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Integumentary System

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Basics of Epithelial Tissue • Sheet of cells that covers a body surface or lines a

body cavity – Covering and Lining: outer layer of skin, inner and

outer lining of most organs and body cavities – Glandular: creates the glands; one or more cells that

make and secrete an aqueous fluid

• Barrier that most substances received by or given off from the body must pass through

• Rest upon and supported by connective tissue • Avascular (no blood supply), but innervated (has

supplied by nerve fibers) – Nourished by blood vessels in the underlying

connective tissue

Functions of Epithelial Tissue

• Protection

• Absorption

• Filtration

• Excretion

• Secretion

• Sensory Reception

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Coverings and Linings • Continuous multicellular sheets composed of at least 2

primary tissue types – Epithelium bound to underlying connective tissue proper

• Cutaneous Membrane: skin – Organ system consisting of keratinized epithelium

(epidermis) attached to a layer of dense irregular connective tissue (dermis)

• Mucous Membranes: line body cavities that open to the exterior – Moist membranes bathed in secertions (or urine)

• Serous Membranes: found in closed body cavities – Thin, clear serous fluid that lubricates the membranes and

surrounding organs

Overview

• Skin is the largest organ in the body

• Accounts for about 7% of total body weight in adult

• Aka, Integument = “covering”

• Composed of two distinct regions: epidermis and dermis ( 3rd hypodermis)

– Each region of epidermis consists of several layers; each layer is called a stratum

Integumentary System: Functions

• Protection

• Body Temperature Regulation

• Cutaneous Sensation

• Metabolic Functions

• Blood Reservoir

• Excretion

• Absorption

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Functions: Protection • Chemical Barriers

– Skin secretions—low pH (aka, acid mantle); natural antibiotics

– Melanin—barrier preventing UV damage

• Physical/Mechanical Barriers

– Continuity of skin

– Keratinized cells—hard, “shell-like” barrier

• Biological Barriers

– Immune cells in both epidermis and dermis; i.e., dendritic cells in epidermis, macrophages in dermis

Functions: Body Temperature Regulation

• Body Temperature Rises – Nervous system stimulates dermal blood vessels to dilate – Sweat glands are stimulated into vigorous secretory

activity – Visible output of sweat is called sensible perspiration

• Body Temperature Falls – Dermal blood vessels constrict – Warm blood bypasses skin temporarily – Skin temperature drops to external environment

temperature – Passive heat loss from body is slowed, conserving body

heat

Functions Continued • Cutaneous Sensation

– Receptors part of the nervous system located in skin that respond to stimuli arising outside the body (touch, pain)

• Metabolic Functions – Vitamin D production when exposed to UV from the sun – Keratinocyte enzymes can “disarm” many cancer-causing

chemicals that penetrate epidermis

• Blood Reservoir – Dermal vascular supply can hold about 5% of the body’s entire

blood volume

• Excretion – Nitrogen-containing wastes (i.e., ammonia, urea, and uric acid) are

eliminated from the body in sweat

• Absorption – Oxygen, Nitrogen, Carbon Dioxide, Nicotine, anything lipid soluble

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Epidermis

• Outer part of skin

• Composed of four to five strata depending on location (i.e., thickness of skin)

• Deep to Superficial – Stratum Basale

– Stratum Spinosum

– Stratum Granulosum

– Stratum Lucidum

– Stratum Corneum

Stratum Basale (Basal Layer)—

• aka, Stratum Germinativum- deepest layer of epidermis – In this layer the cells of the epidermis “germinate”

or are formed • Cells undergo rapid division

• Consists of a single row of the youngest Keratinocytes

• Located at the junction between the epidermis and dermis

Stratum Spinosum (Prickly Layer)—

• Between the Stratum Basale and Stratum Granulosum

• Cells start to round up like little balls

– cells change shape, dehydrate, and protrude into the other layers from here—hence the name from the spiny architecture of this layer

• Melanin granules and Langerhans’ cells (non-fixed) are abundant in this layer

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Stratum Granulosum (Granular Layer)

• Between Stratum Spinosum and Stratum Corneum

• Here is where keratin production occurs – stratum gets its name from granules of keratin found

there

– Keratin - a tough, durable protein that is secreted and fills this stratum for protection • holds up to lots of wear-and-tear and waterproofs the body

• actual protective mechanism in the epidermis

• 3-5 cell layers in which drastic changes in keratinocyte appearance occurs

Stratum Lucidum (Clear Layer)— • Between Stratum Granulosum and Stratum

Corneum in THICK skin only

• Protects soles of feet and palms of hands from abrasion

– Occurs in reposne to pressure

• Thin transparent band that contains no pigment

– A few rows of flat, dead keratinocytes

Stratum Corneum (Horny Layer) • Outermost layer of keratinized cells

– dead cells that have flattened out

• Varying ages of cells are found in this layer with oldest near the surface and youngest closest to the layer below. – cells will remain there for two to four weeks until

they are lost or washed off.

• These cells are held together by very strong cellular connections called tight junctions and desmosomes – Peel off in sheets when you get sunburned.

