Integumentary System

Organs are two or more tissues which together perform a specialized function.

Membranes are thin structures that usually contain both epithelial and connective tissue. They line body cavities and cover body surfaces.


An epithelial membrane is an epithelial layer overlying a connective tissue layer.

Serous Membranes ( serous means watery) line closed cavities and cover the organs in the cavities. They are made of mesothelium ( simple squamous epithelium ) over loose areolar connective tissue. The membrane secretes serous fluid which acts as a lubricant.

pleura, pericardium, peritoneum

Mucous Membranes line cavities that open to the exterior. The epithelial layer is important in preventing microbes and other pathogens from entering the body. The cells have tight junctions, and goblet cells secrete mucus. It also secretes enzymes and absorbs nutrients and water in the intestines. The connective tissue layer is called the lamina propria, which anchors the epithelium to the underlying tissue and provides it with a blood supply.

The Cutaneous membrane (skin) and its accessory organs make up the integumentary system.

Synovial Membranes line the cavities of movable joints. They do not contain epithelium, but are made up of areolar connective tissue with elastic fibers and varying amounts of adipose tissue. They secrete synovial fluid, which lubricates and nourishes the cartilage covering the ends of the bones. They also line bursae (cushioning fluid filled sacs), and tendon sheaths.



The skin and the organs derived from it (hair, glands, and nails) constitute the integumentary system. It is one of the largest organs of the body.


Functions of the skin:

        1. Temperature regulation
                 Set and regulated by the hypothalamus
                    High body temp. - hyperthermia
                            Dilation of surface blood vessels


                    Low body temperature -Hypothermia

                           Constriction of surface blood vessels



    2. Protection - protects underlying tissues from:

                physical abrasion


                ultraviolet radiation

                Physical barrier to bacteria and other pathogens

                Hair and nails also have protective functions.

    3. Sensation - skin is our largest sense organ, with receptors that detect 
                   temperature, pain, pressure, and touch.

    4. Excretion - sweat is also a way of removing a small quantity of ions , from the
                     body as well as several organic compounds.

        5. Immunity- skin contains cells that are involved in defense mechanisms.
                  Fatty acids in sebum lower pH, and directly inhibit the growth of microbes.


        6. Blood reservoir - blood vessels in the skin carry 8-10% of the total blood flow in a resting adult. This reservoir can be used during hard exercise or in an emergency (skin turns pale.)

        7. Synthesis of vitamin D - begins with the activation of a precursor molecule in the skin by UV rays. Modified by the liver and kidney to the produce calcitrol. Vitamin D aids in the absorption of calcium from the intestinal tract. Vit. D acts as a hormone - skin acts as endocrine organ

            Tissue layers:



                    Hypodermis or subcutaneous layer



            Stratum basale (stratum germinativum)

                    Stem cells produce keratinocytes.

                    Melanocytes produce the pigment melanin in melanosomes.

                    Skin color; protects from UV rays

            Stratum spinosum

                        Appearance due to staining process.

                        Projections of melanocytes are phagocytized by kertainocytes
                                 -Cytocrine secretion

            Stratum granulosum

                        Cells contain granules of keratohyalin, a precursor to keratin.

                        Nuclei begin to break down.

            Stratum lucidum

                        May be absent in thin skin.
                        Cells are clear and dead. Have droplets of a substance (eleidin) which is eventually transformed into keratin.


                Stratum corneum

                            Dead, flat cells filled with keratin.


            Papillary layer - loose areolar connective tissue and is highly vascularized

                        dermal papillae

(net) layer (region)- dense irregular connective tissue containing collagen and elastic fibers

                    Sebaceous (oil) glands, hair follicles

                    ducts of sweat (sudoriferous) glands

                    hair follicles and nerves

                    Extreme stretching causes tears which remain as striae or stretch marks.

Hypodermis or subcutaneous- or superficial fascia - areolar connective tissue and adipose tissue. Contains the major blood vessels to the skin and nerve endings that are sensitive to pressure, cold and heat.

        rete cutaneum


Accessory organs of the skin:

                Hair - function in protection
                        Shaft, root and hair follicle

                    Associated with hairs are:
                                sebaceous (oil) glands

                                arrector pili muscle

                                hair root plexuses (touch)

                Cyclic pattern of growth and loss

                'Male-pattern' baldness - androgens and heredity


   Sebaceous glands

            empty into hair follicles

            holocrine glands - fat, cholesterol, proteins and inorganic salts and cell debris.

            moistens hairs and lubricates and waterproofs the skin.

           Excess sebum secretion leads to blackheads, pimples, and boils.

Sweat or Sudoriferous glands

            Eccrine glands

                    coiled tubular merocrine glands

                    secretory portion is in the deep dermis or in the hypodermis

                    Sweat consists mostly of water with some dissolved salts, metabolic wastes, lactic acid and vitamin C. pH 4-6.

                    Main function is to cool the body, although it is also a nervous reaction.


            Appocrine glands

                    still merocrine glands

                    open onto hair follicles

                    secretion is more viscous and contains fatty acids and proteins

                    odor is caused by action of bacteria

                    in axillary, and groin regions and around nipples.

                    Function in emotional stress and sexual excitement


        Ceruminous glands

                are modified sudoriferous glands that secrete cerumen (earwax).

                Found in the external auditory meatus (ear canal).

                Traps foreign bodies.

        Mammary glands

                    specialized sudoriferous glands which secrete milk.

Skin Color

            The amount of melanin produced is determined by genes .

            Lack of pigment production is called albinism

            Exposure to UV light or X-rays       

            State of oxygenation of the blood - low concentrations of oxygen cause cyanosis.

         The amount of blood flowing through the skin.

            Too much carotene in the diet can cause skin to appear yellow

            Liver disorders that prevent the liver from breaking down and excreting bilirubin, give the skin a yellow color called jaundice.


Wound healing

            Inflammatory phase

            Migratory phase

                        granulation tissue

            Proliferative phase

            Maturation phase


Hypertrophic scar



First degree or superficial partial-thickness burns


Second degree or deep partial-layer burns


Third degree or full-thickness burns