Skin Physiology: Receptors, Blood Flow, Thermoregulation, and Burns

Vocabulary flashcards covering skin receptors, skin blood flow control, thermoregulation, sweating, and burns.

Free nerve endings

Most common skin receptor; unmyelinated C-fibers (and some Ad fibers) that respond to nociceptive, thermal, and chemical stimuli, with roles in temperature, pain, itch, and light touch via hair follicles.

Nociceptors

Free nerve endings that specifically respond to painful stimuli.

Merkel discs (Tactile discs)

Deep epidermal mechanoreceptors with Merkel cells; have Piezo2 channels; small receptive fields enabling high two-point discrimination and detailed object features.

Meissner corpuscles

Located in the papillary dermis of glabrous skin; encapsulated endings sensitive to light touch, shape, texture changes, and low-frequency vibration (10–50 Hz).

Pacinian (Lamellar) corpuscles

Deep dermis/hypodermis mechanoreceptors with layered capsule; rapidly adapting and primed for deep pressure and high-frequency vibration (~250 Hz).

Ruffini endings

Bulbous corpuscles in dermis; detect sustained deep pressure and skin stretch; contribute to proprioception and grip modulation.

Root hair plexus

Nerve endings around hair follicles that detect bending of hairs and contribute to light touch.

Precapillary sphincters

Smooth muscle rings around small arteries that regulate skin blood flow; controlled by the sympathetic nervous system via α1 receptors.

Cutaneous vascular plexus

Network of blood vessels in the dermis supplying the skin, regulated by sympathetic vasomotor activity.

Subpapillary plexus

Vascular network beneath the dermal papillae; part of the skin’s blood flow regulation.

Vasomotor tone

Baseline SNS control of cutaneous vessels; α1 receptor activation causes vasoconstriction; withdrawal leads to dilation; heat stress can induce active vasodilation.

α1-adrenergic receptors

G protein–coupled receptors on vascular smooth muscle; noradrenaline binding causes vasoconstriction in the skin.

Eccrine sweat glands

Sympathetic glands that secrete via ACh on muscarinic receptors; some glands can be activated by adrenaline on β receptors (nervous sweating).

Central thermoreceptors

Heat/cold sensors in the hypothalamus (preoptic area) that monitor blood temperature and set body temperature responses.

Peripheral thermoreceptors

Skin temperature sensors that feed into hypothalamic control to regulate heat gain or loss.

Heat loss center

Hypothalamic mechanism activated by elevated temperature; stimulates vasodilation, sweating, increased respiration, and behavioural adjustments.

Heat gain center

Hypothalamic mechanism activated by cooling; promotes heat production and retention (shivering, non-shivering thermogenesis, etc.).

Shivering

Oscillatory skeletal muscle contractions producing heat as ATP is consumed.

Non-shivering thermogenesis

Heat production via increased metabolic rate and catecholamine action, notably brown fat with mitochondrial uncoupling of oxidative phosphorylation.

Brown adipose tissue

Fat tissue specialized for non-shivering heat production; abundant in infants and responsive to sympathetic stimulation.

Thyroxine (T4)

Hormone increasing basal metabolic rate; prolonged cold exposure raises TRH/TSH, boosting heat production.

Arrector pili muscle

Smooth muscle attached to hair follicles; contraction causes hair to stand (goosebumps) and can trap insulating air.

Goosebumps

Hair standing due to arrector pili contraction; provides limited insulation and a protective/feeder-forward response to cold.

Burns complications

Severe burns can cause infection, dehydration, hypothermia, electrolyte imbalances (e.g., hyperkalemia), renal failure, pulmonary edema, GI ulcers, and hypermetabolism.

Parkland formula

Fluid resuscitation: 4 mL × body weight (kg) × TBSA% burned; half in first 8 hours, remainder over next 16 hours (first 24 h total).

TBSA

Total Body Surface Area burned; used to calculate fluid needs and assess burn severity.

Two-point discrimination

Ability to distinguish two close touch points as separate; enhanced by Merkel discs with small receptive fields.

Aβ fibers

Myelinated, medium-diameter sensory fibers transmitting fine touch and texture information.

TRP channels

Transient receptor potential ion channels in free nerve endings that contribute to temperature and nociceptive sensing.

H1 receptors

Histamine receptors on free nerve endings contributing to itch and inflammatory signaling.