Anatomy & Physiology Of Integumentary

System

By:Mr. M. Shivananda Reddy

Structure Of Skin

• The integumentary system is the largest body organ and is composed of the skin, hair, nails, and glands.

• The skin is further divided into three layers: a) Epidermis b) Dermis And c) Subcutaneous tissue

Epidermis• The epidermis, the thin avascular superficial layer of

the skin, is made up of an outer dead cornified portion that serves as a protective barrier and a deeper, living portion that folds into the dermis.

• Together these layers measure 0.05 to 0.1 mm in thickness.

• The epidermis regenerates with new cells every 28 days.

Layers of Epidermis:Layers (from deep to superficial):

• Stratum basale or germinatum – single row of cells attached to dermis; youngest cells

• Stratum spinosum – Made up of bundles of protein resist tension

• Stratum granulosum – layers of flattened keratinocytes producing keratin.

• Stratum lucidum layer that is present only on palms and soles

• Stratum corneum – horny cornified superficial layer

Layers of epidermis:

Cells of Epidermis:• The two major types of epidermal cells are

melanocytes (5%) and keratinocytes (90%).• Melanocytes are contained in the deep,

basal layer (stratum germinativum) of the epidermis.

• They contain melanin, a pigment that gives color to the skin and hair and protects the body from damaging ultraviolet (UV) sunlight.

• Sunlight and hormones stimulate the melanosome (within the melanocyte) to increase the production of melanin.

• The wide range of skin color is caused by the amount of melanin produced; more melanin results in darker skin color.

• Keratinocytes are synthesized from epidermal cells in the basal layer.

• As they mature (keratinize), they move to the surface, where they flatten and die to form the outer skin layer (stratum corneum).

• Keratinocytes produce a fibrous protein, keratin, which is vital to the skin’s protective barrier function.

Dermis

• The dermis is the connective tissue below the epidermis.

• Dermal thickness varies from 1 to 4 mm. The dermis is very vascular.

• The dermis is divided into two layers, an upper thin papillary layer and a deeper, thicker reticular layer.

• The papillary layer is folded into ridges which extend into the upper epidermal layer.

• These exposed surface ridges form congenital patterns called fingerprints and footprints.

Subcutaneous Tissue.

• The subcutaneous tissue lies below the dermis and is not part of the skin.

• The subcutaneous tissue is often discussed with the skin because it attaches the skin to underlying tissues such as muscle and bone.

• The subcutaneous tissue contains loose connective tissue and fat cells that provide insulation.

• This layer also stores lipids, regulates temperature, and provides shock absorption.

Skin Appendages

Appendages of the skin include:• Hair• Nails• Glands (Sebaceous, Apocrine, And

Eccrine).

Hair• Grows on most of the body except for the lips,

the palms of the hands, and the soles of the feet • The color of the hair is a result of heredity and is

determined by the type and amount of melanin in the hair shaft.

• Hair grows approximately 1 cm per month. • On average 100 hairs are lost each day.• When lost hair is not replaced, baldness results.

Parts of Nail:

Nails:• Nails grow from the matrix. • The nail matrix is located at the proximal area of

the nail plate. • The matrix is commonly called the lunula, which

is the white crescent-shaped area visible through the nail plate.

• The nail bed that is under the nail matrix and nail plate is normally pink and contains blood vessels.

• Fingernails grow at a rate of 0.7 to 0.84 mm per week, with toenail growth 30% to 50% slower.

Glands:• Two major types of glands are associated with the

skin: Sebaceous and Sweat (apocrine and eccrine) glands.

• The sebaceous glands secrete sebum, which is emptied into the hair follicles.

• Sebum prevents the skin and hair from becoming dry.

• Sebum is somewhat bacteriostatic and fungistatic and consists mainly of lipids.

• These glands depend on sex hormones, particularly testosterone, to regulate sebum secretion and production.

• Sebum secretion varies according to sex hormone levels.

• Sebaceous glands are present on all areas of the skin except the palms and the soles.

• These glands are most abundant on the face, scalp, upper chest, and back.

• The apocrine sweat glands are located in the axillae, breast areolae, umbilical and anogenital areas, external auditory canals, and eyelids.

• The eccrine sweat glands are widely distributed over the body, except in a few areas, such as the lips.

Functions of Integumentary System• Regulates body temperature– regulates heat loss

• Helps regulate fluid balance – absorbs water – prevents excessive water & electrolyte loss. – Slow loss up to 600 ml daily by evaporation

• Immune Response Function

• Vitamin production – exposure to UV light allows for the conversion of

substances necessary for synthesizing vitamin D – Necessary to prevent osteoporosis, rickets

• Excretion:Partial excretion of metabolic wastes occurs through the skin.

• Transmits sensation – nerve receptors

• allows for feelings of temperature, pain, light touch and pressure

Functions of hair:

Head:o UV protectiono Cushion from traumao InsulationNostrils, Ear canals, Eyelashes:• Prevent entry of foreign materialBody Hair:• sensory detection