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The Cardiovascular System Blood Vessels and Circulation Blood Vessels Have Two Functions 1. Carry blood to and from the lungs for oxygenation 2. Carry blood to and from every cell in the body • Blood vessel diameters range from 2.5 cm (at the aorta of the heart) to microscopic (capillaries) in tissues Blood Has Two Primary Functions 1. Deliver Oxygen (O2) gas and nutrients to every cell in the body 2. Remove Carbon Dioxide (CO2) gas and waste from every cell in the body • Blood is made of both cells and liquid (plasma) Pulmonary Circuit – Systemic Circuit • Arteries always carry blood away from the heart and veins always carry it back to the heart • Pulmonary Circuit - Right Side of heart • Arteries to lung carry deoxygenated blood • Veins back to heart carry oxygenated blood • Systemic Circuit - Left Side of heart • Arteries to body carry oxygenated blood • Veins back to heart carry deoxygenated blood • 60,000 miles of blood vessels in each person Layers 1. Smooth lining 2. Smooth muscle 3. Outer covering Function 1. Smooth flow 2. Vasoconstriction /dilation 3. Support, attachment more vessels? Blood Vessels – Arteries • Blood moves fast, away from heart • Thick walls – have more smooth muscle to regulate vasodilation or vasoconstriction • Large arteries narrow or branch to smaller arteries and finally to “arterioles” before becoming capillaries • “Elastic” arteries near heart to smooth out the initial force • “Muscular” arteries farther out for vasoconstriction – controlled by hormones, nerves Blood Vessels – Capillaries • The goal of the cardiovascular system occurs here • Only vessels where fluid, gas, and nutrientexchange occurs with tissue cells • Microscopic – small diameter – single RBC file • Blood slows – lots of branching • Capillary beds ~ 1 mm. Feed all tissues • Can be turned on or off depending on need Leaky Capillaries • One-cell thin inner wall, occasional smooth muscle for stabilizing them. Leakiness depends on the tissue they serve, the size of the molecules transferred, or how fast they need to transfer • A little leaky – small clefts – very tight in brain • Leaky – small pores – kidney, digestive tract • Very leaky – large pores, bigger clefts – liver, bone marrow, lymphatics. Allow cells to pass through Capillary Beds • Interweaving networks – “Microcirculation” • Contains 10-100 capillaries • Contains one bypass shunt vessel • Has its own control features – sphincters • Depends on local tissue chemistry or nerve signals • Example – digestion and exercise Blood Vessels – Veins • From capillaries, blood moves to “venules,” that merge into small veins, larger veins, then “dumps” back into heart • Much less smooth muscle in their walls • Slower blood flow. Skeletal muscle helps flow • Have valves to keep blood moving forward • > 60% of all blood in body is in veins at any time Control of Blood Flow Anatomical Features • Arteries’ Smooth Muscles (SM) • Arterioles’ SM • Capillary SM sphincters • Veins’ SM • Valves in veins • Large diameter of veins Specific Regulation • Local tissue chemistry effects vessels – self regulation • Hormones effect vessels • Brain signals heart rate • Brain signals vessels External Help • Squeegee effect • Breathing • Skeletal Muscle movement Increased blood flow to disease or damage • Allergies – histamines are vasodilators • Vasodilators also released during injury or infection • More fluids and proteins to a site – not RBCs • Increased tissue fluid pressure causes swelling and pain • • • • Cut Stomach ache Cold Injury Vascular Diseases • Hypertension • Hypotension • Blockage • Large and medium arteries, thickening of walls, plaque • Can rupture and form clots their or elsewhere • Varicose Veins – valve malfunctions Angiogenesis and Collateral Arteries • Occurs in some tissues that experience moderate ischemia from blockage or increased demand • New arteries form at those sites (angiogenesis) • Collateral Arteries • Pre-existing redundancy • Angiogenesis over weeks and months Circulatory Shock • Organs can’t get enough O2 from loss of blood flow – tissues die • Massive blood loss outside the body • Massive fluid loss (plasma volume, not RBC) from vessels into tissues • Too many blood vessels “open” at one time • Allergies, anaphylaxis • Heart Failure