Lecture 1 anatomy of the skin part 1 Flashcards
Skin
The skin is the largest and most visible organ of the body.
It is 16% of body weight and covers 1.5-2 m^2 of surface area
Why does the skin make us uniquely human?
Our bare, sweaty skin makes us unique
Functions of the skin
Protects underlying tissues and organs against impact, abrasion, fluid loss and chemical attack
Excrete salts, water, and organic wastes by integumentary glands
Maintain normal body temperature through either insulation or evaporative cooling, as needed
Produce melanin, which protects underlying tissues from ultraviolet radiation
Produce keratin, which protects agains abrasion and serves as a water repellent
Synthesis vitamin D3, a steroid that is subsequently covered to calcitriol, a hormone important to normal calcium metabolism
Store lipids in adipocytes in the dermis and in adipose tissue in the subcutaneous layer
Detect touch, pressure, pain and temperature stimuli, and relay that information to the nervous system
How does skin anatomy relate to its function or performance?
Aging
Pigmentation
Skin cancer
Tattoo
4 types of tissue
Nervous, muscle, Connective and epithelial tissue
Epithelial tissue
Covers exposed surfaces
Lines internal passageways and chambers
Forms secretory glands
Connective tissue
Fills internal spaces
Provides structural support
Stores energy
Muscle tissue
Contracts to produce movement. Includes skeletal muscle, cardiac muscle and smooth muscle
Nervous tissue
Conducts electrical impulses. Carries information.
Skin and tissue types
Skin is an organ made up of all 4 tissue types/the skin is a composite organ that contains all these different cell types
3 primary layers of skin
Epidermis (outermost layer)
Dermis
Hypodermis
Epidermis
Stratified barrier Mostly keratinocytes (skin cells that have heaps of the keratin protein which helps to protect the skin) No circulation (avascular)
Dermis
Protein fibres present for strength - elastin and collagen
Vascular (nourishes the epidermis)
Not shed - if a cell dies in the dermis, it gets broken down through the vasculature just like any other cell in the internal part of our body
Hypodermis
Contains adipose tissue - insulation and also important for storing energy
Subcutaneous
Cutaneous layer
epidermis and dermis
Subcutaneous layer
hypodermis
Cutaneous vs subcutaneous
Cutaneous is anything which is related to the skin. Subcutaneous - anything that lies below the skin, and between that and the fascial layers, like Fat, Blood vessels etc.
Papillary layer
Part of the dermis
Made up of little protrusions and capillaries that sit right under it that provides nourishment to the dermis and the epidermis
Projects into the epidermis
Reticular layer
Part of the dermis
Made up of elastin and collagen that form a mesh for strength (mesh/mat-like structure)
Layers of the epidermis
Stratum corneum(most superficial layer) Stratum lucidum (only found in thick skin, not found in thin skin ) Stratum granulosum Stratum spinosum Stratum basale
Stratum corneum (horny layer)
Outermost layer of the epidermis
Dead, dried-out hard cells without nuclei (provides protective mechanisms) (consists entirely of dead cells)
Horny because of the large amount of keratin (can remember because the HORN of a rhino has a lot of keratin)
What is the layer of the epidermis that is only present in thick skin?
Stratum lucidum (not in thin skin)
Stratum granulosum (granular layer)
Contains granules that promote dehydration of the cell, cross linking of keratin fibres - as these cells are dying and being shed and coming towards the outside they progressively dehydrate and there is cross linking of keratin fibres to try make a very strong, hard barrier to the outside
Waxy material is secreted into the intercellular spaces
Stratum spinosum(spiny layer)
Intercellular bridges called desmosomes link the cells together. This creases a barrier fruition to the outside and you need these very tight junctions as an epithelial cell barrier (protective) (Characterised by desmosomes (and as the tissue sections start to dry out they start to become long and spindly hence their name))
The cells become increasingly flattened as they move upward.
Stratum basale (basal layer)
Columnar (tall) regenerative cells
As the basal cell divides, a daughter cell migrates upwards to replenish the layer above. The flow of cells is from here upwards.
Strip-taping
Stratum corneum (horny layer) can be completely removed and very easily too (with tape)
The epidermis as keratinocyte conveyor belt…
Start off with producing cells in the stratum basal and then moving their way upwards. The skin is constantly regenerating, the skin cells turnover every 7 to 10 days.
Infections and the skin
Infection cannot really bother the outer layer because it is dead therefore the dead layer is important.
Perhaps you can get an infection in one of the layers that are living underneath in the granulosum or spinous layers, because the skin cells turnover every 7 to 10 days so we would essentially grow out that infection and this therefore protects us from getting infections.
What tissue type dominates in the epidermis?
Epithelial tissue
Epithelial cell types
Simple epithelia (one layer) - squamous, cuboidal and columnar Stratified epithelia (many layers)- squamous, cuboidal and columnar
Epidermis mainly consists of which epithelial cell type?
Epidermis = stratified squamous epithelium (mainly)
Thick vs thin skin
Palms of hands and soles of the feet have thick skin as these are area of high abrasion, more exposure to environment
No hair on thick skin and there is also an extra epidermal layer (stratum lucidum)
What happens as skin ages?
Thin epidermis
Thin dermis (sagging and wrinkling) - reduced collagen. The protein network/reticular layer starts to degrade and become thinner therefore there is less structure which means the individual is more susceptible to sagging and wrinkling
Slower skin repair
Drier epidermis (less sebum) - less oils and protective substances therefore a less effective barrier
Impaired cooling (less sweat) - this is why the older generation is more prone to be affected by overheating
Less pigmentation - pale skin and grey hair (fewer melanocytes)
Altered hair and fat distribution and fewer active hair follicles
Smoking and skin ageing
There is a claim that smoking increases skin ageing
“Reactive oxygen” damages collagen and elastin - which would give the individual more wrinkles
Vasoconstriction - nicotine increases vasopressin, this decreases circulation to the outer dermis