Skin Flashcards
What are the functions of skin?
Physical protection - pathogens, UV light, chemical stress, waterproof - top layer has keratin
Thermoregulation- arterio-venous shunts provides a superficial blood supply.
Sensation - receptors for touch, pressure, pain, temperature
What are the more chemical functions of skin?
Metabolic functions - subcutaneous fat, adipose tissue produces vitamin D, triglyceride storage.
Indicator of general health
What are the 3 layers of skin?
Epidermis - brown/purple with many cells
Dermis - pale pink, many collagen fibres
Hypodermis - yellow, adipose tissue and sweat glands with ducts.
What is the classification of epidermis?
Keratinised stratified squamous epithelium.
Mostly filled with keratinocytes
Squamous because the squamous layer is at the top.
What is the classification of dermis?
Mainly dense irregular connective tissue.
Some loose connective tissue underlying epidermis.
What is the classification of hypodermis?
Connecting to underlying tissues
Mainly adipose tissue.
What are the layers of the epidermis?
Basal layer
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
What is the basal layer?
Cuboidal cells.
At the bottom of the epidermis, attaches to basement membrane via hemidesmosomes.
Mitosis occurs to replenish above layers.
Melanocytes present.
What is the stratum spinosum?
Connected by desmosomes.
Gives prickly apperance on dehydration.
Produces cytokeratin - which aggregate as tonofibrils, found attached to desmosomes.
What does the epidermis look like?
see image
What is the stratum granulosum?
Basophilic granules - stains strongly with haemotoxylin - very dark purple.
Granules have lots of keratohyalin.
Become squamous cells.
How does keratin mature in the epidermis?
Some cytokeratin in basal layer.
Cytokeratin is arranged into tonofibrils in stratum spinosum.
Keratohyaline granules in stratum granulosum.
Mature keratin in stratum corneum - combination of keratohyaline and cytokeratin.
What does keratin do in the stratum corneum?
Mature keratin is overproduced and epidermal cells begin to die.
All the organelles are kicked out - no nuclei present, become squames and flake off.
The epidermal cells are constantly regenerating, with new cells being created by mitosis in the stratum basale and moving up the epidermis.
What is the stratum lucidum?
The layer between the stratum granulosum and corneum.
Only present in thick skin - palms of hands, fingers, soles of feet.
Very thick layer of keratin, no hairs.
What are melanocytes?
Found in the basal layer.
Long cellular processes extend into the stratum spinosum for UV protection.
Melanin creates a barrier around nucleus to protect from UV.
What do melanocytes look like?
see image
What are Merkel cells?
In the stratum basale, associated with free nerve ending.
For sensory processes - light touch.
What are Langerhan’s cells?
Immune cells found in all epidermal layers and the dermis.
Antigen presenting cell, similar to macrophages but only found in skin.
What is the papillary dermis?
Found directly underneath epidermis, a small layer.
Dermal papillae are ridges and extensions of dermis into the epidermis.
Loose connective tissue.
What is the reticular dermis?
Reticular dermis is a much larger layer below the papillary dermis.
It is dense irregular connective tissue - has more collagen.
Elastin is present throughout the dermis to provide stretch.
What does the papillary layer of dermis look like?
see image
What does dermis look like?
see image
What is the function of the papillary dermis layer?
Allows space for vasculature and capillaries to be present directly under the epidermis.
Also allows for diffusion through ground substance.
How does the dermis bring about thermoregulation?
The subpapillary plexus and cutaneous plexus have shunting vessels between them.
Shunting vessels can be open or closed.
When closed, blood flow to the epidermis is reduced, in extreme temperatures - hypothermia.
This is controlled by the autonomic nervous system.
What receptors are found in the dermis?
Encapsulated: Meissner’s corpuscle - in papillary layer.
Pacinian corpuscle - dermis and hypodermis.
Ruffini’s corpuscles.
Merkel’s discs are associated with the Merkel’s cells - unencapsulated.
What does Meissner’s corpuscle look like?
see image
What does the Pacinian corpuscle look like?
see image
What is hair?
A skin appendage found on thin skin.
Hair develops from hair follicles - invaginations of the epidermis.
Hair is made from keratin, and has a sebaceous gland attached to secrete oily sebum.
What does hair look like histologically?
see image
What is arrector pili muscle?
Makes hair stand on end when innervated by the sympathetic nervous system.
What are the differences between sweat glands and sebaceous glands?
Sebaceous gland is large, attached to hair follicles, found in dermis.
Sweat glands are found in the superficial hypodermis (subcutis), and secretes watery fluid.
Both are epithelial based tissues.
What are the types of sweat glands?
Eccrine
Apocrine
What are eccrine glands?
Function in heat loss.
Less viscous
Found everywhere.
What are apocrine sweat glands?
Open into hair follicle.
Regulated by hormones.
More viscous.
Location limited to genitals.
What are disorders of the epidermis?
Psoriasis - abnormal epidermal growth - flaky skin.
Malignant melanoma - growth of melanocytes.
Vitiligo - autoimmune destruction of melanocytes.
Dermatitis - inflammation of skin.
Contact dermatitis - mediated by Langerhan cells.
What are burns?
Damage to skin from heat, electricity, chemicals or radiation.
What are full thickness burns?
Affects the whole of the skin - to subcutaneous tissues.
Skin is dry and white with no blisters.
Painless
What are partial thickness burns?
Superficial dermal - epidermis and upper dermis affected.
Skin is pale pink and painful with blistering.
Deep dermal - all dermis is affected, blisters, can be painful or painless.
What are superficial burns?
Affects only the epidermis.
Skin is red and painful but not blistered.
Why are some burns painless?
Pain receptors are found in the dermis.
Damage to pain receptors in the dermis means it is painless.
What are autografts?
Uses tissue from their own body - no rejection but longer recovery time.
What are allografts?
Uses tissue from another person’s body - plenty of donor tissue available, but more rejection, disease transmission, higher cost.
