Integumentary System

Functions of Skin

Functions of Skin

• thermoregulation through sweating and blood flow regulation

• protection by keratin, sweat, sebum and melanin

• tactile and thermal sensation

• excretion of water (sweat)

• absorption of lipid soluble substances

• vitamin D synthesis from UV stimulation

Skin

• less complex than other organs

• largest organ in the body and takes up 7% of the total body weight

• consists of the epidermis, dermis and hypodermis

Organs

• group of tissues working together to form certain functions

Epidermis

• more than 1 layer of stratified epithelium

• avascular

• surface consists of dead cells packed with keratin (tough structured protein)

• sparse nerve endings for touch and pain

• 4 to 5 layers of distinct cell types (4 kinds)

Keratinocytes

• main cell type of epidermis that provides structure to skin, hair and nails

• mature cells of keratin

• produce keratin intermediate filaments

• water-proofing (protective function) while also keeping water in

• Keratinized tissue = dry

• Non-keratinized tissue = wet

Melanocytes

• type of cell in epidermis that are mature cells of melanin

• produce pigments eumelanin/pheomelanin giving skin and hair its colour

• protects from harmful UV rays

Merkel Cells

• small amount of cells in epidermis

• associated with underlying nerve fibers

• allows for sense of touch

Langerhans Cells or Dendrite Cells

• type of cell in epidermis

• macrophages that originate in bone marrow

• stand guard against toxins and pathogens

• alerts the immune system

Layers of the Epidermis

1. Stratum Corneum

2. Stratum Lucidum

3. Stratum Granulosum

4. Stratum Spinosum

5. Stratum Basale

Stratum Basale

• last layer of the epidermis consisting of cuboidal or columnar stem cells

• sits on top of the basement membrane

• continuously produce keratinocytes

• contains merkel cells and melanocytes

Stratum Spinosum

• superficial to stratum basale consisting of many layers of keratinocytes

• upper layers of cells become flattened and lose the capacity to divide

• produces most of the keratin

• contains Langerhans cells that are hard to see

Stratum Granulosum

• middle layer of the epidermis

• consists of 3-5 layers of flattened keratinocytes undergoing apoptosis (programed cell death)

• none of the cells above this layer receive any nutrients from blood vessels in dermis and therefore die

• secrete a substance between cells that acts as a waterproofing agent

Stratum Lucidum

• second layer of the epidermis found only in thick skin

• consists of a few rows of flattened keratinocytes

Stratum Corneum

• outermost layer of the epidermis

• many layers of dead keratinocytes

• cells are completely filled with keratin to protect skin against abrasion and penetration, also makes the skin waterproof

• layer becomes very prominent in thick skin (soles of feet and fingertips)

Dermis

• well supplied with blood vessels, glands, nerve endings

• hair follicles and nail roots embedded here

• smooth muscle attached to hair follicles

• in face, skeletal muscle attached to dermal collagen fibers

• important in facial expression

Function of the Dermis

• friction ridges that results from epidermal ridges/dermal papillae

• stretch marks that result from tearing of elastic fibers when the skin stretches

• cleavage lines, tension lines that run parallel to collagen in dermis

Cleavage Lines

• important for surgeries

• incisions across these lines heal more slowly than incisions along the lines

Hypodermis

• also known as the subcutaneous layer

• protects underlying structures

• contains fat cells for thermal regulation and storing energy

Hair

• very important accessory structure of the integumentary system

• slender filaments of keratinized cells that grow from follicles in the dermis or hypodermis

• found almost everywhere on the body

Arrector Pili Muscle

• cause goosebumps when the body temperature lowers

Lanugo Hair

• fine, downy, unpigmented hair of a fetus that usually disappears prior to birth

• can appear in malnourished individuals and is a diagnostic sign of eating disorders

Vellus Hair

• finer hair than lanugo but is unpigmented

• usually on children and adult women

Terminal Hair

• longer, course and pigmented hair

• replaces some vellus hair

• develops after puberty

• more

Sebaceous Glands

• oil glands that secrete sebum

• usually connected to hair

• keeps the hair and skin soft

• has antibacterial properties

Sudori Ferous Glands

• sweat glands that are simple, coiled tubular *complete with madis notes

Ceruminous Glands

• modified sweat glands in the external ear

• produce cerumen (earwax) to trap dust and small particles before they enter the ear

• antibacterial

Mammary Glands

• accessory structure of the skin

• modified apocrine sweat glands that produce a richer secretion through ducts to the nipple

Skin Colour

• determined by hemoglobin, melanin and carotene

Hemoglobin

• blood pigment that causes light complexions to look pink or blue if there is a lack of oxygen

Melanin

• pigment produced by melanocytes

• increases in people exposed to more UV rays but everyone has the same number

• in darker-skinned people, more melanin is produced and it breaks down slower

• melanin disperses into adjacent keratinocytes that protects nuclei from further UV exposure, the skin lightens as keratinocytes are sloughed off at the skin surface

Carotene

• yellow-orange pigment from food that builds up in the skin

Cyanosis

• often observed in newborns

• blueness of skin resulting from a lack of oxygen

Erythema

• increased blood flow leads to abnormal redness of the skin

• can be caused by anger, exercised or embarrassment

Pallor

• opposite of erythema when so there is so little blood flow that the white colour of dermal collagen shows through

Juandice

• yellowing of the skin and whites of highs due to high levels of bilirubin in the blood

Aging

• epidermis gets thinner and harder to repair when damaged

• amount of collagen in dermis decreases (reduced skin firmness)

• elasticity of the tissue decreases (appearance of wrinkles)

• cumulative UV exposure increases risk of skin cancer

• hair thins, nail growth slows, glandular secretions decrease

Life Cycle of a Keratinocyte

• mitosis of stem cells -as new cells form, older ones are pushed towards the surface

Psoriasis

• skin disorder of the epidermis where cells divide more quickly than normal (7-10 days)

• causes abnormal development of keratin

• treatments are designed to decrease the rate of cell division

Fungal Infections

• can cause itching, redness and cracking of the skin

• more bacteria can enter and cause an infection

Warts

• local growths in the skin that are caused by a HPV infection

• typically disappears on their own with time

Acne

• can be caused when sebaceous glands are stimulated by elevated levels of hormones when the ducts are more likely to clog

Eczema

• general term for many types of skin inflammation when the barrier of the skin doesn't work properly

Skin Cancer

• usually isolated to the upper regions of the skin

• three different kinds

Basal Cell Carcinomas

• occurs on sun-exposed regions of the skin

• rarely spreads to other regions and is rarely fatal

Squamous Cell Carcinomas

• will spread more easily, especially if it is found on the lips or ears

• appears as a red, crusted or scaly patch

Melanoma

• spreads easily and is the most serious

• asymmetrical, irregular border