Physiology of Skin Flashcards
In foetal skin development what are the first three layers formed?
Periderm
Basal layer
Dermis
What are the final five layers of skin?
Keratin Layer Granular Layer Prickle Cell Layer Basal Cell Layer Dermis
What are blaschko’s lines?
Developmental growth patterns of skin not following vessels, nerves or lymphatics
What type of cell makes up the epidermis?
Stratified squamous epithelium
Describe the basal layer
Usually one cell thick contains lots of stem cells & free nerve endings
Describe the prickle cell layer
Cells move upwards to fit into each other - contains lots of desmosomes to connect intermediate filaments. Keratin is produced.
What substance does the granular layer contain that contributes to skin hydration?
Filaggrin - repeat amino acid gets broken down by enzymes. The free amino acid binds to water resulting in a natural moisturiser
What happens to the cell structure in the granular layer?
Cell nuclei are lost and lamellar bodies present
Name the lamellar bodies
Odland bodies (secretory organelle)
What is the other name for the keratin layer?
Stratum corneum
Describe the keratin layer
Insoluble cornfield envelope, 80% keratin and filaggrin. Granules release lipids to produce a waterproof barrier
What are corneocytes?
Overlapping non-nucleated cell remnants
Define a scar
Loss of skin appendages
Where can mucosal membranes be found?
Eyes, genitourinary tract, GI tract & mouth
Name three specialised epidermal cells
- melanocytes
- langerhans cells
- merkel cells
Where are melanocytes found?
Basal layers & above
What is the function of melanocytes?
Contains melanosomes where tyrosine is converted to melanin in response to UV. Once full of melanin granules the melanosomes are transferred to adjacent keratinocytes by dendrites and the melanin cap protects the nuclei in basal cells from further UV exposure.
Where are langerhans cells found?
Originate in the bone marrow - found in the prickle cel layer, dermis & within lymph nodes
What is the function of langerhans cells?
Part of the immune system - present antigens & circulate to lymph nodes
Describe Merkel cells
In basal layer between keratinocytes & nerve fibres act as mechanoreceptors
What is the name of the unit which contains a hair?
Pilosebaceous unit
What does the pilosebaceous unit consist of?
Epidermal component plus dermal papilla - adjacent sebaceous gland with arrestor pili muscle
What are the three phases of hair growth?
anagen - growing
catagen - shrinking
telogen - resting
Describe the impact of hormonal secretion on the pilosebaceous unit
Cells at the centre of the gland fall apart to produce sebum - holocrine secretion
Give an example of a hormone that acts on the pilosebaceous unit
Androgens
What does the nail matrix consist of?
Rapidly dividing epidermal cells situated at the proximal end of each nail - protected by the cuticle & nail fold
What is the nail bed made of?
Tough collagen
State the name of the white bit at the bottom of a nail
Lunula
What is the epithelium underlying the free edge known as?
Hyponychium
State the role of the dermo-epidermal junction
support, anchor & adhese basal cells
How is the dermo-epidermal junction maintained?
Hemi-desmosomes (whereas the prickle cell contains desmosomes)
How is the DE junction strengthened & increased in surface area?
Papilla from both layers - rete pegs from the epidermis
Name the general components of the dermis
- ground substance
- cells
- fibres
- muscles/blood vessels/lymphatics/nerves
What cells can be found in the dermis?
fibroblasts, macrophages, mast cells, lymphocytes, langerhans
What fibres can be found in the dermis?
Collagen & elastin
Describe the ground substance
Semisolid matrix of glycosaminoglycans which allow some dermal structures to move
What is the role of fibroblasts?
Synthesise - collagen, elastin & glycosaminoglycans
Describe the relationship between supply and metabolic need in the dermis
Supply > need (vessel walls are well supported for blood flow)
Describe the role of lymphatic vessels in the dermis
Provide continual drainage of plasma proteins, extravasated cells & excess interstitial fluid
What is the somatic sensory supply to the dermis?
Free nerve endings - dermatones
Pacinian - pressure
Meissners - vibration
What is the autonomic supply to the dermis?
Through blood vessels, nerves and glands
Name the three types of skin gland
Sebaceous
Apocrine
Eccrine
Describe the sebaceous gland
Hormone sensitive they grow & activate in puberty. Produce sebum by holocrine secretion which cells disintegrate & then release their lipid cytoplasm
What is the function of the sebaceous gland?
- controls moisture loss
- protects from fungal infections
Describe the apocrine gland?
Part of the pilosebaceous unit in the axilla and perineum - androgen dependent it produces an odour after bacterial decomposition
Describe the eccrine gland
Found everywhere on skin surface, cholinergic nerve supply (mental, thermal, gustatory). Role is to cool & moisten.
State six functions of skin
- barrier
- metabolism & detoxification
- thermoregulation
- immune defence
- communication
- sensory function
In what ways does the epidermis act as a barrier
- physical barrier trauma/UV
- immune system stops pathogens entering body
- chemical barrier
What happens if the skin loses its barrier function?
Fluid & protein loss, potential infection
How does the skin help with metabolism?
Vitamin D metabolism - UVB converts 7- dehydrocholesterol to vitamin D
Thyroid metabolism - thyroxine (T4) is converted to triiodothyronine (T3)
What happens if the skin can no longer help with metabolism?
- Rickets
- Disordered thyroxine metabolism (hypothyroidism)
How does the skill control temperature and what will failure result in?
Regulates heat to prevent extremes by thermoreceptors failure will result in heat loss
Describe the skins role in immune defence
Prevents infection by acting as a barrier, produces a response to sunlight & allergic reactions - both specific and non-specific
What will happen if the skin does not adequately defend against infection?
Spread of infection into the body
Name three ways the skin contributes to communication
- visual
- odour
- sociosexual
Massively contributes to skin stigma and social exclusion
What will failure in sensory function of skin result in?
Pain/Injury
