SKIN APPENDAGES

•         ARE DERIVED FROM DOWNGROWTHS OF EPIDERMAL EPITHELIUM

•         Hair follicles: hair

•         Sebaceous glands: sebum

•         Sweat glands: sweat

•         Nails

•         Mammary glands

•         Both hair and sweat glands play specific roles    in regulation of body tempreture

•         Sebaceous glands secrete an oily substance that may have protective function

STRUCTURE OF HAIR FOLLICLE

•         A hair follicle consists of a compound sheath derived from from epidermis.

•         Externally there is a dermal root sheath

•         Internally, an epidermal root sheath

•         Hair follicle is divided into three segments.

–            Infundibulum

–            Isthmus

–            Inferior segment( bulb and dermal papilla)

Dermal root sheath

1) Glassy layer

Composed of amorphous ground substance and reticular  fibers

2) Middle layer

Composed of circularly arranged collagen fibers

3) Outer layer

Longitudinally arranged coarse collagen fibers

Epidermal Root Sheath

An outer and an inner epidermal sheath

•      OUTER ROOT SHEATH

1)        Columnar layer: single layer of taller cell next    to the glassy membrane

2)        Prickle-cell layer: Several layers of cells,with intercellular bridges

INNER ROOT SHEATH

1)        HENLE”S LAYER

–        Outer, single layer of cuboidal cells

–        Clear cells containing hyaline fibrils

2)    HUXLEY’S LAYER

–        Consists of one or two layers of transparent, precornified flattened cells

–        Contain acidophilic trichohyalin granules and

–        Bundles of tonofibrils

3)      CUTICLE

–        This is a single layer of squamous cells

Pilosebaceous unit

•         Associated with hair follicle are one or more sebaceous glands,and arrector pilli muscle

Hair

•         Hairs are elastic keratinized threads that develop from epidermis

•         Has free shaft and root embedded in skin

•         Length: 1 mm. to 5 feet

•         Thickness: 0.005 mm. (lanugo) to 0.2 mm. (beard)

STRUCTURE OF SHAFT AND ROOT

1)         Medulla(large Vacuolated cells)

2)          Cortex(Cuboidal cells with Keratin)

3)          Cuticle (Squamous cells)

The Nails

The nails are horny plates that form a protective covering on the dorsal surface of the terminal phalanges of the fingers and toes

•         Humans & primates (claws in other forms)

•         Convex, rectangular structure

•       Components:

ü      Nail plate (horny)

ü      Nail bed (less modified)

•         The nail plates consists of intimately fused highly keratinized cells                                   .

This plate has three parts

1.Body

2.Free edge

3.Root

Nail bed

•         Nail bed – under nail plate

•         Consists of germinative layer of epidermis and underlying dermis

Hyponychium

•         Epidermis of nailbed is continous distally with epidermis of fingure tip under free edge of nail

•         At junction st corneum is thickened

•         This is known as hyponychium

Eponychium

•         Cells of st corneum extend from the nail wall onto the free surface of of nail plate as eponychium,or cuticle

Sweat glands (sudoriferous glands)

•         widely distributed on body

•         Sweat – is a blood filtrate

–        99% water with some salts

–        Contains traces of metabolic wastes

•         Vital for thermoregulation

•         Also influence water and ion balance

Types of Sweat Glands

•         Eccrine

•         Apocrine

•         ECCRINE GLAND

•         Most numerous – produce true sweat

•         Secretion is mostly water with solutes

•         Cools body down

•         APOCRINE GLAND

•         Confined to axillary, anal, and genital areas

•         Produce a special kind of sweat Develops scent as bacteria metabolize secretion

•         Stimulated when frightened, during pain, during emotional upset

Structure Of Eccrine Sweat Gland

•         Simple, coiled, tubular gland.

•         The secretory portion lies deep in the dermis

•         This portion is coiled into a mass 0.3 to 0.4 mm. in diameter.

•         The tubule is about 3.0 mm. long and 0.06 mm. wide in ordinary sweat glands.

•         The duct joins the epidermis, and spirals through it to the free surface.

•         Its opening, the sweat pore, is a minute pit.

•         Two type of cells are seen

•         Dark cells

Dark in colour,secretory granules,thick secretion containing glycoprotein

•         Clear cells

Stain light,no secretory granules,infolding of basal plasmalema,secrete water&electrolyte content

Apocrine glands.

•         less coiled than are ordinary sweat glands.

•         The lumen of the secretary tubule is conspicuously wider.

•         Single type of cells in secretary part.

•         Myo-epithelial cells are larger and more numerous.

•         The secretion is thicker, more pigmented and contains larger fat droplets and proteins

Sebaceous Glands

•         One to several sebaceous glands always connect with a hair

•         A gland usually is located in the angle between the follicle and its muscle

•         Its short duct empties into the follicle at a level three-fourths of the way up

•         Occur over entire body

•         Except palms and soles

•         Secrete sebum – an oily substance

•         Simple alveolar glands

•         Most are associated with a hair follicle

•         Functions of sebum

•         Collects dirt; softens and lubricates

Exocrine gland associated with follicle secretes oily substance

Holocrine gland

•         Examples:

margin of lips;

•         external genitalia

•         (Meibomian) glands of eyelids.

•         Entirely lacking from the palm and sole.