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© 2017 Pearson Education, Inc.
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Vascular Pathway of Blood Flow (13-1)
Arteries Carry blood away from the heart Branch into smaller vessels called arterioles Arterioles branch into capillaries Capillaries Smallest vessels of the venous system Where chemical and gaseous exchange occurs Drain into venules Venules drain into veins Return blood to the atria of the heart
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Structure of Vessel Walls (13-1)
Tunica intima (or tunica interna), the innermost layer Lined by endothelium (epithelial tissue) with basement membrane Surrounded by layer of connective tissue with elastic fibers Tunica media Smooth muscle with loose connective tissue containing collagen and elastic fibers Controls diameter of vessel Tunica externa (or tunica adventitia) Sheath of connective tissue around vessel May stabilize and anchor vessel to other tissues
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Differences in Vessel Structure (13-1)
Arteries have: Smaller lumen than veins Thicker tunica media with more elastic fibers and smooth muscle Contraction causes vasoconstriction or decrease in size of the lumen Relaxation causes vasodilation or increase in size of the lumen
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Figure 13-1 A Comparison of a Typical Artery and a Typical Vein.
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Elastic Arteries (13-1) First type of arteries leaving the heart
Examples: pulmonary trunk and aorta Have more elastic fibers than smooth muscle fibers Large, resilient vessels Absorb pressure changes readily Stretched during systole, elastic fibers recoil during diastole Prevent very high pressure during systole Prevent very low pressure during diastole
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Muscular Arteries (13-1) Also called medium-sized arteries or distribution arteries Examples: external carotid arteries Distribute blood to skeletal muscles and internal organs Compared to elastic arteries, tunica media contains: Higher proportion of smooth muscle Fewer elastic fibers
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Arterioles (13-1) Arterioles
Tunica media has only 1–2 layers of smooth muscle Diameter changes in response to various stimuli Changing diameter alters blood pressure and flow
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Capillaries (13-1) Tunica interna only
Endothelial cells with basement membrane Ideal for diffusion between plasma and interstitial fluid Thin walls provide short diffusion distance Small diameter slows flow to increase diffusion rate Enormous number of capillaries provide huge surface area for increased diffusion
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Figure 13-2 The Structure of the Various Types of Blood Vessels.
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Capillary Beds (13-1) An interconnected network of capillaries
Entrance to each capillary is regulated by precapillary sphincter, a band of smooth muscle Relaxation of sphincter allows for increased flow Constriction of sphincter decreases flow Anastomosis A joining of blood vessels May form alternate routes for blood flow
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Figure 13-3 The Organization of a Capillary Bed.
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Veins (13-1) Collect blood from tissues and organs and return it to the heart Classified based on internal diameters Venules average 20 µm in diameter Smaller venules lack a tunica media Medium-sized veins range from 2 to 9 mm Several smooth muscle layers in tunica media Thick tunica externa of elastic and collagen fibers Large veins Thin tunica media surrounded by thick tunica externa
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Vein Features (13-1) Relatively thin walls
Low blood pressure inside Medium-sized veins in limbs contain valves Folds of tunica interna Prevent backflow of blood Improve venous return Improper functioning valves results in distended vessels Examples: varicose veins or hemorrhoids
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Figure 13-4 The Function of Valves in the Venous System.
closed Valve opens above contracting muscle Valve closed Valve closes below contracting muscle Figure 13-4 The Function of Valves in the Venous System.
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Maintaining Adequate Blood Flow (13-2)
Normally, blood flow equals cardiac output (CO) Increased CO leads to increased flow through capillaries Decreased CO leads to reduced flow Blood flow also influenced by pressure and resistance Increased pressure increases flow Increased resistance decreases flow
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Pressure (13-2) Liquids exert hydrostatic pressure in all directions
Liquid flows from higher pressure to lower pressure Pressure gradient is difference in pressure from one end of a vessel to the other Flow rate is directly proportional to pressure gradient
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Circulatory Pressure (13-2)
Largest pressure gradient Difference between pressure at base of aorta and entrance to right atrium Divided into three components Arterial pressure is blood pressure Capillary pressure Venous pressure
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Resistance (13-2) Any force that opposes movement
Sources of this resistance include: Vascular resistance The longer the vessel, the higher the resistance The smaller the diameter, the greater the resistance Viscosity Turbulence Caused by variance in flow speed Slow flow near the walls of vessels, faster flow in center
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Blood Pressure (13-2) Arterial pressure fluctuates
Systolic pressure Peak pressure measured during ventricular contraction Diastolic pressure Minimum pressure at the end of ventricular relaxation Blood pressure recorded as systolic over diastolic (e.g., 120/80 mm Hg) Pulse is rhythmic alternating changes in pressures Pulse pressure is the difference between systolic and diastolic pressures
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Figure 13-5 Pressures within the Systemic Circuit.
