Integumentary system (skin) The Integumentary system.

Integumentary system (skin)

The Integumentary system

Skin: roles

• 1- Protects against infection, mechanical shock, chemical injury

• 2- Prevents fluid loss• 3- Sensor for touch, pain, temperature• 4- Excretion of sweat• 5- Immunity• 6- Synthesis of vitamin D• 7- Thermoregulation

Integumentary system (skin)• Three layers:- Epidermis: the

outer/superficial protective layer

- Dermis: Deepest and thickest layer of the integumentary system, comprising 2 layers, the papillary and reticular layers

- The “hypodermis” or subcutaneous tissue layer binds the dermis of the skin to the underlying muscle

EpidermisSeveral layers:

-The main layer is located at the base

- formed by the active, dividing cells or keratinocytes

- -The keratinocytes multiply and push up, toward the surface of the skin

- As they move away from the base and the blood supply, they die off, dry

- Left are dried cells rich in keratin, a stringy protein

- They form the upper layer, rich in keratin or corn

This keratin (corn) layer (in addition to an oily secretion) has a number of roles:

Keratin is somewhat water repellent (water proofs your skin)

Integumentary system (skin)

Skin colorDerived from 3 skin pigments:

• Melanin• Carotene• Hemoglobin

• Melanin (brown/black) – brown pigment secreted by the melanocytes. Stimulated by UV exposure to protect the basal layer from UV damages. Increased exposure lead to increased melanin synthesis

• African American and Caucasian have the same number of melanocyte. However, the amount of melanin secreted varies with the human origin and the exposure to UV

Integumentary system (skin)

Note: difference between the melanized cells of the stratum basale between the two skin tones. Also recall how the stratum corneum is transparent.

• Skin color

– Excess melanin:–Freckles = patches of

dense melanin–“liver spots” = sun

spots or age spots – excess melanocyte activity–seborrheic

hyperkeratosis excess growth of keratinocytes

Skin color• Carotene: yellow

pigment found in food (carrot)

• Hemoglobin – red pigment found in the blood– Lack of oxygen (Hb only)

turns the skin blue (cyanosis)

Sun damages

Tatoos

Integumentary system (skin)• Below the epidermis = Dermis

- Variations in the layers forms valleys and grooves, seen on the surface of the skin as fingerprint.

- The collagen fibers are distributed along a certain orientation surgeons tries to cut along the fibers, not across them, to minimize scarring

Integumentary system (skin)

Integumentary system (skin)

The dermis• Contains:• blood vessels• nerve fibers• Touch, pressure, temperature sensors• Muscle, the arrector pili• glands

Hypodermis• Below the dermis

– Subcutaneous tissue (not actually part of the skin).

– Can be thick, if rich in adipose tissue– Tthickness varies with location and

individuals

Epidermal derivatives:

• Even though these structures are mostly located in the dermis they originate from the epidermis:– Hair– Nail– Glands

- sebaceous glands- sweat glands

- apocrine glands- eccrine glands

Epidermal derivatives: Hair• Each hair made of a shaft, root and bulb

– Shaft is what you see (dead cells)– Root is below the skin– Bulb located at the base of the root within the

follicle– Follicle is the sheath of epidermal cells around

the root

• Cells divide in the bulb, push their way up– This is how hair grows in length…cells growing– Roughly 1mm every 3 days

» Speed of growth varies with individual and hair location

Hair

Note how the stratum basale of the epidermis lines the hair follicle.

Hair• Defined lifespan: 3-4 months for eyelash, 3-4 years

for scalp– Each hair is replaced by a new hair that pushes the old

hair shaft out from the follicle» You have the same number of follicles…new hair just

“reboots” the hair bulb to form a new unit.– In-grown hair often results when the new hair shaft

cannot leave the follicle (due to restriction/constriction of the root).

