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Integumentary System
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The Integumentary System

Components of the integumentary system

skin

hair

nails

glands

Structure of skin

In terms of volume of tissue, the skin is the largest organ of the body

Two main layers: the outer epidermis and the inner dermis. Deep to the skin are the supporting tissues that include adipose tissue (fat) and connective tissue layers called fascia. There are differences in distribution of the subcutaneous fat in women and men.

Epidermis

stratified squamous, keratinised epithelium

can be of different thicknesses and types: thick & hairless (eg: sole of foot); thin and hairy (eg: scalp)

new cells formed in basal layer

Cells gradually migrate to surface

Shedding (desquamation) of surface cells

Pigmented cells: melanocytes

Undulating interface with dermis to enhance attachment

Invagination of surface to form hair follicles and glands.

Dermis

connective tissue: fibroblasts, collagen

blood vessels

nerve supply: sensory and motor

Keratinization

new cells formed in stratum basale

cells accumulate keratin & lipid-filled lamellar bodies (stratum spinosum)

keratohyalin & degenerating organelles - protein envelope forms (stratum granulosum)

 

cells die & become transparent (stratum lucidum)

dead cells containing soft keratin, surrounded by lipids, connected by desmosomes (stratum corneum)

takes 40-56 days

Hair

 

distribution of hair is related to age (lanugo, secondary sexual hair distribution, baldness)

has a protective role in relation to eyes, ears, and nasal cavities

protects head from ultra-violet light and cold

Nails

protective role

fingernails used in fine manipulation

Glands

sebaceous glands

sweat glands - merocrine, apocrine

mammary glands

 

ceruminous glands (ear)

Skin colour

melanin

Carotene

Blood supply

Functions

Physical barrier

The skin provides a physical barrier between the internal and external environment

Protection

The skin forms a major part of the body's external defence mechanisms against infection and harsh chemicals

Potentially harmful disease-producing micro-organisms (pathogens) are prevented from gaining entry into the body when the skin is intact

Skin commensals such as Staphylococcus aureus cause no harm on the surface of the body but can cause serious problems if the skin surface is broken and the organisms enter deeper tissues. In severe burns infection is a major complication because underlying tissues will be immediately exposed to skin commensals and airborne organisms

The skin protects against fluid loss

The skin protects against ultra-violet radiation

The skin and nails protect against wear and tear

Sensation

The skin contains receptors for touch, pain, temperature, pressure, vibration and hair movement

Temperature regulation

The flow of blood through the dermis is regulated to help maintain a constant core temperature for the body. Temperature receptors inform the hypothalamus of temperature changes centrally and peripherally and the hypothalamus influences the vaso-motor centre in the brainstem. Sympathetic nerves under the control of the vasomotor centre bring about either vasoconstriction or vasodilation in peripheral blood vessels. Vasoconstriction reduces blood flow close to the surface and thus conserves heat, while vasodilation increases blood flow and allows dissipation of excess heat

Heat is lost from the body by radiation, conduction, convection and evaporation of sweat:

radiation - the skin radiates heat in the form of infra-red rays and warms nearby objects
conduction - body heat is also transmitted by direct contact to objects in contact: e.g. clothing, the seat that one is sitting on or any objects being held
convection - air passing over the skin is warmed. This warm air rises and colder air is drawn in to take its place
evaporation - sweat on the skin surface evaporates and as a result the skin surface is cooled; providing the surrounding air is less than 100% humid. The skin therefore influences fluid homeostasis

Adipose tissue has insulating properties in addition to being an energy store

Excretion

Waste products are excreted through the sweat glands in the skin. Water and sodium are the most obvious examples but other substances can be excreted if their normal excretory pathway fails. For example, more urea is excreted by sweat glands when a person has renal failure, unless corrective measures have been instigated

Synthesis of vitamin D

The action of the ultra-violet component of sunlight on the skin converts a precursor molecule into vitamin D

Vitamin D facilitates the uptake of calcium and phosphorus from the diet - a deficiency results in rickets

Body shape

The skin contributes to the shape of the body as does the skeleton, the muscular system and adipose tissue.

Some important information on Integumentary System:

● The word INTEGUMENT comes from a LATIN word that means to COVER.

● THE MOST IMPORTANT FUNCTION OF THE INTEGUMENTARY SYSTEM IS PROTECTION.

KERATIN IS A TOUGH FIBROUS PROTEIN AND FORMS THE BASIC STRUCTURE OF HAIR, NAILS, AND CALLUSES.

● Eventually, the Keratin-producing Cells (KERATINCYTES) DIE AND FORM A TOUGH, FLEXIBLE WATERPROOF COVERING ON THE SURFACE OF THE SKIN. Our thickest Epidermis in on the palms and soles.

● THIS OUTER LAYER OF DEAD CELLS IS SHED OR WASHED AWAY ONCE EVERY 14 TO 28 DAYS.

● BOTH LIGHT SKINNED AND DARK SKINNED PEOPLE HAVE ROUGHLY THE SAME NUMBER OF MELANOCYTES, THE DIFFERENCE IN OUR SKIN COLOR IS CAUSED BY THE AMOUNT OF MELANIN THE MELANOCYTES PRODUCE AND DISTRIBUTE.

● The Amount of Melanin produced in Skin depends on TWO Factors - Heredity and the Length of Time the Skin is Exposed to Ultraviolet Radiation (Tanning).

● Melanin is important for protection, by absorption of Ultraviolet Radiation from the sun. All people, but especially people with Light Skin, need to minimize exposure to the sun and protect themselves from its Ultraviolet Radiation, which can Damage DNA in Skin Cells and lead to deadly forms of Skin Cancer such as MELANOMA CANCER.

● THERE ARE NO BLOOD VESSELS IN THE EPIDERMIS, WHICH IS WHY A SMALL SCRATCH WILL NOT CAUSE BLEEDING.

Burns:

FLAMES, HOT WATER OR STEAM, SUNLIGHT, ELECTRICITY, OR CORROSIVE CHEMICALS MAY CAUSE BURNS OF THE SKIN.

● THE SEVERITY OF BURNS RANGES FROM MINOR TO FATAL AND THE CLASSIFICATION OF BURNS IS BASED ON THE EXTENT OF DAMAGE.

FIRST-DEGREE BURN- ONLY THE SUPERFICIAL EPIDERMIS IS BURNED, AND IS PAINFUL BUT NOT BLISTERED. Causes death of Epidermal Cells.

SECOND-DEGREE BURN- DEEPER LAYERS EPIDERMIS ARE EFFECTED, COULD HAVE INFLAMMATION, BLISTERS, AND THE BURNED SKIN IS OFTEN PAINFUL.

THIRD DEGREE BURN- THE ENTIRE EPIDERMIS IS CHARRED OR BURNED AWAY, AND THE BURN MAY EXTEND INTO THE DERMIS. OFTEN SUCH A BURN IS NOT PAINFUL AT FIRST, IF THE RECEPTORS IN THE DERMIS HAVE BEEN DESTROYED.

EXTENSIVE THIRD-DEGREE BURN- POTENTIAL LIFE-THREATENING BECAUSE OF LOSS OF SKIN, WITHOUT THIS NATURAL BARRIER, LIVING TISSUE IS EXPOSED TO THE ENVIRONMENT AND IS SUSCEPTIBLE TO INFECTION AND DEHYDRATION.