The pressure generated by the beating heart forces the blood forward and stretches the elastic walls of the arteries. In between heartbeats, as the heart muscle relaxes, the arterial walls snap back to their original shape, moving the blood forward to the body’s tissues. With hypertension, the pressure in the arteries is high enough to eventually produce damage to the blood vessels.
Investigations into the pathophysiology of hypertension, both in animals and humans, have revealed that hypertension may have an immunological basis. Studies have revealed that hypertension is associated with renal infiltration of immune cells and that pharmacologic immunosuppression (such as with the drug mycophenolate mofetil) or pathologic immunosuppression (such as occurs with HIV) results in reduced blood pressure in animals and humans. Evidence suggests that T lymphocytes and T-cell derived cytokines (eg, interleukin 17, tumor necrosis factor alpha) play an important role in hypertension. [14, 15]
It is common for there to be a development of visceral fat, after which the adipocytes (fat cells) of the visceral fat increase plasma levels of TNF-α and alter levels of a number of other substances (e.g., adiponectin, resistin, and PAI-1). TNF-α has been shown not only to cause the production of inflammatory cytokines, but also possibly to trigger cell signaling by interaction with a TNF-α receptor that may lead to insulin resistance. An experiment with rats fed a diet with 33% sucrose has been proposed as a model for the development of metabolic syndrome. The sucrose first elevated blood levels of triglycerides, which induced visceral fat and ultimately resulted in insulin resistance. The progression from visceral fat to increased TNF-α to insulin resistance has some parallels to human development of metabolic syndrome. The increase in adipose tissue also increases the number of immune cells present within, which play a role in inflammation. Chronic inflammation contributes to an increased risk of hypertension, atherosclerosis and diabetes.
Fortunately, since peaking in 2001-2002, the overall prevalence of metabolic syndrome in the United States has fallen, primarily due to decreases in the prevalences of hypertriglyceridemia and hypertension—and in spite of increases in the prevalences of hyperglycemia and obesity/waist circumference.  Data from the 2009-2010 National Health and Nutrition Examination Survey (NHANES) showed that the age-adjusted prevalence of metabolic syndrome had fallen to approximately 24% in men and 22% in women. 
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It has not been contested that cardiovascular risk factors tend to cluster together; the matter of contention has been the assertion that the metabolic syndrome is anything more than the sum of its constituent parts. Phenotypic heterogeneity (for example, represented by variation in metabolic syndrome factor combinations among individuals with metabolic syndrome) has fueled that debate. However, more recent evidence suggests that common triggers (for example, excessive sugar-intake in the environment of overabundant food) can contribute to the development of multiple metabolic abnormalities at the same time, supporting the commonality of the energy utilization and storage pathways in metabolic syndrome.
Hypertension with certain specific additional signs and symptoms may suggest secondary hypertension, i.e. hypertension due to an identifiable cause. For example, Cushing's syndrome frequently causes truncal obesity, glucose intolerance, moon face, a hump of fat behind the neck/shoulder (referred to as a buffalo hump), and purple abdominal stretch marks. Hyperthyroidism frequently causes weight loss with increased appetite, fast heart rate, bulging eyes, and tremor. Renal artery stenosis (RAS) may be associated with a localized abdominal bruit to the left or right of the midline (unilateral RAS), or in both locations (bilateral RAS). Coarctation of the aorta frequently causes a decreased blood pressure in the lower extremities relative to the arms, or delayed or absent femoral arterial pulses. Pheochromocytoma may cause abrupt ("paroxysmal") episodes of hypertension accompanied by headache, palpitations, pale appearance, and excessive sweating.
Between 2006 and 2011, there was a 25% increase in the number of people visiting US emergency rooms for essential hypertension, according to an analysis of data from the Nationwide Emergency Department Sample in 2014.  The reason for the increase, however, remained uncertain. The rate of emergency department visits also increased significantly, according to the study, rising from 190.1 visits per 100,000 population in 2006 to 238.5 visits per 100,000 population in 2011. Over the same period, however, admission rates decreased, from 10.47% in 2006 to 8.85% in 2011. 
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Research shows that Western diet habits are a factor in development of metabolic syndrome, with high consumption of food that is not biochemically suited to humans. Weight gain is associated with metabolic syndrome. Rather than total adiposity, the core clinical component of the syndrome is visceral and/or ectopic fat (i.e., fat in organs not designed for fat storage) whereas the principal metabolic abnormality is insulin resistance. The continuous provision of energy via dietary carbohydrate, lipid, and protein fuels, unmatched by physical activity/energy demand creates a backlog of the products of mitochondrial oxidation, a process associated with progressive mitochondrial dysfunction and insulin resistance.
Metabolic syndrome is a cluster of metabolic risk factors that come together in a single individual. These metabolic factors include insulin resistance, hypertension (high blood pressure), cholesterol abnormalities, and an increased risk for blood clotting. Affected individuals are most often overweight or obese. An association between certain metabolic disorders and cardiovascular disease has been known since the 1940s.