THE INTEGUMENTARY SYSTEM

The INTEGUMENT is the external covering of the animal. The organs that make up the integumentary system of the body are the skin and its derivatives, such as hair, nail, glands, scales, hooves, feathers, and nerve endings.

It primarily protects against mechanical and chemical injury, and invasion by microorganisms.

What are the general FUNCTIONS of integuments? 1. Regulation of Body Temperature. (thermoregulation) Through the production of sweat or decrease in production. Changes in the flow of blood to the skin also regulates body temperature. 2. Protection. It provides a physical barrier that protects un-derlying tissues from abrasion, bacterial invasion, dehydra-tion, and UV radiation. 3. Sensation. It allows reception of environmental stimuli because it has abundant nerve endings and receptors that detect stimuli related to temperature, touch, pressure, and pain. 4. Excretion. (hydroregulation) Removes heat and some water from the body. Sweat contains some excretory prod-ucts like small amount of salts, and several organic com-pounds. 5. Immunity. Certain cells of the epidermis are important components of the immune system which fends off foreign invaders. 6. Blood Reservoir. The dermis of the skin houses exten-sive networks of blood vessels that carry 8-10% of the total blood flow in a resting adult. 7. Synthesis of Vitamin D. The skin produces the precursor molecule needed to synthesize vitamin D.

What are the integuments of LOWER FORMS OF OR-GANISMS?1. Epidermis (the integument of most multicellular inverte-brates) It consists of a single layer of columnar epithelial cells and rests on a basement membrane. Some epidermal cells may possess cilia, some may contain glandular cells. 2. Plasma membrane (the amoebas’ integument) This membrane is structurally and chemically like the plasma membrane of multicellular organisms. Gas exchange and removal of excretory wastes occur here by simple diffusion. The large surface area also facilitates the uptake of dis-solved nutrients from surrounding fluids.3. Pellicle (thick protein coat outside the plasma membrane of other protozoans like the Paramecium) This offers further environmental protection. 4. Cuticles: are integuments found in some invertebrates; a waxy waterproof covering. Found in rotifers, where cuticles are thin and elastic, and in crustaceans, arachnids, and in-sects where cuticles are thick and rigid. Such cuticles con-sist of chitin and proteins in rigid plates. 5. Tegument (the integument of flukes and other tape-worms) Its main functions are nutrient ingestion and protec-tion against digestion by host enzymes.6. Shell (the integument of jellyfishes, mollusks, and squids) These are produced by means of their mucous glands that secrete calcium carbonate, thus producing shell.

VERTEBRATES’ INTEGUMENTS

FISHESJawless fishes like the lampreys and hagfishes have rel-atively thick skin. They have epidermal glandular cells that secrete protective cuticle. Slime glands, producing large amounts of slime, may also be found. This protects the animals from external parasites.Cartilaginous fishes like the sharks have mucous and sensory cells. The dermis contains bone in the form of pla-coid scales called denticles. Being similar to vertebrate teeth, it does not grow too and are continually worn down. Bony fishes contain scales composed of dermal bone. Their skin is permeable and functions in gas exchange. The dermis is richly supplied with capillary beds for use in respi-ration. The epidermis also contains mucus glands. Mucus prevents bacterial and fungal infections, and reduces friction as the fish swims. Some species have granular glands that secrete an irritating or poisonous alkaloid. Bony fishes that live in deep habitats have photophores that facilitate species recognition or act like lures and warning signals.

AMPHIBIANSAmphibians’ skin consists of a stratified epidermis and a dermis containing mucous and serous glands plus pig-mentation cells. The mucus helps prevent dessication, fa-cilitates gas exchange, and makes the body slimy to facili-tate escape from predators. Within the dermis of some am-phibians are poison glands that produce an unpleasant-tast-ing or toxic fluid that deters predators.

REPTILESThe skin of reptiles reflect their greater commitment to ter-restrial existence. The outer layer of the epidermis is thick, lacks glands, and is modified into keratinized scales, scutes in snakes and lizards, beaks in turtles, rattles in snakes, and claws, plaques, and spiny crests on most other reptiles. The thick, keratinized layer resists abrasion, inhibits dehydration, and protects like a suit of armor.

BIRDSThe epidermis of birds is usually thin (2-3 cell layers thick). They have no epidermal gland except the uropygial or preen gland. The most prominent part of the epidermis are the feathers. Feather position is important in thermal regula-tion, flying, and behavior.

HUMANSSKIN: • the largest and heaviest organ of the body.• covers all of the exposed surface of the body• continuous with the mucous membranes lining

openings into the body surface like digestive, respiratory, and urogenital surface.

• covers about 2 square meters (22 square feet), weights 4.5-5 kg (10-11 lb) and varies in thickness (1.5 to 4.0 mm) depending on what part of the body it covers.

• TWO LAYERS:

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1. EPIDERMIS• Derived from embryonic ectoderm and is made of

keratinized stratified squamous epithelium• It thickness varies: 0.07-0.12 mm over most of

the body to 0.8 mm on the palms and 1.4 mm on the soles.

• Serves as protective barrier against UV light, bacteria, many chemicals and abrasion

• Epidermal cells: a. Keratinocytes – produce keratin (waterproof cov-ering of the skin that protects underlying tissues from heat, microbes, abrasion, and chemicals)

b. Merkel cells – sensory receptors (touch) c. Melanocytes – synthesize melanin pigments

which protect the skin from UV damage. d. Langerhans cells–macrophages used in the de-

fense against microorganisms• Layers of cells: (from the deepest to the most

superficial) a. Stratum Basale/Germinativum

i. Mostly stem cells that divide rapidly to produce new keratinocytes

ii. 10%-25% of the cells are melanocytesiii. consists of one row of cuboidal to colum-

nar shaped cellsiv. with Merkel cells also

b. Stratum Spinosumi. Where most of Langerhans cells are

found. c. Stratum Granulosum

i. Keratinization process begins and cells begin to die.

ii. This layer is called granulosum because the cells contain granules of the precursor of keratin.

d. Stratum Corneumi. Composed of dead, flat, keratinized cells

2. DERMIS• Contains lots of nerve fibers, sensory receptors,

blood and lymphatic vessels as well as hair folli-cles and sebaceous and sweat glands

• The average thickness is about 1 to 2 mm and varies from 0.6 mm on the eyelids to 3 mm or more on the soles and palms.

• Layers: a. Papillary layer

i. Layer closest to the epidermisii. Composed of areolar loose connective

tissue properiii.Contains DERMAL PAPILLAE (indents

the epidermis causing the formation of fingerprints); contain capillaries, bare nerve endings (pain receptors)

iv. Contains MEISSNER’S CORPUSCLES (touch receptors)

b. Reticular layeri. Deep layer; thickestii. Made of dense irregular connective tis-

sue proper

iii. contains thick bundles of interlacing col-lagen fibers and some coarse elastic fibers that run. The collagen fibers in the reticular region provides the skin with strength and extensibility (= ability to stretch) and elastic fibers provide its elasticity (= ability to return to the original shape after stretching).

iv. The reticular layer is richly supplied with blood vessels and nerves, and contains sensory endings for touch (Pacinian corpuscle for sensing deep pressure such as bumps), pain, heat, cold, etc. 3. HYPODERMIS

• Subcutaneous tissue which anchors the skin loosely to underlying tissues

• Not part of the skin• Consists of adipose and areolar tissue• shares the skin’s protective functions: it stores

fat and thus helps prevent heat loss and acts as a shock absorber; it anchors the skin to the un-derlying structures allowing the skin to slide al-most freely over them. These features ensure that blows just glance of the body without injur-ing the tissues below.

SKIN APPENDAGES 1. HAIR

Protection: hairs protect scalp from injury, from the sun’s rays, and decrease heat loss

Eyebrows and eyelashes protect the eye from foreign particles Hairs in the nostrils filter the air we inhale Hairs in the external ear canal prevent foreign particles to penetrate there.

Made of dead keratinized cellsTwo regions of the hair:

Shaft – portion of the hair that projects from the surface of the skin.

- The shape of the shaft determines the curliness of your hair:

round shaft - straight hair oval shaft - wavy hair flat shaft - kinky hair

Root – portion of the hair embedded in the skinAssociated with each hair follicle is a tiny band of

smooth muscle: the arrector pili. Contraction of the arrector pili in hairy mammals raises the hair, thus increasing the thickness of its coat. This provide in-creased protection against heat loss in cold weather or increase in body size to intimidate potential adver-saries. In human, contraction of these muscles causes only "goose pimples".

2. SEBACEOUS GLANDS/OIL GLANDSSecrete sebum

Helps hair from becoming brittlePrevents excessive evaporation of water from the skinKeeps skin soft and contains bactericidal agent that inhibits growth of bacteria

Scattered all over the surface of the skin except in the palms, soles, and side of feet

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3. SWEAT/SUDORIFEROUS GLANDSTwo types:

Eccrine – most common. Secretory portion is lo-cated either in the dermis or hypodermis. They produce sweat, a watery mixture of salts, anti-bodies and metabolic wastes. Sweat prevents overheating of the body and thus helps regulate body temperature.Apocrine – found mainly in the skin of the armpits, of the anogenital areas and of the are-ola of the breasts. Secretory portion is located either in the dermis or hypodermis. Excretory ducts open in to the hair follicle.

4. CERUMINOUS/EAR WAX GLANDSModified apocrine sweat glandsSecretes the ear wax.

5. NAILSThree regions:

nail body - portion of the nail that is visible. It rests onto the nail bed: an epithelium made only of the stra-tum basale and the stratum spinosum. There are no stratum granulosum, stratum lucidum and stratum corneum in the nail bed.

free edge - visible portion of the nail that extend past the end of the digit. It is the distal part of the nail that you clip every now and then.

nail root - hidden portion of the nail that is embed-ded in a fold of skin (or nail fold). The cuticle is the stratum corneum of the nail fold that is pushed forward over the nail.

Nail matrix – site of nail growth. found beneath the nail root. The nail matrix is thick and is only com-posed of the deeper layer of the epidermis: the stra-tum basale (or germinativum). The keratinization of the cells of the nail matrix proceeds in the absence of a stratum granulosum and lucidum and this re-sults into formation of a of a rigid and durable plate. Look at your nail, you will see a white crescent called the lunula that reflects the presence of the thick matrix underneath.

WHAT HAPPENS WHEN WE GROW OLD?1. collagen fibers decrease in number, break apart,

stiffen, and form into a shapeless, matted tangle.2. elastic fibers lose some of their elasticity, thicken

into clumps, and fray resulting into the formation of crevices and furrows known as wrinkles.

3. fibroblasts, which help produce both collagen and elastic fibers, decrease in number also and macrophages become less efficient phagocytes.

4. hair and nails grow more slowly.5. langerhans cells dwindle in number thus decreasing

the immune responsiveness of older skin.6. decreased size of sebaceous glands leads to dry

and broken skin that is more susceptible to infec-tion.

7. production of sweat diminishes, which probably contributes to the increased incidence of heat stroke.

8. melanocytes also decrease in number resulting in gray hair and atypical skin pigmentation.

9. increase in the size of some melanocytes produces pigmented blotching or liver spots.

10.blood vessels in the dermis becomes thicker-walled and less permeable.

11.subcutaneous fat is lost.12. it becomes thinner than young skin especially the

dermis because migration of cells from the basal layer to the surface slows considerably.

13. the skin heals poorly and becomes more suscepti-ble to pathological conditions such as skin cancer, shingles, itching, and pressure sores.

COMMON DISORDERS OF THE SKIN• SUNBURN: Injury to the skin because of overexposure

to the sun. characterized by a leathery skin texture, wrinkles, skin folds, sagging skin, warty growths, pre-mature skin aging

• ACNE: Inflammation of the sebaceous glands. Usually occurs when sebaceous glands are colonized by bac-teria.

• ATHLETE’S FOOT: Superficial fungus infection of the skin of the foot.

• CHICKENPOX: Caused by the virus Varicella zoster. Chickenpox can be spread by direct contact, droplet transmission, and airborne transmission. Even those with mild illness after the vaccine may be contagious. When someone becomes infected, the pox usually ap-pear 10 to 21 days later. People become contagious 1 to 2 days before breaking out with pox. They remain contagious while uncrusted blisters are present.

• BED SORE: A bed sore develops when blood supply to the skin is cut off for more than two to three hours. As the skin dies, the bed sore first starts as a red, painful area, which eventually turns purple. Left untreated, the skin can break open and become infected. A bed sore can become deep, extending into the muscle. Bed sores are ulcers that occur on areas of the skin that are under pressure.

• CALLUSES AND CORNS: Calluses are protective pads made up of the thickened upper layer of skin due to re-peated rubbing of the area. Corns are small calluses that develop on the top of the toes due to pressure or rubbing against shoes or other toes.

• PSORIASIS: Psoriasis is a chronic skin condition char-acterized by inflamed, red, raised areas that often de-velop as silvery scales on the scalp, elbows, knees, and lower back.

• DANDRUFF: When the scalp sheds its skin as flakes in hair and on clothing, it is called dandruff. Dandruff flakes grow in size with the accumulation of dirt and oil.

• Overactive oil glands are thought to be possible causes for dandruff. The actual cause of the condition is un-known.

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• CELLULITIS: an infection at the deepest layer, called the subcutaneous layer. This kind of infection is caused by bacteria, which can get into the body through broken skin of any kind (such as a cut, scratch, animal bite, or a bug bite if you scratch it). Caused by streptococcus and staphylococcus

• WARTS: generally found as skin "bumps". They are commonly found on feet, where they are called plantar warts, and on hands. They may appear on any skin area, including genitals. They are contagious, caused by a family of viruses called the Human Papilloma Viruses.

TRIVIA• Fingernails grow at an average of 1 mm (0.04 in) per

week.• Fingernails grow faster than toe nails.• The longer the digit, the faster the growth rate.

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