Chapter 5: Integumentary System

Integumentary system

The skin (integument), hair, nails and cutaneous glands

Skin

largest organ of the body

Epidermis

Epithelium of skin, superficial, avascular, and sparse nerve endings

Dermis

Fibrous connective tissue of the skin, vascular, rich in collagen fibers and contains cutaneous glands, hair follicles, arrector muscles and nail roots

Hypodermis (subcutaneous fat layer)

Connective tissue just underneath the skin (deep)

True skin layers

epidermis and dermis

Thick (acral) skin location

Palms, front of fingers, soles and plantar toes

Acral skin characteristics

Hairless, no sebaceous glands and sweat (thin/wattery)

Acral skin function

adaptive for high friction

Thin skin location

Covers most of the body

Thin skin characteristics

Hairy, has both sebaceous oil glands and sweat glands

Functions of the skin

- resistance to trauma and infection

- water retention

- synthesis of vitamin D

- sensation

- thermoregulation

- nonverbal communication

Keratinized stratified squamous epithelium

Superficial cells are dead and is much thicker on acral skin

Avascular

Nutrients must diffuse from deeper connective tissue

Cells of the epidermis

Keratinocytes, stem cells, tactile (merkle) cells, dendritic (langerhans) cells and melanocytes

Keratinocytes

Synthesize keratin, vast majority of epidermal cells (found in many layers)

Stem cells

Divide and produce keratinocytes, and only in stratum basale

Melanocytes

Make melanin and is located in the stratum basale

Melanin

Taken up by keratinocytes and used to protect their DNA from UV rays

Tactile (merkel) cells

Touch receptors that join with nerves and only found in stratum basale

Dendritic (langerhans) cells

Immune surveillance and found in the stratum spinosum and stratum granulosum (middle layers)

Layers (Strata) of the Epidermis

stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum basale -> dermis

Mnemonic for layers of epidermis (superficial to deep)

Come, Let's Get Some Bitches

Stratum basale

A single layer of cuboidal/columnar cells that rest on the basement membrane is the primary site of mitosis, consists of stem cells, keratinocytes, melanocytes, and tactile cells.

stratum spinosum (spiny layer)

Many layers of keratinocytes (shrunken in fixed tissues but attached via desmosomes) and progressively get flatter as they get further from the dermis. Contain a lot of dendritic cells.

stratum granulosum

Two to five layers of cells with dark-staining keratohtalin granules and scanty in thin skin

Stratum lucidum

clear, featureless, narrow zone that is only in thick skin and the cells lack organelles

stratum corneum

several layers of dead, scaly keratinized cells on the surface of the skin (flakes off -> corn flakes!)

Layers of the dermis

papillary layer and reticular layer

papillary layer of dermis

superficial/thin layer of the dermis that forms dermal papillae (loose areolar connective tissue) and is rich in blood vessels

reticular layer of dermis

dense irregular connective tissue and the remaining four fifths of the dermis

Striae (stretch marks)

Stretching of the dermal collagen

Hypodermis

Not a true layer of the skin, located deep to the dermis, contains adipose (subcutaneous fat) and areolar tissue

Functions of hypodermis

Energy storage, thermal insulation and connections to deeper tissue

Cyanosis

bluish discoloration of the skin due to lack of oxygen (poor blood supply)

Erythema

Redness due to increased blood flow (ex. superficial skin infection)

Pallor

pale or ashen, reduced blood flow (decreased blood pressure and poor circulation)

Albinism

white skin due to genetic lack of melanin

Jaundice

Yellowing of skin due to liver dysfunction (bilirubin).

Hematoma

bruise (blood leaking under the skin)

Friction ridges of fingertips

aid in sensitivity to texture and the ability to grasp (cause fingerprint patterns)

Flexion lines

Where skin near joint attaches to deeper tissue

Freckles

flat melanized patches that vary with heredity and exposure to the sun (UV)

Mole (nevus)

Elevated patch of melanized skin

"Beauty marks"

Hemangiomas (birthmarks)

discolored skin caused by benign tumors of capillaries

Hair (pilus/pili)

An accessory organ of the skin and is composed of a filament of keratinized cells that grows from the hair follicle on most thin skin

Where does hair not grow?

Lips, nipples, parts of genitals and distal segments of fingers

downy hair (lanugo)

Fine, unpigmented hair of fetus

Vellus hair

Fine, unpigmented hair of children (except eyebrows, eyelashes and scalp), (2/3) women, (1/10) men.

Terminal Hair

Coarse, pigmented and found on the eyebrows, eyelashes and scalp pre-puberty and axillary, pubic, facial (men), and trunk/limb regions after puberty

Scalp hair

heat retention and sunburn protection

Beard, pubic, and axillary (armpit) hair

Advertises sexual maturity; associated with apocrine scent glands in these areas and modulates the dispersal of sexual scents (pheromones) from these glands

guard hairs (vibrissae)

help keep foreign objects out of nostrils and auditory canal; eyelashes help keep debris from eyes

Eyebrows

enhance facial expression and protect eyes from glare (sun) and perspiration

Hair shaft

visible part of the hair

sebaceous glands

secrete sebum (oil) into the hair follicles where the hair shafts pass through the dermis

Hair receptor

sensory nerve fibers entwining follicles

Hair root

The part of the hair located below the surface of the epidermis.

apocrine sweat glands

produce true sweat plus fatty substances and proteins; found in the axillary (armpit) and anogenital areas of the body

Hair matrix

actively dividing area of the hair bulb that produces the hair

Hair bulb

Lowest part of a hair strand; the thickened, club-shaped structure that forms the lower part of the hair root.

