BIOLOGY OF SKIN Flashcards
what are some functions of the skin?
physical barrier to water, chemicals, particles and infectious agents
temperature regulation
vitamin D synthesis
immune defence
protection against UV
site of pathology
specialised appendages e.g. skin and nails
what are the 3 layers of the skin?
epidermis
dermis
hypodermis
what is the histology of the epidermis?
continuous sheets of stratified squamous epithelium
what is the histology of the dermis?
a thick layer of dense, irregular connective tissue
what is the histology of the hypodermis?
loose connective tissues with adipose cells
has skin appendages e.g. hair follicles
describe the main differences between thick and thin skin?
thin skin is more abundant
thick skin has a much more prominent stratum corneum
thick skin doesnt contain hair or sebaceous glands like thin skin
thick skin may contain a stratum lucidum unlike thin skin
outline the structure of the epidermis?
stratum corneum stratum lucidum stratum granulosum stratum spinosum stratum basale basement membrane
describe the stratum basale?
this layer is on top of the basement membrane and is a single layer of cuboidal cells with stem like properties.
describe the stratum spinosum?
the cuboidal cells from the stratum basale migrate upwards, proliferating to form the stratum spinosum which is a few cells thick and is characterised by irregular cells and tight junctions forming tonofibrils
what are tonofibrils?
a tiny fibre occurring in bundles in the cytoplasm of cells that lie in contact
describe the stratum granulosum?
cells from the stratum spinosum migrate upwards again and differentiate to develop keratohyalin granules and lamellar bodies
what are keratohyalin granules?
granules containing proteins which bind to and aggregate keratin filaments
what are lamellar bodies?
they store and secrete lipids- important for keeping skin hydrophobic
describe the stratum corneum?
the cells from the stratum lucidum/stratum granulosum migrate upwards and undergo apoptosis to form the tough surface layer of the skin
what do keratinocytes do?
they produce keratin
the degree of keratinisation increases with increased proliferation and differentiation as you move up towards the epidermis
what do melanocytes do?
they produce melanin which is responsible for skin pigmentation and protection against UV damage
what do melanosomes do?
they are transferred from melanocytes into keratinocytes and contain melanin
what are rete ridges?
extensions of the epidermis into the dermal layer- forms the undulating structure of the epidermis with the dermal papillae
what are dermal papillae?
protrusions of dermal connective tissue into the epidermal layer- forms the undulating structure of the epidermis with the rete ridges
why is the undulating structure of the epidermis important?
it creates a greater surface area and increases attachment between the epidermis and dermis which prevents mechanical damage
how does blood flow nourish the epidermal layers?
The epidermis does not contain blood vessels; instead, cells in the deepest layers are nourished by diffusion from blood capillaries that are present in the upper layers of the dermis and enter through the dermal papillae
what is the structure of the dermis?
its formed of the papillary dermis and the reticular dermis
whats the papillary dermis?
a thin layer underlying the epidermis made up of loose connective tissue with fine collagen and elastic fibres
whats the reticular dermis?
a thick layer making up most of the dermis formed from dense, irregular connective tissue containing thick collagen bundles
contains fibroblasts, immune cells, blood vessels, nerves and skin appendages
what is the hypodermis?
aka subcutaneous layer
the layer under the dermis thats composed of mature adipose tissue
whats the function of the hypodermis?
insulation, protection and energy store
what are the main skin appendages?
hair
nails
glands
what are the 3 glands found in the skin?
sebaceous glands
eccrine sweat glands
apocrine glands
what is the nail plate?
a hard keratinised plate at the distal end of each digit
describe the structure of hair follicles?
at the base, there is a bulbous expansion containing the hair papilla where epithelial cells divide and develop
the hair shaft grows upwards
the 3 layers of the hair from inwards to outwards are the medulla, cortex and cuticle
what are sebaceous glands?
glands that secrete sebum (lipid substance) to keep hair soft, supple and waterproof
they grow and burst to release their contents into the hair folllicles
what are eccrine sweat glands?
tubular glands in the reticular dermis that secrete sweat directly onto skin surfaces by merocrine secretion
what are apocrine glands?
coiled tubular structures in the reticular dermis localised to the axillae, mammary and groin that become activated during puberty. they secrete a substance containing pheromones and cause body odor upon reaction with skin bacteria
how do superficial wounds heal?
the epidermis can regenerate from the basal layer
how do wounds extending into the dermis heal?
haemostasis, inflammation, fibroplasia, angiogenesis, epithelisation and remodelling
what is haemostasis?
formation of a fibrin clot to stop blood loss
what is fibroplasia?
fibroblasts laying down new collagen
what is angiogenesis?
formation of new blood vessels
what is epithelialisation?
migration and mitosis of keratinocytes from wound edges to form a new basal layer
how do deepest wounds heal?
if the dermis and deep parts of appendages are destroyed then spontaneous healing is not possible
what is an ulcer?
loss of epidermis and papillary dermis
what is a bruise?
leakage of blood into the dermis
what is a callus?
hyperplasia of epidermis following pressure
