THE INTEGUMENTARY SYSTEM

 

The Integumentary system is an organ that consist of the skin, its derivatives (sweat and oil glands), nails and hair. The basic function of the skin is protection.  The skin consists of epidermis and dermis.

 

 

I.   EPIDERMIS

 

    A.  Cells of the Epidermis

Cells: consists of keratinocytes, melanocytes, Merkel cells    and Langerhans cells.

·        Keratinocytes: tightly packed and connected to desmosomes; originate from stratum basale; produce keratin

·        Melanocytes: spider-like cells that produce melanin (forms a pigment shield that protects the nucleus from the UV rays).

·        Langerhans cells: star-shaped cells from bone marrow. Function to activate the immune system as macrophages.

·        Merkel cells: function as sensory receptors

 

B.   Layers of the Epidermis

·        Stratum basale: consist of predominantly single row of keratinocytes; some melanocytes (10-25%) and Merkel cells;

·        Stratum spinosum: several layers thick; Contains flattened irregularly-shaped keratinocytes, pre-keratin intermediate filaments.

·        Stratum granulasum: consist of flattened keratinocytes which accumulate keratohyaline granules (granules form keratin) and lamellated granules (produce water-resistant chemical).

·        Stratum lucidum: present only in thick skin and made up

    of a few rows of clear, flat, dead keratinocytes.

·        Stratum corneum: outermost layer, conts many layers of cells (cornified or horny cells). Dead skins slough off.

 

II.      DERMIS

 

Richly supplied with nerves (sensory receptors), blood vessels, lymphatic vessels, sweat and sebaceous glands derived from the epidermis.  Contains two layers: papillary and reticular

·        Papillary layer: Consists of areolar connective tissue made up of loose collagen and elastic fibers, projections called papillae which contain touch and pain receptors (Messsner’s corpusles).  The papillae also form epidermal ridges found on the surfaces of palms, fingers and feet. On the palm and fingers they form the fingerprints (genetic markers of individualilty).

·        Reticular layer: account for about 80% of thickness of dermis; consist of dense irregular connective tissue. The ECM of this layer consist of bundles of collagenous fibers which run in parallel and opposite directions. The fibers give strength and resilience (toughness) and recoil, while collagen absorbs water and keep the skin hydrated. Stretch marks found on the buttocks, thighs, abdomen and breast are due to these fibers.

·        Disturbances of the skin

Stretch and tear; blisters

 

Skin Coloration

Skin color is due to a combination of three pigments: melanin, carotene and hemoglobin. 

·        Melanin is a brown-black pigmentation formed in cells called melanocytes. Cells are found in the stratum basale and spinosum. The amount of melanin produced by an individuals is based on inheritance. Freckles are small patches of Melanin on the skin due to uneven distribution.

·        Hemoglobin is the molecules found in RBC that gives blood its red coloration. It is made of non-protein (heme which contains iron) and the protein (globin).

·        Carotene is the yellowish pigment found in the corneum and the dermis.

·        Skin color of human races occur as a result of the relative abundance of melanin and carotene. Dark-skin coloration is due to melanin. Caucacians produce more carotene than melanin.

·        Melanin protects the skin and cells of the skin by shielding the UV light of the sun against the nucleus.

 

III.    ACCESSORY STRUCTURES

 

Accessory structures include hair, nail, and glands.

·        Hair: formed of keratinized cells and consist of two parts: a shaft and root.  The shaft is above the skin and root embedded in the dermis, in a hair follicle connected to blood supplies and arrector muscle.

·        Nail: they are formed of keratinized epidermal cells and occur on the finger and toes. Consist of a visible area (body) and the root (embedded in the dermis).

·        Glands:  There are there exocrine (conts ducts) glands:   sebaceous, sudoriferous and ceruminous glands. These glands secrete their contents to the exterior unlike endocrine which secrete their contents directly into blood.

a.        Sebaceous glands: produce oil (sebaum) which keeps the skin oily. The glands are branched and attached to the hair follicle. Blockage of the gland causes acne.

b.       Sudoriferous(sweat) gland: produce sweat or perspiration composed of water, salt, urea and uric acid. They are coiled and tubular shaped and of two types:  Eccrine (found on forehead, back of palm and soles), and Apocrine (larger that eccrine, found in pubic regions and secrete into hair follicles).   Mammary glands: are specialized form of sudoriferous gland secrete milk.

c.        Ceruminous glands: found only in the external auditory canal where they secrete cerumen (earwax). Cerumen is an insect repellant and also keep the eardrum (tympanic membrane) from drying out. Excess amount may block.

 

  Skin Cancers

·        Basal cell carcinoma: originate from the stratum basel (about 70% of skin cancers). Treated by excision.

·        Squamous carcinoma: originate from cells immediately above the basale layer.  Treatment consist of X-ray and excision.

·        Malignant melanoma: most life-threatening arises from melanocytes in the basale. Most often begins as a mole-like growth and enlarges. May change and metastatize. Often removed by excision, x-ray.

 

Temperature Regulation

·        The regulation of body temperature is carried out by the hypothalamus in conjunction with the skeletal muscle. The system works similar to the thermostat in buildings.

·        Normal body temperature is 37 C(98.6F). This temperature is produced as a result of metabolic activities which produce heat in the body.

·        During the cold when heat loss is excessive, the blood vessel constrict (therefore less blood to the surface) the muscle contract frequently (shivering) to produce heat.

·        In the summer, the vessels dilate (more blood to the skin surface, more heat loss), sweat pores open and produce perspiration that cool the surface as heat is lost.

 

 Skin Aging

·        After 50 years, wrinkles and sagging of the skin become more noticeable.

·        Effects of aging are a result of deterioration of collagen, elastic fibers; decrease in sebaum production, decrease in melanin production, decrease in content and decomposition of cutaneous fat.

 

Disorders of the skin

·        There are several types of skin disorders associated with the skin. Some of them are infectious (contagious) or non-infectious.

·        These disorders include acne, athletes foot, boils, fever blisters, impetigo, warts, alopecia, burns, calluses (corns), cancers, dandruff, eczema, moles psoriasis and others.

 

Contagious skin disorders

A.         Contagious disorders are caused by bacteria or virus or fungus

·        Acne: characterized by plugged hair follicles that form pimples. Caused by bacteria, prevalent in teenage years.

·        Boils: painful infection of hair follicles and sebaceous glands by Staphylococcus bacteria.

·        Fever blisters: cold sores…fluid filled blisters on the lips or oral membrane caused by Herpes simplex virus and transmitted by oral and respiratory exposure. Genital Herpes are painful blisters on the genitals and transmitted by sexual contact.

·        Impetigo:  highly contagious skin infection caused by bacteria, occurs in children and characterized by fluid-filled pustules forming yellow crust over infected area.

·        Warts: small skin tumors caused by viral infection that stimulate excessive growth of epithelial cells

 

  B.  Non-contagious skin disorders

·        Alopecia: loss of hair (pattern baldness) is most prevalent in males and inherited.  May also be caused by factors such as poor nutrition, sensitivity to drugs, and eczema.

·        Eczema: inflammation producing redness, itching, scalding and cracking of skin. Seborrheic eczema is produced by hyperactivity of the sebaceous glands.

·        Psoriasis:  a chronic dermatitis characterized by reddish raised patches of skin covered with whitish scales. Result from excessive cell production caused by emotional stress or poor health.  Occurs often on the buttocks, elbows, scalp and knees.  Others conditions are: dandruff, cancers, calluses, hives, burnes.