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
What type of epithelium is found in the trachea and upper respiratory tract?
Pseudo-stratified columnar epithelium - cilia and secretions
Describe the formation of exocrine and endocrine glands
- During development, epithelial cells grow downward into their supporting connective tissue.
- In the development of exocrine glands, they remain connected to the parent epithelium, and a hollow center, or lumen, forms to create a duct that provides a passageway for secretions to move to the surface of the epithelium and into the external environment.
- In endocrine glands, they lose the connecting bridge of the cells that links them to the parent epithelium. Their secretions then go directly into the bloodstream.
Describe the components of the ECM
Fibres e.g. collagen, elastin, reticulin
Ground substance/matrix - proteoglycans
Tissue fluid
Give examples of loose connective tissue
Permanent fixed cells e.g. fibroblasts, macrophages, adipocytes
Transient cells e.g. white blood cells
Give examples of dense regular and dense irregular tissues
Dense regular - made up of parallel collagen to form tense structures e.g. tendons and ligaments
Dense irregular - randomly aligned collagen e.g. muscles, nerves, sheaths, sebaceous glands
What type of epithelium makes up the epidermis?
Stratified squamous keratinising epithelium
What is another term for epidermal cells?
Keratinocytes
What are the 4 basic cell types of the epidermis?
Keratinocytes - waterproofing
Melanocytes - pigment
Langerhans cells - immune surveillance
Merkel cells - touch
What influences skin colour?
Blood
Carotene
Melanin - produced in stratum basale
Describe the origin of hair follicles
Form in epidermis in utero. from the down growth of epithelial cells which invade a knot of blood vessels. This leads to hair growth
Give examples of sebaceous, apocrine and eccrine glands
Sebaceous - hair follicles and sebum secretion
Apocrine - axillary sweat glands connected to hair follicles, protein rich secretions
Eccrine - simple and tubular sweat glands, watery secretion for thermoregulation
Describe the 4 main sensory nerve endings in the skin
Meissners corpuscles - light touch
Paccinian corpuscle - vibration and pressure
Pain receptors
Thermoreceptors
What detects light touch?
Meissners corpuscle
What detects vibration and pressure?
Paccinian corpuscle
What are the 4 basic cell types of the epithelium?
Keratinocytes
Melanocytes
Langerhans cells
Merkell cells/receptors
Describe the cells of the stratum basale
Tall columnar cells, constantly proliferating (undifferentiated stem cells) interspersed with melanocytes and merkel cells. Bound to the basal lamina by hemidesmosomes
Describe the stratum spinosum
Post mortem production of spines (desmosome junctions). Preparative layer for keratinisation
What are the granules in the stratum granulosum made up of?
Keratohyalin (precursor of keratin)
What bonds are formed between the cells of the stratum corneum?
Disulphide
Whats the turnover of the stratum corneum?
15-30 days
What is the aetiology of psoriasis?
AI disorder affecting keratinisation
What is the source of variety in epithelial thickness around the body?
Stratum corneum layers and dermis
Describe the dermis
Layer between epidermis and subcutaneous fat. 2 layers:
Papillary layer - loose connective tissue, blood vessels and nerve endings
Reticular layer - dense irregular tissue (collagen and elastic fibres)
What is the difference between the secretions of the sebaceous, apocrine and eccrine sweat glands?
Sebaceous - sebum
Apocrine - protein rich and thick e.g. sweat
Eccrine - watery e.g. sweat
Describe the structure of eccrine sweat glands
Simple tubular coiled glands
Straight and coiled in dermis
Spiral channel in epidermis
Involved in thermoregulation
What is involved in thermoregulation?
Eccrine sweat glands
Blood vessel dilation
Hair
Name the 4 sensory nerve endings found on the skin
Ruffini corpuscle - stretch
Meissners corpuscle - light touch
Pacinian corpuscle - vibration and pressure
Merkel receptors - pressure, position and isotonic touch
What do ruffini corpuscles feel?
Stretch
What do Meissners corpuscles feel?
Light touch
What do Pacinian corpuscles feel?
Vibration and pressure
What do Merkel receptors feel?
Pressure, position and isotonic touch
