the skin

Question 1

what does the integumentary system consist of

Answer 1

-hair
- nails
-cutaneous glands (sweat, sebaceous filaments)
-skin is the largest organ (12-15% of body weight)
-barrier to external
-insight to internal health

Question 2

what’s the structure of skin

Answer 2

-epidermis (uppermost- faces external world ) epithelia layer
-dermis
-hypodermis is the areolar or adipose tissue which binds skin to the underlying tissue- technically not part of the skin

Question 3

what are fibroblasts and how do they produce ECM proteins

Answer 3

-found in dermis
-mainly collagen but can also be laminin/fibronectin forming elastic and reticular fibres
-2 zones which are papillary layer and reticular layer

Question 4

what’s the papillary layer in fibroblasts

Answer 4

-papillary layer is thin and loose connective tissue region (areolar) used for mobility of leukocytes, mast and macrophage cells

Question 5

what’s the reticular layer in the fibroblasts

Answer 5

-thick dense irregular connective tissue layer
-contains less cells and adipocyte clusters

Question 6

what does the dermis contain which is useful for thermoregulation

Answer 6

-rich layer of blood and lymphatic vessels

Question 7

why is there a high sensitivity in the dermis

Answer 7

-numerous nerve endings

Question 8

what’s the dermal-epidermal boundary

Answer 8

-wavy boundary of finger like projections increasing connections e.g. dermal papillae(raised area) and epidermal ridges
-interdigitation prevalent which Is the epidermal and dermal layers going into the tissues of one another which increases surface area contact and stops the tissue from slipping away from one another

Question 9

what do tall dermal papillae facilitate

Answer 9

-nerve fibres reaching close to the surface in highly sensitive areas

Question 10

what is the epidermis

Answer 10

-keratinised stratified squamous epithelium
-very stratified (lots of layers)
-self-regenerative throughout life cycle 2-4 weeks

Question 11

what are the stratified layers of epidermis

Answer 11

-stratum basale (base)
-stratum spinosum (spindly)
-stratum granulosum (granular in histology slide)
-stratum lucidum (translucent 2-3 extra layers in thick skin which protects from mechanical stress (eleidin)
-stratum corneum (most superficial because there iuds multiple layers)

Question 12

what are the different skin types in the epidermis

Answer 12

-thick skin (palms including fingertips, feet are smooth as they have no hair)- 5 layers
-thin skin (rest of body, 4 layers, non glabrous meaning it doesn’t have stratum lucidum

Question 13

what does the lack of blood vessels in the epidermis mean

Answer 13

-diffusion occurs from underlying connective tissue

Question 14

what does the stratum basale consist of

Answer 14

-keratinocytes- mitotically active and in touch with basement membrane- these produce cells which migrate upwards
-melanocytes which gives skin colour
-tactile/merkel cells which are connected to sensory nerves

Question 15

what are melanocytes

Answer 15

-release melanin for UV absorption, antioxidant and radical scavenging, as well as protecting skin from the UV damage
-skin pigmentation: carotene pigments (orange-yellow) in subcutaneous fat and stratum corneum in the heels of the feet
-blood perfusion and O2 content

Question 16

what are the two different types of pigments in melanocytes

Answer 16

-pheomelanin - red/yellow pigment
-eumelanin- brown/black pigment

Question 17

what’s melanosomes

Answer 17

-the branching process
-phagocytosed (takes in the melanosomes) by keratinocytes which surround the nucleus

Question 18

what’s the stratum spinosum

Answer 18

-several keratinocyte layers
-usually the thickest layer except in thick skin e.g. stratum corneum
-deepest cells mitotic, pushed upwards which cease to divide
-produce keratin filaments which are flat (more in upper layer)
-keratinocytes strongly linked by desmosome
-tight junctions ensure water retention of skin
-dendritic cells present

Question 19

what’s stratum granulosum

Answer 19

-3-5 layers of flat keratinocytes
-high barrier function
-post-mitotic, tight junction claudins- used for barrier functions NB
-contain dark staining granules- bind to cytoskeleton (keratin precursors )
-cells undergo apoptosis
-produce glycolipid-filled vesicles (lamellar bodies/granules) which spread over cell surface creating a waterproof barrier between stratum spinosum

Question 20

what’s the stratum corneum

Answer 20

-most superficial and its has a lot of proteins
–15-30 layers of flattened, dead, corneocytes/squames which are enucleated terminally differentiated dead keratinocytes
-contains stratum disjunctum and storm compactum
-contaisn cornified envelope
-especially resistant to abrasion, penetration and water loss

