HUBS PT1

Features of the epidermis

Mostly made of keratinocytes, avascular

Features of the dermis

Made of protein fibers like collagen and elastin for strength, vascular (nourishes epidermis)

Features of the hypodermis

Mainly adipose fat tissue

Keratinocytes

Cells that produce keratin

Cutaneous layer

Epidermis and dermis

Subcutaneous layer

Hypodermis

Epidermis of thin skin

Corneum, granulosum, spinosum, basale

Come Get Some Burgers

Epidermis of thick skin

Corneum, lucidum, granulosum, spinosum, basale

Come Lets Get Some Burgers

Stratum corneum

15-30 layers of dead keratinocytes, physical barrier remaining intact for 2 weeks before being shed, water resistant but not waterproof, mostly stratified squamous epithelium

Stratum granulosum

3-5 layers of keratinocytes producing lots of keratin, contains granules that dehydrate and kill cells, cell membranes are thick and impermeable

Stratum spinosum

8-10 layers of keratinocytes, cells increasingly flattened as you move up, contain dendritic cells producing immune responses

Stratum basale

Tall columnar stem/basale cells that divide into keratinocytes, the basal cell divides so daughter cell pushed upwards to add to and replenish the layer above

Function of the dermal papilla and epidermal ridge

To bind dermis and epidermis together and increase the surface area

2 layers of the dermis

Reticular (mesh-like, collagen/elastin fibers for strength) and papillary (vascular layer)

Cutaneous plexus

Network of blood vessels at the junction of the dermis and hypodermis, supplies the dermis and deeper dermis including capillaries for hair follicles and sweat glands

Subpapillary plexus

Branches of cutaneous plexus under the papillary layer, provide oxygen and nutrients to the upper dermis and dermis

Function of the hypodermis

Dominated by subcutaneous fat which stores energy and provides insulation, a common site of injuries

Desmosomes

Bridges found throughout the epidermis layers, a firm attachment by linking cytoskeletons, keratin fibers linked, required in dead corneum to be a good barrier

Hemidesmosomes

Half of a desmosome, anchors the stratum basale to the basement membrane and dermis, prevents the epidermis from sliding off

Mnemonic for functions of the skin

MDS PETS

M - skin function

Melanin synthesis for UV protection

D - skin function

Vitamin D3 synthesis

S - skin function x 2

Storage, support and sensation

P - skin function

Protects tissues internally

E - skin function

Excretion

T - skin function

Thermoregulation

Extra skin function

Produces keratin which is a water repellent and protects against abrasions

The layer of skin that tattoo ink is deposited into

The dermis as it is not shed, captured in immune cells which hold the ink in position, can be transported in lymph nodes and seen as a melanoma, painful process as pain receptors and nerve endings in dermis

1st degree burns

Heals within 3-10 days, red and painful but no blisters, skin remains a water/bacteria barrier, superficial and only involves the outer layers of the epidermis

2nd degree burns

Normal:

Epidermis, some dermis, painful and blistered, heals within 1-2 weeks with good dressings

Deep:

More dermis, some whiteish waxy areas, can affect hair follicles and sweat glands, usually heal in one month, may have some loss of sensation and scarring

3rd degree burns

Full thickness burns extending into the subcutaneous tissue and may involve muscle and bone, way white, red or even black, hard, dry and leathery skin, no pain as sensory nerves have been destroyed, weeks to regenerate and scarring, skin grafting may be required

Vellus hairs

Smaller, shorter, more delicate, found on body surface

Terminal hairs

Large, thick, darkly pigmented, found on scalp and armpits

Hair follicle

Produces non-living, keratinized cells

Hair shaft

The visible part projecting from the follicle

Root hair plexus

Network of sensory nerves around the base of each hair follicle that heighten sensation

Arrector pili muscle

Contraction produces goosebumps, improves insulation

Sebaceous glands

Produces oily secretion called sebum, nourishes hair shaft, moisturizes skin, water repellent