– Hirsutism: excessive body hairHypertrichosis

Hair color• Hair color is define by the type and amount

of pigment made in the stratum basale– Melanin (more = dark)– Red hair = presence of iron (trichosiderin)– Grey-white hair = lack of pigment due to dying

melanocytes (and presence of air bubbles in the shaft)

• Hair shape- round straight hair, oval curly hair

• Hair thickness– - Depends on the size of the follicle and root

Nails• Composed of a compressed layer of

stratum corneum cells

• Hardness derived from dense keratin deposits.

• Sometimes, the edge get stuck under the skin ingrown nail

Sebaceous glands• Derived from the epidermal

cells• Open in the hair shaft• Secrete an oily substance,

the sebum, making the skin water repellent

• Accumulation of sebaceous secretion in a gland lead to the formation of a black head

• If the gland becomes infected acne

Sudoriferous glands: sweat glands• Eccrine sudoriferous gland

– Distributed all over the body (sweaty palms, back, chest etc.)– Non-smelly– Open on the skin

• Apocrine sudoriferous gland– Armpits (axillary) and pubic regions – open into a hair shaft– Smelly sweat– Open into the hair shaft

Sudoriferous glands• Ceruminous glands: ear wax

– Only located in the outer auditory canal» Cerumen = ear wax» For protection of the auditory canal from pathogenic

invasion,» Also to lubricate the tympanic membrane.

Dermal structures

• Arrector pili:– small muscle attached to hair root and

base of epidermis– When pulled hair shaft stands up

goose bumps

• Vascular supply– nourish epidermis, hair root and dermis

itself

Dermal structures: Sensory endings

• Touch, pressure- sense touch and pressure

• Temperature receptors– sense heat and cold

• Pain receptors– Sense tissue damages

Clinical considerations

• Wounds

• Burns

• Skin cancer

• Aging

Wounds• Open skin is an entry door for

bacteria risk of infection.• Gravity depends on depth and area

involved. • Phases of healing:

– Clot formation scab– Inflammatory response– Fibroblasts multiply granulations– Macrophages phagocytize debris– When dermis has filled up, epidermis

can grow to cover the area– If severe wound: scar tissue

Wound examples

Inflammation • 4 cardinal symptoms– Bacteria in the wound

make contact with defense cells such as mast cells mast cells release histamine

– Histamine promotes increased permeability of blood vessels tissue swelling

– Tissue swelling Pain

IInflammation Symptoms of inflammation:- Redness- heat- Swelling-- pain

• Bacteria also attract macrophages which release chemical promoting dilation of the capillaries (=vasodilation) more blood skin area becomes red (redness) and hot (heat)

Burns• Gravity of burns is

determined by surface, depth and location– Surface: law of 9

Burns

• Gravity of burns is determined by

• 1) surface, 2) depth and 3) location

• Depth:– First degree burn:

involves epidermis only redness (erythema) – sun burn - painful

- Skin heals and peals within 10 days no scarring

Burns• Depth:– Second degree burn: upper

dermis involved blister - painful

– Epidermis heals within few days little/no scarring

Burns

• Depth:– Third degree burn:

involves epidermis and entire dermis (and sometimes more)

– Not painful! Why?

Skin tumors (benign and not)• Warts: due to a virus.,

treated by cryosurgery

• Skin cancers– Basal cell carcinoma:

most common, due to UV exposure, arises from basal cells, easily treated

– Squamous cell carcinoma: from cells above basal cells, more invasive

– Malignant melanoma:Due to melanocytes – changing

moles – very invasive

Skin tumors (benign and not)• Skin cancers– Basal cell carcinoma: most

common, due to UV exposure, arises from basal cell,,easily treated

– Squamous cell carcinoma: from cells above basal cells, more invasive

– Malignant melanoma:Due to melanocytes – changing moles –

very invasive

Melanomas• Usually, starts from a

mole

• Watch for changes in shape, height or color of the mole

• Melanomas are one of the deadliest cancers

Aging• Decrease in sebum

secretion dry skin• Decrease in sweat

gland secretion difficulties to cope with heat

• Decrease in elastin fibers wrinkles

• Decrease in adipose tissue in the dermis difficulties to cope with cold