STRUCTURES MET IN DISSECTION

SKIN

ByDr Samina AnjumSKINOrigin

EPIDERMIS

CELL TYPES IN EPIDERMISKeratinocytes produce keratin (tough fibrous protein)

Melanocytes Merkel cells associated with sensory nerve endings, specialized in the perception of light touch.

Langerhans cells Bone marrow origin, located in basal, spinous and granular layers, act as antigen-presenting cells.

LAYERS OF DERMIS 1.PAPILLARY LAYER

Composed of looseareolar connective tissue. Fingerlike projections called papillae, that extend towards the epidermis. The dermal papillae interdigitates with the epidermal ridges, strengthening the connection between the two layers of skin.

2.RETICULAR LAYERSThe reticular region lies deep in the papillary region and is usually much thicker contains the skin appendages It is composed of dense irregular connective tissue Fibers: mainly collagen, also elastic and reticular fibers present, giving the dermis its properties of strength, extensibility, and elasticity. Cells: fibroblasts, macrophages, mast cells, WBCs

Skin Color of skin depends upon:Blood flow (Hemoglobin)Thickness of skinDegree of pigmentation (Melanin, carotene)Skin is the best indicator of general health

APPENDAGES OF SKIN

SWEAT GLANDSEccrineApocrineSEBACEOUS GLANDSHAIR FOLLICLESNAILSECCRINE SWEAT GLANDSAre coiled tubular glands that discharge their secretions directly onto the surface of the skinAre smaller than apocrine sweat glandsThey do not extend deep into the dermisThey are supplied by cholenergic sympathetic fibers

ContAre distributed all over the skin except:Tympanic membranesLip marginsNipplesSome parts of external genitaliaGreatest concentration is in thick skin of palms and soles, and on the face

APOCRINE SWEAT GLANDSAre large modified sweat glands composed of a coiled secretory portion located at the junction of thedermisandsubcutaneous fat, from which a straight portion inserts and secretes into theinfundibularportion of thehair follicle or may open directly on the skin surface.

ContIn humans, apocrine sweat glands are found only in certain locations of the body: theaxillae(armpits), theareolaof the nipples, and the genital and perianal regions. Specialized types of apocrine sweat glands present on the eyelids are calledMoll's glands.Contsecrete a milky, viscous, odorless fluid which only develops a strong odor when it comes into contact with bacteria on the skin surface. They enlarge at puberty and undergo cyclic changes in relation to menstrual cycle in females.They are supplied by adrenergic sympathetic fibersSEBACEOUS GLANDSThesebaceous glandsare branched type ofacinar gland in theskinthat secrete an oily/waxy matter, calledsebum, to lubricate and waterproof the skin and hair

ContPresent throughout the skin except in thepalms of the handsandsoles of the feet. Sebaceous glands can usually be found in hair-covered areas, where they are connected tohair follicles.

ContSebaceous glands are also found in non-hairy areas of lips ,eyelids,nose,penis, labia minoraandnipples and areolaeHere, the sebum traverses ducts that terminate insweat poreson the surface of the skin.At the rim of the eyelids,meibomian glandsare a specialized form of sebaceous gland. Their secretion slows the evaporation oftears.HAIRHard keratin that grows out of the follicle by invagination of epidermis into the dermisThe follicles lie obliquely to the skin surfaceThe hair follicle may be divided anatomically into four parts:

HAIR Each hair is formed from hair matrix, a region of epidermal cells at the base of follicle, which extends deeply into the dermis and subcutaneous tissueAs cells move up they loose their nuclei and become converted into hard keratin hair shaft Melanocytes in the hair matrix impart pigment to hair cells

PILOSEBACEOUS UNITThe structure consisting of hair, hair follicle,arrector pilimuscle, and sebaceous gland is known as apilosebaceous unit.

NAILSAre the keratinized plates on the dorsal surfaces of fingers and toesNail plate. The nail plate is the actual fingernail, made of translucent keratin. Nail folds:The nail is surrounded and overlapped by the folds of skin on three sides.Nail bed: is the skin beneath the nail plate and containsnerves,lymphandblood vessels.

Nail plate. The nail plate is the actual fingernail, made of translucent keratin. The pink appearance of the nail comes from the blood vessels underneath the nail. The underneath surface of the nail plate has grooves along the length of the nail that help anchor it to the nail bed.

Nail foldsThis is the skin that frames each of your nails on three sides.

Nail bedYour nail bed is the skin beneath the nail plate.

CuticleThe cuticle of the fingernail is also called the eponychium. The cuticle is situated between the skin of the finger and the nail plate fusing these structures together and providing a waterproof barrier. Your cuticle tissue overlaps your nail plate at the base of your nail.

LunulaThe lunula is the whitish, half-moon shape at the base of your nail.

PerionychiumThe perioncyhium is the skin that overlies the nail plate on its sides. It is also known as the paronychial edge. The perionychium is the site of hangnails, ingrown nails, and an infection of the skin called paronychia.

HyponychiumThe hyponychium is the area between the nail plate and the fingertip. It is the junction between the free edge of the nail and the skin of the fingertip, also providing a waterproof barrier21ContMatrix/Root of the nail: is the hidden part of the nail bed that lie beneath the proximal nail fold. The matrix is responsible for producing cells that become the nail plate.Lunula: is the visible part of matrix at the base of nail. It is the whitish and half-moon shaped part

ContCuticle / eponychium: This tissue overlaps the nail plate at the base of the nail, providing a waterproof barrier True cuticle: The skin on the underside of the nail fold sheds constantly.These dead skin cells attach to the nail plate and become visible as the nail grows. These needs to be removed.

ContPerionychium: is the skin that overlies the nail plate on its sides.Hyponychium: is the area between the nail plate and the fingertip. It is the junction between the free edge of the nail and the skin of the fingertip, also providing a waterproof barrier

Cutaneous blood supplyThe dermis contains horizontally arranged superficial and deep plexuses, which are interconnected via communicating vessels oriented perpendicular to the skin surface.

LymphaticsBlind-ended lymphatic capillaries arise within the interstitial spaces of the dermal papillae. These unvalved, superficial dermal vessels drain into valved deep dermal and subdermal plexuses.

Skin InnervationFree nerve endings in the basal layer of the epidermis detect pain Merkel cells of the epidermis detect light touch. Meissners corpuscles also detect light touch. These are found in the dermal papillae and are most concentrated in the fingertips. Pacininian corpuscles are found deep within the dermis or even in the subcutaneous tissue. These structures detect pressure.

Surface tension linesForm a network of linear furrows which divided the surface into polygonal or lozenge shaped areas . These lines to some extent correspond to variations in the pattern of collagen fibers in the dermis.

Tension lines/Cleavage lines/Langer linesThe tension lines of skin forms due to the patterns of arrangement of collagen fibers in the dermis. These lines were first described by Langer in 1861 on cadaver. Tend to spiral longitudinal in the limbs and run transversely in the neck and trunk.At the elbow , knee, wrist and ankles are parallel to the transverse creases that appear when the limbs are flexed.

Skin incisionsSkin incisions that are given parallel to the tension lines usually heal well with minimal scarring because of minimum disruption of collagen fibers.Stretch marks in skinDamage to the collagen fibers in dermis due to over stretching as in pregnancy or abdominal enlargement.

Wrinkle linesCaused by contraction of underlying muscles, present perpendicular to their axis of shortening.On face, they are known as lines of facial expression, aging makes them permanent due to loss of skin elasticity.

Flexure lines or joint linesMajor markings found in the vicinity of synovial joints where the skin is attached strongly to underlying deep fascia.Prominent on the flexor surfaces of palms, soles and digits.Skin lines don't necessarily coincide with the underlying joint line.

Flexure lines

Papillary/epidermal/friction ridgesA friction ridge is a raised portion of the epidermis on the fingers and toes, palms and soles. Are caused by the underlying interface between the dermal papillae of the dermis and the interpapillary (rete) pegs of the epidermis.Along the summit of each ridge the apertures of sweat ducts open at regular intervals.Dermis determines the developmental pattern of epidermis

FINGER PRINTA fingerprint is an impression left by the friction ridges of a human fingerThis is genetically determined, unique to the individual, stable through out life & serves as a mean of personal identification.The analysis of ridge patterns by studying finger and foot prints is known as dermatoglyphics.

The dermis is the receptive site for the pigment of tattoos

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