Chapter 26: Disorders of Blood Flow and Pressure Regulation

Disorders of Blood Flow and Pressure Regulation explores the structural components and regulatory mechanisms governing systemic blood flow and arterial pressure, detailing a wide array of associated pathophysiological disorders. Vessel anatomy, encompassing the endothelium and vascular smooth muscle cells (SMCs), is foundational, with emphasis on how endothelial dysfunction initiates many disease states. Regulation of systemic arterial blood pressure involves acute neural controls like baroreceptor reflexes and humoral mechanisms such as the renin-angiotensin-aldosterone system (RAAS), alongside long-term regulation primarily vested in renal fluid volume control. Arterial flow disorders are thoroughly examined, beginning with dyslipidemia—the imbalance of lipoproteins (LDL, HDL, triglycerides)—which serves as a major risk factor for atherosclerosis. Atherosclerosis development is described as a progressive process from fatty streaks to complex lesions, involving endothelial injury, macrophage infiltration, and foam cell formation, leading to ischemia and potential thrombosis. Other arterial conditions discussed include vasculitis (inflammation/necrosis of vessel walls), acute arterial occlusion, peripheral artery disease (PAD), Thromboangiitis Obliterans, and Raynaud phenomenon. The chapter also distinguishes between various aneurysms (true, false, saccular, fusiform) and the acute, life-threatening nature of aortic dissection. Systemic venous circulation disorders are covered, detailing the role of the skeletal muscle pump and valves in preventing retrograde flow, and exploring the etiology of varicose veins, chronic venous insufficiency, and venous thrombosis (DVT), often linked to Virchow triad factors. Finally, disorders of blood pressure regulation focus on hypertension, categorized as primary (essential) or secondary (caused by conditions like kidney disease or adrenal disorders). Chronic hypertension significantly contributes to target-organ damage in the heart, brain, kidneys, and eyes, and different classifications apply to adults, children, and pregnancy (e.g., preeclampsia). The chapter concludes with orthostatic hypotension, describing the abnormal drop in blood pressure upon standing and the failure of cardiovascular and neurohumoral reflexes to compensate.