Adrenal Medullary System

Two major neuro-endocrine systems have been associated with stress. The first one is associated with acute stressful states such as fear, anger and excitement (Amkraut and Solomon 1975) and is called the sympathetic-adrenal-medullary system (SAM). SAM activation has been associated with action proneness and raised effort and it has also been described as the fight or flight system . It is activated when the organism is challenged in its control of the environment, and is accompanied by the release of catecholamines (epinephrine and norepinephrine) into the bloodstream. Catecholamine output is increased in response to a challenge to perform well (Frankenhaeuser et al. 1980 Lundberg and Frankenhaeuser 1980). 

Psychological stress may influence the immune system by activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic-adrenal-medullary axis (SAM). The well-described innervation of primary and secondary lymphoid tissues by the autonomic nervous system also has been implicated in stress-related modulation of the immune response. These pathways operate by producing biological mediators that interact with and affect cellular components of the immune system.13... 

Two PNS neurotransmitters, acetylchohne and norepinephrine, have particular chnical importance. Both are synthesized and stored primarily in the nerve terminals until released by a nerve impulse. It should be noted, to avoid confusion, that in the United States the transmitter in the sympathetic nervous system is referred to as norepinephrine and the major adrenal medullary hormone is referred to as epinephrine. In Europe and most of the world these two substances are called noradrenaline and adrenaline, respectively. 

General activation of the sympathetic system during stress, fear, or anxiety is accompanied by increased secretion of adrenal medullary hormones, which consist primarily of epinephrine in the human. The secretory activity of the adrenal medulla is regulated by the CNS. 

The primary purpose of the endocrine system is to maintain homeostasis — that is, to maintain a relatively constant internal environment in the face of a constantly changing external environment. The endocrine system consists of hormones and the glands and tissues that produce the hormones. A hormone is a chemical substance released by certain cells to effect the function of other distant cells (endocrine function). Many compounds act as endocrine hormones as well as having paracrine and autocrine functions. Paracrine and autocrine describe actions on nearby cells and on other cells that produce the substance, respectively. There is considerable overlap between substances classified as hormones and other chemical messengers such as neurotransmitters and cytokines. Many substances function in more than one of these categories. For example, epinephrine and norepinephrine function as both neurotransmitters and adrenal medullary hormones. 

Mescaline causes hallucinogenic effects by stimulating serotonin and dopamine receptors in the central nervous system. The sympathomimetic effects of mescaline are probably also centrally mediated. Changes in catecholamine metabolism and adrenal medullary function may be responsible for the agent s... 

Sympathetic Nervous Function, Disorders of Adrenal Medullary Function, and Genetic Disorders of Catecholamine Systems... 

Familial dysautonomia, dopamine [i-liydroxylase deficiency, norepinephrine transporter deficiency, and congenital adrenal hyperplasia include dysautonomias or conditions associated with adrenal medullary dysfunction in which the specific genetic abnormalities have been identified. There are also other disorders involving mutations of genes coding for proteins involved in catecholamine synthesis and metabolism in which the clinical manifestations do not clearly involve the sympathoadrenal systems or may be so globally severe that abnormalities of autonomic or adrenal medullary function are obscured (Table 29-5). 

The hormones of (he adrenal glands are essential for survival. The adrenal cortex is the source of the two important steroid hormones, aldosterone and cortisol (Fig. 1). The adrenal medulla is embryologically and histologically distinct from the cortex anil is part of the sympathetic nervous system. Medullary cells synthesize, store and secrete adrenaline, along with noradrenaline and dopamine. The adrenal medullary hormones arc discussed further on pages 126-127. 

The sympathetic adrenal medullary (SAM) system with the secretion of the catecholamines epinephrine and norepinephrine (or adrenaline and noradrenaline) has been of particular interest in the study of stress. 

Tobacco smoke includes 4000 chemical species with varying potential which cause adverse effects. Nicotine is stimulating to the autonomic nervous system ganglia and neuromuscular junction. The most prominent effects relate to stimulation of the adrenal medulla, central nervous system (CNS), cardiovascular system (release of catecholamines), gastrointestinal tract (parasympathetic stimulation), salivary and bronchial glands, and the medullary vomiting center. There is subsequent blockade of autonomic ganglia and the neuromuscular junction transmission, inhibition of catecholamine release from the adrenal medulla, and CNS depression. 

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