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Dermis • The inner subdivision of skin

– Contains strong, flexible connective tissue

• Serves several functions

– Makes Sweat (Sudoriferous Glands)

– Secretes Oils (Sebaceous Glands)

– Gives rise to Hair & Nails

– Contains many sensory receptors and blood vessels

Dermis

• Contains two types of connective tissue fibers

– Collagen

• Gives skin strength and resistance to stretching

– Elastin

• Allows your skin to stretch and then recoil back to normal length

Dermis • Two Layers

• Papillary Layer—forms projections into the epidermis

– Contains sweat and oil glands, hair follicles, blood vessels, lymph vessels, and the sensory nerves that sense changes on the surface of the epidermis

• Reticular Layer—innermost layer of dermis

– Contains the network of collagen and elastic fibers that gives skin its properties of strength and flexibility

– 80% of the thickness of skin

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Hypodermis

• Subcutaneous tissue just deep to the skin; aka, superficial fascia

• Adipose tissue and areolar connective tissue

• Anchors skin to the underlying structures

– mostly muscles

• Strictly speaking, this is not part of the skin, but it shares some of the skin’s protective functions.

Skin Color • Determined by the amount of melanin produced

– darker skin = more melanin production

• Melanocytes produce melanin – located between the epidermis and dermis.

• Brown pigment serves two important purposes – Primary way skin gets its color

– Protects from harmful UV rays

• 2 Additional Pigments – Carotene: yellow to orange pigment (palms and

soles)

– Hemoglobin: reddish pigment yields pinkish hues

Glands Associated with Skin: Sweat • Exocrine Glands = glands that secrete through a

tube/duct onto the surface; generally, have a local effect.

• Sweat (Sudoriferous) Glands – Sweat is composed mostly of water (99%); 1% =

potassium ions, lactic acid, ammonia, and sodium chloride (making sweat taste salty)

• Types of sweat glands – Merocrine: thin sweat

– Apocrine: thick sweat

– Ceruminous: cerumen (ear wax)

– Mammary: milk during lactation

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Merocrine Glands • Most numerous on the skin

• Produce watery perspiration that cools your body temperature and aids in excretion

• Most abundant on the soles, palms, and forehead

• On average, you will sweat five hundred milliliters per day without realizing it

– With heavy exercise, you could lose up to one liter of sweat per hour.

Apocrine • Associated with hair follicles

– Help reduce friction between the hair follicle and the surrounding skin.

• Anogenital and axillary regions, areola, beard region of men

• Scents associated with body odor

– particularly active with stress and sexual stimulation

Sebaceous (oil) Glands • Produce an oily secretion called sebum

– keeps the skin and hair supple and prevents it from becoming dry, brittle, and scaly

• Acne is a condition in which the sebaceous glands ducts become blocked

– secretions accumulate, and a bacterium colonizes the area

– genetic predisposition, or by hormone fluctuations

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Hair • One hair is called a pilus; many hairs are called pili • Filamentaous strands of dead keratinized cells

produced by hair follicles – hard keratin- tougher and more durable than the soft

keratin of the skin

• Hair originates in the dermis of the skin at the bulb • Composed of three layers – core called a medulla,

cortex, outermost cuticle • Pigmented by melanocytes at the base of the hair

and transferred to the cells of the cortex – Yellow, brown, black – Red hair also has an iron-containing pigment called

trichosiderin.

Hair Function and Distribution • Functions

– Maintain warmth

– Alert body to insects on skin

– Guarding scalp against heat loss, sunlight and physical trauma

• Hair is distributed over the entire skin surface except

– Palm, soles, lips, nipple and portions of external genitalia

Nails • Scale-like modification of the epidermis

• Forms a clear protective covering

• Changes in nail appearance may help diagnose certain conditions

– Yellow-tinged nails = respiratory or thyroid gland disorders

– Yellow-tinged and thickened nails = fungal infection

– Outwardly concave nail (spoon nail) = iron deficiency

– Horizontal lines (Beau’s Lines) = malnutrition

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Skin Cancer • 3 Major Types of Skin Cancer

– Basal Cell Carcinoma: cells of Stratum Basale proliferate and invade the dermis and hypodermis

• Least malignant, most common

– Squamous Cell Carcinoma: arises from keratinocytes of the Stratum Spinosum

• Scalp, ears, lower lip

– Melanoma: cancer of melanocytes

• Most dangerous – highly metastatic

Melanoma ABCD (E) Rule

• Asymmetry: two sides of pigmented area don’t match

• Border: irregular and exhibits indentations

• Color: pigmented area is black, brown, tan and sometimes red or blue

• Diameter: larger than 6mm (pencil eraser)

• Elevation: raised

Burns • Critical if…

– 25% of the body has second degree burns

– 10% of the body has third degree burns

– Third degree burns on face, hands, feet

• First Degree: only the epidermis

• Second Degree: epidermis and upper regions of the dermis

• Third Degree: entire thickness of the skin is damaged – Painless because the nerves have been damaged

– Dehydration, infection

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Integumentary System

Picture Slides

3 Layers Become the 4 Tissues

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Epithelial Tissue - Covering

Connective Tissue - Support

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Skin: More Than Epithelial Cells

Squamous Cell Epithelium

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Layers of Epidermis

Layers of the Dermis

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Hypodermis

Sweat Glands

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Sebaceous Glands

Hair

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Nail

Skin Cancer

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