The Integumentary System chpt. 5

Integumentary system

(integument)

– Largest system of the body

• 16% of body weight

• 1.5 to 2 m² of surface area

Two major parts of the Integument

– Cutaneous membrane (skin)

– Accessory structures

What are the components of the Cutaneous membrane?

– Epidermis (outer layer)

• superficial epithelium

– Dermis (inner layer)

• Connective tissues

Accessory structures

– start in the dermis —>Extend through the epidermis to skin surface

• Hair and hair follicles

• Exocrine glands

• Nails

What does the Integument also have thats special?

blood vessels & sensory receptors

• blood vessels through the dermis make it vascularized

Subcutaneous layer

(hypodermis)

– loose areolar connective tissue

– under the dermis

• Not considered part of the integumentary system

Functions of the integument

– Protection of underlying tissues & organs

– Excretion of salts, water, & organic wastes (sweat)

– Maintenance of normal body temperature (constrict/dialate)

– Production of melanin (darknesss)

– Production of keratin (hardness)

– makes vitamin D3

– Storage of lipids/fat

– Detection of touch, pressure, pain, etc. (senses)

– Coordination of the immune response

Epidermis

– Stratified (stacked) squamous epithelium

– Avascular, like all epithelia (no blood vessels)

– Nutrients & oxygen diffuse (arrive) from capillaries in the dermis!

Cells of the epidermis

Keratinocytes

Keratinocytes

cell of the epidermis;

• The body’s most abundant epithelial cells

• have large amounts of keratin (hard)

• resist to tearing

• in basement membrane

Two types of skin

Thick skin & Thin skin

Thin skin

• Covers most of the body

• Has four layers of keratinocytes

(Doesn’t have the stratum lucidum)

Thick skin

• Covers the palms of the hands and soles of the feet

• Has five layers of keratinocytes

(includes thinnest layer; stratum lucidum)

**joe burns feet in sand; THICK skin is on bottom of the feet

What are the 5 layers of keratinocytes in thick skin, from deepest to surface?

• Stratum corneum (SURFACE)

• Stratum lucidum (only in THICK skin)

• Stratum granulosum

• Stratum spinosum

• Stratum basale (DEEPEST) READ FIRST GO UP

Stratum basale

Deepest stratum; (stratum germinativum)

– Attached to basement membrane by hemidesmosomes

– Forms a strong bond between epidermis & dermis

– Contains epidermal ridges

– Has many basal cells, or germinative cells

Epidermal ridges

ridges formed by the Stratum basale that lie on top of the dermal papillae (egg crates) belonging to dermis; go tgt like puzzle to form Epidermis & Dermis strong bond

Basal cells

(germinative cells); in stratum basale

• Stem cells that divide to replace superficial keratinocytes; cells that have died/shed on epithelial surface

Specialized structures of stratum basale

• Tactile discs

• Melanocytes

Tactile discs

in stratum basale;

• Tactile (Merkel) cells w/ sensory nerve ending

• Found in hairless skin

• Respond to light touch & pressure.

Melanocytes

in stratum basale; contain the pigment melanin

Stratum spinosum

• “spiny layer” looks like pincushion w needles

• 8-10 layers of keratinocytes bound by desmosomes

• Cells look spiny (spikes or prickly) in histological sections

• made by division of cells in stratum basale (go up to form new layer), cells continue dividing in this layer

• Contains dendritic (Langerhans) cells; active in immune response

Stratum granulosum

• “granular layer”

– 3-5 layers of keratinocytes; produced from cells of stratum spinosum (went up to make)

– Most cells stop dividing & produce protiens: Keratin & Keratohyalin (mix=deyhradtion)

– After production of proteins, cells die (bc of dehydration)

Keratohyalin

made by Stratum granulosum;

– Forms dense granules

– Promotes cellular dehydration & cross-linking of keratin fibers

results in the keratinocytes dying

Stratum lucidum

• “clear layer”; thinnest layer

• Covers stratum granulosum; on top

• in thick skin only (palms & soles)

Stratum corneum

• “horny layer”

– Exposed surface of skin; water resistant

– 15 to 30 layers of keratinized cells (from Keratinization)