Holocrine gland

A secretory cell that bursts and releases its contents to coat hair shaft, oily hair

Lanolin

Sheep sebum that is used commercially in skincare

Produced when hair follicles are blocked

Acne due blocked hair follicles and increasing sebum production causing blocked gaps and pimples

Apocrine sweat glands

Found in groin, armpits and nipples, glands found in the hypodermis, secretes sticky/oily odorous secretions into the base of the hair follicle, influenced by hormones e.g. lactation

Eccrine sweat glands

Normal, pour watery secretions directly onto the skin surface, secretory cells release a vesicle that breaks open, important in thermoregulation, secretion and has antibacterial properties

Nail bed

A portion of the epidermis covered by the nail body

Nail body

The visible portion of the nail made of dead, tightly compressed keratinocytes

Nail root

An epidermal fold not visible from the surface, the site of nail production

Lunula

A thickened portion of the stratum basale that conceals dermal blood vessels, appears as white crescent shape at bottom of nail

Hyponychium

Thickened skin located under the free edge of the nail body, a protective seal against pathogens and debris

Eponychium

Thickened layer of skin at the base of the nail, not the cuticle which is dead skin

Functions of nails

Protects dorsal surfaces of fingertips and toes from injury and infections, limits the distortion of digits when exposed to mechanical stress e.g. running and grasping objects, enhances sensation and fine motor skills, indicative of overall health - appearance changes

Skin ageing

Due to a reduced blood supply, thin epidermis, thin dermis - sagging as less collagen/elastin, slower skin repair, diminished immune response, direr epidermis, impaired cooling, fewer active hair follicles, fewer melanocytes so pale skin and grey hair

Smoking effect on skin

Damages elastic/collagen, accelerates ageing

Vaping effect on skin

Nicotine reduces blood circulation in the dermis

Melanin

Absorbs UV light, protects cells from UV damage, more sun=more melanin, production and therefore pigmentation varies across population

Melanocytes

Melanin producing cells, in stratum basale so not shed

Melanosomes

Melanin containing vesicles, into epidermal layers, shed with keratinocytes

Mole

Cluster of melanocytes, over proliferation an be caused by sun exposure

Freckle

Melanocytes overproduce melanosomes, over production triggered by sun exposure

Functions of vitamin D3

Calcium metabolism, bone health and mood regulation

Source of vitamin D3

UV to skin to vitamin D3 to calcitriol to calcium metabolism

Low vitamin D3 in infants

Causes Ricketts which is weak and flexible bones

Low vitamin D3 in adults

Not Ricketts, darker people are more at risk when they live at extreme/higher altitudes

Basal cell carcinoma

Most common skin cancer, benign, originates in stratum basale, affects basal cells, commonly seen on areas overexposed to the sun, pale smooth red lump, easily treatable and doesn’t spread

Malignant melanoma

Originates in the stratum basale, affects melanocytes, highly mestatic and spreads rapidly

As tumor thickness increases…

Mortality also increases

How we experience different temperatures

TRP receptors are activated at different ranges

Free nerve ending structure

Terminals of sensory axons with small swellings at distal ends, C-fibres, A-delta fibres (pin sharp and then achey feeling), sensory terminals have their own receptors in cell membrane, nerve terminals are located in the lower epidermis

Free nerve ending stimuli

Temperature (peripheral thermoreceptors), pain, some movement/pressure, some itch (histamine), light tough as bend sensed by root hair plexus

Tactile Merkel disc structure

Located in the deepest layer of epidermis (basale), in fingertips so a small receptive field, specialized sensory nerve endings associated with large disc shaped Merkel cells, act as mechanoreceptors - Piezo 2 receptors cause depolarization and AP generation, A-beta fibres

Tactile Merkel disc stimuli

Touch and light pressure, texture, shape, edges, two point discrimination, low frequency vibration (5-15Hz)

