Structure and Function of the Skin Flashcards
what are the 5 functions of skin?
Protection
Thermoregulation
Sensation
Sexual signalling
Metabolic functions
explain protection as a function of the skin
Against UV light
Thermal/mechanical stress
Barrier to harmful pathogens causing infection
explain thermoregulation as a function of the skin
maintaining a constant body temperature.
The rich vascular layers available in the Dermis of the skin vasoconstrict and vasodilatation to control body temperature
When hair stand on end it traps an insulating layer of air near the surface of the skin, again minimising heat loss.
Sweat production also aids heat loss.
The subcutaneous fatty layer under the skin acts as insulation, minimising heat loss to the environment
explain sensation as a function of the skin
Many different receptors for touch, temperature, pain and pressure.
Largest sensory organ in the body.
Number of receptors vary depending on the region of the body. For example, most numerous on hands and feet and least numerous on back
explain sexual signalling as a function of the skin
Sex pheromones are produced by apocrine sweat glands.
explain metabolic functions as a function of the skin
Vitamin D3 synthesis through the action of UV light.
The subcutaneous fatty layer under the skin contains adipose tissue which is a major source of energy
what does variation in skin colour depend on?
Skin colour depends on the amount of melanin pigment secreted by melanocytes of the epidermis
what does variation in skin thickness depend on?
The degree of keratinisation, and therefore the skin thickness varies on different parts of the body.
Thickness is increased by mechanical stress (skin on the sole of the foot in a baby less than in an adult)
what helps with the skins gripping ability?
Dermal ridges on the hands and feet improve the skin’s ability to grip and are important in texture recognition
what reduces in the skin with age?
The elasticity of skin is reduced as you age. The skin becomes lined, sags and recovers poorly after deformation.
what are epidermal appendages?
give examples
anatomical skin- associated structures that serve a particular function including sensation, contractility, lubrication and heat loss
Nails- provide a firm base for the finger or toe pulp. Most of the nail bed appears pink because of the underlying capillaries.
Hairs - density differs between regions. Abnormal hair distribution can be due to an endocrine imbalance.
Sweat glands- vary in character and density.
what are the 2 types of sweat glands?
Eccrine sweat glands:
- Cover most of the body
- They are simple tubular glands important in thermoregulation through the evaporation of odourless sweat.
- Their activity is under the control of the sympathetic nervous system.
Apocrine sweat glands:
- They are large and are only present at the axilla, the ano-genital region and the mammary areola.
- Their duct invariably opens into a hair follicle.
- The saline-based product (odourless) produced is more viscous than the product of eccrine sweat glands.
- It contains an organic product that once decomposed by bacteria produces pheromones which has odour e.g. armpits.
where in the body are sebaceous glands present?
Sebaceous glands are present everywhere but the palm of the hand or sole of the foot. Their duct also open up into the hair follicle. The sebum they produce provides a protective covering for the skin.
what are the 3 layers of skin?
epidermis
dermis
hypodermis
what is the epidermis layer of skin?
The epidermis is the superficial layer of skin.
It made up of 4/5 layers of epithelium on the basement membrane (connective tissue).
Adulations in the base of the epidermis (dermo-epidermal junction) allow the skin to be tethered to the dermis.
no vasculature
what is a blister?
the accumulation of fluid between the epidermal and dermal layer.
what is the dermis layer of skin?
(Main component of leather)
Underlying the epidermis is a thicker layer called the dermis
It is made of dense collagenous connective tissue - which provide support for blood vessels.
The extracellular matrix includes type 1 collagen, elastin and fibroblasts (produce the matrix & fibres)
Blood vessels provide nutritional support for dermal and epidermal cells (epidermis has no blood vessels) and are involved in thermoregulation.
The dermis also has hair follicles, sebaceous glands, sweat glands, lymphatic vessels and mast cells.
what are the different unencapsulated and capsulated nerve endings?
Unencapsulated:
Merkel cells
Free nerve endings
Encapsulated:
Pacinian corpuscle
Ruffini corpuscles
Meissner’s Corpuscle
what is an example of the sensory receptors in the dermis?
Pacinian corpuscle: found deep in the dermis and responsible for detecting pressure
Meissner’s corpuscle: found just below the dermal epidermal junction. These are responsible for detecting light and fine touch.
what are the 2 sublayers of the dermis?
Papillary layer:
Consists of connective tissue with especially types I collagen fibres and some type III.
Also contains fibroblasts (spindle-shaped cells), scattered mast cells, macrophages and other leukocytes.
Fibrils of type VII collagen insert into the basal lamina, helping to bind the dermis to the epidermis – called anchoring fibrils.
Reticular layer:
Consists of dense irregular connective tissue with more fibres and fewer cells than the papillary layer.
The network of elastic fibres present provides elasticity to the skin
what are the 5 sublayers within the epidermis?
(Corn Lovers Grow Several Bales)
Stratum Corneum
Stratum Lucidum
Stratum Granulosum
Stratum Spinosum
Stratum Basale
what is the stratum corneum?
The most superficial layer (20-30 layers of cells).
The cells are dead keratinocytes (corneocytes) which have lost their nuclei and cytoplasm.
They form the keratin layer which makes the skin impermeable to water.
what is the stratum lucidum?
Only in thick skin
2-3 layers of flattened dead translucent keratinocytes.
Their cytoplasm consists of eleidin (a clear protein), which an intermediate form of keratin.
what is the stratum granulosum?
