Over 60,000 Cardiovascular System – Vessels miles of vessels Cardiovascular System: Vessels Blood Vessel Anatomy: per human body (branch / diverge / fork) Elastic Muscular Arterioles Arteries Arteries Vessel Types: Heart (nutrient 1) Arteries (away from heart) exchange) 2) Capillaries Capillaries 3) Veins (toward heart) Veins Venules (join / merge / converge) Cardiovascular System – Vessels Cardiovascular System – Vessels Blood Vessel Anatomy: Blood Vessel Anatomy: Only tunic present in capillaries Vessels composed of distinct tunics : O2-rich; CO2-poor 1) Tunica intima Pulmonary circuit Tunica intima • Endothelium (simple squamous epithelium) (short, low pressure loop) • Connective tissue ( elastic fibers) O2-poor; CO2-rich (long, high pressure loop) 2) Tunica media Systemic circuit • Smooth muscle / elastic fibers • Regulates pressure / circulation • Sympathetic innervation Lumen O2-poor; O2-rich; Vasa CO2-rich CO2-poor 3) Tunica externa vasorum • Loose collagen fibers • Nerves / lymph & blood vessels • Protects / anchors vessel % / volume not fixed: Function: • Alteration of arteriole size 1) Circulate nutrients / waste • Alteration of cardiac output Vasomotor stimulation = vasoconstriction Tunica media 2) Regulate blood pressure • Combination of two above Vasomotor relaxation = vasodilation Tunica externa Costanzo (Physiology, 4th ed.) – Figure 4.1 Cardiovascular System – Vessels Relative tissue Cardiovascular System – Vessels Relative tissue makeup makeup Blood Vessel Anatomy: Blood Vessel Anatomy: Arteriosclerosis: Arteries: Hardening / stiffening of arteries Capillaries: Endothelium Endothelium Elastic tissue Elastic tissue Elastic Fibrous tissue Fibrous tissue Fibrous Smooth muscle Smooth Major groups: muscle Smooth D = Diameter T = Thickness 1) Capillaries: 1) Elastic Arteries (conducting arteries): D: 9.0 m D: 1.5 cm • Location of blood / tissue interface T: 1.0 m • Large, thick-walled (near heart) T: 1.0 mm • Stabilized by pericytes (smooth muscle cells) • [elastic fibers] (pressure reservior) Types of Capillaries: 2) Muscular Arteries (distributing arteries): • Deliver blood to organs D: 6.0 mm T: 1.0 mm • [smooth muscle] (vasoconstriction) 3) Arterioles: • Control blood into capillaries D: 37.0 m T: 6.0 m A) Continuous 2) Fenestrated 3) Sinusoidal: • Neural / hormonal / local controls • Uninterrupted lining • Oval pores present • Holes / clefts present • Found throughout body • Located in high absorption / • Allow passage of large (most common type) filtration regions (e.g., kidney) molecules (e.g., liver) Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Table 19.1 Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Table 19.1 / Figure 19.3 1 Cardiovascular System – Vessels Cardiovascular System – Vessels Relative tissue makeup Blood Vessel Anatomy: Blood Vessel Anatomy: Leukocyte Capillaries: Veins: margination Capillaries do not function independently – Instead they Endothelium Elastic tissue Elastic Fibrous tissue Fibrous Major groups: muscle Smooth form interweaving networks called capillary beds 1) Venules: Vascular True capillaries Not all capillaries are perfused D: 20.0 m shunt with blood at all times… • Formed where capillaries unite T: 1.0 m • Extremely porous 2) Veins (capacitance vessels): D: 5.0 mm • Large lumen; “volume” sink T: 0.5 mm • Low pressure environment Terminal Postcapillary Precapillary sphincters Venous sinuses: arteriole venule Specialized, flattened veins • 10 - 100 capillaries / bed • Sphincters control blood flow composed only of endothelium; supported by surrounding tissues a) Vascular shunt through capillary bed b) True capillaries Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 19.4 Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 19.3 / 19.5 Cardiovascular System – Vessels Vascular anastomoses: Blood Vessel Anatomy: Regions where vessels unite, forming interconnections Heart Heart Venous anastomoses are common; vein blockages collateral rarely lead to tissue death Arteriovenous channels anastomosis Arterial anastomoses provide alternative channels for blood to reach locations • Joints • Abdominal organs • Brain Retina, spleen, & kidney have Great saphenous limited collateral circulation vein harvest Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 19.2 Cardiovascular System – Vessels Cardiovascular System – Vessels To stay alive, blood must Would you want be kept moving… Pathophysiology: Most common form to find this pipe Hemodynamics: of arteriosclerosis in your house? Atherosclerosis: Blood Flow: Formation of atheromas (small, patchy thickenings) Volume of blood flowing past a on wall of vessel; intrude into lumen point per given time (ml / min) 1) Endothelium injured 3) Fibrous plaque forms The velocity of