Skin: structure, vessels and nerves

The skin is the largest organ, serving simultaneously as a barrier, sensory system, and thermoregulatory platform. It's more than just a covering: it protects against microbes and chemicals, retains water, responds to injury, and forms part of the innate immune response. [1]

The skin has three major layers: the epidermis, dermis, and subcutaneous tissue. The epidermis acts as a barrier and is constantly renewed, the dermis provides strength and elasticity, and the subcutaneous tissue acts as a shock absorber, heat insulator, and "highway" through which blood vessels and nerves pass to the upper layers. [2]

An important principle: the epidermis contains no blood vessels and relies on diffusion from the dermis for nutrition. Therefore, many processes that appear "superficial" are in fact closely linked to the state of dermal microcirculation and the intercellular matrix. [3]

The dermis is divided into the papillary and reticular layers. The papillary layer is looser and particularly rich in vessels, while the reticular layer is denser and provides mechanical strength, forming the basis for blood vessels, nerves, follicles, and glands. [4]

Table 1. Skin layers and key structures

Level	What prevails	Vessels	Nerves and receptors	Clinical significance
Epidermis	Keratinocytes, barrier lipids	No	Intraepidermal nerve fibers, free endings	Itching, pain, sensitivity, barrier dryness
Papillary dermis	Loose connective tissue	Superficial vessels, capillary loops	Touch receptors, free endings	Redness, swelling, urticarial reactions
Reticular dermis	Collagen and elastin, a dense network of fibers	Larger vessels and plexuses	Nerve trunks, pressure receptors	Scarring, fibrosis, mechanical strength
Subcutaneous tissue	Fat lobules, fascial septa	Large vessels, perforators to the dermis	Passing nerve trunks	Thermal protection, shock absorption, highway path

[5]

Vascular architecture of the skin: from highways to plexuses

The skin's blood supply is organized to simultaneously address two objectives: tissue nutrition and heat management. To achieve this, the vessels form plexus systems that connect deep sources of blood flow with superficial capillary loops at the epidermal interface. [6]

The classic model of cutaneous microcirculation describes two horizontal vascular plexuses: a superficial plexus, located approximately 1-1.5 mm from the surface, and a deep plexus, located at the junction of the dermis and subcutaneous tissue. Between them pass ascending arterioles and descending venules, forming "vertical pairs" of vessels. [7]

Capillaries branch off from the superficial plexus, forming loops in the dermal papillae. These loops are the main "nutrient" component for the epidermis, which itself has no vessels. This explains why microvascular spasm, inflammation, or endothelial damage alter skin color, healing rate, and cold tolerance. [8]

Venous outflow is also organized through networks and plexuses, and it is the venous component that often determines "stagnant" skin tones and increased edema. In practical dermatology, this is important for interpreting mottling, cyanosis, venous hypertension, and some vascular dermatoses. [9]

Table 2. Two vascular plexuses of the skin and their role

Element	Where is it located?	What feeds	Main function
Superficial plexus	Upper dermis	Capillary loops of the papillae, superficial structures	Nutrition, involvement in inflammation, redness
Deep plexus	The border between the dermis and subcutaneous tissue	Skin appendages, part of the dermis, connection with highways	Flow distribution, reserve for thermal regulation
Vertical connections	Between the plexuses	Connect levels	Quick recalculation of blood flow under stress
Capillary loops of the papillae	Dermal papillae	Subepidermal area	Delivery of oxygen and nutrients to the epidermis

[10]

Microcirculation and thermoregulation: why skin manages heat through blood vessels

The skin is the body's primary, regulated "radiator." By altering the lumen of its blood vessels, the body can dramatically alter heat loss: when blood vessels dilate, the skin reddens and releases heat; when they constrict, it pales and reduces heat loss. This mechanism is particularly effective due to the skin's large surface area. [11]

A significant difference is the difference between hairy skin and the hairless skin of the palms and soles. Hairless skin contains numerous arteriovenous anastomoses, that is, direct connections between arteries and veins, which can quickly "shunt" blood into the venous plexuses, dramatically increasing or decreasing heat exchange. [12]

These anastomoses are richly innervated by sympathetic fibers, so stress, cold, and emotion can significantly alter their tone. This is why cold reactions of the hands and feet, Raynaud's syndrome, and many functional vascular phenomena are often more pronounced in the fingers and palms than on the trunk. [13]

Thermoregulation also involves a sensory component: skin temperature serves as a signal to the nervous system, which triggers vascular responses and sweating. Therefore, disturbances in cutaneous sensitivity or autonomic regulation can manifest not only as pain or numbness, but also as unstable heat transfer, dry skin, and heat intolerance. [14]

Table 3. Rapid vascular responses of the skin and their “visible” signs

Situation	What happens to the blood vessels?	What is visible on the skin	Typical meaning
Cold	Vascular constriction, closure of anastomoses	Paleness, cold fingers	Heat retention
Heat	Vasodilation, increased blood flow	Redness, warm skin	Heat transfer
Stress	Redistribution of flow, spasm in some people	Spotting, cold hands	Sympathetic response
Inflammation	Vasodilation, increased permeability	Redness, swelling, local warmth	Immune response

[15]

