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  • 1. The Cardiovascular System:Blood Vessels and Circulation Chapter 16
  • 2. Blood Vessels Arteries  Carries blood away from the heart to body tissues  2 large arteries  aorta and pulmonary trunk  Arteries smaller and smaller arteries arterioles  Arterioles  capillaries
  • 3. Blood Vessels Veins  Convey blood from the tissues back to the heart  Veins  smaller and smaller veins  venules  Venules  capillaries
  • 4. Blood Vessels Capillaries  Microscopic vessels that connect arterioles to venules  “Exchange Vessels”  permit exchange of nutrients and wastes between body’s cells and blood
  • 5. Blood Vessel Structure Arteries  Three layers  Inner layer: endothelium, a basement membrane, internal elastic lamina  Middle layer: smooth muscle and elastic tissue  Outer layer: elastic and collagen fibers
  • 6. Blood Vessel Structure Veins  Similar structure to arteries  Thinner middle and inner layers, outer layer is the thickest  The lumen is wider than artery  Some veins, inner layer folds inward  valves to prevent backflow
  • 7. Capillary Information• Capillaries – layer of endothelium surrounded by basement membrane• Connected from arterioles  venules in networks – Sometimes direct route from arteriole to venule• Filling controlled by small arterioles & pre-capillary sphincters
  • 8. Vessel Functions Muscular arteries & arterioles regulate flow Sympathetic activity to smooth muscle  vasoconstriction (narrowing) Decreased sympathetic activity or NO causes relaxation or dilation
  • 9. Vessel Functions Arterioles adjust flow into capillaries Systemic veins & venules serve as blood reservoirs (~64% total blood volume)
  • 10. Capillary Exchange Slow flow through capillaries Capillary Exchange – movement of substances into and out of capillaries Capillary Blood Pressure – pressure of blood against the walls of capillaries
  • 11. Capillary Exchange• Osmosis (protein concentration) – Reabsorption of fluid from outside to inside• Balance determines fluid in circulation – Excess fluid returned via lymphatic system – Local signals can adjust capillary flow
  • 12. Venous Return Volume of blood flowing back to the heart through the systemic veins Happens due to pressure generated in 3 ways:  Contractions of the heart  The skeletal muscle pump  Respiratory pump
  • 13. Venous Return Contractions of the heart –  BP generated by ventricular systole  Measured in mm of Hg (mercury)  Small pressure difference between venules and right atrium is sufficient
  • 14. Venous Return Skeletal muscle pump –  Standing at rest – venous valves in leg are open, blood flows up to heart  Contraction of leg muscles compresses vein  pushes blood through valve closer to heart, called milking
  • 15. Venous Return Skeletal muscle pump cont.  Same time as milking, valve farther from heart closes as some blood is pushed against it  After muscle relaxation, pressure drops in compression and open valve closes, and now farther valve opens since BP is higher in foot than leg, vein fills with blood from foot
  • 16. Venous Return Respiratory pump –  During inhalation  Diaphragm moves down, causes a drop in pressure in the thoracic cavity and rise in abdominal(ab) cavity  Ab veins compressed, greater volume of blood from compressed ab veins  decompressed thoracic veins  rt atrium  During exhalation, pressures reverse
  • 17. Blood Flow• From high pressure  low pressure – Greater gradient = greater flow • BP – pressure exerted by blood on the walls of a blood vessel
  • 18. Blood Pressure BP is highest in aorta and large systemic arteries BP depends on total volume of blood Normal volume of an adult ~5 L
  • 19. Blood Pressure BP rises to ~110 mmHg (systole) and drops to ~70 mmHg (diastole) BP drops as blood enters veins and reaches 0 mmHg as blood returns  right atrium
