Outer Body coverings 1&2 Flashcards
Properties and Function of Skin
- Maintenance of body integrity
- Waterproofing
- Protection from injury
- Protection from infection
- Sensory functions
- Immune functions
- Absorption / excretion
- Control of body temperature
- Vitamin D metabolism
- Personal, social and sexual significance
Structure of the skin
Epidermis (epithelium of ectodermal origin)
Dermis (connective tissue of mesodermal origin)
Subcutaneous adipose tissue
Variability according to site
- Thick, hairless
- Thin, hairy
two types of skin:
Glaborous, thick, hairless skin - fingers, palms, toes, soles, lips, labia minora, glans penis
Thin, hairy skin - everything else
Epidermis - characteristics
Stratified squamous epithelium composed of keratinocytes undergoing terminal differentiation (approx. 4 weeks)
Basement membrane at the junction with the dermis (collagen)
What are the four layers of epidermis?
Four important layers: Horn cell layer (stratum corneum)
Granular cell layer (str. granulosum)
Prickle cell layer (str. spinosum)
Basal cell layer (stratum basale)
What are squamous desmosomes and their functions?
Desmosomes are intercellular junctions that provide strong adhesion between cells.
They form the adhesive bonds in a network that gives mechanical strength to tissues.
Squamous cell carcinoma
4 abnormalities in this picture
Dysplasia
much thicker
variable nuclei shapes
nuclei are too dark
nuclear chromatin pattern is abnormal (variation in nucleus colour)
If you find a desmosome in a tumour what does it tell you?
diagnostic of a squamous cell carcinoma
Cell types of the epidermis?
Keratinocytes
Melanocytes
Langerhans cells
Merkel cells
Melanocytes:
origin?
location?
function?
- Origin from the neural crest (S-100 +)
- They are not epithelial cells
- Stuck to the basement membrane
- Melanin, formed in melanosomes
- One melanocytes delivers melanin to 36 keratinocytes
- Keratinocytes phagocytose the tips of melanocyte dendrites
- Melanin provides protection against UV
What is the neural crest?
the crest that forms in early neurulation at the top of the embryo.
this is where melanocytes originate and they spread out into the skin from there.
they use melanin instead of neurotransmitters
Melanoma: mortality
if caught early and excised then you are cured.
if it becomes malignant and metastasises then mortality increases sharply
how do you diagnose melanoma?
melanocytes in the dermis across the basement membrane.
Pagetoid pattern - abnormal melanocytes that ascend into the epidermis
Langerhans cells
Origin and marker?
Function?
Originate from the bone marrow (CD1a +)
Also dendritic
Antigen presenting cells
Merkel cells
Origin?
Function?
Originates in Neural Crest
Mediate tactile sensation
Not very recognisable in normal sections
Associated with sensory nerve endings
Basement membrane:
Composition?
Stain?
Function?
Collagen type IV
Highlighted by PAS stain as a red stripe
Function
- Resistance to shearing forces
- Structural significance
- Control of epithelial – mesenchymal
- interactions (e.g. invasion)
Basement membrane and Disease.
Increased fragility and impaired wound healing
Control of invasion in SCC and melanoma
Blistering diseases of the skin
Autoimmune diseases
- Bullous pemphigoid
- Dermatitis herpetiformis
Genetic diseases
- Epidermolysis bullosa
Dermis:
Composition?
- non- cellular and cellular
two types of dermis?
- Dense connective tissue (collagen, elastin, extracellular matrix)
- Nerves, blood vessels, lymphatics, histiocytes, mast cells, plasma cells, lymphocytes
- Mechanoreceptors, thermoreceptors
- Subcutaneous fat
Epidermal appendages
- Pilosebaceous units
- Sweat glands
two types of dermis:
Papillary dermis - Fingerprints
Reticular dermis
why does papillary dermis form fingerprints?
In thick skin the dermis-epidermis interaction is in a serrated form.
this increases the SA between the EPI and dermis
Skin appendages
Hairs and sebaceous glands
= pilosebaceous unit
Sweat glands
- eccrine
- apocrine
Temperature Regulation in the skin.
Vasodilatation causes increased blood flow, hence loss of heat = cooling.
Evaporation of sweat lowers surface temperature.
Basal Cell Carcinoma characteristics:
Similar presentation to SCC
NOT an epidermal tumour - arises from hair follicle
Invasive and locally destructive but very unlikely to metastasize
Will continue to grow locally
Related to sun exposure (UV light)
Eccrine Sweat Ducts histology (How are they different to the glands)
Two layers of epithelia
Duct has one layer of cuboidal cells and a second layer of dark cells (myoepithelial cells) epi cells that have contractile ability (expels fluid onto the surface).
What is cancer of the eccrine tissue called?
Eccrine spiradenoma
