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Blood Vessels Blood is carried in a closed system of vessels that begins and ends at the heart The three major types of vessels are arteries, capillaries, and veins Arteries carry blood away from the heart, veins carry blood toward the heart Capillaries contact tissue cells and directly serve cellular needs Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Generalized Structure of Blood Vessels Arteries and veins are composed of three tunics – tunica interna, tunica media, and tunica externa Lumen – central blood-containing space surrounded by tunics Capillaries are composed of endothelium with sparse basal lamina Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Generalized Structure of Blood Vessels Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.1b Blood Vessel Anatomy Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 19.1 Elastic (Conducting) Arteries Thick-walled arteries near the heart; the aorta and its major branches Large lumen allow low-resistance conduction of blood Contain elastin in all three tunics Withstand and smooth out large blood pressure fluctuations Serve as pressure reservoirs Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscular (Distributing) Arteries and Arterioles 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 constriction Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Capillaries Capillaries are the smallest blood vessels Walls consisting of a thin tunica interna, one cell thick Allow only a single RBC to pass at a time Pericytes on the outer surface stabilize their walls There are three structural types of capillaries: continuous, fenestrated, and sinusoids Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Vascular Components Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.2a, b Continuous Capillaries Continuous capillaries are abundant in the skin and muscles Endothelial cells provide an uninterrupted lining Adjacent cells are connected with tight junctions Intercellular clefts allow the passage of fluids Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Continuous Capillaries Continuous capillaries of the brain: Have tight junctions completely around the endothelium Constitute the blood-brain barrier Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Continuous Capillaries Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.3a Fenestrated Capillaries Found wherever active capillary absorption or filtrate formation occurs (e.g., small intestines, endocrine glands, and kidneys) Characterized by: An endothelium riddled with pores (fenestrations) Greater permeability than other capillaries Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Fenestrated Capillaries Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.3b Sinusoids Highly modified, leaky, fenestrated capillaries with large lumens Found in the liver, bone marrow, lymphoid tissue, and in some endocrine organs Allow large molecules (proteins and blood cells) to pass between the blood and surrounding tissues Blood flows sluggishly, allowing for modification in various ways Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sinusoids Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.3c Capillary Beds A microcirculation of interwoven networks of capillaries, consisting of: Vascular shunts – metarteriole–thoroughfare channel connecting an arteriole directly with a postcapillary venule True capillaries – 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Capillary Beds Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.4a Capillary Beds Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.4b Blood Flow Through Capillary Beds Precapillary sphincter Cuff of smooth muscle that surrounds each true capillary Regulates blood flow into the capillary Blood flow is regulated by vasomotor nerves and local chemical conditions Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Venous System: Venules Venules are formed when capillary beds unite Allow fluids and WBCs to pass from the bloodstream to tissues Postcapillary venules – smallest venules, composed of endothelium and a few pericytes Large venules have one or two layers of smooth muscle (tunica media) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Venous System: Veins Veins are: Formed when venules converge Composed of three tunics, with a thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks Capacitance vessels (blood reservoirs) that contain 65% of the blood supply Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Venous System: Veins Veins have much lower blood pressure and thinner walls than arteries To return blood to the heart, veins have special adaptations Large-diameter lumens, which offer little resistance to flow Valves (resembling semilunar heart valves), which prevent backflow of blood Venous sinuses – specialized, flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Vascular Anastomoses Merging blood vessels, more common in veins than arteries Arterial anastomoses provide alternate pathways (collateral channels) for blood to reach a given body region If one branch is blocked, the collateral channel can supply the area with adequate blood supply Thoroughfare channels are examples of arteriovenous anastomoses Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Blood Flow