blood flow is not related to proximity of heart, but depends • Infection / hypertension • Collagen / elastin fibers on the diameter and cross-sectional area of blood vessels deposited around dying or 2) Lipids accumulate / oxidize dead foam cells • LDLs collect on tunica intima 4) Plaque becomes unstable Foam cells: • Calcium collects in plaque v = Q / A Macrophages engorged • Vessel constricts; arterial wall with LDLs; form fatty streak frays / ulcerates (= thrombus) v = Velocity (cm / sec) Link Q = Flow (mL / sec) Outcome: A = Cross-sectional area (cm2) Statins: • Myocardial infarctions Cholesterol-lowering 2 drugs • Strokes A = r • Aneurysms Angioplasty / Stent Bypass surgery Costanzo (Physiology, 4th ed.) – Figure 4.4 2 Cardiovascular System – Vessels Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… v = Q / A Blood Flow: A man has a cardiac output of 5.5 L / Volume of blood flowing past a min. The diameter of his aorta is point per given time (ml / min) estimated to be 20 mm, and the total cross-sectional area of his systemic capillaries is estimated to be 2500 cm2. The velocity of blood flow is not related to proximity of heart, but depends on the diameter and cross-sectional area of blood vessels What is the velocity of blood flow in the aorta relative to the velocity v = Q / A of blood flow in the capillaries? Blood velocity is highest in the aorta cm3 (1 cm) and lowest in the A = r2 A = (3.14) (10 mm)2 A = 3.14 cm2 capillaries Capillaries (5500 mL) Artery Vein 5.5 L / min 5500 cm3 / min vcapillaries = vaorta = 2500 cm2 3.14 cm2 800x difference vcapillaries = 2.2 cm / min vaorta = 1752 cm / min Randall et al. (Eckert Animal Physiology, 5th ed.) – Figure 12.23 Cardiovascular System – Vessels Cardiovascular System – Vessels To stay alive, blood must To stay alive, blood must Hemodynamics: be kept moving… Hemodynamics: be kept moving… Blood flow through a blood vessel or a series of blood vessels is Heart determined by blood pressure and peripheral resistance generates initial pressure Blood Pressure: Force per unit area on wall of vessel (mm Hg) • The magnitude of blood flow is directly proportional to the size of the pressure difference between two ends of a vessel Blood Flow (Q) = Difference in blood pressure ( P) • The direction of blood flow is determined by the direction of the pressure gradient Vessel resistance generates Always moves from high to low pressure pressure gradient Costanzo (Physiology, 4th ed.) – Figure 4.8 Cardiovascular System – Vessels Cardiovascular System – Vessels To stay alive, blood must To stay alive, blood must Hemodynamics: be kept moving… Hemodynamics: be kept moving… Blood flow through a blood vessel or a series of blood vessels is (difference in voltage) determined by blood pressure and peripheral resistance (current) Difference in blood pressure ( P) Blood Flow (Q) = Peripheral Resistance: Peripheral resistance (R) Amount of friction blood encounters (electrical resistance) passing through vessels (mm Hg / mL / min) Analogous to Ohm’s Law (V = I x R OR I = V / R) • Blood flow is inversely proportional to resistance encountered in the system Q = P / R 1 A man has a renal blood flow of 500 Blood Flow (Q) = mL / min. The renal atrial pressure R = P / Q is 100 mm Hg and the renal venous Peripheral resistance (R) pressure is 10 mm Hg. 100 mm Hg – 10 mm Hg R = What is the vascular resistance of 500 mL / min The major mechanism for changing blood flow in the the kidney for this man? cardiovascular system is by changing the resistance of blood vessels, particularly the arterioles R = 0.18 mm Hg / mL / min 3 Cardiovascular System – Vessels Cardiovascular System – Vessels To stay alive, blood must To stay alive, blood must Hemodynamics: be kept moving… Hemodynamics: be kept moving… The factors that determine the resistance of a blood vessel to The total resistance associated with a set of blood vessels also depends blood flow are expressed by Poiseuille’s (pwä-zwēz) Law: on whether the vessels are arranged in series or in parallel A) Series resistance: Powerful relationship! R = Resistance 8Lη Slight diameter change η = Viscosity of blood R = Sequential arrangement (e.g., pathway within single organ) equals r4 L = Length large resistance change r = Radius 1) Blood viscosity 2) Vessel Length 3) Vessel Diameter Arteriolar resistance is the greatest which equates to the area with the greatest decrease in pressure The total resistance is equal to the sum of the individual resistances viscosity = resistance length = resistance diameter = resistance Costanzo (Physiology, 4th ed.) – Figure 4.5 Cardiovascular System – Vessels Cardiovascular System – Vessels To stay alive, blood must To stay alive, blood must Hemodynamics: be kept moving… Hemodynamics: