SKIN

ByDr Samina Anjum

SKIN

Origin

EPIDERMIS

CELL TYPES IN EPIDERMIS Keratinocytes – 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 loose areolar 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 LAYERS The 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 skin Degree of pigmentation (Melanin, carotene)

Skin is the best indicator of general health

APPENDAGES OF SKIN

SWEAT GLANDSEccrineApocrine

SEBACEOUS GLANDS HAIR FOLLICLES NAILS

ECCRINE SWEAT GLANDS Are coiled tubular

glands that discharge their secretions directly onto the surface of the skin

Are smaller than apocrine sweat glands

They do not extend deep into the dermis

They are supplied by cholenergic sympathetic fibers

Cont…

Are distributed all over the skin except:

Tympanic membranes Lip margins Nipples Some parts of external genitaliaGreatest concentration is in thick skin

of palms and soles, and on the face

APOCRINE SWEAT GLANDS

Are large modified sweat glands composed of a coiled secretory portion located at the junction of the dermis and subcutaneous fat, from which a straight portion inserts and secretes into the infundibular portion of the hair follicle or may open directly on the skin surface.

Cont…

In humans, apocrine sweat glands are found only in certain locations of the body: the axillae (armpits), the areola of the nipples, and the genital and perianal regions.

Specialized types of apocrine sweat glands present on the eyelids are called Moll's glands.

Cont…

secrete 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 fibers

SEBACEOUS GLANDS

The sebaceous glands are branched type of acinar gland  in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair

Cont… Present throughout

the skin except in the palms of the hands and soles of the feet.

Sebaceous glands can usually be found in hair-covered areas, where they are connected to hair follicles. 

Cont…

 Sebaceous glands are also found in non-hairy areas of  lips ,eyelids, nose, penis, labia minora and nipples and areolae

 Here, the sebum traverses ducts that terminate in sweat pores on the surface of the skin.

At the rim of the eyelids, meibomian glands are a specialized form of sebaceous gland. Their secretion slows the evaporation of tears.

HAIR Hard keratin that grows out of the follicle by

invagination of epidermis into the dermis The follicles lie obliquely to the skin surface

The 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 tissue

As 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 UNIT

The structure consisting of hair, hair follicle, arrector pili muscle, and sebaceous gland is known as a pilosebaceous unit.

NAILSAre the keratinized plates on the dorsal

surfaces of fingers and toes Nail 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 contains nerves, lymph and blood vessels.  

Cont…

Matrix/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

Cont…

Cuticle / 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.

Cont… Perionychium: 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 supply

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

Lymphatics

Blind-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 Innervation Free nerve endings in the

basal layer of the epidermis detect pain

Merkel cells of the epidermis detect light touch.

Meissner’s 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 lines

Form 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 lines

The 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 incisions

Skin 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 skin

Damage to the collagen fibers in dermis due to over stretching as in pregnancy or abdominal enlargement.

Wrinkle lines

Caused 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 lines Major 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 ridges

A 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 PRINT A fingerprint is an

impression left by the friction ridges of a human finger

This 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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