– New cells move from stratum basale to stratum corneum in 7 to 10 days

– Exposed cells are shed after two weeks

Keratinization

cornification; the formation of protective layers of cells filled with keratin

Insensible perspiration

way water is lost from the skin

• Water diffuses across stratum corneum & evaporates from skin

• 500 mL per day

• Rate increases if stratum corneum is damaged (e.g., from burns)

**water loss can’t be felt/seen

Sensible perspiration

way water is lost from the skin; milky white appearance

• Water excreted by sweat glands

**very aware; hot=sweat (sensible)

Dermis

– Located between epidermis & subcutaneous layer

– Anchors epidermal accessory structures (e.g., hair follicles & sweat glands)

Components of the Dermis

• Papillary Layer (outer)

• Reticular Layer (deeper)

Papillary layer

outer layer of dermis;

– Consists of areolar tissue

– Contains capillaries, lymphatic vessels, & sensory neurons (receive info & sense things)

– Named for dermal papillae that connect between epidermal ridges (hills)

– Becomes inflamed in dermatitis

Dermatitis

• Caused by infection, radiation, mechanical irritation, or chemicals (e.g., poison ivy)

• May produce itching or pain of papillary layer

Reticular layer

– Consists of dense irregular connective tissue

– has collagen & elastic fibers

– dermis has all cells of connective tissue proper

How does the Dermal (dermis) keep its strength and elasticity

• Collagen Fibers

• Elastic fibers

• skin turgor

Collagen fibers

• Very strong, resist stretching

• Easily bent or twisted

• Limit flexibility to prevent tissue damage

Elastic fibers

• Permit stretching & then recoil to original length

• Provide flexibility

Skin Turger

Fibers and water provide flexibility & resilience; dehydrationg = loss of skin turger

Types of Skin damage where elasticity may be lost?

• Dehydration (reversible)

• Aging

• Hormones

• UV radiation

– Excessive distortion of skin from pregnancy or weight gain may cause stretch marks

Tension lines

(cleavage lines)

– parallel bundles of collagen & elastic fibers in the dermis

– Resist forces applied to skin

– A cut made parallel to a tension line remains shut, heals well

• A cut at a right angle pulls open and scars=more scarring

**doctors try to cut parallel to line to support good healing

How does the Dermal/dermis get its blood supply?

• Cutaneous plexus

• Subpapillary plexus

Cutaneous plexus

• Deeper network of arteries & blood vessles along the reticular layer (bottom)

bleed bleed bleed alot bc more blood

Subpapillary plexus

• Network of small arteries in papillary layer (closer to top)

• supply to capillary loops that line epidermis-dermis boundary (epidermal ridgees; then capillaries drain into small veins that lead to larger veins in subcutaneous layer

Contusion

bruise; Caused by damage to blood vessels in dermis that rupture

In the Dermis the Nerve fibers in skin do what?

• Control blood flow

• Adjust gland secretion rates

• Monitor sensory receptors

Dermis specialized receptors?

• Tactile (Meissner) Corpuscles

• Lamellar (Pacinian) corpuscles

Tactile (Meissner) Corpuscles

sensory receptors in the skin that detect light touch; in dermal papillae

Lamellar (Pacinian) corpuscles

sensory receptors that detect deep pressure and vibration

Nails

– Protect tips of fingers & toes

– Made of dead cells packed with keratin

– Metabolic disorders can change nail structure

• ex: pitted nails may result from psoriasis

Structure of a nail

• Nail body

• Sides of nails

• Skin beneath the distal free edge (nail that grows past nail bed) of the nail is the hyponychium (tissue under tip of the nail)

Nail body

• Visible portion of the nail

• Covers the nail bed

Sides of nails

• Lie in lateral nail grooves; indented side part

• Surrounded by lateral nail folds; outside skin that folds in on sides

Nail production

– happens in an epidermal fold called nail root

– The visible nail emerges from eponychium (cuticle) under part of nail root

– Near the root, blood vessels are obscured creating the Lunula (pale crescent at the base of the nail)

Effects of aging on skin

– Epidermis thins

– Dermis thins & elastic fiber network shrinks

– Number of dendritic cells decreases

– Vitamin D3 production declines

– Function of hair follicles declines

– Melanocyte & glandular activities decline

– Blood supply to dermis is reduced

– Sex-specific hair & body fat distribution fades

– Repair rate slows