Skin Flashcards
Recognise the skin as an organ
The skin is a combination of tissues. It has its own blood supply and accounts for 16% of the total body weight. It is the largest organ in the body and acts as a major compartment separator. It also helps with body homeostasis, sensory reception and protects us from the external environment.
Describe the layers of the skin (epidermis, dermis, hypodermis)
The skin is composed of 3 layers
o Epidermis - epithelium, forms boundary between internal and external compartments
o Dermis - connective tissue, gives structural strength.
o Hypodermis - Fat (sometimes not seen as a layer of skin)
Understand the mechanism and importance of keratinisation of epithelium.
Epithelium contains 4 types of cells, including keratinocytes. Keratinization is an organic process whereby keratin is deposited in cells and these become horny, as in dead skin, nails, hair etc. Important in the production of secondary structures of skin, and waterproofs the skin by filling the intercellular spaces with hydrophobic “cement”.
Describe the 5 layers of the epidermis
There are 5 layers of the epidermis. They aren’t sharply defined, but act in a continuum from the basement membrane to the surface.
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
- Dermi
Describe the 5 layers of the epidermis
Stratum Germinativum • Bound to basement membrane by hemidesmosomes. • Bound to other cells by desmosomes • Regular assortment of organelles • Stem cells
Stratum Spinosum
• Spinous layer
• Created after cell death
• Cells shrink but desmosome junctions create “spines”
Stratum Granulosum
• Defined by presence of keratohyalin granules
• Accumulations of protein around keratin intermediate filaments
(Stratum Lucidum) Stratum Corneum • St. Lucidum hard to identify. • Keratohyalin converted to Keratin. • Disulphide linkages give strength. • No organelles • Desmosomes bind cells • 30 day turnover
Dermis
• Layer between epidermis and subcutaneous fat, made up of 2 layers:
– Papillary layer : Loose connective tissue, cellular
– Reticular layer : Dense irregular connective tissue, fibrous
Describe the organisation of connective tissue in the dermis
The dermis is composed to 2 layers:
o Papillary Layer • Loose connective tissue • Irregular interface with epidermis • Cellular eg macrophages • Blood vessels • Nerve endings
o Reticular Layer
• Dense irregular connective tissue
• Collagen bundles in 3 planes
• Elastic fibres
Describe the nerve tissue of the skin, including sensory receptors.
o Meissner’s corpuscles - light touch e.g. fingertips
o Paccinian corpuscles - vibration & pressure
o Pain receptors
o Thermoreceptors
Describe the function of melanin and its production
Skin colour influenced by:
– Blood
– Carotene
– Melanin - protects against UV
Melanocytes produce melanin in the stratum germinativum and “injects” melanin between cells. Mainly found on “Sun” side of nuclei to protect the nuclear DNA of the skin cells from mutations by damaging ionizing radiation of the suns UV rays.
Describe the physical characteristics of melanoma
ABCD
A - asymmetry (unsymmetrical)
B - border (ragged or irregular)
C - colour (if it varies)
D - diameter (larger than pencils eraser)
Define epithelium and their basic functions
Lines cavities of the body, and covers surfaces while also separating compartments. Also form glands for the secretion of hormones.
Define glands and the basic function of glandular epithelium
Secretory cells grouped together for the secretion of various molecules e.g. hormones, enzymes, muffins from single celled goblet cells. Can be single cells or multicellular, and can be exocrine and endocrine
Define endocrine and exocrine glands and quote examples of both
Exocrine - release their secretions to the body external environment e.g. goblet cells, sweat ducts
Endocrine - ductless and release their secretions directly into the bloodstream or the bodies extracellular compartment
Explain how the structure of glands varies with function
Acinar - small and round, linked to secretion (hard in long or branched ducts to secrete sticky substances e.g. mucins)
Describe the consequences of abnormal function of glands
Over secretion of growth hormone from the pituitary gland - pituitary gigantism
Unders excretion of growth hormone from the pituitary hormone - pituitary dwarfism
Describe tight junctions and where they can be found
Occluding junctions which restrict the movement of all material between the cells they link. Cell membranes of adjacent cells partly fuse together with the help of claudins and occludent to form a barrier e.g. BBB
Consider the consequences of abnormal function of connective tissue
Leukaemia
Osteoporosis
Epidermolysis bullosa - defect in anchoring of epidermis to dermis
Describe the basement membrane of the skin
Forms a layer of ECM between the different layers of the skin (epithelium, mesothelium and endothelium.
Also called the matrix layer, and its composed of basal lamina cells and reticular lamina, which are made up of a network of collagen and laminin filaments embedded in proteoglycans
Name a junction between a cell and the ECM
Hemidesmosomes - anchor intermediate fibres of the cytoskeleton of the skin cells to the fibrous matrix proteins such as laminin of the basal lamina
What is simple epithelium?
One layer thick
What type of epithelium is found in the urethra and ureters?
stratified transitional epithelium