Systolic 120 Pulse pressure 100 Blood pressure (mm Hg) 80 Diastolic 60 40 Medium-sized veins Muscular arteries Elastic arteries Large veins Venae cavae Arterioles Capillaries Venules Aorta 20
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Capillary Pressures (13-2)
Pressure of blood within a capillary bed Drops from 35 to 18 mm Hg along capillary length Capillaries are permeable to ions, nutrients, wastes, gases, and water Capillary pressures cause filtration of water and solutes out of bloodstream and into tissues Some materials reabsorbed into capillaries Remainder picked up by lymphatic vessels
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Four Functions of Capillary Exchange (13-2)
Maintains constant communication between plasma and interstitial fluid Speeds distribution of nutrients, hormones, and gases Assists in transport of insoluble molecules Flushes bacterial toxins and other chemicals to lymphatic tissues for body defense and immune response
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Mechanisms of Capillary Exchange (13-2)
Diffusion Movement of ions or molecules from area of high concentration to area of low concentration Filtration Movement of solute due to “push” of water or hydrostatic pressure down fluid pressure gradients Water is filtered out of capillary by fluid or hydrostatic pressures Reabsorption Water is reabsorbed into capillary by osmosis Movement due to osmotic pressure
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Forces across Capillary Walls (13-2)
Capillary hydrostatic pressure (CHP) High at arterial end, low at venous end Tends to push water out of plasma into tissues at arterial end, favoring filtration Blood osmotic pressure (BOP) Higher than osmotic pressure in interstitial fluid Due to dissolved proteins Constant along length of capillary As CHP drops over length of capillary, BOP remains the same, favoring reabsorption at venous end
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Figure 13-6 Forces Acting across Capillary Walls.
Return to circulation 3.6 L/day flows into lymphatic vessels Tissue cells Arteriole Venule Filtration Reabsorption 24 L/day 20.4 L/day 35 mm Hg 25 mm Hg 25 mm Hg 25 mm Hg 18 mm Hg 25 mm Hg CHP = BOP No net movement of fluid CHP > BOP Fluid forced out of capillary BOP > CHP Fluid moves into capillary KEY CHP (Capillary hydrostatic pressure) BOP (Blood osmotic pressure)
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Venous Pressure (13-2) Gradient is low compared to arterial system
Large veins provide low resistance, ensuring increase in flow despite low pressure Two factors help blood flow overcome gravity when standing Muscular compression pushes on outside of veins Venous valves prevent backflow Respiratory pump results from changes in thoracic pressures during inhalation
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Autoregulation of Perfusion (13-3)
Adjustments in blood flow made by precapillary sphincters Automatic, immediate, local changes in response to changing tissue conditions Vasodilators Factors that promote dilation of precapillary sphincters and increased blood flow Low O2 or pH, high CO2, histamine, nitric oxide (NO) Vasoconstrictors Factors that stimulate constriction of precapillary sphincters and decreased blood flow If homeostasis not restored, neural and endocrine processes activated
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Neural Control of Blood Pressure and Perfusion (13-3)
Cardiovascular center in the medulla oblongata Responds to changes in arterial pressure or blood gas levels to maintain adequate blood flow Cardiac center contains: Cardioacceleratory center that increases cardiac output Cardioinhibitory center that reduces cardiac output Vasomotor center Controls diameter of arterioles and peripheral resistance Controls venoconstriction (constriction of peripheral veins)
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Reflexes for Neural Processes (13-3)
Two types of reflexes involved in adjusting cardiac output and peripheral resistance to maintain tissue perfusion Both regulated by negative feedback Baroreceptor reflexes Respond to changes in blood pressure Chemoreceptor reflexes Respond to changes in chemical composition
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Baroreceptor Reflexes (13-3)
Baroreceptors monitor degree of stretch in walls of expandable organs (including blood vessels) Carotid sinuses Expanded chambers near bases of internal carotid arteries of the neck Very sensitive to ensure adequate blood flow to the brain Aortic sinuses Located in pockets in walls of ascending aorta Aortic reflex adjusts blood flow through systemic circuit
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Baroreceptor Reflex Process (13-3)
Increased blood pressure Increases output from baroreceptors Inhibits cardioacceleratory center Stimulates cardioinhibitory center Inhibits vasomotor center Results are: Decreased cardiac output Widespread peripheral vasodilation Opposite process occurs with decreased blood pressure
