The Skin and Its Parts Integumentary System. A complex association of tissues and cells that play critical roles in maintaining homeostasis. A complex

The Skin and Its PartsThe Skin and Its Parts

Integumentary SystemIntegumentary System

Integumentary SystemIntegumentary System A complex association of tissues and cells A complex association of tissues and cells

that play critical roles in maintaining that play critical roles in maintaining homeostasis.homeostasis.

The largest organ systemThe largest organ system composed of:composed of:

– blood vesselsblood vessels– connective tissue structuresconnective tissue structures– glandsglands– hairhair– nailsnails– nervesnerves– skin (skin (integumentintegument))

The skin’s structure is organized The skin’s structure is organized based on genetic programming based on genetic programming during development.during development.– inborn or inborn or inherentinherent features features

exampleexample nails: nails: the genes for making the genes for making nails only turn on in the upper tips of the nails only turn on in the upper tips of the toes and fingerstoes and fingers

Some flexibility is designed into the Some flexibility is designed into the genetics of skin cells.genetics of skin cells.– envirome or envirome or adaptiveadaptive features features

The integumentary system has genes The integumentary system has genes that allow adaptation to the environment.that allow adaptation to the environment.

examplesexamplescalluses: calluses: calluses on the feet are produced in calluses on the feet are produced in response to walking barefoot on rough response to walking barefoot on rough surfacessurfacesThe callus protects the underlying tissues and The callus protects the underlying tissues and bones from damagebones from damageMany peoples’ skin darkens with regular Many peoples’ skin darkens with regular exposure to the Sun: this prevents sunlight exposure to the Sun: this prevents sunlight from damaging sensitive cells underneath the from damaging sensitive cells underneath the skinskinSkin stretches as the body grows to prevent Skin stretches as the body grows to prevent exposure of internal organs to protection and exposure of internal organs to protection and shrinks as in postpartum recoveryshrinks as in postpartum recovery

Human skin does best under certain Human skin does best under certain environmental conditions:environmental conditions:

temperaturestemperatures above freezing, but not too above freezing, but not too much heat – the body temporarily much heat – the body temporarily compensates for extreme temperatures by compensates for extreme temperatures by adjusting blood flow and glandular activityadjusting blood flow and glandular activity

Skin uses Skin uses sunlightsunlight to carry out some to carry out some functions, but too much causes damagefunctions, but too much causes damage

Optimum Optimum moisturemoisture – too much moisture – too much moisture → → infection, too little moisture → weakens skin’s infection, too little moisture → weakens skin’s ability to be a protective barrierability to be a protective barrier

SkinSkin

Skin is a continuous body covering Skin is a continuous body covering Includes associated structures and Includes associated structures and mucous membranes mucous membranes – anus, mouth, nose, reproductive tractanus, mouth, nose, reproductive tract

mucous membranesmucous membranes – lubricated – lubricated inner linings that secrete mucousinner linings that secrete mucous

The integumentary system is The integumentary system is composed of layered structures composed of layered structures formed through embryonic formed through embryonic developmentdevelopment

epidermis and dermis layers

Skin is found as 2 different types:Skin is found as 2 different types:

1) thick skin1) thick skin palms of handspalms of hands soles of feetsoles of feet thicker epidermis thicker epidermis no hair folliclesno hair follicles

2) thin skin2) thin skin the rest of the bodythe rest of the body

Integumentary DevelopmentIntegumentary Development

Integumentary development Integumentary development anatomy begins 4 – 5 weeks after anatomy begins 4 – 5 weeks after fertilization from 2 embryological fertilization from 2 embryological layerslayers


ectodermectoderm becomes the outermost becomes the outermost layer of skinlayer of skin– starts as simple squamous tissue that starts as simple squamous tissue that

becomes stratified as embryo developsbecomes stratified as embryo develops– some areas of the embryo, ectoderm some areas of the embryo, ectoderm

forms nervous tissue that later becomes forms nervous tissue that later becomes integrated skinintegrated skin

– ectodermal layer doesn’t develop ectodermal layer doesn’t develop further until inner layers of skin formfurther until inner layers of skin form


mesodermmesoderm becomes deeper parts of becomes deeper parts of the skinthe skin– development begins 6-7 weeksdevelopment begins 6-7 weeks– at 8-9 weeks group of stem cells, at 8-9 weeks group of stem cells,

mesenchymemesenchyme, begin maturing, begin maturing


mesenchymemesenchyme embryonic connective tissueembryonic connective tissue star-shaped cellsstar-shaped cells gel-like matrixgel-like matrix

fibroblastsfibroblasts develop from mesenchyme develop from mesenchyme cellscells

secrete collagen fibers that provide secrete collagen fibers that provide strengthstrength


As mesenchyme develops, small As mesenchyme develops, small dents begin to form in the upper dents begin to form in the upper squamous layer squamous layer → body and head hair→ body and head hair


At 10 weeks, small ridges begin to form At 10 weeks, small ridges begin to form between the outer and inner layers of skinbetween the outer and inner layers of skin

large area of contact between layerslarge area of contact between layers prevents separation of layers when skin is prevents separation of layers when skin is

stretched or rubbedstretched or rubbedAt 11 weeks, small nails begin to grow at At 11 weeks, small nails begin to grow at the tips of fingers and toesthe tips of fingers and toesAfter nail formation, special blood vessels After nail formation, special blood vessels begin to form in the inner layers of skin.begin to form in the inner layers of skin.

initiated by secretions, initiated by secretions, angiogenic factorsangiogenic factors, , from newly developing skin from newly developing skin → → angiogenesis formation of blood vesselsangiogenesis formation of blood vessels


At 20 weeks, glandular structures At 20 weeks, glandular structures begin to formbegin to form

inward growths of outermost inward growths of outermost squamous layersquamous layer

may not be functional until after birthmay not be functional until after birth will eventually produce oils and will eventually produce oils and

sweatsweatModel of skin


At 25 weeks, melanoblasts At 25 weeks, melanoblasts differentiate from mesenchymedifferentiate from mesenchyme

At 27 weeks, melanoblasts mature At 27 weeks, melanoblasts mature into into melanocytesmelanocytes– pigment pigment producing cellsproducing cells– not usually functional until after birthnot usually functional until after birth

Nervous tissue structures that Nervous tissue structures that transmit sensations of pain, transmit sensations of pain, temperature, and touch form at this temperature, and touch form at this point of developmentpoint of development


Many genes are involved in the Many genes are involved in the development of skin = many errors development of skin = many errors can occur during developmentcan occur during development

These errors lead to a variety of These errors lead to a variety of problemsproblems

Errors can be due to:Errors can be due to:– genetic defectsgenetic defects– environmental factors that affect environmental factors that affect

devlopment of particular cellsdevlopment of particular cells

The complexity of skin

Comparison of thick and thin Comparison of thick and thin skinskin

epidermis

dermis

pigment – chemical that emits a pigment – chemical that emits a particular particular color when color when exposed to lightexposed to light

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The Skin and Its Parts Integumentary System. A complex association of tissues and cells that play critical roles in maintaining homeostasis. A complex