Actual volume of blood flowing through a vessel, an organ, or the entire circulation in a given period: Is measured in ml per min. Is equivalent to cardiac output (CO), considering the entire vascular system Is relatively constant when at rest Varies widely through individual organs Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Blood Pressure (BP) Force per unit area exerted on the wall of a blood vessel by its contained blood Expressed in millimeters of mercury (mm Hg) Measured in reference to systemic arterial BP in large arteries near the heart The differences in BP within the vascular system provide the driving force that keeps blood moving from higher to lower pressure areas Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Resistance Resistance – opposition to flow Measure of the amount of friction blood encounters Generally encountered in the systemic circulation Referred to as peripheral resistance (PR) The three important sources of resistance are blood viscosity, total blood vessel length, and blood vessel diameter Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Factors Aiding Venous Return Venous BP alone is too low to promote adequate blood return and is aided by the: Respiratory “pump” – pressure changes created during breathing suck blood toward the heart by squeezing local veins Muscular “pump” – contraction of skeletal muscles “milk” blood toward the heart Valves prevent backflow during venous return PLAY InterActive Physiology ®: Anatomy Review: Blood Vessel Structure and Function, pages 3–27 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Factors Aiding Venous Return Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.6 Maintaining Blood Pressure Maintaining blood pressure requires: Cooperation of the heart, blood vessels, and kidneys Supervision of the brain Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Maintaining Blood Pressure The main factors influencing blood pressure are: Cardiac output (CO) Peripheral resistance (PR) Blood volume Blood pressure = CO x PR Blood pressure varies directly with CO, PR, and blood volume Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Temperature Regulation As temperature rises (e.g., heat exposure, fever, vigorous exercise): Hypothalamic signals reduce vasomotor stimulation of the skin vessels Heat radiates from the skin Sweat also causes vasodilation via bradykinin in perspiration Bradykinin stimulates the release of NO As temperature decreases, blood is shunted to deeper, more vital organs Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Circulatory Pathways The vascular system has two distinct circulations Pulmonary circulation – short loop that runs from the heart to the lungs and back to the heart Systemic circulation – routes blood through a long loop to all parts of the body and returns to the heart Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Differences Between Arteries and Veins Arteries Veins Delivery Blood pumped into single systemic artery – the aorta Blood returns via superior and interior venae cavae and the coronary sinus Location Deep, and protected by tissue Both deep and superficial Pathways Fair, clear, and defined Convergent interconnections Supply/drainage Predictable supply Dural sinuses and hepatic portal circulation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pulmonary Circulation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.18b Systemic Circulation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.19 Internal carotid artery External carotid artery Vertebral artery Brachiocephalic trunk Axillary artery Ascending aorta Brachial artery Abdominal aorta Superior mesenteric artery Gonadal artery Inferior mesenteric artery Common iliac artery External iliac artery Digital arteries Femoral artery Common carotid arteries Subclavian artery Aortic arch Coronary artery Thoracic aorta Branches of celiac trunk: • Left gastric artery • Splenic artery • Common hepatic artery Renal artery Radial artery Ulnar artery Internal iliac artery Deep palmar arch Superficial palmar arch Popliteal artery Anterior tibial artery Posterior tibial artery Arcuate artery (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.20b Superficial temporal artery Basilar artery Occipital artery Vertebral artery Internal carotid artery External carotid artery Common carotid artery Thyrocervical trunk Costocervical trunk Subclavian artery Axillary artery (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Ophthalmic artery Maxillary artery Facial artery Lingual artery Superior thyroid artery Larynx Thyroid gland (overlying trachea) Clavicle (cut) Brachiocephalic trunk Internal thoracic artery Figure 19.21b Arteries of the Brain Anterior Frontal lobe Optic chiasma Middle cerebral artery Internal carotid artery Pituitary gland Cerebral arterial circle (circle of Willis) • Anterior communicating artery • Anterior cerebral artery • Posterior communicating artery • Posterior cerebral artery Basilar artery Temporal lobe Pons Occipital lobe Vertebral artery Cerebellum (c) (d) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Posterior Figure 19.21c,d Common carotid arteries Right subclavian artery Left subclavian artery Left axillary artery Brachiocephalic trunk Vertebral artery Thyrocervical trunk Costocervical trunk Suprascapular