Appendages of the skin FDF

Dr Mesfin Hunegnaw

Consultant Dermatologist & Venerologist

AAU, Medical faculty

Dept. of Dermtovenerology

Epidermal appendages:

Sebaceous glands,

Sweat glands,

Apocrine glands,

Mammary glands,

Nails,

Hair follicles.

Sebaceous glandsDvt. The rudiments of the sebaceous glands appear on the posterior

surfaces of the hair pegs; by 13-15 weeks, the glands are clearly distinguishable.

The glands reach a peak of activity in the third trimester, and their secretion forms part of the vernix caseosa.

The vernix lipids resemble sebum in their content of FAs, squalene and wax esters, sterols and sterol esters.

Sebaceous…

They are found over the entire surface of the body except the palms, soles, and dorsum of the feet.

They are largest and most concentrated in the face, scalp… On the scalp, forehead, cheeks and chin, there are 400 - 900

glands per square centimetre: Elsewhere < 100 glands per square centimetre.

Free sebaceous glands in the margin of the upper lip are often visible to the naked eye as pale-yellow bodies, which vary in size from minute specks to about 1.5 mm in diameter:

=> Fordyce's spots. The gland consists of a series of lobes, each with a duct lined

by a keratinizing squamous epithelium.

Peak function in infancy…quiet…flourish in puberty. Sebaceous glands function is to produce and secrete sebum, A group of complex oils including triglycerides and fatty acid

products, wax esters, squalene, cholesterol esters & cholesterol.

Squalene the major Cpt.

Lipid production varies according to site: 5-10 mic,gm/cm on the trunk and limbs, compared with 150-300 on the forehead.

When amounts are in the range 5-10mic.g/cm, the skin surface lipid contained virtually no wax esters or squalene.

However, as the quantity of surface lipid increased, so did the proportion of wax esters and squalene, while at the same time the proportions of cholesterol esters decreased.

The proportion of each of the constituents became nearly constant when the amount of lipid reached 50-100 mic.gm/cm.

Function of Sebum :

Lubricates the skin to protect against friction and makes it more impervious to moisture.

Fungistatic, Bacteriostatic?. Barrier?

Shuster et al: P.acnes inc DTHr immunomodulation.

"Endocrine control of sebaceous gland activity"

Androgens Estrogens: suppress gonadotropin secretion by the pituitary reduced the levels of testosterone in the plasma. Progesterone? Adrenocortical hormones

Drugs: Antiandrogens, Spiranolactone, Cimetidine, Vit A, Azeliac acid.

Brainstorming:

1-Pure sebum Vs surface lipid ?

2-Is SD a ds of sebaceous glands?

Sweat glands

Sweat glands, or eccrine glands, are found over the entire surface of the body except the lips, external ear canal, and labia minora.

They are most concentrated in the palms and soles of the feet. The number varies greatly with site, from 620/cm2 on the soles

to about 120/cm 2 on the thighs. The total number on the body surface is 2 - 5 million.

Each gland consists of a coiled secretory intradermal portion that connects to the epidermis via a relatively straight distal duct.

No new sweat glands develop after birth. They have no developmental relationship with the

pilosebaceous follicles.

The duct consists of two or more layers of relatively uniform cuboidal cells.

The duct, especially that part within the coil, is not an inert conducting channel;

It has active enzyme systems: sodium potassium adenosine triphosphatase (ATPase), and performs an active part in modifying the secretion produced by the coil.

Sweat glands cool the skin by evaporation. The thermoregulatory center in the hypothalamus controls

sweat gland activity through sympathetic nerve fibers that innervate the sweat glands.

Sweat excretion is triggered when core body temperature reaches or exceeds a set point,

Set point is activated by: Changes in temperature of the blood perfusing it, The osmolarity of fluid perfusing it. And by afferent stimuli from the skin.

The other main function of eccrine sweat glands is to moisten the skin on the palms and soles at times of activity, and thus improve their grip.

