Cardiovascular system, sympathetic regulation

Vasomotor center. Autonomic nervous activity to the cardiovascular system is regulated by the vasomotor center (see Figure 15.4). Located in the lower pons and the medulla of the brainstem, the vasomotor center is an integrating center for blood pressure regulation. It receives several sources of input, processes this information, and then adjusts sympathetic and parasympathetic discharge to the heart and blood vessels accordingly. 

In the peripheral nervous system, norepinephrine is an important neurotransmitter in the sympathetic branch of the autonomic system. Sympathetic nerve transmission operates below the level of consciousness in controlling physiological function of many organs and tissues of the body. The sympathetic system plays a particularly important role in regulating cardiovascular function in response to postural, exertional, thermal, and mental stress. With sympathetic activation, the heart rate is increased, peripheral arterioles are constricted, skeletal arterioles are dilated, and the blood pressure is elevated. In addition, sympathetic nerve stimulation dilates pupils inhibits smooth muscles of the intestines, bronchi, and bladder and closes the sphincters. Sympathetic signals work in balance with the parasympathetic portion of the autonomic nervous system to maintain a stable internal environment. 

The adrenergic system is an essential regulator that increases cardiovascular and metabolic capacity during situations ofstress, exercise, and disease. Nerve cells in the central and peripheral nervous system synthesize and secrete the neurotransmitters noradrenaline and adrenaline. In the peripheral nervous system, noradrenaline and adrenaline are released from two different sites noradrenaline is the principal neurotransmitter of sympathetic neurons that innervate many organs and tissues. In contrast, adrenaline, and to a lesser degree noradrenaline, is produced and secreted from the adrenal gland into the circulation (Fig. 1). Thus, the actions of noradrenaline are mostly restricted to the sites of release from sympathetic nerves, whereas adrenaline acts as a hormone to stimulate many different cells via the blood stream. 

Baroreflexes involving the sympathetic nervous system are responsible for the rapid moment-to-moment regulation of blood pressure. A fall in blood pressure causes pressure-sensitive neurons (baroreceptors in the aortic arch and carotid sinuses) to send fewer impulses to cardiovascular centers in the spinal cord. This prompts a reflex response of increased sympathetic and decreased parasympathetic output to the heart and vasculature, resulting in vasoconstriction and increased cardiac output. These changes result in a compensatory rise in blood pressure (Figure 19.3, and Figure 3.5, see p. 31). 

The family of adrenergic receptors (ARs the ar, a2-, and P-ARs) are key regulators of the sympathetic division of the autonomic nervous system, involved in both central and peripheral cardiovascular function. Here, we review our current understanding of the cellular localization and trafficking properties of the ar, a2-, and P-ARs. We then examine recent evidence indicating that the cellular localization of these receptors and their excursion into intracellular compartments play an underappreciated role in the activation of both G protein and novel non-G protein-dependent cellular signaling. 

P-Adrenergic receptors (P-ARs) are members of the superfamily of G protein-coupled receptors (GPCRs) that are stimulated by the catecholamines epinephrine and norepinephine (1). P-ARs have been shown to play important roles in the regulation of cardiovascular, respiratory, metabolic, central nervous system, and reproductive functions by the sympathetic nervous system. Three distinct subtypes of P-ARs have been identified and cloned Pj, P2, and P3 (2-4). All three P-ARs are believed to signal by coupling to the stimulatory G protein Gsa, leading... 

The pharmacology of hallucinogens such as mescaline and related bases has been reviewed and the cardiovascular and renal actions of dopamine have been discussed with a view to potential clinical applications. The proceedings of a symposium on the regulation of catecholamine metabolism in the sympathetic nervous system have appeared. The mass spectra of ephedrine derivatives have been discussed. ... 

Heart rate (HR), heart rate variability and blood pressure are regulated, in part, by the sympathetic and parasympathetic nervous systems. Changes in one or more may inerease the risk of cardiovascular events (e.g. arrhythmias, myocardial infarction). Decreases in heart rate variability have been associated with cardiovaseular mortality/morbidity in older adults and those with significant heart disease. Eine particles in ambient concentrations have recently been implicated in deereases of heart rate variability (Timonen et al. 2006), increased risk of arrhythmias (Metzger et al. 2004 Lanki et al. 2006) and increased blood pressure (Timonen et al. 2006) in particular in older subject with compromised health. Additionally inhaled particles seem to enhance blood coagulation (Riickerl et al. 2007a, b). 

The same cardiovascular control system regulates blood distribution and blood pressure by affecting the small arterioles of the peripheral blood vasculature. The entrance to each of these vessels is surrounded by a sphincter muscle (a ring of involuntary muscle that surrounds the arteriolar aperture) with sympathetic, and in some cases, parasympathetic, nerve fibers. The sphincter is usually contracted. When the signal comes for the muscle to relax, the neuron produces nitric oxide at the neuromuscular junction, and this gas relaxes the sphincter. When the sphincter muscle expands, it increases the area through which blood flows and decreases its resistance. With decreased resistance, blood pressure falls. 

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