Structure and Function of the Skin Flashcards
What are the three layers that form the skin?
+ Epidermis
+ Dermis
+ Hypodermis
Describe the epidermis
+ Avascular epithelium
+ Undergoes proliferation
+ Synthesises keratin
Describe the dermis
+ Vascular, tough
+ Contains blood vessels, lymphatics and cutaneous nerves
+ Collagen and elastic fibres not replaced with age
Describe the hypodermis
+ Superficial fascia, varies in thickness
+ Contains blood vessels, lymphatics and cutaneous nerves
+ Contains adipose tissue
+ Contains skin ligaments, loose skin or taut skin implication in scarring and inscisions
What are the multiple functions of skin?
+ Temp. regulation
+ Metabolic function
+ Internal homeostasis
+ Protection
+ Psycho-social signals
+ Sensation
What are the 5 layers that form epithelium only found in thick skin areas around body (palms, soles)
+ S. Corneum: waterproof cell ghosts
+ S. Lucidum: specialised cell death programme
+ S. Granulosum: keratohyaline granules, keratin aggregation
+ S. Spinosum: IF (keratin) linkage via desmosomes
+ S. Basale: cell division (stem cells)
Describe features of stratum basale
+ Hemidesmosomes (junctions) anchor basal cells to the basal lamina
+ Dermis is anchored to basal lamina by Collagen VII (binds epidermis to dermis)
What is it called when Collagen VII can be mutated into forming blisters?
Dystrophic epidermolysis bullosa
Describe features of stratum spinosum
+ Intermediate filaments (keratin) K1/K10 expressed
+ Linked from cell to cell by desmosomes
+ Hemisdesmosomes also link basal cells with basement membrane
What does filaggrin in keratohyaline granules do?
Aids cornification
What is the role of filaggrin and its precursor profilaggrin in the S. granulosum?
+ Filaggrin and its precursor profilaggrin maintain the optimal skin barrier
+ Main component of keratohyaline granules in S. granulosum
+ Aids keratin filament aggregation
+ Inhibits water loss (filagrin cleaved into amino acids which aid in maintaining moisture)
What is there to know about mutations associated with filaggrin and keratinisation?
+ The most common cause of keratinisation orders; icythyosis vulgaris
+ Cause filaggrin expression and exzema. Implicated in eczema (found in 50% of severe cases)
+ Null mutations associated with asthma
Where are melanocytes found and what do they synthesise and release?
+ In the basal layer of the epidermis
+ Synthesise and release brown pigment called melanin
What are some features of melanin?
+ Amount varies between different races and individuals
+ Absorbs UV-B and prevents DNA damage to the underlying cells of the hypodermis
+ Lower incidence of skin cancer in individuals with more melanin
+ Melanoma is the tumour of these cells and is caused by exposure to UV radiation
What are some features of melanocytes?
+ Derived from neural crest cells that originate near the developing nervous system and spread into the embryo (become mesodermal by nature)
+ Synthesise specialised lysosomes that undergo exocytosis (contain pigment “melanosomes”)
Where do “melanosomes” go?
Transferred to keratinocytes
What are features of Langerhans cells?
+ Derived from monocytes
+ Macrophage-like
+ Dendritic in form
+ Mostly in stratum spinosum
+ Capture, process and present antigens
+ Activated in skin but migrate to lymph nodes
+ Express Langerin which helps degrade viruses such as HIV in specialised endosomes called Birbeck granules
Describe features of the dermis
+ Dermo-epidermal junction
- complex to prevent shearing
- papillae flatten with age, skin becomes more vulnerable
+ Papillary dermis
- comprises of fine collagen and elastin fibres, small blood vessels and nerves
+ Reticular dermis
- comprises coarser collagen and elastic fibres, larger blood vessels and nerves
Describe features of the hypodermis
+ Consists of loose connective and adipose tissue which varies in thickness in different parts of the body
+ It supports:
- deepest part of hair follicles
- eccrine and apocrine glands
+ Vascular: superficial blood vessels and lymphatics
+ Cutaneous nerves
+ Skin ligaments determine the mobility of skin implicated in scarring and incisions
+ Responsible for vitamin D production
Describe features of eccrine sweat glands
+ Simple, coiled, tubular
+ Secrete a water fluid via a duct which opens onto the surface of the skin
+ Controlled by sympathetic nervous system important in thermoregulation, also response to fear (fight/flight response)
Describe features of apocrine sweat glands
+ Found in the axillae and genital region
+ Open into the hair follicles
+ Secrete a milky secretion containing pheromones
Describe the features of hair follicles
+ Cylindrical, epithelial structures anchored in hypodermis
+ Hair shaft grows from bulb
+ Hair shaft composed of keratin
+ Follicle shaft associated with sebaceous glands that open into the follicle
+ Secrete sebum to lubricate the hair and adjacent skin
What is the function of arrector pili?
+ Contraction of smooth muscle (attached to papillary dermis and sheath of the follicle) pulls the hair upright (goosebumps)
+ Controlled by sympathetiv nervous system
What does the pilosebaceous unit consist of?
+ Hair follicle
+ Sebaceous glands
+ Hair shaft
+ Arrector pili
