Structure and Function of Skin Flashcards
what is the stratum corneum
large flat plate like envelopes filled with cross linked keratin and lipids between cells providing a after barrier. Flattened dead cells that have lost their nuclei.
what is the stratum granulosum?
cells become flattened and contain keratohyalin granules, cells are starting to lose nucleus and cytoplasm
what is stratum spinosum?
Made up of several layers of keratinocytes held together by desmosomes. keratinocytes rich in desmosomes which hold it together
what is stratum basale?
cuboidal/low columnar cells which are mitotically active, constant regeneration of other layers (responsible for populating all other layers of the epidermis). connected to the BM by hemidesmosomes. continually dividing to populate other layers
what is the basement membrane?
a sheet like layer of extracellular matrix proteins
where is the stratum lucidum found
only found in thicker skin eg soles of feet
what is the dermis made up of?
connective tissue; collagen type I, elastin, fibroblasts and ground substance
what does the dermis do?
contains fibroblasts, has an immune role, contains blood vessels and nerves, allows stretch,
what is the dermo- epidermal junction?
attached to epidermis and dermis, assigns cells of the epidermis, serves as a base for reepithelialisation in wound healing and has a barrier function
what is the subcutous/ hypodermis?
provides an energy source, shock absorption and insulation
what are adnexal structures?
hair, nails and glands
what are eccrine glands?
excrete sweat, everywhere on human skin except nails lips ect. most abundant on palms ect
what are apocrine glands?
scent glands, their role is unclear in humans. found in axillae and genitals (modified ear/eyelid/breast)
what are sebaceous glands?
formed from hair follicle, present everywhere apart from palms and soles, produces sebum, they greatly enlarge at puberty in response to androgens
what is the epidermis?
it is made of stratisfied keratinised epithelial cells
what is the dermis?
an example of dense irregular connective tissue
what is the stratum corneum?
first line of defence against the environment. compromised of keratin and helps protect against bacteria and UV damage. helps prevent moisture escape
what is the stratum lucidum?
a thin clear layer which is only present in skin that is commonly damaged eg palms. it is meant to help body withstand friction
what is the stratum granulosum?
it acts as the waterproofing layer and keeps body from loosing water. the types of fats in this layer keep the skin cells attached to each other
what is the stratum spinosum?
also called the prickle cell layer. contains dendritic cells which are part of the immune system and help fight foreign invaders such as germs. enables the epidermis to better withstand abrasion and friction
what is stratum basale?
the deepest layer of the epidermis. the layer where cell division occurs and skin cells are replenished. the cells in this layer produce keratinocytes which produce keratin, protein and fat which help produce vitamin D when exposed to sunlight. this layer also contains melanocytes which produce melanin and colour the skin.
what is the papillary layer?
connects the dermis and the epidermis. contains capillaries that bring nutrients to the skin to increase or decrease bloodflow and regulate temp. contains sensory neurons. the layer of skin that creates fingerprints.
what is the reticular layer?
the deepest level of the dermis. it is a thick layer composed of dense connective tissue. it contains hair follicles sweat glands and sebaceous glands. main functions are strengthening the skin and providing elasticity
what is responsible for the synthesis of collagen?
fibroblasts
what are the 3 phases of wound healing?
inflammatory, proliferation, remodelling
what is inflammation/ vascular phase?
platelets initiate haemostats/ blood clot and also the healing cascade. attracts other cells to the wound to fight infection and transition from inflammation to repair.
what is the proliferative phase?
epithelial cells loosen cell-cell adhesions and migrate to the wound site, cover the granulation tissue and meet in the middle. once the layer is covered in a single layer of keratinocytes all of them start to proliferate. formation of granulation tissue.
what is the remodelling phase?
granulation tissue becomes mature scar tissue. collagen is organised into thick bundles and extensively cross linked to form a mature scar. switch in type II collagen to type I. f
What muscle is connected to the hair follicle?
Arrector pili muscle
What happens when the erector pili muscle contracts?
Causes hair to stand on end, trapping a layer of air to help warm the body (goosebumps)
What makes up nails?
Composed of plates of heavily compacted, highly keratinised epithelial cells that form the nail plate. Occupies the stratum corneum.
Which layer is thicker, dermis or epidermis?
Dermis
Which area of their dermis is mostly populated by elastin fibres?
Lower dermal layer
Where are most of the blood vessels found in the dermis?
Most superficial layer of the dermis. Along with very fine interlacing collagen fibres
What are the 2 layers of the dermis?
Papillary (superficial) and reticular (deep)
What does the reticular layer consist of?
Strong collagen bundles, larger elastin fibres. This layer also contains blood vessels and nerves but not as highly concentrates as the papillary layer.
What is the function of the dermis?
-tensile strength via collagen
-allows stretch through elastin fibres
-contains some important immune cells
-contains blood vessels and nerves
How is skin regenerated?
Daughter cells from basal layer migrate upwards and begin the process of differentiation
How long does it take for cells to migrate from the basal layer to the granular cell layer?
Around 2 weeks
How long does it take cells to move from the granular layer to cross the stratum corneum surface where they are shed off?
2 weeks
Where are most of the free nerve endings in the skin?
Dermis, the ones that extend into the epidermis are attached to merkel cells.
What are meissners corpuscles?
Rapidly acting mechanoreceptors responsible for touch. Found in the papillary dermis of hands and feet.
What detects deep pressure and vibration
pacinian corpuscles
Where are pacinian corpuscles usually found?
Subcutis
Where are langerhans cells typically found?
Epidermis, most abundant in the stratum spinosum layer.
Where are melanocytes found?
Basal layer
What are fibroblasts?
Synthesise collagen, elastin and other ECM components. Also growth factors
How do melanocytes protect from damage from UV?
Within a keratinocyte they form a cap over the nucleus protecting the DNA from damage
Which collagen type is mainly found in the skin?
Type I
What is an ulceration?
Damages structures deep to epidermis
What is partial thickness?
Epidermis + varying parts of dermis
What is full thickness?
Epidermis + all of dermis + deeper structures
How long does the coagulation/inflammation phase last?
24-48 hours
What are keratinocytes roles in the proliferative phase?
They loosen cell to cell adhesions in order to migrate to the wound site and cover granulation tissue and met in the middle. They can do this by dragging each other along like a train or leapfrog over each other.
What happens if the wound is deeper than the epidermal layer?
Re-epithelialisation also occurs, epithelium covers over the clot and forming tissue underneath. Fibroblasts are being recruited to the area to replace the lost molecules. Specifically type III collagen to form granulation tissue. Endothelial cells also proliferate to repair and form new blood vessels.
How long does the remodelling phase last?
Can last for several months
What do Myo-fibroblasts do?
Generate contractil force to close the wound
What percentage of the skin strenth pre injury should the new healed skin achieve?
80%
What does EGF signal?
Reepithelialisation (keratinocytes)
What kind of receptor are merkel cells?
Sensory mechanoreceptors
Which layer of the skin are langerhans cells mostly found?
Most prominent in stratum spinosum
what type of junctions connect the stratum basal layer to the basement membrane?
hemidesmosomes
what layer of the skin is responsible for making fingerprints
papillary layer of dermis
