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Cardio System II: Vasculature and Pressure
Blood Vessel Anatomy Arteries and arterioles Capillaries (3 types) Veins and venules Pulse and Pressure Points Blood Pressure Factors Regulating Blood Pressure
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Blood Vessels: The Vascular System
Venous system Arterial system Large veins (capacitance vessels) Heart Elastic arteries (conducting vessels) Large lymphatic vessels Lymph node Muscular arteries (distributing vessels) Lymphatic system Small veins (capacitance vessels) Arteriovenous anastomosis Lymphatic capillary Sinusoid Arterioles (resistance vessels) Postcapillary venule Terminal arteriole Metarteriole Thoroughfare channel Precapillary sphincter Capillaries (exchange vessels) Figure 19.2
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Layers of Blood Vessels
Tunica intima • Endothelium Valve • Subendothelial layer Internal elastic lamina Tunica media (smooth muscle under control of symp. n.s. and elastic fibers) External elastic lamina Tunica externa (fibrous connective: collagen fibers) Lumen Vein Lumen Artery Capillary network Basement membrane Endothelial cells (b) Capillary Figure 19.1b
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Differences Between Blood Vessel Types
Walls of arteries are the thickest, while lumen is smaller in diameter Walls of veins are thinner, while lumens of veins are larger Walls of capillaries are only one cell layer thick to allow for exchanges between blood and tissue
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Cardio System II: Vasculature and Pressure
Blood Vessel Anatomy Arteries and arterioles Capillaries (3 types) Veins and venules Pulse and Pressure Points Blood Pressure Factors Regulating Blood Pressure
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Arteries, Compared Elastic Arteries
Large thick-walled arteries with elastin in all three tunics Aorta and its major branches Large lumen offers low-resistance Act as pressure reservoirs—expand and recoil as blood is ejected from the heart Muscular Arteries Distal to elastic arteries; deliver blood to body organs Have thick tunica media with more smooth muscle Active in vasoconstriction Arterioles Smallest arteries Lead to capillary beds Control flow into capillary beds via vasodilation and vasoconstriction Table 19.1 (1 of 2)
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Cardio System II: Vasculature and Pressure
Blood Vessel Anatomy Arteries and arterioles Capillaries (3 types) Veins and venules Pulse and Pressure Points Blood Pressure Factors Regulating Blood Pressure
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Capillaries and Capillary Beds
Venous system Arterial system Large veins (capacitance vessels) Heart Elastic arteries (conducting vessels) Large lymphatic vessels Lymph node Muscular arteries (distributing vessels) Lymphatic system Small veins (capacitance vessels) Arteriovenous anastomosis Lymphatic capillary Sinusoid Arterioles (resistance vessels) Postcapillary venule Terminal arteriole Metarteriole Thoroughfare channel Capillaries (exchange vessels) Precapillary sphincter Figure 19.2
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Capillaries Found in all tissues except for cartilage, epithelia, cornea and lens of eye Three structural types Continuous capillaries Fenestrated capillaries Sinusoidal capillaries (sinusoids)
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Continuous Capillaries
Abundant in the skin and muscles Tight junctions connect endothelial cells Intercellular clefts allow the passage of fluids and small solutes Continuous capillaries of the brain Tight junctions are complete, forming the blood-brain barrier
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(a) Continuous capillary. Least permeable, and
Pericyte Red blood cell in lumen Intercellular cleft Endothelial cell Basement membrane Tight junction Pinocytotic vesicles Endothelial nucleus (a) Continuous capillary. Least permeable, and most common (e.g., skin, muscle). Figure 19.3a
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Fenestrated Capillaries
Some endothelial cells contain pores (fenestrations) More permeable than continuous capillaries Function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys)
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(b) Fenestrated capillary. Large fenestrations
Pinocytotic vesicles Red blood cell in lumen Fenestrations (pores) Endothelial nucleus Intercellular cleft Basement membrane Tight junction Endothelial cell (b) Fenestrated capillary. Large fenestrations (pores) increase permeability. Occurs in special locations (e.g., kidney, small intestine). Figure 19.3b
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Sinusoidal Capillaries
Fewer tight junctions, larger intercellular clefts, large lumens Usually fenestrated Allow large molecules and blood cells to pass between the blood and surrounding tissues Found in the liver, bone marrow, spleen
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(c) Sinusoidal capillary. Most permeable. Occurs in
Endothelial cell Red blood cell in lumen Large intercellular cleft Tight junction Incomplete basement membrane Nucleus of endothelial cell (c) Sinusoidal capillary. Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen). Figure 19.3c
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Capillary Beds Interwoven networks of capillaries form the microcirculation between arterioles and venules Consist of two types of vessels Vascular shunt (metarteriole—thoroughfare channel): Directly connects the terminal arteriole and a postcapillary venule True capillaries 10 to 100 exchange vessels per capillary bed Branch off the metarteriole or terminal arteriole
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Blood Flow Through Capillary Beds
Vascular shunt Precapillary sphincters Metarteriole Thoroughfare channel Low O2, high CO2, high pH, low nutrients, hot external temperatures, relaxation True capillaries Terminal arteriole Postcapillary venule (a) Sphincters open—blood flows through true capillaries. High O2, low pH, nutrients, low CO2, cold external temperatures, fight or flight conditions Terminal arteriole Postcapillary venule (b) Sphincters closed—blood flows through metarteriole thoroughfare channel and bypasses true capillaries. Figure 19.4