The activity of the sympathetic nerves to the sweat gland is controlled by stimuli of three types: thermal, mental and gustatory.

Apocrine glands

They are epidermal appendages, and develop as part of the pilosebaceous follicle in the fourth to fifth mo of IUL.

In the embryo they are present over the entire skin surface, but most glands subsequently disappear.

Apocrine glands are similar in structure but not identical to eccrine glands.

. The apocrine system, also includes the mammary

glands, ceruminous (wax) glands of the ear canal,and glands of Moll in the eyelid.

Apocrine sweat glands derive their name from the way their secretion appears, derived by pinching off parts of the cytoplasm.

The epithelium of the secretory coil produces its secretion continuously, with some variation depending on hormonal factors: menstruation and pregnancy.

They are concentrated in the axillae and anogenital regions, scattered over trunk, face & scalp.

Apocrine glands are poorly developed in childhood, and begin to enlarge with the approach of puberty.

The activity of the glands is androgen dependent, and the glands show marked testosterone 5-a-reductase activity.

The glands are larger than eccrine glands, and in the dissected specimen are visible to the naked eye.

They are situated in the subcutaneous tissue. Each consists of a tubule and a duct. The latter is often quite short, and opens into the neck of the

hair follicle above the sebaceous gland. They probably serve a vestigial sexual function, because they

produce odor and do not function prior to puberty.

Apocrine glands secrete very small quantities of an oily fluid which may be coloured.

This secretion is odorless on reaching the surface, and bacterial decomposition is responsible for the characteristic odor.

Trans-3-methyl-2-hexenoic acid, is one of the substances which contributes to the odor.

The glands have no thermoregulatory function in humans.

The ducts have an adrenergic sympathetic nerve supply and are also stimulated by circulating adrenaline.

Expulsion of apocrine sweat may occur continuously or be provoked by emotional stimuli.

Apoeccrine glands

Apoeccrine glands have features of both eccrine and apocrine glands, but seem to be nearer to eccrine in function.

They open onto the surface, and produce a copious watery fluid.

They may account for 10-45% of adult axillary glands.

Innervation

Summary:

The difference b/n Eccrine & Apocrine secretion:

Eccrine: Like glomeruli concentrates its secretions & mainly is water & electrolytes.

Secret direct to the skin via duct openings.

-Apocrine: the cells of the secretary glands are shed togther & hence has odor.

Secret via the follicles; like sebaceous glands!

The nail

The nail

The nail apparatus consists of a horny 'dead' product, the nail plate, and

Four specialized epithelia: The nail folds, The nail matrix, The nail bed, and The hyponychium.

1-Nail FoldsProximal Nail Fold Is a skin fold consisting of dorsal and ventral portions. The dorsal portion is similar to the skin of the dorsum of

the digit but thinner and devoid of pilosebaceous units. The ventral portion IS continues proximally with the

germinative matrix, covers 1/4 of the nail plate.Lateral nail folds A narrow margin of the sides of the nail plate is occluded by the

lateral nail folds.

2-Hyponychium The area between the nail bed and the distal groove,

where the nail plate detaches from the dorsal digit. Its anatomic structure is similar to that of plantar and

volar skin. keratinization occurs through the formation of a

granular layer. The hyponychium is covered by the distal nail plate.

3-Nail Matrix In longitudinal sections, the matrix has a wedge-shaped

appearance; It consists of a proximal (dorsal) and a distal (ventral)

portion. Nail matrix keratinocytes divide in the basal cell layer

and keratinize in absence of a granular zone. Cornified onychocytes are composed mainly of

keratin filaments, high-sulfur matrix proteins, and the marginal band, which consists of precipitated proteins on the cytoplasmic side of the cell membrane.

Matrix…The lunula In some fingers, the matrix is not completely covered

by the proximal nail fold but is visible through the nail plate as a white half moon–shaped area, the lunula.

This area represents the most distal region of the matrix.

Nail matrix cells: Keratinocytes, Melanocytes, LCs, Merkel cells.

