The Integumentary System Flashcards
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
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)
dermis
connective tissue, beneath epidermis
thicker than epidermis 0.2-2mm
mainly collagen with elastic and reticular fibres, 2 zones (unclear boundary)
zone 1 of dermis
papillary layer
thin region of loose connective tissue (areolar) allowing mobility of leukocytes, mast and macrophage cells
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
fibroblasts
porduce proteins, laminin and fibronectin of ECM
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
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
epidermis
keratinised stratified sqaumous epithelium
skin types
thick - palms, feet, no hair, 5 layers of stratum
thin - rest of body, 4 layers
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
cells of epidermis (5)
stem cells keratinocytes melanocytes langerhans mencel cells
stem cells in epidermis
give rise to keratinocytes only in deepest layer of epidermis, in contact with basement mem, maintain ability to replicate
keratinocytes in epidermis
80-90% cell composition of epidermis, make keratin
melanocytes in epidermis
synthesis melanin
langerhans in erpidermis
dendritic cells of skin, originate in bone marrow
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