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Cardio System II: Vasculature and Pressure
Blood Vessel Anatomy Arteries and arterioles Capillaries (3 types) Veins and venules Pulse and Pressure Points Blood Pressure Factors Regulating Blood Pressure
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Venules and Veins Venules Formed when capillary beds unite
Very porous; allow fluids and WBCs into tissues Postcapillary venules consist of endothelium and a few pericytes Larger venules have one or two layers of smooth muscle cells Veins Formed when venules converge Have thinner walls, larger lumens compared with corresponding arteries Blood pressure is lower than in arteries Thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks Called capacitance vessels (blood reservoirs); contain up to 65% of the blood supply Table 19.1 (2 of 2)
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Veins Adaptations that ensure return of blood to the heart
Large-diameter lumens offer little resistance Valves prevent backflow of blood Most abundant in veins of the limbs Venous sinuses: flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain) One-way valves in veins prevent backflow where positive pressure is at a mininum
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Most of the Blood is in Veins and Venules
Pulmonary blood vessels 12% Systemic arteries and arterioles 15% Heart 8% Capillaries 5% Systemic veins and venules 60% Figure 19.5
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Vascular Anastomoses Interconnections of blood vessels
Arterial anastomoses provide alternate pathways (collateral channels) to a given body region Common at joints, in abdominal organs, brain, and heart Vascular shunts of capillaries are examples of arteriovenous anastomoses Venous anastomoses are common
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Cardio System II: Vasculature and Pressure
Blood Vessel Anatomy Arteries and arterioles Capillaries (3 types) Veins and venules Pulse and Pressure Points Blood Pressure Factors Regulating Blood Pressure
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Pulse Pulse – pressure wave of blood
Monitored at “pressure points” where pulse is easily palpated Figure 11.16
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Physiology of Circulation: Definition of Terms
Blood flow Volume of blood flowing through a vessel, an organ, or the entire circulation in a given period, measured in ml/min Blood pressure (BP) Force per unit area exerted on the wall of a blood vessel by the blood, expressed in mm Hg Measured as systemic arterial BP in large arteries near heart Peripheral Resistance Opposition to flow; a measure of the amount of friction blood encounters Generally encountered in the peripheral systemic circulation Three important sources of resistance Blood viscosity (relatively constant) Total blood vessel length (relatively constant) Blood vessel diameter (Resist. varies inversely with the fourth power of vessel radius (e.g., if the radius is doubled, the resistance is 1/16 as much)
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Local Blood Pressures Systemic pressure
Highest in the aorta, declines throughout the pathway; 0 mm Hg in the right atrium Arterial pressure Reflects two factors of the arteries close to the heart Elasticity (compliance or distensibility) Volume of blood forced into them at any time Blood pressure near the heart is pulsatile Systolic pressure: pressure exerted during ventricular contraction Diastolic pressure: lowest level of arterial pressure Pulse pressure = difference between systolic and diastolic pressure Mean arterial pressure (MAP): pressure that propels the blood to the tissues MAP = diastolic pressure + 1/3 pulse pressure Pulse pressure and MAP both decline with increasing distance from the heart Capillary blood pressure Low capillary pressure is desirable; low pressure forces filtrate into interstitial spaces Venus blood pressure - near zero
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Comparison of Blood Pressures
Blood pressure results when flow is opposed by resistance Disease causing blood pressure change Arteriosclerosis: Hardening of the artery walls and decrease of elasticity, restricting flow and increasing blood pressure. Atherosclerosis: A specific type of arterosclerosis where arteries are clogged by an accumulation of plaques: cholesterol particles (lipoproteins), fat, calcium, cellular waste and other substances.
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Factors Aiding Venous Return
Respiratory “pump”: pressure changes created during breathing move blood toward the heart by squeezing abdominal veins as thoracic veins expand Muscular “pump”: contraction of skeletal muscles “milk” blood toward the heart and valves prevent backflow Vasoconstriction of veins under sympathetic control
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Measuring Arterial Blood Pressure
Measurements by health professionals are made on the pressure in large arteries Systolic – pressure at the peak of ventricular contraction Diastolic – pressure when ventricles relax Pressure in blood vessels decreases as the distance away from the heart increases Normal BP is 120/75-80 Blood pressure animation online Listen for the sounds of Kortokoff
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Cardio System II: Vasculature and Pressure
Blood Vessel Anatomy Arteries and arterioles Capillaries (3 types) Veins and venules Pulse and Pressure Points Blood Pressure Factors Regulating Blood Pressure
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Variations in Blood Pressure
Human normal range is variable Normal mm Hg systolic or just 120/70 70-80 mm Hg diastolic Hypotension Low systolic (below 110 mm HG) Often associated with illness or physical conditioning Hypertension High systolic (above 140 mm HG) Can be dangerous if it is chronic Caused by many things, including a high saturated fat and/or salty diet, little exercise, & chronic stress
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Cardio System II: Vasculature and Pressure
Blood Vessel Anatomy Arteries and arterioles Capillaries (3 types) Veins and venules Pulse and Pressure Points Blood Pressure Factors Regulating Blood Pressure
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