FTM 50 - Integument 1 Flashcards
What is the cutis?
The skin
What percentage of body mass is the skin?
15-20%
Describe the two main layers of the cutis and their components.
Epidermis - stratified squamous keratinized epithelium
Dermis - loose connective tissue followed by dense irregular connective tissue
What determines whether a region of cutis is classified as thick or thin skin?
The thickness of the epidermal layer only
What are the common epidermal derivatives (epithelial skin appendages) we need to know and are they located in thick or thin skin?
What are the primary functions of the integumentary system
List the layers of the epidermis and briefly describe the cells found within each layer.
What is the predominant cell type of the epidermis?
Keratinocytes
Describe the junctional complexes associated with keratinocytes.
Keratinocytes are attached to each other by desmosomes and to the basal lamina by hemidesmosomes.
Describe the keratinocyte life cycle
They originate in the stratum basale and sequentially move through the layers until undergoing a special type of programmed cell death. They will then eventually be sloughed off from the surface of the stratum corneum.
What is the primary purpose of a keratinocyte?
Maintain attached to other keratinocytes, continually produce keratin to strengthen the epidermis, and continually produce lamellar bodies to act as a water barrier.
What regulates keratinocytes sloughing off from the stratum corneum?
Proteolytic activity on the desmosomes holding the keratinocytes to each other
Describe the structure, appearance, and the junctional complexes associated with melanocytes.
What are melanocytes derived from?
The neural crest - dendritic cells
What is the primary function of melanocytes?
Produce melanin that is transferred to surrounding keratinocytes via cytocrine secretion.
What is the typical melanocyte to keratinocyte ratio and how does that ratio vary across the different races?
1:4 to 1:10 and that is consistant throughout all races. Skin colour is from the amount of melanin produced NOT by the number of melanocytes.
Describe how a melanocyte makes melanin.
It oxidizes tyrosine into DOPA (3,4-dihydroxyphenylalanine) and then utilizes DOPA to make melanin
What is the lease abundant cell found in the epidermis?
Merkel’s cells
Unless you’re talking specifically about skin where sensory perception is acute (fingertips)
What is the primary function of Merkel’s cells and how does it perform this function?
They detect touch sensations and relay this information to the brain by releasing neurosecretions to the closely associated terminal bulb of afferent myelinated nerve fibres (aka merkel’s corpuscle)
Briefly describe some of the unique structural characteristics that Merkel’s cells possess.
They have desmosomes and contain keratin filaments
Their nuclei are lobed
Their cytoplasms contain neurosecretory granules
What are the primary functions of a Langerhans cell?
What does the langerhans cell arise from?
The common lymphoid progenitor
Briefly describe the structure, functional complexes, and microsopic appearance of the langerhans cell.
They have dendritic processes like melanocytes
Nucleus stains heavily blue while the cytoplasm remains clear (H & E)
Possess no desmosomal junctions
What is a delayed-type hypersensitivity reaction and which epidermal cell is involved with it?
Hyersensitivity reactions are a set of undesirable reactions produced by the normal immune system. Delayed type hypersensitivity reactions take several days to develop and Langerhans cells can be involved.
What is this an image of and in what cell type is this found?
That is a birbeck granule which is a small vessicle in the shape of a tennis racquet (function unknown). These structures are found in Langerhans cells
Describe the structure, microscopic appearance, and junctional complexes of the cells of the stratum basale.
Single layer of cuboidal cells
Intensely basophilic due to less cytoplasm and closely packed nuclei
Contains many melanin granules
Rests on basal lamina and is attached to it by hemidesmosomes
Extensive desmosomal junctions
What cells compose the stratum basale?
Keratinocyte stem cells
Melanocytes
Merkel cells
What is the primary function of the stratum basale?
Provide for epidermal cell renewal
Describe the microscopic appearance of the cells of the stratum spinosum and discuss any junctional complexes that may be present in this layer.
What happens to the cells of the stratum spinosum as they move to the surface?
They increase in size and become flattened in a plane parallel to the surface.
What layer contains the most superficial of the non keratinized cells? How many cellular layers thick is this layer usually?
Stratum Granulosum
Varies from one to three cell layers thick
What is important to note about the appearance of the stratum granulosum? What gives this layer that appearance?
The SG has a granular appearance because it contains “conspicuous granules” or keratohyalin granules.
What are keratohyalin granules?
What is a lamellar body?
A lipid containing vesicle created by the golgi apparatus of the cells of the stratum granulosum. When the lipid within these vesicles is released it will become an important component of the epithelial water barrier.
Describe the formation and structure of the epithelial water barrier.
Lamellar body contents are released by stratum granulosum cells and the contents adhere to the bottom layer PM of the stratum corneum cells. This combined with the insoluble proteins on the the inside of the PM of SC cells forms the water barrier. These insoluble proteins are also associated with keratin filaments to provide mechanical strength to the water barrier.
Essentially, the water barrier is formed by the deepest cell layer of the stratum corneum which contain thick plasma membranes covered with an extracellular layer of lipid.
Things to know about the stratum lucidum
What cells make up the stratum corneum? What is unique about these cells?
Dead keratinocytes
They contain no organelles or nuclei and are filled with keratin filaments aggregated into tonofibrils
What are tonofilaments and tonofibrils? How are they made and where are they found?
Tonofilaments are keratin intermediate filaments that are commonly found looping through desmosomes. The protein filaggrin is believed to hold tonofilaments together to form tonofibrils. The cells of the stratum corneum become filled with more and more tonofibrils as they ascend to the surface of the epithelium
List the processess that occur as a keratinocyte advances through the stratum corneum and eventually sloughs off
Briefly expain what psoriasis is. What other condition is similar to psoriasis?
A disorder where the keratinocytes of the skin turnover at a higher rate than usual.
The formation of dandruff is a mild form of psoriasis on the scalp
Describe how the junction between epidermis and dermis appears in thick and thin skin.
What names are used to describe the epidermal protrusions into the dermis and the dermal protrusions into the epidermis?
