1. No category

Skin,
Integumentum
commune
Surface
area
of the skin:
cca 2 m2
thin skin (hirsute)
thick skin (glabrous)
– covers the greater part of the body
– hair, sweat- and sebaceous glands
– fingertip, palmar- and plantar surfaces
– hairless, only sweat glands
Layers:
Epidermis (thin skin 100 µm-25 cell layers, thick skin 1 mm – 100 cell layers)
stratified keratinized squamous epithelium, no vessels
Dermis - mechanical resistance,
numerous papillae or rete ridges
glands and hair follicles
Epidermis + Dermis: Cutis
Subcutis (subcutaneous tissue) – (loose) connective tissue, fat pad
Epidermis+Dermis+Subcutis: Skin, Integumentum commune
Skin appendages: 1. Hair and Nail (short – vellus hairs... long – terminal hairs)
2. Glands
3
Epidermis
1 stratum basale/germinativum
2 stratum polygonale/spinosum
3 stratum granulosum
(4 stratum lucidum – absent in thin skin)
5 stratum corneum: str. compactum + disjunctum
1+2: Malpighi layer
4
3
2
1
1
2 3
5
Keratinocyte
Langerhans cell
Merkel cell
Melanocyte
Cell types in the epidermis
1. Keratinocytes (90 %)
- basal living cells, dead keratinized cells superficially
→ str. basale – mitotic activity
→ prickle cells – desmosomes with tonofilaments (cytokeratin)
→ str. granulosum – profillagrin providing clumping of tonofilaments in
keratohyalin granules
- release of extracellular lipids from lamellar bodies
→ str. corneum: fillagrin (matrix) + keratin filaments → KERATIN
cell is lacking nucleus
cornified envelope – involucrin protein - (inner surface of the membrane)
cornified lipid envelope – ceramide (outer surface of the membrane,
which is linked to the cornified envelope by covalent bounds
epidermal turnover time (from stratum basale until desquamation): 52-75 days
(in psoriasis around 8 days)
stratum
spinosum
(prickle
cell layer)
Cell types in the epidermis
2. Langerhans cells (Mononulcear-Phagocyte System), antigenpresenting cells
Cell types in the epidermis
3. Melanocytes - its dendritic processes are contact with cca 36
keratinocytes, the most are clear because the melanosomes are
transferred to the keratinocytes by cytocrine secretion (stimulated by UV
radiation, TNF-alpha, ACTH, alpha-MSH)
melanin – tyrosine/tyrosinase reaction (its mutation – albinism)
in darker skin: more large superficial melanosomes
eumelanin (brown-black), pheomelanin (red-yellow)
Marker D5 in Nucleus...
Sunless bronze: dihydroxyacetone binds to proteins of stratum corneum only
Cell types in the epidermis
4. Merkel cells - later, with receptors....
Dermo-epidermal junction
◘ molecular anchorage
1. tonofilaments – Desmosomes
2. basal cells –lamina densa –
hemidesmosomes
anchoring filaments attach the
cells to lamina densa
(laminin5, BP 180/ coll XVII)
3. anchoring fibrils of type VII
collagen bind lamina densa to
collagen fibers (type III) in
papillary dermis
4. microfibrils link the elastic
fibers to collagen fibers
Skin diseases! Autoantibodies against hemidesmosomes or specific
proteins, coll. XVII, VII, etc. → formation of blisters, epidermolysis
DERMIS
◘ papillary layer – loose connective tissue,
fine collagen fibers (type I and III)
capillary loop, nerve endings,
Meissner‘s-corpuscles
◘ reticular layer: dense connective tissue,
thick collagen fibers (type I) & elastic
fibers, smooth muscles cells in some
cases such as tunica dartos of penis &
scrotum
Langer‘s lines (long axis of rhomboids)
– long axis of rhomboids frequently coincide (but not always) with relaxed skin
tension lines (Kraissle‘s lines) (wrinkle lines are related to muscle contraction)
- excision line must be parallel to the relaxed skin tension lines
dermal papillae – friction ridges
fingerprint - dermatoglyphics
flexure (joint) line
SUBCUTIS or HYPODERMIS (also known as superficial fascia)
loose (adipose) connective tissue - mediates increased mobility of skin
-panniculus adiposus: shock absorber,
energy store,
thermal insulation
-retinaculum cutis (dense collagenous):
strong binding to underlying tissues
in certain areas of the skin:
(sole, palm, scalp) – no significant sliding
- very delicate in eyelids, forskin
skin turgor – exsiccation (dehydration)
Glands of the skin recapitulation!!!
1. sebaceous - holocrine: open into hair follicles (or onto the skin surface:
lips, inner surface of prepuce, minor labia, glans of penis/clitoris, areola/nipples)
- missing in the sole & palm
2. sudoriferous – merocrine (eccrine) sweat : open onto the skin surface
- missing in lips, inner surface of prepuce, minor labia, glans of penis/clitoris
- cholinergic sympathetic innervation
3. odoriferous - apocrine (sweat): open into hair follicles
- axillary, areolar, anal genital regions + (glands of Moll & ceruminous glands)
- adrenergic sympathetic innervation
branched alveolar
simple coiled tubular
branched alveolar
- arteriovenosus anastomoses
or shunts
against heat loss
in certain areas of the skin
(fingertips, nose, ear)
superficial (subpapillary) plexus
mid-dermal venous plexus
deep (subdermal) plexus
lymphatic vessels begin in the dermal papilla
dermatome
cutaneous area supplied by one spinal nerve
- dermatomes of adjacent spinal nerves
overlap markedly
Functions of the skin
◘ Receptor organ
◘ Mechanical and chemical protection (stratified epithelium,
(hemi)desmosomes etc, fiber network in dermis and subcutis)
◘ Thermoregulation: passive – (insulation by subcutis – panniculus adiposus)
active – sweat glands, vessels, m. arrector pili
◘ Photoprotection: stratum corneum reflects UV rays
melanin – scavanger of harmful free radicals
◘ Permeability barrier: stratum corneum keratin & extracellular lipid
+ stratum granulosum tight junctions
→ sealing against water loss (in reptiles first – terrestrial life)
◘ Protection against pathogens: sweat pH 4-6, fatty acids in sebum, (RNases!)
◘ Synthesis of vitamin D, cytokines and growth factors (EGF)
--------------------------------------------------------------------------------------------◘ Barrier also to penetration of hydrophilic molecules
→ only lipophilic medications (creams/ointments) can penetrate through the
intact epidermis
hair everywhere except on palms, soles, lips, nipples, glans penis/clitoris,
labia minora, inner aspects of forskin and labia majora
infundibulum
X
isthmus
inf. segment
hair bulb
pilosebaceous unit: hair, hair follicle, m. arrector pili, sebaceous gland
X follicular bulge
inner root sheath
outer root sheath
hair
glassy membrane
connective tissue
sheath
hair
cuticle
cortex
medulla
dermal papilla
melanocyte
capillary loop
cuticle
Huxley‘s layer
Henle‘s layer
hair bulb
inner root sheath
Hair (pilum) - Hair follicle (downgrowth of epidermis)
Hair shaft – Hair sheats
Hair bulb - 1. germinal matrix cells differentiate into
medulla, cortex, cuticle, inner root sheath
- 2. connective tissue dermal papilla
hair grows outwards, nuclei of the matrix cells are
lost, keratinization
Hair – 3. medulla
4. cortex
5. cuticle – shingle-like (upside down) several
layers of cornified squames by interdigitations
with the cuticle of inner root sheat achieves a
firm anchorage of hair root within its sheath
9
8
7
6
5
4
3
1
2
hair root is surrounded by the hair follicle (folliculus
pili)
◘ 6.inner root sheath
- sheath cuticle, Str. lucidum →Huxley‘s layer,
Str. granulosum → Henle‘s layer
◘ 7.outer root sheath (Malpighi layer)
◘ 8.glassy membrane (basal membrane)
◘ 9.connective tissue sheath
cross section of the hair follicle
-(adipose tissue of the subcutis)
- connective tissue sheath
- glassy membrane
- outer root sheath (cell-rich and
basophil)
- inner root sheath (indistinct cell
borders, eosinophil)
- cuticle of the inner root sheath
(followed by a white gap)
-cuticle of hair
- cortex of hair
- medulla of hair
Role of hair: thermoregulation, against UV radiation (scalp), sensory function
Hair cycle
Growth
Involution
Rest
Shedding of hair
normal hair loss: 50-100/day
when synchronised: shed of hair (mammals and newborns....)
chemotherapy – harmful effects on matrix cells or on their blood supply,
rupture of hair root
cross section: round – straight hair, oval – curly hair
androgen (DHT) induces hair loss (alopecia) – short anagen phase
color of hair depends on the amount and type of pigments
dermis of the nail bed is anchored to the periosteum
– no subcutis, distinct compartment
painful infections/haematoma – excision of plate!
Nail
Nail plate
Nail matrix
Nail bed