Week 1 - A - Skin structure/function 1&2 - Epidermis (layers), dermis, Keratin/Melanocytes,Langerhans,Merkel cell, appendages Flashcards
What is the largest organ in the human body?
The skin
What is the outer layer of skin? What type of epithelium forms this outer layer? What is the layer that is deep to this? What type of tissue forms this layer?
The outer layer of skin is the epidermis formed by stratified squamous epithelium The layer deep to this is the dermis which is formed by connective tissue
What germ layer forms the epidermis? What is the layer that the germ cells form and how does this become the epidermis? (what is the layer that is formed and gives rise to all epidermal cells)
The ectoderm is the germ cell that forms the epidermis Ths ectorderm forms a single layer periderm- this is a temporary layer and the periderm cells are cast off once the gradual increase in layers of cells has resulted in the stratum basale (basal layer) being formed The basal layer gives rise to all epidermal cells
Which germ cell layer forms the dermis? What are melanocytes? What forms these?
The dermis is formed from the mesoderm below the ectoderm Melanocytes are pigment producing cells which are formed from the neural crest - a temporary group of cells arising from the ectoderm
What is the stage of embryo development where the germ layers are formed? * Which germ layer forms the epidermis? * Which germ layer forms the dermis?
Gastrulation is the stage of embryo development where the germ layers are formed Epidermis forms from the ectoderm Dermis forms from the mesoderm
Foetal skin development At 4 weeks ,the periderm, basal and dermis have formed What week is it when the epidermal and dermal layers have formed? Give the other names for the epidermal layers * Keratin layer * Granular layer * Prickle cell layer * Basal layer * Dermis
After 16 weeks, there is the: * Keratin layer (stratum corneum) * Granular layer (stratum granulosum) * Prickle cell layer (stratum spinosum) * Basal layer (stratum basale) * and Dermis
What is the difference between Blaschko’s lines and Langer lines? Which type of line is useful to follow when making an incision in the skin?
Blaschko’s lines represent the normal development growth pattern of the skin Langer’s line represent the natural oritentation of the collagen fibres in the skin (in the dermis to be precise) - useful to make incisions parellel to these lines for improved wound healing and less scarring
* What are the four layers in the epidermis? * What are the main cells of the epidermis and what protein does this contain?
Four layers of the epidermis Keratin layer Granular layer Prickle cell layer Basal layer Keratinocytes are the main cells in the epidermis (95%) and contain structural keratins (also found in hair and nails)
Where do keratinocytes migrate from and how long does this take? What does this site separate?
Keratinocytes migrate from the basement membrane and this takes up to 28 days The basement membrane is what separates the epidermis from its underlying tissue, the dermisent membrane.
What is the highly metabolically active epidermal layer? What type of epithelium forms it?
The highly metabolically active epidermal layer is the basal layer - it is formed of small cuboidal epithelium and is usually once cell thick
What are the shapes of the types of cell that make up the prickle cell layer is made ? There are intermediate filaments eg keratin in each cell layer What connects the intemediate filaments in the prickle cell layer?
The prickle cell layer is formed from larger polyhedral cells It contains lots of desmosomes which connect the intermediate filaments
Which epidermal layer contains lamellar bodies? What is a lamellar body and what is another name for it?
The granular layer of the epidermis contains lamellar bodies Lamellar bodies are secretory organells found in the Type II alveolar cells in the lungs and in keratinocytes in the skin They are also known as Odland bodies
Lamellar bodies contain a high lipid content What is the function of the lamellar bodies in both the lungs and the skin?
In the lungs, the lamellar bodies contained within the type II alveolar cells secrete pulmonary surfactant which acts to reduce alveolar surface tension and prevent collapse of the alveoli In the skin, the high lipid content lamellar bodies are secreted from the keratinocytes and result in the formation of an impermeable lipid containing barrier that serves as a water barrier in the keratin layer and is required for correct skin barrier function.
How many layers is the granular layer? Why is it known as the granular layer?
Basal cell layer - usually one cell thick Prickle cell layer- large polyhedral cells Granular layer - usually 2-3 layers thick Known as the granular layer because here the keratinocytes lose their nuclei and the cytoplasm therefore looks granular (eg grain like)
What is the terminal differentiate of the keratinocytes and where are these found? What is released from these cells here to form a tight waterproof barrier?
The terminal differentiation of the keratinocytes is into the corneocytes - these are found in the keratin layer (stratum corneum) From the keratincoytes, lamellar bodies release lipid to form a tight waterproof barrier at the skin - happens in the granular layer
As a stratified squamous epithelium, the epidermis is maintained by cell division within the stratum basale. Differentiating cells delaminate from the basement membrane and are displaced outward through the epidermal layers, undergoing multiple stages of differentiation until, in the stratum corneum. * What is the process where dead keratinocytes (corneocytes) are shed from the stratum corneum and replaced by the new keratinocytes? How long does it take for migration?
Desquamation, the process of cell shedding from the surface of the stratum corneum, balances proliferating keratinocytes that form in the stratum basale. The proliferating kertinocytes that form in the basal layer take roughly 28 days to migrate from the basement membrane to the keratin layer
Name 3 epidermal cells other than keratinocytes (95% of epidermal cells are keratinocytes)?
3 epidermal cells other than keratinocytes are Melanocytes Langerhans cells - immunological cells Merkel cells - mechanoreceptors
What are melanocytes? Where do they migrate from?Where are they found?
Melanocytes are pigment producing dendritic cells They migrate from the neural crest to the epidermis in the first 3 months of feotal development and are found in the basal layer and above
What is the site for synthesis, storage and transport of melanin within the melanocyte? How do melanocytes produce the melanin pigment and what is it trasnferred to?
Melanocytes contain organelles known as melanosomes which synthesis, store and transport melanin Melanocytes produce melanin by converting tyrosine to melanin pigment and transferring the full melanosomes (melanin granules) onto adjacent keratinocytes via dendrites
What are the two melanin pigments and what colour are they?
The two melanin pigments are Eumelanin - brown or black and Phaeomelanin - red or yellow
What protects the nuclear DNA in the basal cells?
The nuclear DNA in the basal cells is protected by protective caps formed by melanin
Give an example of an autoimmune disease due to the loss of melanocytes? Give an example of a genetic disorder causing the complete or partial absence of pigment in the skin?
Vitiligo represents an autoimmune disease with loss of melanocytes Albisim is a genetic disorder causing the complete or partial absence of pigment in the skin
What is the syndrome where melanin stimulating hormone is produced in excess by the pituitary gland and what is it usually caused by?
This is known as Nelson’s Syndrome- usually due to the development of an ACTH producing pituitary tumour after bilateral adrenalectomy in Cushing’s syndrome ACTH build up –> acth contains the sequence for MSH therefore when broken down by proteases releases MSH causing hyperpigmentation
Where in the epidermis are langerhans cells found? Where else are they found?
Langerhans cells are found in the prickle cell level in the epidermis as well as being found in the dermis and lymph nodes
