Anatomy and Physiology of the Disease

8/8/2019 Anatomy and Physiology of the Disease

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ANATOMY AND

PHYSIOLOGY OF THEDISEASE


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THE SKIN


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The SKIN is the largest organ in the human body. For theaverage adult human, the skin has a surface area ofbetween 1.5-2.0 square meters (16.1-21.5 sq ft.), most of itis between 23 mm (0.10 inch) thick. The average squareinch (6.5 cm) of skin holds 650 sweat glands, 20 bloodvessels, 60,000 melanocytes, and more than a thousandnerve endings.

The skin is the outer covering of the body. In humans, it isthe largest organ of the integumentary system made up ofmultiple layers of mesodermal tissue, and guards theunderlying muscles, bones, ligaments and internal organs.Skin of a different nature exists in amphibians, reptiles,birds. Human skin is not unlike that of most othermammals except that it is not protected by a pelt andappears hairless though in fact nearly all human skin iscovered with hair follicles. The adjectivecut an

eous literally means "of the skin" (from Latin cut is, skin).


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Because it interfaces with the environment, skin plays a

key role in protecting (the body) against pathogens andexcessive water loss. Its other functions are insulation,temperature regulation, sensation, synthesis of vitamin D,and the protection of vitamin B folates. Severely damagedskin will try to heal by forming scar tissue. This is oftendiscolored and depigmented.

In humans, skin pigmentation varies among populations,and skin type can range from dry to oily. Such skin variety

provides a rich and diverse habit for bacteria whichnumber roughly a 1000 species from 19 phyla.


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Skin has mesodermal cells, pigmentation, or

melanin, provided by melanocytes, whichabsorb some of the potentially dangerousultraviolet radiation (UV) in sunlight. It alsocontains DNA-repair enzymes that help reverseUV damage, and people who lack the genes forthese enzymes suffer high rates of skin cancer.One form predominantly produced by UV light,malignant melanoma, is particularly invasive,causing it to spread quickly, and can often be

deadly. Human skin pigmentation varies amongpopulations in a striking manner. This has ledto the classification of people(s) on the basis ofskin color.


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THREE PRIMARY LAYERSOF THE SKIN:

The epidermis, whichprovides waterproofing

and serves as a barrier toinfection; The dermis, which serves

as a location for theappendages of skin; and

The hypodermis(subcutaneous adiposelayer).


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EPIDERMIS

Epidermis, "epi"coming from the Greekmeaning "over" or "upon",is the outermost layer ofthe skin. It forms thewaterproof, protectivewrap over the body's

surface and is made up ofstratified squamousepithelium with anunderlying basal lamina.


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COMPONENTS

The epidermis contains no blood vessels,and is nourished by diffusion from thedermis.The main type of cells which makeup theepidermis are keratinocytes, melanocytes,Langerhans cells and Merkels cells. The

epidermis helps the skin to regulate bodytemperature.

Epidermis is divided into the following 5sublayers or strata:

Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum germinativum (also called

"stratum basale")


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Stratum Basale

Deepest layer- single row of cells (AKA: stratumgerminativum)

Combination of merkel cells, melanocytes,keratinocytes & stem cells that divide repeatedly

Scattered protein that forms keratin higher up

Stratum Spinosum

8 to 10 cell layers

Melanin taken in by phagocytosis from nearbymelanocytes

Stratum Granulosum

3 - 5 layers of flat dying cells (apoptosis)

keratohyalin granules: (converts protein to

keratin)

Contain granules that release lipids that repelswater

Stratum Lucidum

Only in thickskin: palms, fingers, & soles 3 - 5 layers of clear, flat, dead cells

Dead keratinocytes w/ lots of keratin

Stratum Corneum

25 to 30 layers of flat dead cells lots of keratin andsurrounded by lipids

Continuously shed


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DERMIS

The dermis is the layer of skin beneaththe epidermis that consists of connectivetissue and cushions the body from stress andstrain. The dermis is tightly connected to theepidermis by abasement membrane. It alsoharbors many Mechanoreceptor/nerve

endings that provide the sense of touch andheat. It contains the hair follicles, sweat glands,sebaceous glands, apocrine glands, lymphaticvessels and blood vessels. The blood vessels inthe dermis provide nourishment and wasteremoval from its own cells as well as from the

Stratum basale of the epidermis.

