Hypertension is a disorder that may occur throughout life; it is defined as the continued elevation of blood pressure beyond defined limits (see Table 15-4). In adults the criterion of moderate hypertension is where the systolic and diastolic pressures exceed 160 and 100 mm Hg, respectively. As many as 50 million Americans have elevated blood pressure. Hypertension has a worldwide incidence of 9-18% in the adult population. In the presence of continuing uncontrolled hypertension, there is frequently a high incidence of heart disorders (congestive failure, coronary heart disease), stroke, kidney disease, and/or aneurysms of the aorta.
There are three general causative factors that may lead to the development of hypertension: (a) primary aldosteronism, which results in the unrestrained production of aldosterone by the adrenals (see Chapter 10); (b) a pheochromocytoma, which is a tumor that produces catecholamines (see Chapter 11); and (c) renovascular hypertension, which results in a lowered blood supply to one kidney with normal blood flow to the second kidney.
An important component of the diagnosis of the etiology of hypertension is a determination of the level of Na+ excretion in relation to the plasma levels of renin and also the daily amount of aldosterone excreted in the urine. Such an analysis may provide the formulation of a rational basis of treatment, which can include the use of inhibitors of the renin-angiotensin system such as the antagonist saralasin, use of /3-blocking
FIGURE 15-22 Enzyme cascades associated with the inflammation response. The processes are initiated at the time of local injury when plasma leaks into the tissues as a consequence of increased vascular permeability. The complement components are indicated by CI, C2, etc. V indicates a postcapillary venule. The coagulation cascade results, at the site of injury, in the conversion of fluid blood into a solid gel or clot of blood. The principal event is the conversion of soluble fibrinogen into insoluble fibrin; the blood coagulation cascade involves at least 13 tissue factors. When the coagulation system is activated, the fibrinolytic cascade or clot-dissolving process also becomes operative. This involves the action of plasminogen activators. Plasminogen activators are serine proteases that cleave an Arg-Val bond in plasminogen to release the enzyme plasmin. Plasmin is a trypsin-like enzyme that cleaves Arg-Lys bonds in the local fibrin clot. (Plasminogen, a /3-globulin of 143 kDa, is a constitutive blood protein that forms a complex with the fibrin strands of the blood clot.) The kinin cascade results in the production of bradykinin (see Figure 15-16), which causes vasodilation and increased vascular permeability. The complement cascade is an enzyme system with nine major components; the system is activated by substances derived from microorganisms. The ultimate objective of the complement system is to release chemotaxins (which attract phagocytic cells), histamines, and opsonin (which attaches to the surface of microorganisms and facilitates their ingestion by macrophages and granulocytes). Adapted with permission from M. M., Dale, J. C., Foreman, and T.-P., Fan (1994). "Textbook of Immunopharmacology," 3rd ed. Blackwell Scientific Publications, Oxford.
drugs such as propanolol, or dietary restriction of salt intake. It is beyond the scope of this presentation to consider this topic in detail.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...