Flashcards in Lecture 1 - Skin Deck (49):
What are the 2 main layers of skin?
How are the dermis and epidermis different to each other?
Epidermis is avascular containing mostly keratinocytes and forms appendages (such as hair, nails, glandular structures)
Dermis is a deeper connective tissue layer containing nerves and muscles and makes up most of the skin.
What is hairless thick skin also known as?
What is thin hairy skin also known as?
What is the dermis vascular supply like?
It is rich in vascular and nerve supply.
What are the important functions of skin?
Protection (+ self repair)
Attraction + repulsion
How does skin regenerate itself?
Skin has a high cell turnover of ~10 - 30 days (epidermus) due to presence of epidermal stem cells which proliferate and differentiate and slowly migrate and die. Other stem cells form appendages.
Why does burnt skin regenerate without hair often?
Due to presence of way more epidermal stem cells than hair follicle (or sebaceous gland) stem cells
What does skin regeneration depend on?
It is layer dependent. Epidermis is faster and easier than dermis.
How does epidermis regenerate?
Stratum basale epidermal stem cells proliferate, migrate and fill gaps left by the injury
How does the dermis regenerate?
More difficult, Bleeds, results in immune response, secretion of matrix takes place (collagen and elastin) to fill wound.
What are the stages of wound repair?
Inflammation (injury +48 hrs): Hypoxic, fibrin clot is formed, platelets + neutrophils, full of microbes
New tissue formation (2 - 10 days post injury): Scab formed, angiogenic, epithelial cells migrate in.
Remodelling (Can last >1 year): Disorganized collagen, distorted shape/density, absence of normal appendages.
How are burns classified?
By how deep tissue involved in burn is
What are the effects of first degree burns?
Involves only epidermis and is characterised by redness, slight edema, and pain, heals in days.
What are the effects of second degree burns?
May appear red, tan, or white; blistered and painful.
Takes weeks to several months to heal and may leave scars
What are the effects of third degree burns?
Full-thickness involves epidermis, all of the dermis, and some deeper tissues.
How is a third degree burn treated?
What are the important receptors required for light touch sensation?
Tactile (Meissner's) corpuscle is a rapidly adapting mecahnosensor.
Tactile (Merkel's) disks are slowly adapting mechanosensors that sense continuous light touch
What are the important receptors that are required for heavy touch sensation?
Lamellar (pacinian) corpuscle is a rapidly acting mechanosensor for heavy touch.
Bulbous (Ruffini's) corpuscle is a slowly adapting mechanosensor for heavy touch sensation and stretch.
What sensory receptors detect pain, warm and cold feeling?
Free nerve endings which are slowly adapting and have variable gating.
What are thermoreceptors also called?
Transient Receptor Potential (TRP) channels
How do thermoreceptors detect temperature?
They temperature-sensitive ion (excitatory Na+/Ca2+) channels
What are cold receptors also called? How do they detect cold?
TRPM8 channels. Their firing rate increases as temperature decreases and their temperature range spans about 10 - 35 degrees and they also react to menthol and eucalyptus oil.
What are warm receptors called?
TRPV1/3, and TREK1 channels
How do warm receptors detect warm temperatures?
Firing rate increases as temperature increases.
TRPV3 = 22 - 40
TRPV1 = 42+
What other channels besides thermoreceptor channels are temperature dependent in skin?
K+ leak channels
What important physiological process is catalysed by skin?
Vitamin D synthesis
How is vitamin D synthesized?
7-dehydrocholesterol + UV light -> D3
Liver -> 25-hydroxy-D3
Kidneys -> 1,25-dihydroxy D3
How does the skin regulate body temperature?
Evaporative cooling (sweat)
Convective cooling (skin blood flow)
How is skin blood flow regulated?
Hypothalamus detects blood temperature and either activates or deactivates sweat glands and capillaries in skin as well as hair erection.
How much heat is lost from sweating?
0.58kcal/g of water evaporated
What division of the nervous system controls sweating?
Sympathetic nervous system
What is insensible water loss?
Water loss that isn't from sweat glands (~500ml/day)
What is another name for sweat glands?
What are the types of sweat glands?
Eccrine (produce sweat)
Apocrine (secrete onto hairs)
How is sweating regulated?
They contain myoepithelial cells that contract upon nervous stimulation to force sweat into ducts.
Initially protein free filtrate is secreted
Ions are reabsorbed that are hypo-osmolar (~120 mOsm/L)
Reabsorption of Na+ and Cl- and are powered by Na+/K+-ATPase (powers everything important to know for exam!)
What nerves control sweating?
Sudomotor nerves. they are sympathetic postganglionic cholinergic nerves.
What receptors receive signal from postganglionic cholinergic sympathetic nerves that innervate sweat glands?
mAChRs (Muscarinic acetylcholine receptors)
What is used to decrease sweating?
Cholinergic (muscarinic) antagonists will also act to decrease sweating
What is the blood flow to the skin in cold?
What is the blood flow to the skin in hot weather?
What supplies blood to skin?
2 Cutaneous plexuses connected by communicating vessels that form arteriovenous anastomoses (glomus bodies):
Superficial - rich capillary loop system in the superficial dermal papillae
Deep - venous plexus between dermis and fat
What is another name for the arteriovenous anastomoses in the skin?
How is skin perfusion often relative to its needs?
It is normally overperfused for its metabolic requirements.
What innervation do skin blood vessels have?
how is skin blood flow regulated?
Both locally (by temperature and hormones) and systemically (via sympathetic nervous system)
Is the skin's blood flow metabolically regulated?
If a person is both hot and excited how is the sympathetic nervous system used to vasoconstrict and vasodilate the skin?
The sympathetic response causes little change in blood flow to skin unless it stimulates sweating. When sweating we activate NANC nerves which trigger vasodilation.
Post-ganglionic sympathetic nerve fibers that release ACh vasodilate
Non-adrenergic non-cholinergic nerves (NANC) release bradykinin and NO to vasodilate.
2 types of sympathetic nerves innervate skin NA releasing nerves that are vasomotor and ACh releasing nerves that are vasodilator.
As a result: in the cold, sympathetic adrenergic is acting
In the heat sympathetic cholinergic as well as NANC (bradykinin and NO)