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Cardiovascular System BLOOD VESSELS Blood Vessels Delivery system of dynamic structures Closed system Arteries Carry blood away from the heart Capillaries Contact tissue cells and directly serve cellular needs Veins Carry blood toward the heart Venous system Large veins (capacitance vessels) Small veins (capacitance vessels) Postcapillary venule Thoroughfare channel Arterial system Heart Large lymphatic vessels Lymph node Lymphatic system Elastic arteries (conducting vessels) Muscular arteries (distributing vessels) Arteriovenous anastomosis Lymphatic capillary Sinusoid Arterioles (resistance vessels) Terminal arteriole Metarteriole Precapillary sphincter Capillaries (exchange vessels) Figure 19.2 Common carotid arteries to head and subclavian arteries to upper limbs Capillary beds of head and upper limbs Superior vena cava Aortic arch Aorta RA LA RV Inferior vena cava LV Azygos system Thoracic aorta Venous drainage Arterial blood Capillary beds of mediastinal structures and thorax walls Diaphragm Abdominal aorta Inferior vena cava Capillary beds of digestive viscera, spleen, pancreas, kidneys Capillary beds of gonads, pelvis, and lower limbs Figure 19.20 Tissue Layers Tunica interna Tunica media Tunica externa Tunica intima (interna) • Endothelium • Subendothelial layer Internal elastic lamina Tunica media (smooth muscle and elastic fibers) External elastic lamina Valve Tunica externa (collagen fibers) Lumen Artery (b) Capillary network Lumen Vein Basement membrane Endothelial cells Capillary Figure 19.1b Vein Artery (a) Figure 19.1a Arteries of the head and trunk Internal carotid artery External carotid artery Common carotid arteries Vertebral artery Subclavian artery Brachiocephalic trunk Aortic arch Ascending aorta Coronary artery Thoracic aorta (above diaphragm) Celiac trunk Abdominal aorta Superior mesenteric artery Renal artery Gonadal artery Common iliac artery Inferior mesenteric artery Internal iliac artery (b) Illustration, anterior view Arteries that supply the upper limb Subclavian artery Axillary artery Brachial artery Radial artery Ulnar artery Deep palmar arch Superficial palmar arch Digital arteries Arteries that supply the lower limb External iliac artery Femoral artery Popliteal artery Anterior tibial artery Posterior tibial artery Arcuate artery Figure 19.21b Arteries Transport blood from left ventricle to body tissues High pressure Three groups Elastic (conducting) Muscular (distributing) Arterioles (resistance) Table 19.1 (1 of 2) Elastic Arteries Conducting arteries Large and thick-walled Near the heart Aorta and major branches Large lumen = low resistance Expand during systole and recoil during diastole Muscular Arteries Distributing arteries Distal to elastic arteries Deliver blood to body organs Thick tunica media with more smooth muscle Active in vasoconstriction Examples Radial, femoral, brachial Resistance Arteries Smallest arterial vessels Lead to capillary beds Control valves to capillary beds Site of most vasodilation and vasoconstriction Table 19.1 (1 of 2) Metarterioles are modified capillaries Precapillary sphincters Vascular shunt Metarteriole Thoroughfare channel True capillaries Terminal arteriole Postcapillary venule (a) Sphincters open—blood flows through true capillaries. Terminal arteriole Postcapillary venule (b) Sphincters closed—blood flows through metarteriole thoroughfare channel and bypasses true capillaries. Figure 19.4 Capillaries Capillary beds Microcirculation between arterioles and venules Two types 1. Continuous 1. 2. 3. 2. Open junctions between adjacent endothelial cells Most common In skin and muscles Fenestrated 1. 2. Pores = permeable Intestines, endocrine organs, kidneys 21_01e Precapillary sphincters Vascular shunt Metarteriole Thoroughfare channel True capillaries Terminal arteriole Postcapillary venule (a) Sphincters open—blood flows through true capillaries. Terminal arteriole Postcapillary venule (b) Sphincters closed—blood flows through metarteriole thoroughfare channel and bypasses true capillaries. Figure 19.4 Capillaries Precapillary sphincters Local chemical conditions Vasomotor nerves 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 Blood Brain Barrier Figure 19.22c Arteries of the head, neck, and brain. Copyright © 2010 Pearson Education, Inc. Pericyte Red blood cell in lumen Intercellular cleft Endothelial cell Basement membrane Tight junction Pinocytotic Endothelial vesicles nucleus (a) Continuous capillary. Least permeable, and most common (e.g., skin, muscle). Figure 19.3a 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 Endothelial cell Red blood cell in lumen Large intercellular cleft Tight junction Nucleus of Incomplete endothelial basement cell membrane (c) Sinusoidal capillary. Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen). Figure 19.3c Capillaries Functions Exchange area for blood and interstitial fluid compartment Diffusion O2 and nutrients from the blood to tissues CO2 and metabolic wastes from tissues to the blood Pinocytotic vesicles Red blood cell in lumen Endothelial cell Endothelial cell nucleus Basement membrane Tight junction Fenestration (pore) Intercellular cleft Figure 19.16 (1 of 2) Veins Functions Collect blood from capillary beds “drain” organs and tissues of blood Become larger as they come closer to the heart Veins of the head and trunk Dural venous sinuses External jugular vein Vertebral vein Internal jugular vein Right and left brachiocephalic veins Superior vena cava Great cardiac vein Hepatic veins Splenic vein Hepatic portal vein Renal vein Superior mesenteric vein Inferior vena cava Inferior mesenteric vein Veins that drain the upper limb Subclavian vein Axillary vein Cephalic vein Brachial vein Basilic vein Median cubital vein Ulnar vein Radial vein Digital veins Veins that drain the lower limb External iliac vein Femoral vein Great saphenous vein Common iliac vein Popliteal vein Internal iliac vein Posterior tibial vein Anterior tibial vein (b) Illustration, anterior view. The vessels of the pulmonary circulation are not shown. Small saphenous vein Dorsal venous arch Dorsal metatarsal veins Figure 19.26b Venules Formed when capillary beds unite Very porous Allow fluids and WBC’s into tissues Pulmonary blood vessels 12% Systemic arteries and arterioles 15% Heart 8% Capillaries 5% Systemic veins and venules 60% Copyright © 2010 Pearson Education, Inc. Figure 19.5 Veins Thinner walls, larger lumens than arteries Blood pressure is lower than in arteries Thin tunica media and a thick tunica externa Capacitance vessels (blood reservoirs) Contain up to 65% of the blood supply Vein Artery (a) Figure 19.1a Venous Blood Pressure Low pressure Due to cumulative effects of peripheral resistance Effect of gravity? Valves Skeletal muscle and action Thoracic pressure changes Valve (open) Contracted skeletal muscle Valve (closed) Vein Direction of blood flow Figure 19.7 Varicose Veins Incompetent valves Pregnancy Obesity Long periods of standing Hemorrhoids Blood Flow Blood flow is involved in O2 delivery Removal of wastes Gas exchange (lungs) Absorption of nutrients (digestive tract) Urine formation (kidneys) Blood Flow Perfusion Rate of blood flow per given volume of tissue Blood flow (F) Volume of blood flowing through a vessel, an organ, or tissue in a given period Measured as ml/min Varies widely through individual organs Based on needs F= ΔP/R Blood Flow • F= Δ P/R o F = Blood flow o ΔP = Difference in pressure between two points o R = Resistance Blood Flow Relationship between blood flow, blood pressure, and resistance If ΔP increases, blood flow speeds up If R increases, blood flow decreases R is more important in influencing local blood flow Changed by altering blood vessel diameter Blood Pressure Blood pressure (BP) Force per unit area exerted on the wall of a blood vessel by the blood Typically expressed as the height of a column of mercury (mm Hg) P = H x D Blood Pressure Factors influencing blood pressure Cardiac output (CO) Peripheral resistance (PR) Blood volume Blood Pressure Systolic pressure Pressure exerted during ventricular contraction Top number Diastolic pressure Lowest level of arterial pressure Bottom number Average value = 120/80 Pulse pressure Difference between systolic and diastolic pressure Systolic pressure Mean pressure Diastolic pressure Copyright © 2010 Pearson Education, Inc. Figure 19.6 Blood Pressure Basic concepts The pumping action of the heart generates blood flow Pressure results when flow is opposed by resistance Systemic pressure Highest in the aorta Declines throughout the pathway Is 0 mm Hg in the right atrium The steepest drop occurs in arterioles Systolic pressure Mean pressure Diastolic pressure Figure 19.6 Arterial Blood Pressure Reflects two factors of the arteries close to the heart Elasticity Volume of blood forced into them at any time Blood pressure near the heart is pulsatile Arterial Blood Pressure Mean arterial blood pressure (MABP) Pressure that propels blood to tissues Represents average blood pressure MABP = diastolic pressure + 1/3 pulse pressure Pulse pressure and MAP both decline with increasing distance from the heart Hypertension “Silent Killer” Resting systolic >140 mm Hg and/or diastolic >90 mm Hg Causes Loss of flexibility in vessel walls Results Heart failure Renal failure Stroke Increased risk of aneurysm Capillary Blood Pressure Not pulsatile Low capillary pressure is desirable High BP would rupture fragile, thin-walled capillaries Most are very permeable, so low pressure forces filtrate into interstitial spaces Systolic pressure Mean pressure Diastolic pressure Copyright © 2010 Pearson Education, Inc. Figure 19.6 Peripheral Resistance The opposition to blood flow exerted by vessel walls The result of friction Influenced by 3 factors Blood viscosity Blood vessel length Blood vessel radius Peripheral Resistance Blood viscosity Albumin Erythrocytes Peripheral Resistance Vessel length The father fluid travels = more cumulative friction Peripheral Resistance Vessel radius Most significant factor Vasoconstriction and vasodilation Flow is proportional to fourth power of radius Alteration of radius profoundly affects blood flow Examples… Poiseuille’s Law Formula representing the factors influencing flow F = ΔPπr4/ 8 nL F= flow ΔP = pressure gradient r4 = vessel radius n = viscosity L = vessel length Poiseuille’s Law Blood flow is directly proportional to pressure gradient and vessel radius Blood flow is inversely proportional to vessel length and blood viscosity F = ΔPπr4/ 8 nL Questions? Homework #1: Artery Labeling Due in lab!