The white color of the lunula results from:

1-The keratogenous zone of the distal matrix contains nuclear fragments that cause light diffraction and

2-The capillaries of the nail matrix are less visible than those of the nail plate.

It is most prominent on the thumb and great toe.

4-Nail Bed The nail bed extends from the distal margin of the

lunula to the onychodermal band and is completely visible through the nail plate.

The nail bed epithelium is thin and consists of two to five cell layers.

Interdigitate with the underlying dermal ridges by a 'tongue and groove' joint.

Nail bed keratinization produces a thin, horny layer that forms the ventral nail plate.

5-The nail plate The nail plate progressively thickens from its

emergence to its distal margin, The mean toenail thickness at the distal margin is 1.65

± 0.43 mm in men and 1.38 ± 0.20 mm in women. Fingernails are thinner, their mean thickness being 0.6

mm in men and 0.5 mm in women. Cell adhesion is provided by desmosomes and

complex interdigitations. It provides adhesion to the underlying nail bed.

There is an increase in nail thickness with age, particularly in the first two decades.

Nail thickness depends on the length of the nail matrix and nail bed.

Thinning of the nails is usually a sign of nail matrix disorders, whereas nail thickening is most commonly a consequence of nail bed disorders.

Fingernails usually present a longitudinal major axis and toenails a transverse major axis.

Schematic diagram of nail

Chemical Properties The nail plate, consists mainly of low-sulfur filamentous

proteins (keratins) embedded in an amorphous matrix composed of high-sulfur proteins rich in cystine.

Nail keratins consist of 80 to 90 % hard 'hair-type' keratins and 10 to 20 % soft 'skin-type' keratin.

The nail contains less than 5 % lipids, mainly cholesterol, and traces of several inorganic elements, the most prominent being iron, zinc, and calcium.

These, do not contribute to the nail's hardness. When the water content falls below 18 %, the nail

becomes brittle; when it increases above 30 %, it becomes opaque and soft.

Physical Properties The nail plate is hard, strong, and flexible. The hardness and strength of the nail plate are due to

its high content of hard keratins and cystine-rich high-sulfur proteins.

Its flexibility depends on its water content and increases with nail plate hydration.

The double curvature of the nail plate along its longitudinal and transverse axes enhances its resistance to mechanical stress.

The physical properties of the nail also depend on:The arrangement and adhesion of onychocytes in the

different portions of the nail plate,On the orientation of the keratin filaments within the

nail plate onychocytes.

The corneocytes of the dorsal nail plate are flat, with their shorter diameter perpendicular to the nail plate's surface.

On average, these cells are 34 m in length, 64 m in width, and 2.2 m in height.

Cell adhesion is strong, and this portion of the nail is responsible for the hardness nail plate.

Nail Growth The nail plate grows continuously during life. Mean growth = 3 mm/ mo. for fingernails; 1 mm/mo for

toenails. Complete replacement of a fingernail requires 6 mo. When the nail plate is extracted, it takes about 40 days

before the new fingernail first emerges from the proximal nail fold.

After a further 120 days, it will reach the fingertip. The total regeneration time for a toenail is 12 to 18

months.

As a consequence of the nail's slow growth rate, diseases of the nail matrix become evident only after a considerable delay and require a long time to disappear after treatment.

The rate of nail growth varies among different individuals and among the different digits of the same individual.

It depends on the turnover rate of the nail matrix cells and is influenced by several physiologic and pathologic conditions.

The nail growth rate is slow at birth, slightly increases during childhood and usually reaches its maximum between the second and the third decades of life.

Then, after the age of 50, it decreases sharply.

Conditions associated with a slow growth rate include: systemic illness, malnutrition, peripheral vascular or neurologic diseases, and treatment with antimitotic drugs.

Nails affected by onychomycosis frequently exhibit a slow growth rate, and an arrest of nail growth is a typical feature of the yellow-nail syndrome.