Hair buldge

contains stem cells for follicle growth and capillaries for blood supply

Arrector muscle

makes hair stand on end (cold) within the follicle structure of wool and mohair

Hair medulla

The central core of a hair, consisting of large cells and air spaces

Hair cortex

Middle, thickest portion of a hair shaft

dermal papilla

small cone shaped elevation located at the base of the hair follicle that fits into the hair bulb

Hair texture

straight hair (round cross section), curly hair (flattened cross section)

Hair color

Dependent on pigment within the cells of the cortex

Nails

Derivative of stratum corneum, composed of thin, dead, scaly cells with parallel rows of keratin.

Primate nails

Flat nails (as opposed to claws) for easier manipulation

Nail plate

free edge, nail body, nail root

Nail body

visible part of the nail

Nail root

fastens the nail to the finger or toe by fitting into a groove in the skin

Nail fold

Fold of normal skin that surrounds the nail plate.

Nail groove

separates nail fold from nail plate

Nail bed components

hyponychium, nail matrix, lunule/lunula and eponychium (cuticle)

Hyponychium

Skin between the free edge and fingertip of the natural nail

nail matrix

responsible for nail growth

Lunule/Lunula

is the white crescent located at the proximal end of the nail

Eponychium (cuticle)

narrow zone of dead skin overhanging proximal end of nail, keeps out bacteria and infectious pathogens

Apocrine gland location

Groin, anal region, axilla, areola and beard

apocrine sweat glands

Ducts open into hair follicles, produce sweat with fatty acids (bacterial metabolism of those fatty acids causes oder) and respond to stress/sexual stimulation. Develop during puberty.

Eccrine (merocrine) sweat glands

Numerous, widespread, and especially abundant on palms, soles, and forehead. Simple ducts lead to pores at skin surface and produce watery perspiration to cool body (contains some wastes found in urine).

Sebaceous glands

Produces oily secretion called sebum, opens into hair follicle, holocrine secretion, and keep skin and hair from becoming brittle.

ceruminous glands

modified sweat glands, located in external ear canal, secretes cerumen (earwax) to keep eardrum pliable, waterproof and kills bacteria/coats guard hairs.

Mammary glands

Produces milk and glands develop during pregnancy and lactation (otherwise scant). Is a modified apocrine gland.

Senescence (age-related degeneration)

-Hair turns grayer, thinner

-Melanocyte stem cells die out

-Mitosis slows down

-Dead hairs not replaced

-Atrophy of sebaceous glands

-Skin becomes thinner and more translucent

Skin and blood supply with aging

- Fewer and more fragile vessels

- Rosacea (dilated blood vessels that cause reddened areas)

- Increased bruising

Thermoregulation

Vulnerability to hypothermia and heat stroke

Acne

Inflammation of the sebaceous glands, especially beginning at puberty; the follicle becomes blocked with keratinocytes and sebum and develops into a blackhead (comedo) composed of these and bacteria (continued inflammation of follicle results in pus production and pimples)

Dermatitis

Any inflammation of the skin, typically marked by itching and redness, is often contact dermatitis, caused by exposure to toxins such as poison ivy

Eczema

itchy, red, "weeping" skin lesions caused by an allergy, usually beginning before age 5; may progress to thickened, leathery, darkly pigmented patches of skin

Psoriasis

Recurring, reddened plaques covered with silvery scale; sometimes disfiguring; possibly caused by an autoimmune response; runs in families

Ringworm

A fungal infection of the skin (not a worm) that sometimes grows in a circular pattern; common in moist areas such as the axilla, groin, and foot.

Rosacea

A red rashlike area, often in the area of the nose and cheeks, marked by fine networks of dilated blood vessels; worsened by hot drinks, alcohol, and spicy food

Warts

Benign, elevated, rough lesions caused by human papillomaviruses (HPV). Common warts appear most frequently in late childhood on the fingers, elbows, and other exposed areas of skin. Plantar warts occur on the soles and venereal warts occur on the genitals. Warts can be treated by freezing with liquid nitrogen, electric cauterization (burning), laser vaporization, surgical excision, and some medicines such as salicylic acid.

Skin cancer

Induced by UV rays (both natural and tanning beds) , elderly and fair-skinned most common

Types of skin cancer

basal cell carcinoma, squamous cell carcinoma, malignant melanoma

Basal cell carcinoma

Most common, least dangerous, rarely metastasizes, arises in stratum basale and invades dermis

Squamous cell carcinoma

- Arises from keratinocytes of the stratum spinosum

- can metastasize to lymph nodes

- can be fatal