In the human body, of course everything is connected to everything else. But some of these connections are intelligent and keep body parts working well together. In particular, there are certain systems that detect problems such as the presence of disease or other stressors, compute solutions designed to maximize the survival of the organism, and send messages out to other body systems and components telling them what to do to get in step with a new or revised survival system.
One such system is the hypothalamic-pituitary-adrenal axis. “The stress system coordinates the adaptive responses of the organism to stressors of any kind. The main components of the stress system are the corticotropin-releasing hormone (CRH) and locus ceruleus-norepinephrine (LC/NE)-autonomic systems and their peripheral effectors, the pituitary-adrenal axis, and the limbs of the autonomic system. Activation of the stress system leads to behavioral and peripheral changes that improve the ability of the organism to adjust homeostasis and increase its chances for survival.” The effects of signaling from this system are widespread. “The CRH and LC/NE systems stimulate arousal and attention, as well as the mesocorticolimbic dopaminergic system, which is involved in anticipatory and reward phenomena, and the hypothalamic beta-endorphin system, which suppresses pain sensation and, hence, increases analgesia. CRH inhibits appetite and activates thermogenesis via the catecholaminergic system. Also, reciprocal interactions exist between the amygdala and the hippocampus and the stress system, which stimulates these elements and is regulated by them (ref).” If you get badly startled the adrenalin kicks in and the whole cascade process is kicked off.
Recent research is revealing that the skin provides another quite similar system. “Described as the body’s largest organ, the skin is strategically located at the interface with the external environment where it has evolved to detect, integrate and respond to a diverse range of stressors. A flurry of recent findings has established the skin as an important peripheral (neuro)endocrine organ that is tightly networked to central stress axes. This capability is contributing to the maintenance of body homeostasis, and in this way could be harnessed for therapeutic strategies(ref).”
Central actors in this regard are our old friends, melanocytes. “More than 15 years ago, we have proposed that melanocytes are sensory and regulatory cells with computing capability, which transform external and/or internal signals/energy into organized regulatory network(s) for the maintenance of the cutaneous homeostasis. This concept is substantiated by accumulating evidence that melanocytes produce classical stress neurotransmitters, neuropeptides and hormones, express corresponding receptors and these processes are modified and/or regulated by ultraviolet radiation, biological factors or stress(ref).” Melanocortins produced by melanocytes have widespread impacts including cardiovascular regulatory effects(ref). Regarding melanocytes, also see the previous posts Anti-inflammatory effects of the hormone alpha-MSH and More research insight on gray hair and adult stem cell reproduction .
In fact, hair follicles just by themselves play an important role(ref)(ref). And see Human hair follicles display a functional equivalent of the hypothalamic-pituitary-adrenal axis and synthesize cortisol. “Thus, even in the absence of endocrine, neural, or vascular systemic connections, normal human scalp hair follicles directly respond to CRH stimulation in a strikingly similar manner to what is seen in the classical HPA axis, including synthesis and secretion of cortisol and activation of prototypic neuroendocrine feedback loops(ref).” Who would think a lowly hair follicle could do things like that – things that regulate my temperament and how I react?
To sum it up: “We are currently experiencing a spectacular surge in our knowledge of skin function both at the organ and organismal levels, much of this due to a flurry of cutaneous neuroendocrinologic data, that positions the skin as a major sensor of the periphery. As our body’s largest organ, the skin incorporates all major support systems including blood, muscle and innervation as well as its role in immuno-competence, psycho-emotion, ultraviolet radiation sensing, endocrine function, etc. It is integral for maintenance of mammalian homeostasis and utilizes locally-produced melanocortins to neutralize noxious stimuli. In particular, the cutaneous pigmentary system is an important stress response element of the skin’s sensing apparatus—(ref).”
I am planning another blog entry where I will discuss another topic related to melanocytes – the afamelanotide analog of alpha-MSH that has been in clinical trials and the “melanotan” commercial products that may or may not work like alpha-MSH and may or may not be safe.