’s homogeneously

pink color is due to the longitudinally oriented subungual capillaries

• It has smooth surface , in elderly → longitudinal ridges

Nail plate• Constituents: water ,

keratins (proteins), lipids, trace elements( zinc, calcium, iron)

• Flexibility of nail plate is due to its water content

• Quite contrary to popular belief, trace elements do not influence the hardness of the nails

Nail plate

• Calcium can accelerate the rate of nail growth

• Low water content → brittle nails

• High water content→ opaque & soft nails

Nail bed

• underlies nail plate from the distal margin of the lunulato the onychodermal band

• The very strong adhesion between the nail bed & the nail plate is provided by the attachment between the longitudinal ridges of the nail plate & the rete ridges of the nail bed

• Onychocorneal band: thin transverse whitish band at the free edge of the nail plate . It is an important anatomic barrier

• Onychodermal band: small pinkish band distal to onychocorneal band

Matrix

• Situated underneath the nail fold.

• Produces the keratin which makes up the nail plate.

• Its damage produces irreversible nail growth defects

Eponychium (cuticle)

• thin epidermal layer that prevents the separation of the proximal fold from the nail plate

• Alteration of blood vessels at the proximal nail fold are of high diagnostic value in autoimmune C.T. diseases.

• (bl. Vessels are arranged in typical regular loops)

Lunula

• A half-moon shaped region that demarcates & covers the visible part of the matrix

Functional properties of nails

• Social & sexual communication (color, shape, length) & aesthetic appearance

• Protection of the distal phalanges from mechanical , chemical & biological trauma

• Contribute to tactile discrimination & fine motor capacities of the finger tips

• Ability to scratch & groom

• Essential for full motor functions of the feet by contributing to pedal biomechanics

Blood supply

• Abundant simple anastmosis arising from branches from digital arteries

• Glomus bodies: large arteriovenous anastmosis. Encapsulated oval structures containing tortuous arterial & venous vessels, a nerve supply & a capsule formed by modified large cholinergic muscle cells & cholinergic nerves

• Glomus bodies are present in all areas of the nail except in the proximal nail fold

• Glomus bodies dilate with cold whereas arterioles contract hence maintaining a sufficient blood supply to the digital periphery even in cold environment

Nerve supply

• branches of digital nerves

Rate of Growth

• Finger nails: 2-3 mm/monthComplete replacement requires 6 months

• Toe nails: 1mm/month Complete replacement requires 18 months

nail

Hair