  • 20. Blood Flow• Resistance – opposition to blood flow due to friction between blood and walls of vessels• Increase in resistance = increase in BP• Decrease in resistance = decrease in BP• Resistance depends on 3 things
  • 21. Resistance• Size of lumen – Smaller lumen  greater resistance• Blood viscosity – Higher viscosity  greater resistance• Total vessel length – Longer length  greater resistance
  • 22. Regulation of Blood Pressure & Flow CV Center (in the medulla oblongata)  Regulate heart rate & stroke volume  Controls neural & hormonal negative feedback systems that regulate BP and flow to tissues
  • 23. Inputs (CV center) Higher centers:  Cerebral cortex  Limbic system  Hypothalamus
  • 24. Inputs (CV center) Sensory receptor input:  Proprioceptors  Monitor movements of joints and muscles  Start HR change as activity starts  Baroreceptors  Monitor pressure changes
  • 25. Inputs (CV center) Baroreceptors (cont.)  ↓ pressure  ↓ parasympathetic stimulation of the heart  ↑ sympathetic stimulation Chemoreceptors  Monitor chemical changes  Low O2, high H+, excess CO2  ↑ sympathetic stimulation vasoconstriction  ↑ BP
  • 26. Output (CV center) ANS to heart  ↑ Sympathetic  ↑ HR & ↑ force of contraction  ↓ Sympathetic  ↓ HR & ↓ force of contraction Vasomotor  to arterioles  ↑ vasomotor tone (sets resting level of vascular resistance)  To veins  move blood  ↑ BP
  • 27. Hormone Regulation Renin – Angiotensin – Aldosterone (RAA) system  Angiotensin II  ↑ BP (vasocontriction) ↑ aldosterone  ↑ Na+ & water by kidneys Epinephrine and Norepinephrine  ↑ CO (↑ HR & force of contraction)
  • 28. Hormone Regulation ADH = Vasopressin  ↑ Constriction  ↑ BP ANP  Vasodilation & loss of salt & water in urine  ↓BP and ↓ blood volume
  • 29. Pulse Pulse strongest in arteries closest to heart  Radial artery (at wrist), Carotid artery, Popliteal artery, Dorsal artery, Brachial artery Tachycardia = rapid rest rate (>100 bpm) Bradycardia= slow rest rate (<50 bpm)
  • 30. Blood Pressure (measurement) Use sphygmomanometer  Usually on brachial artery in left arm Raise pressure above systolic-  To stop blood flow
  • 31. Blood Pressure (measurement) Lower pressure in cuff until flow just starts  Systolic Pressure Lower until sound suddenly gets faint (stops)  Diastolic pressure Normal values <120 mmHg for systolic & < 80 mmHg for diastolic  Ex. 115/75
  • 32. Circulatory Routes Two parts: Systemic & Pulmonary Systemic circulation- throughout body  Oxygenated blood  deoxygenated All systemic arteries branch from aorta
  • 33. Systemic Circulation All systemic veins empty into Superior Vena Cava, Inferior Vena Cava or the Coronary Sinus  Carry deoxygenated blood to heart
  • 34. Pulmonary Circulation Right ventricle  pulmonary trunk R & L pulmonary arteries  Carry deoxygenated blood  R & L lungs  Gas exchange occurs
  • 35. Pulmonary Circulation  R & L pulmonary veins  Carry oxygenated blood  L atrium
  • 36. Hepatic Portal Circulation Portal vein transports blood from one capillary bed to another There are no valves  Splenic & superior mesenteric veins
  • 37. Fetal Circulation Specialized for exchange of materials with maternal blood and bypass of lungs (placenta) Umbilical artery: pathway for blood fetus  mother
  • 38. Fetal Circulation Umbilical vein brings O2 blood from placenta  liver and Ductus Venosus  Inferior Vena Cava  R Atrium
  • 39. Fetal Circulation Foramen ovale - hole in atrial septum allows mixing of blood in heart (eventually becomes fossa ovalis)
  • 40. At Birth Umbilical arteries  medial umbilical ligaments Umbilical vein  ligamentum teres Ductus venosus  ligamentum venosum
  • 41. At Birth Placenta is “afterbirth” Foramen ovalis closes  fossa ovale Ductus arteriosus  ligamentum arteriosum
  • 42. Aging Stiffening of aorta Loss of cardiac muscle strength  Reduced CO & increased systolic pressure Coronary artery disease (CAD) Congestive heart failure Atherosclerosis