Function of the nails:

Protection of the distal phalanges of the digits from mechanical, chemical and biological trauma

Contribute to the tactile discrimination and fine motor capacities of the finger tips

Ability to scratch and groom as rudimentary natural weapons

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

Hair folliclesEmbryology and Anatomy• In human fetuses, the first primordial hair follicles form

at approx. 9 weeks' gestation & are distributed mainly in the areas of the eyebrows, upper lip,& chin.

• The bulk of the remaining follicles begin to develop at approximately 4 to 5 months gestation in a cephalad-to-caudad direction.

• Secondary follicles are formed b\n already existing follicles as the skin expands.

• The secondary follicle develops on each side of the established follicle, producing typical groupings of three hairs.

• New follicles can not develop in adult skin.

Anatomy:CROSSECTION:a series of concentric epithelial cellular compartments

bounded by an acellular basement membrane (glassy membrane).

1-ORS: is the most peripheral of cellular compartments. 2-IRS, which is composed of: Henle's layer, Huxley's layer, and Cuticle.

3-The hair shaft, which Innermost is & has: Cuticle, The cortex that forms the bulk of the hair shaft, & The central medulla.

LONGITUDINAL: seven distinct anatomic regions:1-The hair canal region, strictly only distinct during

fetal development, extending from the skin surface to the level of the epidermal-dermal junction.

Its lower part later becomes the intraepidermal “infundibular unit.”

2-The infundibulum extends down to the level of the opening of the sebaceous duct.

3-Next is the area of the sebaceous gland.4-The isthmus begins at the sebaceous duct and ends

at: The bulge,

5-The bulge, the site of insertion of the arrector pili muscle and region enriched in putative follicular epithelial stem cells.

The transient portion of the follicle begins just below the bulge/arrector pili muscle complex and extends to the deepest levels of the follicle.

6-The lower follicle includes the keratogenous zone and extends from the area of the bulge to the top of the hair bulb.

7-The hair bulb is the deepest portion of the follicular structure and envelops the follicular papilla.

The “critical line of Auber” is at the widest diameter of the bulb & is of significance in that the bulk of the mitotic activity that gives rise to the hair and inner root sheath occurs below this level.

Another important anatomic feature of the follicle is that it lies at an angle relative to the skin surface.

The side of the follicle that forms an acute angle with the skin surface is its anterior aspect; the side that forms an oblique angle is the posterior.

When the arrector pili muscle contracts, as in response to cold external temperature, it pulls on the posterior side.

Temporary alteration in local skin architecture gives rise to “goose bumps.”

They are found deep within the dermis, In the face may even lie in the SC fat. Ability of the face to re-epithelialize even after the deepest

cutaneous wounds.

The Hair Cycle: Follicles undergo cycles of growth, involution, & rest. The hair follicle is not an isolated structure. It is contiguous with the epidermis, part of the

pilosebaceous apparatus, richly innervated and highlyvascularized;

The vasculature is also undergo changes related to the hair growth cycle.

Then entire skin changes during the hair cycle, with a generalized thickening during anagen (growing phase) and a thinning during telogen (resting phase).

During cycling, the follicle may influence the physiology of many cutaneous structures, such as the sebaceous gland & subcutaneous fat.

During anagen , the matrix keratinocytes in the bulb region proliferate rapidly, having the highest proliferative rate as compared with the other regions of the follicle.

The matrix keratinocytes can be considered as pluripotent cells because, after becoming postmitotic, they differentiate into the inner root sheath, cuticle, cortex, and medulla of the hair shaft.

Hair Cycle…

I-Anagen: During anagen, it traverses the entire dermis,

penetrating deep into the subcutaneous fat. Anagen is subdivided into six substages (I to VI), the

first five of which are collectively called proanagen. They are defined by progressively higher levels of new

hair-tip position within the follicle. The sixth stage, metanagen, is defined by emergence

of the hair shaft above the skin surface.

At the end of anagen, morphologic and molecular changes leading to programmed cell death (apoptosis).