artery Thoracoacromial artery Axillary artery Subscapular artery Posterior circumflex humeral artery Anterior circumflex humeral artery Brachial artery Posterior intercostal arteries Anterior intercostal artery Internal thoracic artery Descending aorta Lateral thoracic artery Deep artery of arm Common interosseous artery Radial artery Ulnar artery Deep palmar arch Superficial palmar arch Digitals (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.22b Arteries of the Abdomen Liver (cut) Inferior vena cava Celiac trunk Hepatic artery proper Common hepatic artery Right gastric artery Gallbladder Gastroduodenal artery Right gastroepiploic artery Duodenum Abdominal aorta (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Diaphragm Esophagus Left gastric artery Left gastroepiploic artery Splenic artery Spleen Stomach Pancreas (major portion lies posterior to stomach) Superior mesenteric artery Figure 19.23b Arteries of the Abdomen Opening for inferior vena cava Hiatus (opening) for esophagus Celiac trunk Diaphragm Inferior phrenic artery Middle suprarenal artery Renal artery Kidney Superior mesenteric artery Lumbar arteries Abdominal aorta Median sacral artery Gonadal (testicular or ovarian) artery Inferior mesenteric artery Common iliac artery Ureter (c) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.23c Arteries of the Abdomen Celiac trunk Middle colic artery Right colic artery Ileocolic artery Ascending colon Ileum Superior rectal artery Cecum Appendix Transverse colon Superior mesenteric artery Intestinal arteries Left colic artery Inferior mesenteric artery Aorta Sigmoidal arteries Descending colon Left common iliac artery Sigmoid colon Rectum (d) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.23d Arteries of the Lower Limbs Common iliac artery Internal iliac artery Superior gluteal artery External iliac artery Deep artery of thigh Lateral circumflex femoral artery Medial circumflex femoral artery Obturator artery Femoral artery Adductor hiatus Popliteal artery Anterior tibial artery Posterior tibial artery Fibular artery Popliteal artery Posterior tibial artery Lateral plantar artery Medial plantar artery Anterior tibial artery Fibular artery Dorsalis pedis artery (from top of foot) Plantar arch (c) Dorsalis pedis artery Arcuate artery Metatarsal arteries (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.24b, c Dural sinuses External jugular vein Vertebral vein Internal jugular vein Superior vena cava Axillary vein Great cardiac vein Hepatic veins Hepatic portal vein Superior mesenteric vein Inferior vena cava Ulnar vein Radial vein Digital veins Common iliac vein External iliac vein Femoral vein Great saphenous vein Popliteal vein Posterior tibial vein Anterior tibial vein Fibular vein Dorsal venous arch (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Subclavian vein Right and left brachiocephalic veins Cephalic vein Brachial vein Basilic vein Splenic vein Median cubital vein Renal vein Inferior mesenteric vein Internal iliac vein Dorsal digital veins Figure 19.25b Veins of the Head and Neck Ophthalmic vein Superficial temporal vein Facial vein Occipital vein (b) Posterior auricular vein External jugular vein Vertebral vein Internal jugular vein Superior and middle thyroid veins Brachiocephalic vein Subclavian vein Superior vena cava Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.26b Veins of the Brain Superior sagittal sinus Falx cerebri Inferior sagittal sinus Straight sinus Cavernous sinus Junction of sinuses Transverse sinuses Sigmoid sinus Jugular foramen (c) Right internal jugular vein Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.26c Veins of the Upper Limbs and Thorax Internal jugular vein External jugular vein Brachiocephalic veins Left subclavian vein Right subclavian vein Superior vena cava Axillary vein Azygos vein Accessory hemiazygos vein Brachial vein Cephalic vein Basilic vein Hemiazygos vein Posterior intercostals Inferior vena cava Ascending lumbar vein Median cubital vein Median antebrachial vein Cephalic vein Radial vein Basilic vein Ulnar vein Deep palmar venous arch Superficial palmar venous arch Digital veins (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.27b Veins of the Abdomen Hepatic veins Inferior phrenic vein Inferior vena cava Right suprarenal vein Left suprarenal vein Renal veins Right gonadal vein External iliac vein Left ascending lumbar vein Lumbar veins Left gonadal vein Common iliac vein Internal iliac vein (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.28b Veins of the Abdomen Hepatic veins Liver Hepatic portal vein Gastric veins Spleen Inferior vena cava Splenic vein Right gastroepiploic vein Inferior mesenteric vein Superior mesenteric vein Small intestine Large intestine Rectum (c) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 19.28c Common iliac vein Internal iliac vein External iliac vein Inguinal ligament Femoral vein Great saphenous vein (superficial) Great saphenous vein Popliteal vein Anterior tibial vein Fibular (peroneal) vein Popliteal vein Fibular (peroneal) vein Anterior tibial vein Small saphenous vein (superficial) Dorsalis pedis vein Dorsal venous arch Metatarsal veins Plantar veins (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Posterior tibial vein Plantar arch Digital veins (c) Figure 19.29b, c