Integumentary sys Flashcards
integumentary system ?
skin and accessory structures (hair, glands, nails)
• covers entire body surface
• contains all four tissue types
• boundary between body and external environments
Function of skin
- protection – against: abrasion, ultraviolet light exposure, dehydration, entry of microorganisms
- sensation – specialized sensory receptors detect temperature, pain, touch, pressure, proprioception (awareness of body position)
- temperature regulation - via changes in skin blood flow and sweat gland activity
- defence – contains cells of immune system
- vitamin D production
- excretion – removal of small amounts of waste products
cutaneous membrane
contains the 2 major tissue layer
o epidermis = superficial epithelium
o dermis = underlying connective tissue
♣ accessory structures located in dermis and protrude through epidermis to surface
hypodermis
o hypodermis (superficial fascia) = loose connective tissue
epidermis
- stratified squamous epithelium (Fig 4.3)
- separated from dermis by basal lamina
- no blood vessels
- cells receive nutrients and excrete wastes products by diffusion
- 4 cells types: keratinocytes, melanocytes, Langerhans and Merkel cells
keratinocytes
- most numerous cell type
o produce keratin = protein mixture that makes cell more durable
o aids in ability to resist abrasion and reduce water loss
o can obtain melanosomes (pigment granules) through phagocytosis of the tips of melanocytes
stem cells of epidermis
o located in the deepest layer (stratum basale) of the epidermis continually undergo mitosis
♣ new cells push older cells toward the surface
♣ change shape and chemical composition as they move from deeper epidermal layers to surface
keratinization
accumulation of keratin results in five epidermal layers (strata)
stratum basale
♣ = deepest layer
• single layer of cuboidal stem cells that undergo mitosis
• firmly attached to basal lamina
• desmosomes (specialized cell junctions) hold keratinocytes together
• projects into dermis forming dermal ridges (Fig 4.5)
o ridge pattern determined genetically and forms unique fingerprints
o dermal projections toward epidermis = dermal papillae
stratum spinosum
♣ 8-10 layers of many-sided cells
• flatten as they progress upward
• contain tonofibrils = bundles of protein filaments
act as cross braces, strengthening and supporting cell junctions
stratum granulosum
♣ 2-5 layers of flattened, and elongated diamond-shaped cells that orient parallel to the surface
callus
o localized thickening of skin
forms large quantities of …. in stratum granulosum ?
keratohyalin
non-membrane bound protein granules, and keratin
- increase friction against skin stimulates synthesis
lamellar bodies
• lipid-filled, membrane-bound organelles exocytosed
o coats cells and forms water-resistant layer but prevents diffusion of nutrients to more superficial layers
stratum lucidum
♣ thin clear zone containing several layers of dead cells with indistinct borders
o only found in thick skin (Fig 4.4)
♣ areas subject to pressure or friction – palms of hands, soles of feet, and fingertips
stratum corneum
few layers in thin skin to 25 or more layers of dead, dehydrated cells lacking nucleus and organelles in thick skin
cornfield cells
overlapping dead overlapping cells with a hard protein envelope filled with keratin
part of stratum corner
stratum corneum (shedding)
♣ cells shed in large groups or sheets due to connections (desmosomes) between cells
♣ dry – unsuitable for growth of many microorganisms
how many days for new cells to arrive to surface
o akes 15-30 days to cell to move from stratum basale to surface
♣ cells stay at surface for about 2 weeks before being sloughed off
psoriasis
• arises from malfunction of keratinization process
o stems cells in stratum basale unusually active
• affected areas have red bases and large scales of epidermis that are sloughed off
melanocytes
- found between keratinocytes within the two deepest layers of the epidermis
o irregularly shaped with long processes
o found in high concentration in freckles, moles, the nipples, areolae of the breasts
o produce melanin = group of pigments responsible for skin, hair and eye colour
♣ packaged in vesicles called melanosomes
♣ provides protection against ultraviolet light
langerhans cells
- resident dendritic cells (immune cells) found in the skin
o have phagocytic ability and secretes substances that activate other cells of the immune system
merkel cells
- specialized epidermal cells associated with sensory nerve endings
o responsible for detecting light touch and superficial pressure
skin colour , combination of
o dermal blood flow – hemoglobin produces red tint
o thickness of stratum corneum - thick versus thin skin
o variable quantities of pigment
carotene
♣ yellow/orange pigment that accumulates in keratinocytes
• becomes evident in dehydrated cells of stratum corneum
melanin
♣ produced by melanocytes and passed via melanosomes to keratinocytes
• genetic factors responsible for variation in skin colour among races
o all races have approximately the same number of melanocytes
♣ differ in size, number, distribution and type of melanin within melanosomes
o many genes responsible for skin colour
albinism
o recessive genetic trait that results in lack of tyrosinase – the enzyme required to make melanin so lack pigment in skin, hair and irises of eyes
exposure to UV light
o absorbs UV light
o darkens the melanin already present in skin
o stimulates melanin production
hormones can increase what ?
• can increase melanin production during pregnancy or in disease states
o estrogen and melanocyte-stimulating hormone in pregnant females
Addisons disease
increased adrenocorticotropic hormones
dermis
underlies the epidermis
dermis : what is it ?
- connective tissue containing fibroblasts, a few adipocytes, and macrophages
- collagen is the main connective tissue fiber but also contains elastin and reticular fibers
- contains: some blood vessels, a variety of sensory nerve endings, hair follicles, smooth muscles, glands, and lymphatic vessels
dermis is divided by :
• divided into two layers:
papillary layer = loose connective tissue with thin fibers
reticular layer = dense irregular connective tissue
papillary layer
loose connective tissue with thin fibers
o more superficial layer containing dermal papillae – projections that extend toward the epidermis
o contains capillaries – smallest blood vessels that supply oxygen and nutrients to the epidermis
o lie in parallel curving ridges in the thick skin of the hands and soles of the feet and shape the overlying epidermis
♣ increase friction and improve grip
♣ form unique fingerprints and footprints
reticular layer
dense irregular connective tissue
o main layer of the dermis
o continuous with subcutaneous tissue
o resists stretching in many directions
o orientation of elastin and collagen fibers in some directions more than others
♣ produces tension (cleavage) lines (Fig 4.8)
• important consideration when suturing cut or tear to reduce chance of gapping, infection, and scarring
age, hormones and destructive effects of UV radiation reduce
o reduce thickness and flexibility of dermis
stretch marks
♣ rinkles and creases formed when skin overstretched
• elastin and collagen fibers in dermis rupture
• skin does not recoil to original size leaving lines visible through the epidermis
subcutaneous tissue
not part of the skin but skin rests on top of it
• hypodermis or superficial fascia
• loose connective tissue containing fibroblasts, adipocytes and macrophages
• supplies blood vessels and nerves to skin
• amount of adipose in the subcutaneous layer varies with age, sex and diet
o stores approximately half the lipids of the body
o insulates body
o pads (protects) underlying structures
o energy source
