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The Peripheral Vascular System ST120: Basic Sciences II Concorde Career College, Portland Cardiovascular System Objectives: • Discuss the relevant vessels of the peripheral vascular system • Compare and contrast the structure of an artery and a vein • Describe the mechanisms that regulate blood pressure • Describe the etiology of atherosclerosis and arterial embolism and their treatments • Compare and contrast bypass grafting and endarterectomy Cardiovascular System Blood Vessels and Circulation Types of Blood Vessels • Arteries – Arterioles • Veins – Venules • Capillaries Blood Vessels • Arteries: blood is pumped from the heart through a series of large distribution vessels. Largest artery = aorta • Arteries divide into vessels that become progressively smaller and finally become tiny arterioles that control the flow into microscopic exchange vessels called capillaries • Gas exchange occurs in capillary beds Blood Vessels • Blood exits capillary beds and enters venules • Venules steadily increase in size to eventually become veins • Largest veins are the superior and inferior vena cava Blood Vessels • Arteries carry blood away from the heart • Veins carry blood toward the heart • So do all arteries carry oxygen rich blood and all veins carry oxygen poor blood? Structure • 3 tunics (coats) or layers of veins and arteries – Tunica adventitia- outermost – made of connective tissue, which reinforce the vessel wall so it will not burst – Tunica media- middle – contains smooth muscle – Tunica intima- inner – endothelial cells --- endothelium lines the entire circulatory system Structure • Only arteries, arterioles, veins, and venules can be seen during surgery- capillaries are microscopic • Capillaries are only one layer thick and thin-walled- only tunica intima • This allows for easy exchange of gases and nutrients Systemic and Pulmonary Circulation • Systemic circulation: blood flow from left ventricle of the heart through blood vessels to all parts of the body and back to the right atrium • Pulmonary circulation: venous blood moves from the right atrium to the right ventricle to the pulmonary artery to lung arterioles and capillaries. There the exchange of gases between the blood and the air takes place. This oxygenated blood then flows through lung venules into four pulmonary veins and returns to the left atrium Pulmonary and Systemic Blood Circuits Cardiovascular System Veins contain valves to prevent the backward flow of blood: A. External view of the vein shows wider area of valve. B. Internal view with the valve open as blood flows through. C. Internal view with the valve closed. Blood Vessel Structure Note the valve and the comparison of the artery, vein, and capillary Cardiovascular System Ascending Aorta • Right Coronary • Left Coronary Aortic Arch • Brachiocephalic – Right Common Carotid – Right Subclavian • Left Common Carotid • Left Subclavian Cardiovascular System Major veins and arteries of the neck Branches of the Thoracic and Abdominal Aorta Arterial System Venous System Blood Pressure • Pressure on the blood vessel walls • Highest in arteries, Lowest in Veins • Blood pressure gradient: the graph looks like a hill… aorta is highest point and the venae cavae are the lowest. Defined as the difference between the mean BP in the aorta and the mean BP in the venae cavae. Blood Pressure • Blood pressure keeps the blood circulating • No blood pressure = No blood circulating = death • Average pressure is the MEAN BP • Hypertension- high blood pressure; could rupture blood vessels • Hypotension- low blood pressure; circulation can be too low to sustain life - Hemorrhage can cause hypotension Factors That Influence Arterial Blood Pressure • Blood volume • Strength of ventricular contractions • Resistance • Blood viscosity • Heart rate Blood Pressure • Blood Volume- volume of blood in the vessels – Direct cause of blood pressure • Arterial blood volume is determined by how much the heart pumps into them, which determines how much the arterioles drain out of them; the size of the arterioles are important in determining how much blood is drained from the arteries • Larger the volume, the higher the pressure; conversely, lower blood volume, lower blood pressure; thus hemorrhage = lower blood pressure = not corrected = death • Drop in BP is a major sign of hemorrhage Strength of ventricular Contractions –the strength and rate of the heartbeat affects the stroke volume (amount of blood ejected by the LV into the aorta with one contraction), which in turn affects cardiac output, which affects blood volume, therefore the BP Blood Pressure • Blood Viscosity- aka thickness. Blood that is too diluted causes BP to drop – Less viscous than normal, BP decreases, so for hemorrhage treatment, whole blood or plasma is preferred – More viscous than normal, BP increases • Polycythemia increases viscosity thereby increasing BP Blood Pressure As blood leaves the LV and enters the aorta, its pressure falls progressively as the distance from the heart increases Once in the venae cavae, the pressure is near zero Blood Pressure • Resistance is the hindrance of blood flow with in the CV system due to friction of the blood against the walls of the vessels • Most resistance is in the aterioles, capillaries, and venules • Vasoconstriction and vasodilation influence resistance Blood Pressure • Heart rate affects BP • As the heart beats faster, each contraction of the LV leaves less time for the ventricle to refill, thus less blood is pumped into the aorta. This means less blood volume which is less blood pressure Fluctuations in BP • Doesn’t stay the same all the time. • Increases during exercise, fear, etc. • Decreases at night, while sleeping or relaxing. • Normal is 120/80 for healthy adults (average) Central venous pressure • BP within the RA • CVP is low as it enters the RA • If the heart is weakened, the CVP increases 5 mechanisms that keep venous blood moving • Continued beating of the heart • Adequate BP in the arteries • Semilunar valves preventing backflow thus moving blood in the right direction • Contraction of skeletal muscles squeezing veins with assistance of venous valves • Changing pressures in the chest cavity during breathing acting as a pump Pulse • An artery expanding and then recoiling – alternately is what you are feeling when you take a pulse. • Provides information on the rate, strength, and rhythm of the heartbeat Major pulse points • • • • • • • • • • Temporal – over the temple anterior to the ear Facial – lower margin of the mandible Carotid – neck, along the sternocleidomastoid muscle Axillary – inferiolateral axillary wall Brachial – medial aspect of upper arm Radial – at the wrist Femoral – groin Popliteal – behind and proximal to the knee Dorsalis – dorsal surface of the foot Apical – 5th left intercostal space (requires auscultation) Hepatic Portal System • Veins from the spleen, stomach, pancreas, gallbladder, and intestines send their blood to the liver by means of the hepatic portal vein. Hepatic Portal Circulation • Refers to the route of blood flow through the liver. • Liver cells remove and detoxify various poisonous substances. • This is a variation (detour) of the normal blood route • This means that this blood is sent through a second set of capillaries (in the liver) Pathology • Arteriosclerosis -thickening & loss of elasticity of the walls of the arteries Hardening of the arteries – Atherosclerosis -collection of fatty & other substances on the inner lining of arteries, forming plaques, which progressively occlude the passageways; obstruction of the flow of blood • Atheroma – prototypical lesion of atherosclerosis Arteriosclerosis Obliterans Diagnostic Procedures and Equipment • • • • • Plethysmography Doppler probe Phleborheography CAT scan, MRI, and ultrasonography Angiography Angiography Pathology • Arterial embolism – Treatment - Fogarty catheter Pulmonary Emboli Following Fogarty Embolectomy – Carotid Endarterectomy - removal of arteriosclerotic plaque from an obstructed carotid artery in order to restore circulation. Endarterectomy