The Integumentary System Flashcards by Ellie Stretch

integumentary system key points

skin and accessory organs: hair, nails and cutaneous glands
largest organs. - 12-15% body weight
regulates fluid loss, barrier to external envirnoment
often can indicate underlying issues

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structure - layers

epidermis = upper most layer
dermis
(hypodermis - areolar (loose arrangement of collagenous tissue with elastin fibres) or adipose tissue between skin and muscle - not actually skin)

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dermis

connective tissue, beneath epidermis
thicker than epidermis 0.2-2mm
mainly collagen with elastic and reticular fibres, 2 zones (unclear boundary)

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zone 1 of dermis

papillary layer

thin region of loose connective tissue (areolar) allowing mobility of leukocytes, mast and macrophage cells

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zone 2 of dermis

reticular layer
thick layer of dense irregular connective tissue, less cells, but often with adipocyte clusters
stretching of skin causes striae = stretch marks

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fibroblasts

porduce proteins, laminin and fibronectin of ECM

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accessory organs

hair, nails, oil and sweat glands - all in dermal layer
rich layer of blood and lymphatic vessels
includes arteriovenous anastomoses - important in thermoregulation
numerous nerve endings

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dermal - epidermal boundary

wavy boundary of finger like projections increasing connection to:
dermal papille (raised areas e.g. finger prints) - pointing towards outside
epidermal ridges - point into body

tall dermal papille facilitate nerve fibres reaching close to surface in highly sensitive areas

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epidermis

keratinised stratified sqaumous epithelium

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skin types

thick - palms, feet, no hair, 5 layers of stratum

thin - rest of body, 4 layers

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layers of stratum

basale
spinosum
granulosum
(lucidum - only in thick skin)
corneum
- lack blood vessels, diffusion from underlying connective tissue
- self regernation throughout life cycle, 2-4 weeks

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cells of epidermis (5)

stem cells
keratinocytes
melanocytes
langerhans
mencel cells

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stem cells in epidermis

give rise to keratinocytes only in deepest layer of epidermis, in contact with basement mem, maintain ability to replicate

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keratinocytes in epidermis

80-90% cell composition of epidermis, make keratin

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melanocytes in epidermis

synthesis melanin

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langerhans in erpidermis

dendritic cells of skin, originate in bone marrow

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mencel cells in epidermis

touch receptors, in contact with dermal nerve fibres

stratum basale

aka germinativum
single layer of cuboidal cells (low columnar cells)
keratinocytes most prevalent, mitotically active on basement mem
melanocytes = skin colour = pheomelanin - red soluble pigment e.g. lips, eumelanin - brown insoluble pigment
tactile/mecel cells = connected to sensory nerves

melanocytes

release melanin - UV absorbent, antioxidant and radial scavenging - protect the skin from UV damage
melanin providing pigment depends on:
carotene pigment (orange/yellow) in subcutaneous fat and stratum corneum - in heels of feet
amount of blood and oxygen content
melanosomes - branching process, phagocytoses by keratinocytes to surround nucleus sun side - to protect from radiation

stratum spinosum

several layers of keratinocytes
usually thickest layer, except in thick skin
deepest mitotic cell, pushed up and cease to divide - become more squamous
produce keratin filamentscausing cells to flatten (more in upper layers)
KCs stronly linked by desmosomes
tight junctions ensure water retention
dendritic cells present

stratum granulosum

3-5 layers of flats keratinocytes
post-mitotic, bound by tight junctions
contain dark staininng keratohyalin granules (cytoplasmic organelles packed with electron dense proteins), which bind to cytoskeleton and converted to keratin by transglutaminases
cells undergo apoptosis
produce glycoplipid filled vesicles - spread over cells surface, forms waterproof barrier between spinosum
tight junctions contribute to epithelial barrier by preventing leakage of solutes

stratum lucidum

mechanincal barrier against damage
only in thick skin
thin transleucent zone
contains keratinocytes, densely packed, no nuclei/organelles
indistinct cell boundaries
granules of eledin in proteoplasm - product of keratohyalin
surrounded by oily layer

stratum corneum

most superficial - 15-30 layers
upper terminally differentiated dead keratinocytes - these undergo desquamation, comes off as ‘dead skin’
stratum disjunction beneath apical acid mantle and lipid barrier
stratum compactum - cohesive
cornified envelope: keratins, enclosed within amalgam of proteins, cross linked by transglutaminases
surounded by lipid envelope

accessory structures

nails
hair
glands

nails

derivatives of stratum corneum, nail invaginates into finger, flat in primates composed of dead scaly cells, densely packed with 'hard' keratin fibres new cells added by mitosis in nail matrix - 1mm a week appearance can indicate health issues e.g. iron deficieny = flat/concaved nails long term hypoxemia = clubbed

hair

slender filaments of keratinised (dead) cells from follicle found almost everywhere changes during lifetime: foetus = lanugo hair - fine, downy, unpigmented velus hair = similarly fine and umpigmented terminal hair = longer, coarser, pigmented

hair follicle

``` bulb grows around bud of vascular connective tissue: dermial papilla hair matrix above = mitotically active 3 layer: medulla - loosely arranged cells cortex - keratinised cuboidal cells cuticle - surface, scaly cells ```

glands in skin

skin can be moist, sebaceous or neither depending on glands in that area sebaceous - secrete lipids, antibacterial layer

5 types of skin glands

``` merocrine apocrine sebaceous ceruminous mammary ```

merocrine glands

sweat glands cuboidal, single layer watery perspiration to skin associated with myoepithelial cells

apocrine glands

sweat ducts lead to follicles 'scent' glands, respond to stress and sexual stimulation

sebaceous glands

oily sebum | lubricates skin and hair

ceruminous glands

external ear - wax

mammary glands

in females

barrier function of skin

prevent water loss, physcial injury and infection by mircobes physical barrier = cross linekd keratin layer on scaffold of keratinocytes biochemical barrier = slightly acidic, ph 4-6, bactericidal agents: saturated and unsaturated fatty acids inhibit growth of bacteria and lysozyme cleaves cross linkage in bacterial cell walls - cis-6-hexadecanoic (C6H) can inhibit induction of antibiotic resistance

immunological barrier of skin

langerhans cells in stratum spinosum able to self renew, take up and process antigens: - migrate to lymph nodes for antigen presentation or - present antigens to skin lymphocytes - which circulate to secondary lymphoid organs, activating immune response

temperature regulation - integumentary system

apical skin - areas that can divert blood straight to venous side, stop blood perfusing to surface or can encourage it too, therefore releasing heat or locking it away less blood to apical skin = reduce heat loss e.g. nose, lips, ears

skin in thermoregulation

thermoreceptors in epidermis counter current heat exchange between arterial and veous blood flow in extremities over perfused for nutritional requirements: true capillaries provide nutrition, arteriovenous anastomoses assist in thermoreg. hypothalamus regulates ANS

anastomoses

connection between tubular structures e.g. blood vessels

thermoregulation

dectection = hypothalamus piloerection = hairs stand up = insulation constriction or vasdilation of anastomoses merocrine sweat glands cool body by evaporation

overall pathway: | increased body temperature

e.g. when exercising hypothalamus detects change sweat glands activated = evaporation skin blood vessels dilate = capillaries fill woth warm blood and heat radiates from skin body temp decreases and hypothalamus returns to normal

overall pathway: | decrease in body temperature

e.g. going outside hypothalamus detects change skeletal muscles activated = shivering generates more heat skin blood vessels constrict = blood diverted from skin to deeper tissues - reducing heat loss from surface body temp increases and hypothalamus shuts off