The Integumentary System

Human Anatomy and Physiology

Types of Membranes

S yn ovia llin es jo in ts ;m ad e o f C T

S erou slin es b od y cavit ies th a t lack op en in g s

to th e ou ts id e ; red u ce fric t ion

M u cou slin es cavit ies an d tu b es th a t

op en to th e ou ts id e o f th e b od y

C u tan eou sorg an o f th e in teg u m en ta ry

sys tem ; aka sk in

M em b ran es

Functions of the Integumentary System

Protective covering Prevents harmful

substances and organisms from entering the body

Reduces water loss from deeper tissues

Regulation of body temperature

Houses sensory receptorsContains immune system cellsSynthesizes vitamin DExcretes small quantities of wasteAbsorption of drugs and other agents

Components of the Integumentary System

SkinHairNailsSebaceous glandsSweat glands

Layers of the Skin

EpidermisDermisSubcutaneous layer (hypodermis)

Thick versus Thin Skin

Thick Skin Palms of hands

and soles of feet Hairless Subject to much

abrasion Thicker epidermis

(has an extra layer)

Thin Skin Found everywhere else

on the body Has hair Lacks one layer of the

epidermis

“Thick” and “thin” are not describing actual depth of tissue!!!

Thickest skin = upper back

Thinnest skin = eyelids

Epidermis

Stratified squamous epitheliumLacks blood vesselsGrows from the bottom layer (stratum basale)Keratinization

Layers of Epidermis

Stratum corneumStratum lucidumStratum granulosumStratum spinosumStratum basaleBasement membrane

Epidermal Layers

Stratum corneum – flattened cells, desicated, anucleate cells, keratinized Water barrier Varies in thickness Thickens with unusual amounts of friction

calluses

Stratum lucidum – in thick skin only, cells in process of keratinization

Epidermal Layers continued…

Stratum granulosum – only a few cells thick, appears granular Cells contain numerous keratin granules

Stratum spinosum – several cells thick, numerous cytoplasmic processes called spines, nuclei elongatedStratum basale – single layer of cells on bottom, contains skin stem cells Cells appear cuboidal or low columnar

Dermis

Epidermal ridges and dermal papillaeIrregular dense connective tissueThicker than epidermisMuscle and nerve fibers, blood vessels, hair follicles, sebaceous glands, and sweat glands2 layers: papillary and reticular

Layers of Dermis

Papillary layer Thinner,

superficial layer Loose CT Contains blood

vessels that serve the epidermis

Contains nerve processes

Reticular layer Varies in thickness,

but generally thicker than papillary layer

Contains thicker collagen and elastic fibers

May contain smooth muscle cells

Subcutaneous Layer/Hypodermis

Loose connective tissue and adipose tissueConnective tissue fibers are continuous with dermisPanniculus adiposus – layer of adipose tissue that insulates and stores energyArrector pili muscles originate here

Cells of the EpidermisKeratinocytes Main cell type Produce keratin

Melanocytes In stratum basale Contain melanin granules

Langerhans cells Involved in contact

dermatitis reactions

Merkel cells In stratum basale Most abundant in

fingertips Sense light touch

Skin Color

There are 3 pigments involved in skin color: melanin, carotene, and hemoglobin.Melanin is the only pigment made by the skin (from tyrosine) and ranges in color from yellow red-brown black.Skin color differences result from the kind and amount of melanin made and retained by the skin cells.All humans have relatively the same number of melanocytes.

Skin Color continued…

Freckles and moles are local accumulations of melanin.A tan is darkening of the skin as a result of increased melanin production, usually in response to prolonged exposure to UV radiation.Carotene is a yelloworange pigment found in certain plant products. It tends to accumulate in the stratum corneum and in the fat of the hypodermis, and it is more obvious when large amounts of carotene-rich foods are eaten.

Skin Color continued…Hemoglobin gives a pinkish hue to fair skin which is most noticeable in Caucasian skin. A more crimson pigment results when the hemoglobin is highly oxygenated. Hemoglobin is found in the RBCs of the dermal capillaries.Hair color is genetically determined and results from the amount and type of pigment secreted by melanocytes near hair follicles.Dark hair has more melanin than light hair. Red hair contains an iron pigment called trichosiderin, and gray hair is a mixture of pigmented and unpigmented hair.

Nerve Supply to the Skin

Free nerve endings found in the epidermis and papillary dermis sense temperature, vibration, pain, etc.Encapsulated nerve endings: Pacinian corpuscles – deep dermis and

hypodermis; sense deep pressure Meissner’s corpuscles – in papillary

region of dermis; sense light touch

HairPresent on all surfaces except for palms, soles, lips, nipples, and parts of external reproductive organsMade of keratinized cellsHair follicleHair papillaHair shaftHair colorArrector pili

Nails

Protective coverings on the ends of fingers and toesNail plateNail bedLunula

Sebaceous Glands

Sebaceous glands are associated with hair folliclesSebumFound everywhere except palms and solesAcne

Sweat GlandsIn dermis or superficial subcutaneous layerEccrine glands

Most numerous Produce sweat on hot days

and during exercise

Apocrine glands Become active at puberty Secretions smell because of

bacterial activity Active during emotional

upset, fright, pain, sexual arousal

Ceruminous glands and mammary glands

Healing of Wounds

Inflammation = normal response to injury or stressEpidermal cutsDeep cuts Blood clots Scabs Scars

Healing of BurnsFirst degree burns Superficial partial-

thickness burn

Second degree burns Deep partial-

thickness burn

Third degree burns Full-thickness burn

Rule of 9s

Aging and SkinEpidermal cells reproduce slower larger and more irregular shapeAge spots – sites of oxidation of fats in secretory cells of apocrine and eccrine glandsDermis reduces wrinkling and saggingDrier skin because of less oil from sebaceous glandsGray or white hair from decreased melanin production

Aging – continued…

Slower hair growth and fewer hair follicles thinner hair and/or hair lossLess blood supply to nail beds impaired growthDiminished sensitivity to pain and pressure because of fewer receptorsFewer sweat glands, fewer dermal blood vessels, and declined ability to shiver decreased ability to control temperatureDiminished ability to activate vitamin D reduced skeletal health