Question 21

what’s the stratum disjunctum

Answer 21

-beneath apical acid mantle and lipid barrier
-corneodesomosomes regulate desquamation

Question 22

what’s stratum compactum

Answer 22

compact cells

Question 23

what does the cornified envelope consist of

Answer 23

-keratins
-enclosed within insoluble amalgam of cross-linked protein
-surrounded by extracellular lipid envelope (fused lamellar bodies)

Question 24

structure of nails

Answer 24

-derivatives of stratum corneum (flat in primates)
-composed of dead scaly cells densely packed with ‘hard’ keratin fibres
-new cells added by mitosis in the nail matrix
-appearance can indicate underlying health issues such as iron deficiency (flat or concave) and then long term hypoxemia- clubbed
-naisl grow faster I summer due to more heat therefore enzymes work faster

Question 25

structure of hair

Answer 25

-filament of keratinised (dead) cells from follicle
-densities : 50cm2 trunk to 100,000cm2 scalp
-hair bulb grow around bud of vascular connective tissue-dermal papilla
-3 layers: medulla (loosely arranged), cortex (keratinised cuboidal cells), and cuticle (surface Layer of scaly cells)

Question 26

what are the 5 types of glands

Answer 26

-eccrine/merocrine
-apocrine sweat glands
-holocrine sebaceous glands
-ceruminous glands
-mammary glands

Question 27

what are eccrine/merocrine sweat glands

Answer 27

-merocrine more prevelant
-watery perspiration to skin
-controlled by SNS myoepithelial cells (with muscle component)
-temp related

Question 28

what are apocrine sweat glands

Answer 28

-cells pinch off into ducts
-released into follicles (scent glands)
-respond to sweat + sexual stimulation
-armpits and genitals

Question 29

what are holocrine cells

Answer 29

-cells disintegrates releasing product
-oily sebum lubricating skin and hair
-face, chest, back
-differentiated epithelial cells accumulate lipids, eventually rupture to release sebum

Question 30

what are ceruminous glands

Answer 30

-external ear- wax

Question 31

what are the different types of barrier function

Answer 31

-physical barrier
-biochemical barrier
-immunological barrier
-skin has complex microflora with more than 1000 species- harmless commensals and opportunistic pathogens

Question 32

what consists of the physical barrier

Answer 32

-corss-linked keratin layer on keratinocyte scaffold (cuts, burns, vectors breach)

Question 33

what consists of the biochemical barrier

Answer 33

-mildy acidic (pH 4-6)
-sebaceous glands sebocytes (sebum) contains bactericidal agents such as saturated and unsaturated fatty acids which inhibit bacterial growth e.g. lysozymes cleave cell wall cross-links

Question 34

what are epidermal langerhans cells (LC)

Answer 34

-immunological barrier- LC of stratum spinous are able too self renew
-process of antigens : migrate to lymph nodes for antigen presentation or present antigens to skin lymphocytes which circulate to secondary lymphoid organs which is an immune response

Question 35

examples of papillary and/or reticular dermis

Answer 35

-macrophages and monocytes
-mast cells
- eosinophils
-neutrophils
-B and T lymphocytes
-many have a role in tissues remodelling, repair and proliferation

Question 36

vitamin D synthesis

Answer 36

-vitamin D is a fat soluble hormone
-increase in intestinal absorption of calcium
-Ca2+ homeostasis (bone development and maintenance)
-prohormone acts via nuclear receptor (VDR which is vitamin D receptor) in nearly every tissue there is 100s of nuclear binding sites
-skin is a major natural resort- first step into synthetic pathway (liver+ kidneys)
photochemical reactions (UVB radiations which converts it to previtamin D3)

Question 37

which is sin important in temperature regulation

Answer 37

-periphery= epidermal thermoreceptors
-central= preoptic anterior hypothalamus with warm and cold receptors
-countercurre t heat exchange between arterial and venous blood flow in extremities (dermis) minis heat loss
-over-perfused for nutritional requirements (true capillaries provide nutrition)
-high density of arteriovenous anastomoses (AVA) in apical skin0- rich in sympathetic innervation
-decrease in core temp leads to increase in sympathetic tone which decreases blood flow- vice versa
-non-apical skin though to act via SNS ACh release which eccrine sweat glands cause vasoactive molecules which relaxes the VSMC which increases the perfusion of heat loss