Over 60,000 Cardiovascular System: Vessels miles of vessels per human body Cardiovascular System – Vessels Blood Vessel Anatomy: (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 Blood Vessel Anatomy: O2-rich; CO2-poor Pulmonary circuit (short, low pressure loop) O2-poor; CO2-rich (long, high pressure loop) Systemic circuit O2-poor; O2-rich; CO2-rich CO2-poor % / volume not fixed: Function: • Alteration of arteriole size 1) Circulate nutrients / waste • Alteration of cardiac output 2) Regulate blood pressure • Combination of two above Costanzo (Physiology, 4th ed.) – Figure 4.1 1 Cardiovascular System – Vessels Blood Vessel Anatomy: Only tunic present in capillaries Vessels composed of distinct tunics : 1) Tunica intima Tunica intima • Endothelium (simple squamous epithelium) • Connective tissue ( elastic fibers) 2) Tunica media • Smooth muscle / elastic fibers • Regulates pressure / circulation • Sympathetic innervation Lumen Vasa 3) Tunica externa vasorum • Loose collagen fibers • Nerves / lymph & blood vessels • Protects / anchors vessel Vasomotor stimulation = vasoconstriction Tunica media Vasomotor relaxation = vasodilation Tunica externa Cardiovascular System – Vessels Relative tissue makeup Blood Vessel Anatomy: Arteriosclerosis: Arteries: Hardening / stiffening of arteries Endothelium Elastic tissue Elastic Fibrous tissue Fibrous Major groups: muscleSmooth D = Diameter T = Thickness 1) Elastic Arteries (conducting arteries): D: 1.5 cm • Large, thick-walled (near heart) T: 1.0 mm • [elastic fibers] (pressure reservior) 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 • Neural / hormonal / local controls Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Table 19.1 Cardiovascular System – Vessels Relative tissue makeup Blood Vessel Anatomy: Capillaries: Endothelium Elastic tissue Elastic Fibrous tissue Fibrous Smooth muscle Smooth 1) Capillaries: • Location of blood / tissue interface D: 9.0 m T: 1.0 m • Stabilized by pericytes (smooth muscle cells) Types of Capillaries: A) Continuous 2) Fenestrated 3) Sinusoidal: • 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 / Figure 19.3 2 Cardiovascular System – Vessels Blood Vessel Anatomy: Capillaries: Capillaries do not function independently – Instead they form interweaving networks called capillary beds Vascular True capillaries Not all capillaries are perfused shunt with blood at all times… Terminal Postcapillary Precapillary sphincters arteriole venule • 10 - 100 capillaries / bed • Sphincters control blood flow a) Vascular shunt through capillary bed b) True capillaries Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 19.4 Cardiovascular System – Vessels Relative tissue makeup Blood Vessel Anatomy: Leukocyte Veins: margination Endothelium Elastic tissue Elastic Fibrous tissue Fibrous Major groups: muscleSmooth 1) Venules: D: 20.0 m • 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 Venous sinuses: Specialized, flattened veins composed only of endothelium; supported by surrounding tissues Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 19.3 / 19.5 3 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 Would you want Pathophysiology: Most common form to find this pipe of arteriosclerosis in your house? Atherosclerosis: Formation of atheromas (small, patchy thickenings) on wall of vessel; intrude into lumen 1) Endothelium injured 3) Fibrous plaque forms • Infection / hypertension • Collagen / elastin fibers 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 Macrophages engorged • Vessel constricts; arterial wall with LDLs; form fatty streak frays / ulcerates (= thrombus) Link Outcome: Statins: • Myocardial infarctions Cholesterol-lowering drugs • Strokes • Aneurysms Angioplasty / Stent Bypass surgery Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… Blood Flow: Volume of blood flowing past a point per given time (ml / min) The velocity of blood flow is not related to proximity of heart, but depends on the diameter and cross-sectional area of blood vessels v = Q / A v = Velocity (cm / sec) Q = Flow (mL / sec) A = Cross-sectional area (cm2) A = r2 Costanzo (Physiology, 4th ed.) – Figure 4.4 4 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… Blood Flow: Volume of blood flowing past a point per given time (ml / min) The velocity of blood flow is not related to proximity of heart, but depends on the diameter and cross-sectional area of blood vessels v = Q / A Blood velocity is highest in the aorta and lowest in the capillaries Capillaries Artery Vein Randall et al. (Eckert Animal Physiology, 5th ed.) – Figure 12.23 Cardiovascular System – Vessels v = Q / A A man has a cardiac output of 5.5 L / min. The diameter of his aorta is estimated to be 20 mm, and the total cross-sectional area of his systemic capillaries is estimated to be 2500 cm2. What is the velocity of blood flow in the aorta relative to the velocity of blood flow in the capillaries? cm3 (1 cm) A = r2 A = (3.14) (10 mm)2 A = 3.14 cm2 (5500 mL) 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 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… Blood flow through a blood vessel or a series of blood vessels is determined by blood pressure and peripheral resistance 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 Always moves from high to low pressure 5 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… Heart generates initial pressure Vessel resistance generates pressure gradient Costanzo (Physiology, 4th ed.) – Figure 4.8 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… Blood flow through a blood vessel or a series of blood vessels is determined by blood pressure and peripheral resistance Peripheral Resistance: Amount of friction blood encounters passing through vessels (mm Hg / mL / min) • Blood flow is inversely proportional to resistance encountered in the system 1 Blood Flow (Q) = Peripheral resistance (R) The major mechanism for changing blood flow in the cardiovascular system is by changing the resistance of blood vessels, particularly the arterioles Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… (difference in voltage) (current) Difference in blood pressure ( P) Blood Flow (Q) = Peripheral resistance (R) (electrical resistance) Analogous to Ohm’s Law (V = I x R OR I = V / R) Q = P / R A man has a renal blood flow of 500 mL / min. The renal atrial pressure R = P / Q is 100 mm Hg and the renal venous pressure is 10 mm Hg. 100 mm Hg – 10 mm Hg R = What is the vascular resistance of 500 mL / min the kidney for this man? R = 0.18 mm Hg / mL / min 6 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… The factors that determine the resistance of a blood vessel to blood flow are expressed by Poiseuille’s (pwä-zwēz) Law: Powerful relationship! R = Resistance 8Lη Slight diameter change R = η = Viscosity of blood equals r4 L = Length large resistance change r = Radius 1) Blood viscosity 2) Vessel Length 3) Vessel Diameter viscosity = resistance length = resistance diameter = resistance Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… The total resistance associated with a set of blood vessels also depends on whether the vessels are arranged in series or in parallel A) Series resistance: Sequential arrangement (e.g., pathway within single organ) 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 Costanzo (Physiology, 4th ed.) – Figure 4.5 Cardiovascular System – Vessels To stay alive, blood must Hemodynamics: be kept moving… The total resistance associated with a set