The dermis is structurally divided intotwo areas: a superficial area adjacent to theepidermis, called the papillary region, and adeep thicker area known as the reticular

region.


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PAPILLARY REGION

The papillary region is composed of

loose areolar connective tissue. It is namedfor its fingerlike projections called papil

lae that extend toward the epidermis. The

papillae provide the dermis with a "bumpy"

surface that interdigitates with the

epidermis, strengthening the connection

between the two layers of skin.

In the palms, fingers, soles, and toes,

the influence of the papillae projecting into

the epidermis forms contours in the skin's

surface. These are called friction ridges,

because they help the hand or foot to grasp

by increasing friction. Friction ridges occur in

patterns that are genetically and

epigenetically determined and are therefore

unique to the individual, making it possible

to use fingerprints or footprints as a means

of identification.


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RETICULAR REGION

The reticular region lies deep in thepapillary region and is usually much thicker. It iscomposed of dense irregular connective tissue,and receives its name from the denseconcentration of collagenous, elastic, andreticular fibres that weave throughout it. Theseprotein fibres give the dermis its properties of

strength, extensibility, and elasticity.

Also located within the reticular regionare the roots of the hair, sebaceous glands,sweat glands, receptors, nails, and bloodvessels.

Tattoo ink is held in the dermis. Stretchmarks from pregnancy are also located in thedermis.


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HYPODERMIS

The hypodermis is not part of the

skin, and lies below the dermis. Itspurpose is to attach the skin tounderlying bone and muscle as well assupplying it with blood vessels andnerves. It consists of loose connectivetissue and elastin. The main cell types

are fibroblasts, macrophages andadipocytes (the hypodermis contains50% of body fat). Fat serves as paddingand insulation for the body.

Microorganisms like Staphylococcusepidermis colonize the skin surface. The

density of skin flora depends on regionof the skin. The disinfected skin surfacegets recolonized from bacteria residingin the deeper areas of the hair follicle,gut and urogenital openings


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FUNC

TIONS OF THE

SKIN Protection - an anatomical barrier from pathogens and damagebetween the internal and external environment in bodilydefense; Langerhans cells in the skin are part of the adaptiveimmune system.

Sensation - contains a variety of nerve endings that react to heatand cold, touch, pressure, vibration, and tissue injury.

Heat regulation - the skin contains a blood supply far greaterthan its requirements which allows precise control of energyloss by radiation, convection and conduction. Dilated bloodvessels increase perfusion and heat loss, while constrictedvessels greatly reduce cutaneous blood flow and conserve heat.

Control of evaporation - the skin provides a relatively dry andsemi-impermeable


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Aesthetics and communication - others see our skin and can assess ourmood, physical state and attractiveness.

Storage and synthesis: acts as a storage center for lipids and water, aswell as a means of synthesis of vitamin D by action of UV on certainparts of the skin.

Excretion - sweat contains urea, however its concentration is 1/130ththat of urine, hence excretion by sweating is at most a secondaryfunction to temperature regulation.

Absorption - Oxygen, nitrogen and carbon dioxide can diffuse into theepidermis in small amounts, some animals using their skin for theirsole respiration organ (contrary to popular belief, however, humans donot absorb oxygen through the skin). In addition, medicine can beadministered through the skin, by ointments or by means of adhesive

patch, such as the nicotine patch or iontophoresis. The skin is animportant site of transport in many other organisms.

Water resistance - The skin acts as a water resistant barrier soessential nutrients aren't washed out of the body

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Anatomy and Physiology of the Disease