Anatomy and Physiology of the Autonomic Nervous System
Kenneth J. Broadley in Autonomic Pharmacology, 2017
The innervation and responses of the cutaneous blood vessels have been described above. However, it is in the autonomic innervation of the sweat (sudoriferous) glands that most confusion occurs. Sweat glands of humans are of two types: eccrine and apocrine glands. The eccrine glands are widely distributed in the skin of the body and secrete a dilute sweat in response to sympathetic nerve activity and a rise in body temperature. Eccrine glands that respond to psychological stress are most numerous on the palms of the hands and soles of the feet. They are innervated by sympathetic fibres, the postganglionic neurones originating in the adjacent ganglia of the sympathetic chain (Figure 1.4). In the head region, the postganglionic fibres leave the superior cervical ganglion to innervate sweat glands, cutaneous blood vessels and erector pili muscles. The sympathetic postganglionic nerves to sweat glands utilize Ach and not noradrenaline as the neurotransmitter. It is this that causes confusion in certain textbooks since sweating is variously described as a cholinergic, sympathetic or even parasympathetic response. However, it is clearly a sympathetic response.
Structure and function of skin
Roger L. McMullen in Antioxidants and the Skin, 2018
The eccrine sweat gland is composed of a secretory coil at its base, located deep in the skin, and a long duct that rises up to the skin surface (Figure 1.8). This duct is further classified as intradermal duct (coiled and straight) and intraepidermal duct, which twists as it makes its way through the epidermis.20 The secretory coil is the source of fluid secretion and consists of three principal cell types. The dark (mucoid) cells contain dark granules—hence their name—and are located closest to the inner tube of the gland, known as the lumen. The clear (secretory) cells do not directly interface with the lumen, but gain access to the lumen by intercellular canaliculi, located at the interface of two clear cells, which open up into the lumen. Thus, sweat secreted by clear cells enters the lumen by way of the intercellular canaliculum and makes its way from the secretory coil to the duct, and eventually to the surface of the skin. The clear cells of the secretory coil are supported either by an underlying basement membrane or spindle-shaped myoepithelial cells that contain myofilaments—fibrous muscle proteins (Figure 1.9).
Structure, Function, Type, and Sensitivity of Skin
Frank C. Powell, Jonathan Wilkin in Rosacea: Diagnosis and Management, 2008
There are two main horizontal vascular plexuses in the skin (superficial and deep) with multiple intercommunicating vessels and together they form a vast network of reactive blood vessels (Fig. 3). Alteration of the calibre of these vessels plays an important role in temperature regulation and homeostasis. Under thermal stress conditions, vasodilatation can increase skin blood flow up to 10-fold. This allows body heat to be lost rapidly through the skin because heat conductivity of blood is high and convection and radiation of heat from the skin occurs quickly. Discharge of sweat from the eccrine glands and its subsequent evaporation from the skin surface also helps to reduce body temperature. Thermoreceptor nerve endings in the skin play an important role in the monitoring of skin temperature and, together with the multiple thermostats in the central nervous system, function to coordinate the regulation of core temperature. The skin of the face has an abundance of blood vessels, even though it requires and consumes little oxygen. Some investigators feel that the basis of flushing in patients with rosacea lies in an abnormal reactivity of these vessels, vasodilatating for prolonged periods in response to stimuli such as minor temperature change, emotion or ingestion of agents such as alcohol, hot beverages, or spicy foods.
Physiology of sweat gland function: The roles of sweating and sweat composition in human health
Published in Temperature, 2019
The eccrine glands are functional early in life and, starting at ~2–3 years of age, the total number of eccrine glands is fixed throughout life [12–14]. Therefore, overall sweat gland density decreases with skin expansion during growth from infancy and is generally inversely proportional to body surface area. As a result, children have higher sweat gland densities than adults [11], and larger or more obese individuals have lower sweat gland densities than their smaller or leaner counterparts [13,17]. However, higher sweat gland density does not necessarily translate to higher sweating rate. In fact, most of the variability in regional and whole-body sweating rate within and between individuals is due to differences in sweat secretion rate per gland, rather than the total number of active sweat glands [18,19]. Eccrine sweat is mostly water and NaCl, but also contains a mixture of many other chemicals originating from the interstitial fluid and the eccrine gland itself. The structure and function of eccrine glands and the composition of eccrine sweat will be discussed in more detail in subsequent sections of this paper.
Cannabinoids in hyperhidrosis
Published in Journal of Dermatological Treatment, 2023
Till Kaemmerer, Benjamin Maximilian Clanner-Engelshofen, Tony Lesmeister, Lars Einar French, Markus Reinholz
Although cannabinoid therapy indications are steadily increasing, our understanding of the underlying pharmacodynamics is still incomplete. Cannabinoids bind to G protein-coupled cannabinoid receptors CB1 and CB2. CB1 receptors are primarily distributed in the peripheral and central nervous systems, and among other effects, inhibit presynaptic neurotransmission. The CB2 receptors, on the other hand, are localized predominantly in the peripheral immune and nervous system and have an inhibitory effect. We speculate one effect of cannabinoids in primary hyperhidrosis is presynaptic inhibition of acetylcholine release, and thus, diminished sweat secretion. The pathophysiology of hyperhidrosis does not seem to involve eccrine glands directly, as evidenced by a lack of histopathological changes. Instead, data points to neuronal overexcitations in the context of a more involved autonomic dysfunction (1,13). These hypotheses require validation.
En1 sweat we trust: How the evolution of an Engrailed 1 enhancer made humans the sweatiest ape
Published in Temperature, 2022
Daniel Aldea, Yana G. Kamberov
Humans cool themselves primarily through the evaporation of water from the skin surface. Human eccrine sweat glands, which are responsible of secreting the water for evaporative cooling, are essential for this mechanism of thermoregulation [1]. Among primates, humans have the highest eccrine sweat gland density. Indeed, human eccrine sweat gland density is on average ten times that of chimpanzees and macaques [2]. The high density of eccrine glands in human skin is one of the most dramatic phenotypic differences that distinguishes humans from other primates, and is a key component that makes possible humans’ exceptional ability to cool off by sweating [1]. In spite of its importance, the genetic mechanisms behind the evolution of this adaptative human trait have been poorly studied.