3-5 layers of flattened cells.
Keratinocytes migrating from the underlying stratum spinosum become granular cells.
Their cytoplasm is filled densely with keratohyalin granules which when combined with cytokeratin (produced by the spinosum cell layers) forms keratin.
what is the stratum spinosum?
Thickest layer
Contains several layers of keratinocytes.
This is where terminal differentiation begins and keratinocytes lose their ability to divide.
The cells have central nuclei and are actively synthesising cytokeratin (keratin filaments)
Keratin filaments assemble into bundles called tonofibrils that converge and terminate at the desmosomes - which hold the cell layers together.
They also contain Langerhans cells
what is the stratum basale?
Deepest layer
A single layer of cuboidal cells - Basal cells
If the basal cells die, new skin will not be regenerated – need a skin graft.
Attached to the basement membrane, at the dermal-epidermal junction, by hemidesmosomes.
The adjacent basal cells are attached by desmosomes.
Basal cells are stem cells of the skin. New cells produced by Stratum Basale (by mitotic division) move up through the different layer which provides constant cell turnover and allows for regeneration of the keratin layer.
Also contains Melanocytes and Merkel cells
what does THIN skin consist of?
most predominant type of skin surrounding body
consists of 4 layers:
- stratum corneum
- stratum granuolsum
- stratum spinosum
- stratum basale
dermis of thin skin is more cellular and vascularised than thick skin
generally contains sweat glands, hair follicles and sebaceous glands
less coarse bundles of collagen
what does THICK skin consist of?
only found in 2 primary locations:
palms of hands
soles of the feet
- areas of the body that are routinely subjected to extensive abrasion
significantly thicker epidermis than thin skin
consists of 5 layers of keratinocytes (extra layer of stratum lucidum)
also has thicker stratum spinosum with more abundant tonofibrils and desmosomes
contains sweat glands but lacks hair follicles and sebaceous glands
define hair follicle
a tunnel-shaped structure in the dermis/epidermis.
define hair bulb
forms the base of the hair follicle. In the hair bulb, living cells divide and grow to build the hair shaft.
define hair papilla
penetrates the base of the hair bulb. It contains a capillary network that is required to sustain the hair follicle.
what components does each hair have attached to it?
Each hair is associated with a sebaceous gland- known together as the pilosebaceous unit.
The sebaceous gland secretes an oily lipid substance called sebum onto the hair shaft.
Each hair follicle also has a muscle attached to it, called the Arrector pili muscle.
This Muscle contracts in order to move the hair to a more erect position. This allows the hair to trap a layer of air over the skin which helps keep the skin warm.
describe each component in this transverse section of a hair
Medulla (M): central region of hair root contains large keratinized cells
Cortex (CO): contains compactly grouped heavily keratinised cells
Cuticle (CU): contains the most peripheral cells
The internal root sheath (IRS): surrounds the initial part of the hair shaft.
The external root sheath (ERS): covers the internal sheath and extends all the way to the epidermis, where it is continuous with the basal and spinous layers
Glassy membrane (G): a basement membrane on the outmost part of the hair follicle (separating it from the dermis).
Connective tissue sheath (CTS): The surrounding dermis around the hair follicle.
what is allergic contact dermatitis and what causes the condition?
inflammation of the skin
Overreaction of skin to specific triggers
Caused by epidermal Langerhans cells and T lymphocytes.
Can be caused by metal e.g. nickel but also sprays.
Environment - Atopic dermatitis
Chemical - contact dermatitis
Sebum - Seborrheic dermatitis
what is psoriasis and how is it caused?
A very common skin disease (2% of population).
Excessive growth and differentiation of keratinocytes
Associated with hyperproliferation of the epidermal basal layer.
This causes gross thickening of the spinosum layer and production of excessive stratum corneum cells
This results in excessive scaling of skin - Involves any area of the skin.
Runs In families and is influenced by genetic factors.
what is a malignant melanoma?
An aggressive malignant tumour of melanocytes.
Retention of tumour cells above the epidermal basement membrane is associated with a good prognosis - Superficial spreading melanoma.
If melanocytes end up in dermis it becomes incurable
Common moles are benign growths of melanocytes.
what is vitiligo?
An autoimmune disease in which the immune system attacks melanocytes, usually in symmetrical, localised areas of skin, causing depigmentation.
Much more visible in dark skin.
Sometimes vitiligo affects the whole body.
what is a first degree burn?
Epidermal damage only
Redness with no blisters
Painful
Heals in 5-10 days.
what is a second degree burn (superior partial thickness) ?
include its prognosis
Superior partial thickness (less severe form)
Burn into the papillary dermis
Red with blisters (separation of dermis and epidermis with fluid)
Very painful
Blanches with pressure
Healing time < 2-3 wks
Prognosis - local cellulitis (skin infection)
no scarring
what is a second degree burn (deep partial thickness) ?
include its prognosis
Deep partial thickness (more severe form)
Into the reticular dermis
Appears yellow/white
Pressure & discomfort
Less blanching
Heals 3-8 wks
Prognosis - scarring and contracture (muscle stiffness)
You need a skin graft
what is a third degree burn?
include its prognosis
Burn through entire dermis
Painless (because the nerve endings are destroyed) and stiff (damaged muscle)
White/brown.
No blanching
Healing is prolonged and incomplete
You are susceptible to infection
Prognosis- scarring, contracture, amputation (Recommend early excision)
