Unit 8: Disorders of Cardiovascular Function: Disorders of Arterial Circulation PDF

# Unit 8: Disorders of Cardiovascular Function: Disorders of Arterial Circulation ## Objectives - Describe the etiology and pathogenesis of hyperlipidemia. - Describe the etiology and pathogenesis of atheroscelerosis. - Differentiate between a true and false aneurysm. - Differentiate in terms of b...

# Unit 8: Disorders of Cardiovascular Function: Disorders of Arterial Circulation ## Objectives - Describe the etiology and pathogenesis of hyperlipidemia. - Describe the etiology and pathogenesis of atheroscelerosis. - Differentiate between a true and false aneurysm. - Differentiate in terms of berry and saccular aneurysms. - Describe the etiology and pathogenesis of aortic dissection and abdominal aortic aneurisms. ## Hyperlipidemia - Hyperlipidemia is an excess of lipids in the blood. - Lipids are classified as: - Triglycerides or neutral fat - Phospholipids - Cholesterol - **Triglycerides** are used in energy metabolism, are combinations of three fatty acids condensed with a single glycerol molecule. - **Phospholipids** contain a phosphate group, are important structural constituents of lipoproteins, blood clotting components, the myelin sheath, and cell membranes. - **Cholesterol** is not composed of fatty acids, its steroid nucleus is synthesized from fatty acids, and thus, its chemical and physical activity is similar to that of other lipid substances. - Elevated levels of blood cholesterol (hypercholesterolemia) are implicated in the development of atherosclerosis with its attendant risk of heart attack and stroke. ## Etiology and Pathogenesis of Hyperlipidemia - Most cases of elevated levels of cholesterol are probably multifactorial. - Some people may have increased sensitivity to dietary cholesterol; others have a lack of LDL receptor. - Altered synthesis of the apoproteins, including oversynthesis of apoB-100, the major apoprotein in LDL. - Serum cholesterol levels may be elevated as a result of an increase in any of the lipoproteins (read pages 743-745): - Chylomicrons - VLDL (very low density lipids) - IDL (intermediate density lipids) - LDL (low density lipids) - bad cholesterol - main carrier of cholesterol - HDL (high density lipids) - good cholesterol - reverse transport of cholesterol from peripheral tissues back to the liver. ## Factors that can raise blood lipid levels - Nutrition - Genetics - Medications (beta-blockers, estrogen, protease inhibitors) - Comorbid conditions - Metabolic diseases ## Hypercholesterolemia (Hyperlipoproteinemia) Classifications - **Primary hypercholesterolemia**: describes elevated cholesterol levels that develop independent of other health problems or lifestyle behaviors. - **Secondary hypercholesterolemia** is associated with other health problems and behaviors. ### Primary Hypercholesterolemia - May be caused by a defective synthesis of the apoproteins, a lack of receptors, defective receptors, or defects in the handling of cholesterol in the cell that are genetically determined. ### Secondary Hyperlipoproteinemia - Causes may include obesity with high-calorie intake and diabetes mellitus. - High calorie diets increase the production of VLDL, with triglyceride elevation and high conversion of VLDL to LDL. - Excess ingestion of cholesterol may reduce the formation of LDL receptors and thereby decrease LDL removal. - Diets that are high in triglycerides and saturated fats increase cholesterol synthesis and suppress LDL receptor activity. - In diabetes mellitus and the metabolic syndrome, typical dyslipidemia is seen with elevation of triglycerides, low HDL, and minimal or modest elevation of LDL. - Other systemic disease that may elevate lipids like hyperthyroidism, nephrotic syndrome, and obstructive liver disease. - Medications such as beta-blockers, estrogens, and protease inhibitors (used in the treatment of human immunodeficiency virus (HIV) infection) can also increase lipid levels. ## Atherosclerosis - Atherosclerosis is a type of arteriosclerosis or hardening of the arteries. - The term atherosclerosis, which comes from the Greek words atheros ("gruel" or "paste") and sclerosis ("hardness"), denotes the formation of fibro-fatty lesions in the intimal lining of the large- and medium-sized. Such as the aorta and its branches, coronary arteries, and the large vessels that supply the brain. ## Etiology and Risk Factors for Atherosclerosis - The major risk factor for atherosclerosis is hypercholesterolemia, which can be modified. ### Non-Modifiable Risk Factors - Increasing age - Family history of premature CHD - Male ### Major risk factors for atherosclerosis that can be affected by a change in health care behaviors - High blood cholesterol levels (specifically high LDL cholesterol levels) - Cigarette smoking - Obesity and visceral fat - Hypertension - Diabetes mellitus (traditional cardiovascular risk factors) ## Role of Inflammation in the Etiology of Atherosclerosis - CRP (C-Reactive Protein) is a serum marker for systemic inflammation.  - Several prospective studies have indicated that elevated CRP levels are associated with vascular disease. - The pathophysiologic role of CRP in atherosclerosis has not yet been defined. ## Pathogenesis of Atherosclerosis - The lesions associated with atherosclerosis are of three types: - Fatty streak - Fibrous atheromatous plaque - Complicated lesion ### Complicated lesion - The more advanced complicated lesions contain hemorrhage, ulceration, and scar tissue deposits. - Thrombosis is the most important complication of atherosclerosis. - Slowing and turbulence of blood flow in the region of the plaque and ulceration of the plaque cause it.  - The thrombus may cause occlusion of small vessels in the heart and brain. ## Aneurysms - An aneurysm is an abnormal localized dilation of a blood vessel. - Aneurysms can occur in arteries and veins, but they are most common in the aorta. ## Two types of Aneurysms | Parameters | True Aneurysm | False Aneurysm | | :--------------- | :---------------------------------------------------- | :-------------------------------------------------------------- | | Characteristics | One in which the aneurysm is bounded by a complete vessel wall. The blood in a true aneurysm remains within the vascular compartment. | Represents a localized dissection or tear in the inner wall of the artery with formation of an extravascular hematoma that causes vessel enlargement. | | | | Unlike true aneurysms, false aneurysms are bounded only by the outer layers of the vessel wall or supporting tissues. | ## Classification of Aneurysm | Classifications | Description | Location | | :------------------- | :-------------------------------------------------------------------------------------------------------------------- | :-------------------------------------------------------------------------- | | Berry aneurysm | True aneurysm that consists of a small, spherical dilation of the vessel at a bifurcation. | Found in the circle of Willis in the cerebral circulation. | | Fusiform aneurysm | True aneurysm that involves the entire circumference of the vessel and is characterized by a gradual and progressive dilation of the vessel. | Entire ascending and transverse portions of the thoracic aorta or may extend over large segments of the abdominal aorta. | | Saccular aneurysm | Is a true aneurysm that extends over part of the circumference of the vessel and appears saclike. | Blood vessels | | Dissecting aneurysm | False aneurysm resulting from a tear in the intimal layer of the vessel that allows blood to enter the vessel wall, dissecting its layers to create a blood-filled cavity. | Occurs in aorta and is a life-threatening condition. | ## Aortic Aneurysms - **Etiology**: Two most common causes of aortic aneurysms: - Atherosclerosis - Degeneration of the vessel media. - **Pathophysiology**: Abdominal aortic aneurysms are located most commonly below the level of the renal artery (>90%) and involve the bifurcation of the aorta and proximal end of the common iliac arteries. The infrarenal aorta is normally 2 cm in diameter; an aneurysm is defined as an aortic diameter greater than 3 cm. - They can involve any part of the vessel circumference (saccular) or extend to involve the entire circumference (fusiform). - Most abdominal aneurysms are asymptomatic. - Calcification, which frequently exists on the wall of the aneurysm. - As the aneurysm expands, it may compress the lumbar nerve roots, causing lower back pain that radiates to the posterior aspects of the legs. - An abdominal aneurysm also may cause erosion of vertebrae. - Stasis of blood favors thrombus formation along the wall of the vessel. - With thoracic and abdominal aneurysms, the most dreaded complication is rupture. ## Etiology and Pathogenesis of Aortic Dissection - Aortic dissection is caused by conditions that weaken or cause degenerative changes in the elastic and smooth muscle of the layers of the aorta. ## Incidence of Aortic Dissection - Most common in the 40- to 60-year-old age group. - More prevalent in men than in women. ## Risk Factors for Aortic Dissection - Two risk factors predispose to aortic dissection: - Hypertension - Degeneration of the medial layer of the vessel wall. ## Other factors that predispose to dissection - Congenital defects of the aortic valve (i.e., bicuspid or unicuspid valve structures) and aortic coarctation. - Aortic dissection is a potential complication of cardiac surgery or catheterization. ## Two types of Aortic Dissection - **Type A**: The more common (and potentially more serious in terms of complications) proximal lesions, involving the ascending aorta only or both the ascending and the descending aorta. - **Type B**: Those not involving the ascending aorta and usually beginning distal to the subclavian artery.