The cutaneous lymphatic network: drainage and immune surveillance

Lymphatic vessels perform two fundamental functions: returning excess interstitial fluid back into the bloodstream and transporting immune cells and antigens to the lymph nodes. This is especially important in the skin, which is constantly exposed to external agents and is frequently subject to microdamage. [16]

Lymphatic capillaries are located in the dermis. They collect fluid and cells from the interstitium and then transport the lymph to larger collecting vessels. The lymph then travels to regional lymph nodes, where filtration and adaptive immune responses occur. [17]

The lymphatic system undergoes active restructuring during inflammation, wound healing, and tumor growth. The growth of lymphatic vessels and changes in their permeability can influence the severity of swelling, the rate of inflammation resolution, and even the tendency for dermatological diseases to become chronic. [18]

Impaired lymphatic drainage manifests itself as persistent swelling and skin changes, as well as an increased risk of recurrent skin and subcutaneous tissue infections. Therefore, assessing the lymphatic component is important not only in oncology but also in everyday clinical practice for chronic limb edema. [19]

Table 4. The lymphatic system of the skin: what it does and how malfunctions manifest themselves

Function	How it is realized in the skin	What happens if there is a violation?
Liquid drainage	Collection of interstitial fluid by lymphatic capillaries	Chronic edema, tissue compaction
Transport of immune signals	Transfer of antigens and cells to the lymph nodes	Weakening of local immune control
Participation in healing	Network rewiring during injury and inflammation	Slow recovery, chronicity
Inflammation Balance	Removal of mediators and cells	Prolonged dermatoses in some patients

[20]

Innervation of the skin: receptors, fibers and sensory modalities

The skin is highly innervated, with nerve endings in the epidermis, dermis, and around the skin appendages. The skin's sensory system includes touch, pressure, vibration, pain, temperature, and itching, as well as reflex responses related to vascular tone and sweating. [21]

Most pain and itch signals originate in free nerve endings that extend into the epidermis and upper dermis. These endings are associated with fine fibers, which respond quickly to injury and temperature, as well as slow fibers, which are involved in long-term pain and itch. [22]

Mechanical sensitivity is mediated by several types of receptors located at different depths: superficial receptors are better at detecting light touch, while deeper structures perceive vibration, pressure, and stretch. This distribution explains why tactile sensitivity changes with thickening of the stratum corneum, edema of the dermis, or scarring. [23]

Skin innervation also includes autonomic components: nerves regulate blood vessels and sweat glands. Therefore, damage to autonomic fibers can manifest as dryness, impaired sweating, changes in skin temperature, and delayed healing, even if major sensitivity is partially preserved. [24]

Table 5. The main sensory structures of the skin and what they “feel”

Structure	Where is it most often located?	The main incentive	Clinical example
Free nerve endings	Epidermis and upper dermis	Pain, fever, itching	Burning, itching, pain with inflammation
Meissner's corpuscles	Papillary dermis	A light touch	Decreased fine sensitivity with swelling
Merkel disks	Basal zones of the epidermis and dermis	Constant pressure, texture	Difficulty distinguishing small details on fingers
Pacinian corpuscles	Deep dermis and subcutaneous tissue	Vibration	Perception of instrument vibration
Ruffini's endings	Deep dermis	Stretching	Feeling of skin tension when moving

[25]

Neurovascular and Neuroimmune Connections: Why Nerves Affect Redness, Itching, and Inflammation

The skin is a "neuroimmune organ": signaling molecules released by nerve endings can alter vascular tone, microvascular permeability, and immune cell activity. This helps the skin respond quickly to damage, but under certain conditions, it can also contribute to chronic inflammation and itching. [26]

One mechanism is thought to be neurogenic inflammation: activation of sensory fibers releases neuropeptides that dilate blood vessels and enhance local reactions. Research discusses the role of substance P and calcitonin gene-related peptide in skin reactions, including responses to ultraviolet light and inflammatory stimuli. [27]

Clinically, this manifests itself in the fact that itching and redness can be intensified by stress, overheating, friction, and diseases that disrupt cutaneous innervation. Modern reviews of cutaneous innervation emphasize that sensory and autonomic pathways are closely intertwined and control not only sensations but also blood flow and sweating. [28]

Practical implications: Complaints of "burning without rash," "itching without rash," "spotty redness," and "heat intolerance" often require an assessment of not only dermatological causes but also neuropathic, vascular, and systemic factors. This does not replace an in-person diagnosis, but it does provide a more precise examination logic. [29]

Table 6. Symptoms where vessels, nerves, or both mechanisms are most often at fault

Symptom	A more likely mechanism	What is often clarified in practice
Redness and local warmth	Vascular dilation, inflammation	Triggers, medications, dermatoses, overheating
Marbling and coldness of the fingers	Vasospasm, dysregulation	Cold, stress, Raynaud's syndrome, autonomic dysfunction
Burning and pain with minimal skin changes	Neuropathic component	Tests for fine fibers, diabetes, deficiencies, medications
Itching without a pronounced rash	Neuroimmune pathways, dryness, systemic causes	Liver and kidney function, iron, dermatological examination
Swelling after inflammation	Lymphatic and vascular component	Drainage, chronic venous stasis, lymphedema

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