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NORMAL RANGE OF BLOOD PRESSURE Increased blood pressure
Figure 13-8 The Baroreceptor Reflexes of the Carotid and Aortic Sinuses. Effector Baroreceptors stimulated Medulla oblongata • Cardioinhibitory center stimulated • Cardioacceleratory center inhibited • Vasomotor center inhibited Result in Decreased cardiac output Results in Vasodilation Receptors Baroreceptors in aortic and carotid sinuses Reduced blood pressure Homeostasis DISTURBED BY INCREASING blood pressure Homeostasis RESTORED BY DECREASING blood pressure STIMULUS RESTORED HOMEOSTASIS NORMAL RANGE OF BLOOD PRESSURE Homeostasis DISTURBED BY DECREASING blood pressure Homeostasis RESTORED BY INCREASING blood pressure STIMULUS RESTORED Receptors Increased blood pressure Baroreceptors in aortic and carotid sinuses Effector Medulla oblongata Results in • Vasomotor center stimulated • Cardioacceleratory center stimulated • Cardioinhibitory center inhibited Vasoconstriction Baroreceptors inhibited Result in Increased cardiac output
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Chemoreceptor Reflexes (13-3)
Receptors are: Sensitive to changes in carbon dioxide, oxygen, and pH in blood and cerebrospinal fluid Located in carotid and aortic bodies, medulla oblongata Receptors are activated by: Decrease in pH Decrease in plasma O2 Increase in plasma CO2 Receptors stimulate cardioacceleratory and vasomotor centers Result is increase in arteriolar constriction and blood flow Respiratory centers also activated to increase respiratory rate
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Figure 13-9 The Chemoreceptor Reflexes.
Effector Medulla oblongata Respiratory centers stimulated Result in Respiratory rate increases • Cardioacceleratory center stimulated • Cardioinhibitory center inhibited • Vasomotor center stimulated Increased cardiac output and blood pressure Result in Chemoreceptors stimulated Results in Vasoconstriction Receptors Chemoreceptors in carotid and aortic bodies and medulla oblongata Increased pH and O2 levels, and decreased CO2 levels Homeostasis DISTURBED BY Homeostasis RESTORED BY INCREASING CO2 Levels and DECREASING CO2 Levels and STIMULUS RESTORED HOMEOSTASIS INCREASING pH and O2 levels DECREASING pH and O2 levels NORMAL pH, O2, AND CO2 LEVELS IN BLOOD AND CSF
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Hormones and Cardiovascular Regulation (13-3)
Short-term Epinephrine (E) and norepinephrine (NE) stimulate cardiac output and peripheral vasoconstriction Long-term Antidiuretic hormone (ADH), angiotensin II, erythropoietin (EPO) Raise BP when too low Atrial natriuretic peptide (ANP) Lowers BP when too high
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Inhibition of ADH, aldosterone, norepinephrine release
Figure 13-10a The Hormonal Regulation of Blood Pressure and Blood Volume. Increased Na+ loss in urine Increased water loss in urine Effectors Releases atrial natriuretic peptide (ANP) Response Reduced thirst Kidneys and blood vessels to ANP Inhibition of ADH, aldosterone, epinephrine, and norepinephrine release Receptor Peripheral vasodilation Cardiac muscle cells (right atrium) Decreased blood pressure and volume Homeostasis Homeostasis DISTURBED BY RESTORED BY INCREASING DECREASING STIMULUS RESTORED blood pressure and volume blood pressure and volume HOMEOSTASIS NORMAL BLOOD PRESSURE AND VOLUME
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angiotensin II activation
Figure 13-10b The Hormonal Regulation of Blood Pressure and Blood Volume. HOMEOSTASIS NORMAL BLOOD PRESSURE AND VOLUME Homeostasis Homeostasis DISTURBED BY RESTORED BY STIMULUS RESTORED DECREASING INCREASING blood pressure and volume blood pressure and volume Short-term effects Long-term effects Combined Short-Term and Long-Term Effects Increased blood pressure Receptors Receptors Baroreceptors Kidneys Increased blood volume Endocrine Response of Kidneys Increased red blood cell formation Sympathetic activation and release of adrenal hormones E and NE Erythropoietin (EPO) is released Renin release leads to angiotensin II activation Angiotensin II Effects Antidiuretic hormone (ADH) released Aldosterone secreted Thirst stimulated Effectors Increased cardiac output and peripheral vasoconstriction Heart and blood vessels Respond with
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Circuits of the Cardiovascular System (13-5)
Cardiovascular system divided into: Pulmonary circuit Arteries and veins transporting blood between heart and lungs Begins at right ventricle; ends at left atrium Systemic circuit Arteries and veins transporting blood to and from all other organs and tissues Begins at the left ventricle; ends at right atrium
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Figure 13-11 An Overview of the Pattern of Circulation.
