A&P - 5.1 Layers of the Skin

integumentary system

skin and its accessory structures

functions of the integumentary system

• protection - of underlying tissues and organs against impact, abrasion, fluid loss, and chemical attack

• excretion - of salts, water, and organic wastes by integumentary glands

• maintenance of normal body temperature - through either insulation or evaporative cooling, as needed

• production of melanin - which protects underlying tissue from ultraviolet radiation

• production of keratin - which protects against abrasion and serves as a water repellent

• synthesis of vitamin D₃ - a steroid that is subsequently converted to calcitriol, a hormone important to normal calcium metabolism

• storage of lipids - in adipocytes in the dermis and in adipose tissue in the hypodermis

• detection - of touch, pressure, pain, and temperature stimuli, and the relaying of that information to the nervous system

introduction to skin

• most accessible organ

• skin (integument) accounts for approximately 16% of your total body weight

• skin’s surface is constantly worn away, attacked by micro-organisms, irradiated by sunlight, and expose to environmental chemicals

integument

• a tough outer protective layer

• the tissue surrounding an organism’s body or an organ within, such as skin

layers of skin

• two main layers:

  • epidermis - made of closely packed epithelial cells

  • dermis - made of dense irregular connective tissue that houses blood vessels, hair follicles, sweat glands, and other structures

• hypodermis - beneath the dermis lies the hypodermis, which is composed mainly of loose connective and a lot of adipose tissue

epidermis

• outermost tissue layer of the skin

• composed primarily of keratinocytes arranged into layers called strata

• image shows the difference between thin and thick skin

  • thin skin epidermis has 4 strata layers

  • thick skin epidermis has 5 strata layers (palms and soles)

keratinocytes

cell that produces keratin and is the most predominant type of cell found in the epidermis

strata (layers) of the epidermis

• stratum corneum

• stratum lucidum

• stratum granulosum

• stratum spinosum

• stratum basale

stratum corneum

• the “horny layer”; outermost layer (most superficial layer)

• 15-30 layers of dead keratinized cells (corneocytes) held together by desmosomes

  • corneum; dead skin falling off

• water resistant, not waterproof since we lose water through insensible perspiration (unable to see or feel) and sensible perspiration (sweat)

desmosome

structure that forms an impermeable junction between cells

stratum lucidum

• the “clear layer” THICK SKIN ONLY

• layer of the epidermis between the stratum granulosum and stratum corneum'

• found only in thick skin covering the palms, soles of the feet, and digits

• flattened, densely packed dead cells filled with keratin

keratin

type of structural protein that gives skin, hair, and nails its hard, water-resistant properties

stratum granulosum

• the “grainy layer”

• layer of the epidermis superficial to the stratum spinosum

• 3-5 layers of keratinocytes that have stopped dividing and started producing keratin

• cells grow thinner and flatter and cell membrane becomes less permeable

keratohyalin

granulated protein found in the stratum granulosum which accumulates as lamellar granules within the cells

stratum spinosum

• the “spiny layer”

• layer of the epidermis superficial to the stratum basale, characterized by the presence of desmosomes

• 8-10 layers of keratinocytes bound together by desmosomes

• contains dendritic (langerhans) cells defending against microorganisms and superficial skin cancers

langerhans cells

• specialized dendritic cell found in the stratum spinosum that functions as a macrophage

• dendritic are apart of your immune system (guards); when something goes through they send the signals

stratum basale

• the “basement layer”; innermost layer

• deepest layer of the epidermis, made of epidermal stem cells

• attached to the basement membrane

• most cells here are basal cells

• melanocytes and merkel cells are also found here

basal cell

• type of stem cell found in the stratum basale and in the hair matrix that continually undergo cell division, producing the keratinocytes of the epidermis to replace more superficial keratinocytes

• cuboidal-shaped stem cell that is a precursor of the keratinocytes of the epidermis

merkel cell

receptor cell in the stratum basale of the epidermis that responds to the sense of touch

dermis

• layer of skin between epidermis and hypodermis, composed mainly of connective tissue and containing blood vessels, hair follicles, sweat glands, and other structures

• supports the epidermis

layers of dermis

• papillary layer

• reticular layer

• hypodermis

papillary layer

• named for dermal papillae in this region

• composed of loose areolar connective tissue

• contains capillaries, lymphatic vessels, and sensory neurons

ridges of the skin

spatial relationship between epidermal ridges and dermal papillae

dermal papillae

• extension of the papillary layer of the dermis that increases surface contact between the epidermis and dermis

• dermal papillae are your fingerprints

reticular layer

• interwoven meshwork of dense irregular connective tissue

• contains both collagen and elastic fibers

• collagen fibers from this layer blend into both the papillary layer above and the hypodermis below

• contains blood vessels, lymphatic vessels, nerve fibers, and accessory organs (hair follicles, sweat glands)

elastin fibers

fibers made of the protein elastin that increase the elasticity of the dermis

cleavage lines

• correspond to the orientation of collagen fibers in the dermis, and are generally parallel to the orientation of the underlying muscle fibers

• this is how the collagen fibers run; when surgeons cut you they want to follow this pattern because you’ll get less of a scar

hypodermis

• separate skin from deeper structures (isn’t technically apart of your skin)

• connective tissue connecting the integument to the underlying bone and muscle - connects the dermis to the rest of the body

  • stabilizes position of skin relative to underlying tissue

• allows independent movement

• provides insulation / padding

• dominated by adipose tissue

  • important energy storage site

  • lost of fat in this area (fatty layer; to insulate, cushion, and attach)

pigmentation

• factors influencing skin color:

  • epidermal pigmentation via the amount of melanin and carotene

  • dermal circulation

melanocyte

cell found in the stratum basale of the epidermis that produces the pigment melanin

melanin

• produced my melanocytes

• pigment that determines the color of hair and skin

• protects you from ultraviolet (UV) light

melanosome

intercellular vesicle that transfers melanin from melanocytes into keratinocytes of the epidermis

albinism

genetic disorder that affects the skin, in which there is no melanin production

vitiligo

skin condition in which melanocytes in certain areas lose the ability to produce melanin, possibly due to an autoimmune reaction that leads to loss of color in patches

dermal circulation

• hemoglobin is red pigment found in red blood cells

• blood flows to dermis through subpapillary plexus

  • more blood flow to region results in redder color

  • less blood flow to the region initially results in pale color

• sustained reduction of blood flow decreases available oxygen

  • lower oxygen levels make hemoglobin darker red

  • from surface view, skin has bluish color (cyanosis)