C-fibres

Majority, unmyelinated, small diameter

A-delta fibres

Myelinated axons, small diameter

A-beta fibres

Medium diameter, unmyelinated

Tactile Meissner corpuscle structure

Located in papillary layer of dermis especially in hairless skin, encapsulated, branching/spiraling sensory terminals surrounded by modified Schwann cells and a thin oval fibrous connective tissue capsule, deformation of capsule triggers AP generation

Tactile Meissner corpuscle stimuli

Delicate, fine or discriminative touch (Braille), light pressure, low frequency vibration (10-50Hz)

Lamellar corpuscle structure

Found deep in dermis and hypodermis, onion looking, single sensory axon terminal lying in layers of collagen fibers and fibroblasts (outside) and Schwann cells (inside), layers separated by gelatinous fluid, deformation causes AP generation, inner layers of axon terminal relax quickly so rapidly adapting, isolated from many stimuli

Lamellar corpuscle stimuli

Deep pressure, vibration (250Hz)

Bulbous Ruffini corpuscle structure

Located deep in dermis and subcutaneous tissue, network of axon terminals intertwined with a core of collagen fibres that are continuous with those of surrounding dermis, surrounded by a flattened capsule

Bulbous Ruffini corpuscle stimuli

Deep pressure, stretch, prolonged distortion, found in joint capsules - degrees of joint in knee (proprioception), in fingers have job of sensing objects slipping across skin surface so modulate grip

Radiation

Objects not at absolute 0 emits infrared radiation, loss/gain

Conduction

Transfer to something in contact with that has lower heat

Convection

Heat layer around us to our core body temperature of 37 degrees, heat rises so we lose heat to air/wind

Evaporation

Fluid and sweat evaporates and heat energy required is lost

Precapillary sphincters and blood flow

If we constrict we can control blood flow, innervated by sympathetic nervous system, tone

Noradrenaline activated alpha 1 receptors so constrict and decrease blood flow

Opposite is decreased SNS activation of alpha 1 receptors and dilation increases blood flow

Location of our central thermoreceptors

The pre optic area of hypothalamus which contains heat/cold sensitive neurons, activates heat loss or heat gain center

What happens when our body temperature increases

Activation of heat loss center, behavioral changes, vasodilation = decreased activation of alpha 1 receptors, sweating = increased SNS activation of mAChRs, increased respiratory rate

What happens when our body temperature decreases

Increased generation of body heat: shivering thermogenesis - oscillatory contraction of agonist/antagonist muscle, non shivering thermogenesis = increased sympathetic nerve activity, increased circulation of adrenaline/noradrenaline from adrenal medulla, increased metabolism, brown fat in infants, increased TSH/TRH and increased BMR

Conservation of body heat: countercurrent exchange and vasoconstriction

Eccrine sweat glands

Innervated by sympathetic nervous system, sympathetic cholinergic, release AcH or MAChrs

Arrector pili muscles and thermoregulation

Smooth muscles innervated by SNS alpha 1 receptors, attach hair follicle to upper dermis, contraction pulls hair upright causing goosebumps, traps layer of warm air, good example of physiological feed-forward

Potential complications of severe burns

Infection, dehydration, hypothermia

Can treat with fluid replacement if worse than 2nd degree burns

Blood vascular system

A closed supply and drainage system, a continuous loop

Lymphatic vascular system

An open-entry drainage system, a one way system

Where are major arteries located

To avoid damage, deep in trunk and on flexor part of limbs

Where do deep veins run

Opposite to direction of big supply arteries, superficial veins can accommodate injury

Cross sectional area of veins compared to arteries

At least double to shift the same volume of blood

PMI

Midclavicular line, between 5th and 6th rib

Location of tricuspid valve

RHS of heart

Location of bicuspid valve

LHS of heart

What does the right atrium receive

SVC, IFC, coronary sinus, deoxygenated blood

What does the left atrium receive

4 pulmonary veins, oxygenated blood