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The Pulmonary Circuit (13-6)
Blood exits right ventricle through pulmonary trunk Branches into left and right pulmonary arteries These arteries carry deoxygenated blood Enter lungs and branch repeatedly Smallest pulmonary arterioles provide blood to capillary networks surrounding small air pockets, or alveoli Thin walls of alveoli allow gas exchange between alveolar capillaries and inhaled air Oxygenated blood returns to left atrium through left and right pulmonary veins (two from each lung)
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Figure 13-12 The Pulmonary Circuit.
Aortic arch Ascending aorta Pulmonary trunk Superior vena cava Left lung Right lung Left pulmonary arteries Right pulmonary arteries Left pulmonary veins Right pulmonary veins Alveolus Capillary O2 CO2 Inferior vena cava Descending aorta
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The Systemic Circuit (13-7)
Supplies oxygenated blood to all parts of the body not in the pulmonary circuit Oxygenated blood leaves left ventricle through aorta Returns deoxygenated blood to right atrium through superior and inferior venae cavae and coronary sinus Contains about 84 percent of total blood volume
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The Aorta (13-7) Aorta is the first systemic vessel and largest artery
Ascending aorta Begins at aortic semilunar valve Left and right coronary arteries branch off near base Aortic arch curves across superior surface of heart Descending aorta drops down through mediastinum
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Three Elastic Arteries of the Aortic Arch (13-7)
Brachiocephalic trunk Branches to form right common carotid artery and right subclavian artery Left common carotid Left subclavian
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Figure 13-14 Arteries of the Chest and Upper Limb.
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The Carotid Arteries (13-7)
Common carotid arteries ascend up into the neck and divide into: External carotid artery Supplies pharynx, esophagus, larynx, and face Can be palpated on either side of the windpipe Internal carotid artery Enters skull, supplies brain © 2017 Pearson Education, Inc.
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Figure 13-15a Arteries of the Neck, Head, and Brain.
Anterior cerebral Middle cerebral Branches of the External Carotid Cerebral arterial circle Superficial temporal Posterior cerebral Maxillary Basilar Occipital Facial External carotid Internal carotid Carotid sinus Vertebral Thyrocervical trunk Common carotid Subclavian Internal thoracic Brachiocephalic trunk Clavicle First rib Second rib a The general circulation pattern of arteries supplying the neck and superficial structures of the head Figure 13-15a Arteries of the Neck, Head, and Brain.
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Blood Supply to the Brain (13-7)
Supplied by both the internal carotid arteries and vertebral arteries Vertebral arteries ascend within transverse foramina of cervical vertebrae, enter skull and fuse to form one basilar artery Cerebral arterial circle, or circle of Willis Ring-shaped anastomosis encircling the infundibulum of the pituitary Interconnects internal carotids and basilar arteries
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Figure 13-15b Arteries of the Neck, Head, and Brain.
Cerebral Arterial Circle Anterior cerebral Anterior communicating Anterior cerebral Internal carotid (cut) Posterior communicating Middle cerebral Posterior cerebral Posterior cerebral Basilar Vertebral b The arterial supply to the brain
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Iliac Arteries (13-7) Abdominal aorta divides into the:
Common iliac arteries carrying blood to pelvis and lower limbs Each common iliac artery divides into: Internal iliac artery Supplies pelvis External iliac artery Supplies lower limbs
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Figure 13-16a Major Arteries of the Trunk.
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The Superior Vena Cava (13-7)
Superior vena cava (SVC) Receives blood from: Head and neck Upper limbs, shoulders, and chest
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Venous Return from Head and Neck (13-7)
Small veins in brain drain into dural sinuses Largest is superior sagittal sinus Dural sinuses drain into internal jugular veins External jugular veins Drain blood from superficial head and neck Vertebral veins Drain blood from cervical spinal cord and posterior skull Descend within transverse foramina of cervical vertebrae
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Figure 13-17 Major Veins of the Head and Neck.
Superior sagittal sinus Temporal Great cerebral Maxillary Dural sinuses Facial Vertebral External jugular Internal jugular Right subclavian Clavicle Right brachiocephalic Left brachiocephalic First rib Superior vena cava Internal thoracic
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Inferior Vena Cava (13-7) Inferior vena cava (IVC)
Collects most of the blood from organs inferior to diaphragm
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Figure 13-18 The Venous Drainage of the Abdomen and Chest.
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