This stage is known as catagen.(II) What signals the onset of catagen: unknown! ?Change in the expression of genes implicated in

programmed cell death (apoptosis). At the onset of catagen, the scalp hairs show a

gradual thinning and lightening of the pigment at the base of the hair shaft.

Melanocytes in the matrix portion of the bulb cease producing melanin, resorb their dendrites and undergo apoptosis.

Matrix keratinocytes cease proliferating, undergo terminal differentiation,

The lower follicle involutes and regresses. The connective tissue sheath also becomes quite

thickened during catagen. At the end of catagen, the follicular papilla comes to

rest at the bottom of the permanent portion of the hair follicle and remains there while the follicle is in the telogen phase.

III-The telogen hair has a club-shaped proximal end within the hair follicle and is typically shed from the follicle during telogen or the subsequent anagen.

The new produced anagen hair does not “push out” the hair from the previous cycle, and may on occasion be found adjacent to a so-called retained club hair within a follicle.

The inner root sheath, which normally disintegrates in the anagen follicle at the level of the sebaceous duct opening, is totally absent from the telogen follicle.

Eventually a new growing phase occurs and the cycle is repeated.

The pattern of growth & rest and the rate of growth vary depending on body site.

Hair growth occur in a wave, “synchronized,” or In a mosaic patternmosaic pattern, where the activity of each follicle

is independent of its neighbors. Humans exhibit mosaic pattern of hair cycling.

In utero?

At 26 to 28 weeks' gestation, scalp hairs make the transition to telogen in a wave pattern that spreads from the frontal to parietal regions marking the last stage of the first hair cycle.

Waves of hair growth occur before establishment of the mosaic pattern, which is usually present by the end of the first postnatal year.

Many of these primary hairs are shed in utero,although this may be delayed, with resulting abundant hair at birth.

Length of anagen depends on body site. In the scalp anagen = b/n 2 and 6 years, On the leg 19 to 26 weeks, On the arm from 6 to 12 weeks, From 4 to 14 weeks on the upper lip (mustache).

Catagen and telogen are short, catagen lasting about 2 weeks and telogen between 1 - 3 months in the scalp.

At any one time:At any one time: About 85 to 90 % of scalp hair follicles are in anagen, About 13 % are in telogen, And < 1 % are in catagen.

Each follicle goes through the hair growth cycle 10 to 20 times in a lifetime.

Trichogram

Types of Hair: Hairs can be classified according to their texture and

length. Thus, there is lanugo hair, vellus hair, intermediate

hair, and terminal hair. Lanugo hair is the soft, fine hair that covers much of

the fetus and is usually shed before birth. The other terms have most relevance to scalp hair,

although the basic principles convey some meaning for other hair sites.

Types…The classification is not exact and basically relates to the

final length of the hairs: Vellus scalp hairs achieve lengths less than 1 cm, Indeterminate scalp hairs are approximately 1 cm in

length, and Terminal scalp hairs grow longer than 1 cm.

Eyebrow or eyelash hairs are typically less than 1 cm in length but are considered terminal hairs.

Yet the usual lengths (several millimeters) of beard hairs along with their associated features in normal women would best be described as vellus hair.

Using the phrase “terminal beard hair growth” with regard to a woman would indicate that there is a departure from the norm, with the presence of the longer, coarser hairs typical of hirsutism or hypertrichosis.

Functions of the hair:•Camouflage,

• Protection against chemical and physical damage,• Protection against insects,• Provides sensory ‘antennae’,• Insulation against heat loss, overheating, desiccation,• Cleansing of skin surface of parasites, dirt, debris and

squames by outward moving hair shaft,• Facilitation of sebum, apocrine sweat and pheromone

secretion…

• Organ of scavenging and excretion: melanized hair shaft serves to deposit and extradite unwanted molecules

• Production, extrusion, containment and mooring of pigmented hair shafts

• Crucial stem cell reservoir (e.g. for keratinocytes, melanocytes)

• Reservoir for Langerhans cells• Highly sensitive tactile organs that sense hair shaft

movements• Social and sexual communication (color, shape, length)

and aesthetic appearance