CIRCULATORY SYSTEM

1. CIRCULATORY SYSTEM BLOOD VESSELS

2. CIRCULATORY SYSTEM BLOOD HEART BLOOD VESSELS

3. BLOOD VESSELS ARTERIES CARRY BLOOD FROM THE HEART ARTERY ? ARTERIOLES ? CAPILLARIES CAPILLARIES SITE OF GAS AND NUTRIENT EXCHANGE VEINS RETURN BLOOD TO THE HEART CAPILLARIES ? VENULES ? VEINS

5. ARTERY AND VEIN WALLS THREE LAYERS (TUNICS) TUNICA EXTERNA (OUTERMOST) TUNICA MEDIA TUNICA INTERNA (INNERMOST)

7. ARTERY AND VEIN WALLS TUNICA EXTERNA OUTERMOST LAYER LOOSE CONNECTIVE TISSUE MERGES WITH ADJACENT CONNECTIVE TISSUES ANCHORS VESSEL PASSAGE FOR NERVES, BLOOD & LYMPH VESSELS

8. ARTERY AND VEIN WALLS TUNICA EXTERNA NOURISHMENT OUTER HALF NOURISHED BY SMALL BLOOD VESSELS (VASA VASORUM) INNER HALF NOURISHED BY DIFFUSION FROM BLOOD IN LUMEN

9. ARTERY AND VEIN WALLS TUNICA MEDIA MIDDLE LAYER GENERALLY THE THICKEST LAYER SMOOTH MUSCLE VASOCONSTRICTION & VASODILATION COLLAGEN SOMETIMES ELASTIC TISSUE

10. ARTERY AND VEIN WALLS TUNICA INTERNA SMOOTH INNER LAYER EXPOSED TO BLOOD SQUAMOUS ENDOTHELIUM (EPI) BASEMENT MEMBRANE FIBROUS TISSUE

11. ARTERY AND VEIN WALLS TUNICA INTERNA REPELS BLOOD CELLS (& PLATELETS) SELECTIVELY PERMEABLE BARRIER TO BLOOD SOLUTES SECRETES VASOCONSTRICTORS & VASODILATORS

12. ARTERIES MUST WITHSTAND PRESSURE MORE MUSCULAR THAN VEINS ROUND IN CROSS SECTION THREE SIZE CATEGORIES CONDUCTING (ELASTIC) ARTERIES DISTRIBUTING (MUSCULAR) ARTERIES RESISTANCE (SMALL) ARTERIES

13. ARTERIES CONDUCTING (ELASTIC) ARTERIES LARGEST ARTERIES E.G., AORTA, PULMONARY ARTERIES TUNICA MEDIA NUMEROUS ALTERNATING THIN LAYERS OF PERFORATED ELASTIC TISSUE SMOOTH MUSCLE, COLLAGEN, AND ELASTIC FIBERS EXPAND DURING SYSTOLE RECOIL DURING DIASTOLE MINIMIZES DOWNSTREAM PRESSURE FLUCTUATIONS

15. ARTERIES DISTRIBUTING (ELASTIC) ARTERIES SMALLER BRANCHES E.G., BRACHIAL & FEMORAL ARTERIES FURTHER FROM THE HEART 25 – 40 SMOOTH MUSCLE LAYERS 75% OF WALL THICKNESS

17. ARTERIES RESISTANCE (SMALL) ARTERIES MAINLY UNNAMED UP TO 25 SMOOTH MUSCLE LAYERS LITTLE ELASTIC TISSUE SMALLEST ARE ARTERIOLES 1-3 LAYERS OF SMOOTH MUSCLES 40 – 200 mM DIAMETER

19. ARTERIES METARTERIOLES SHORT VESSELS LINKING ARTERIOLES AND CAPILLARIES TUNICA MEDIA DISCONTINUOUS MUSCLE CELLS FORM PRECAPILLARY SPHINCTER ENCIRCLES CAPILLARY ENTRANCE REGULATES MOVEMENT OF BLOOD INTO CAPILLARIES

20. CAPILLARIES CENTRAL TO CIRCULATORY SYSTEM SITE OF EXCHANGE BETWEEN BLOOD AND TISSUES SMALLEST BLOOD VESSELS ENDOTHELIUM ONLY THIN WALLS (0.2 mM – 0.4 mM) 5 – 9 mM DIAMETER (AVERAGE)

21. CAPILLARY STRUCTURE ~ BILLION IN BODY HUGE COLLECTIVE SURFACE AREA 6,300 SQUARE METERS (M2) > SIZE OF FOOTBALL FIELD < 80 mM FROM ALMOST ALL CELLS SOME EXCEPTIONS E.G., TENDONS, LIGAMENTS, ETC. ORGANIZED INTO CAPILLARY BEDS

22. CAPILLARY BEDS UNIT OF CAPILLARY ORGANIZATION 10 – 100 CAPILLARIES SUPPLIED BY SINGLE METARTERIOLE THOROUGHFARE CHANNEL ARTERIOLE ? VENULE PRECAPILLARY SPHINCTER AT ENTRANCE TO EACH CAPILLARY OPENED OR CLOSED

25. CAPILLARY BEDS BLOOD VOLUME THERE IS NOT ENOUGH BLOOD TO FILL ALL BLOOD VESSELS SIMULTANEOUSLY ~75% OF THE BODY’S CAPILLARIES ARE CLOSED AT ANY GIVEN TIME

26. TYPES OF CAPILLARIES TWO TYPES OF CAPILLARIES CONTINUOUS CAPILLARIES FENESTRATED CAPILLARIES

27. TYPES OF CAPILLARIES CONTINUOUS CAPILLARIES OCCUR IN MOST TISSUES ENDOTHELIAL CELLS HELD TOGETHER BY TIGHT JUNCTIONS FORM CONTINUOUS TUBE INTERCELLULAR CLEFTS 4 nm WIDE GLUCOSE, ETC. CAN PASS THROUGH PLASMA PROTEINS, ETC. CANNOT

28. TYPES OF CAPILLARIES FENESTRATED CAPILLARIES ALLOW RAPID ABSORPTION / FILTRATION KIDNEYS, SMALL INTESTINE, ETC. RIDDLED WITH HOLES FENESTRATIONS / FILTRATION PORES 20 – 100 nm DIAMETER USUALLY COVERED WITH DIAPHRAGM RAPID PASSAGE OF SMALL MOLECULES

31. TYPES OF CAPILLARIES SINUSOIDS IRREGULAR BLOOD-FILLED SPACES BONE MARROW, SPLEEN, ETC. SOME ARE CONTINUOUS CAPILLARIES SOME ARE FENESTRATED CAPILLARIES LARGE PORES PROTEINS AND BLOOD CELLS CAN PASS THROUGH ALBUMIN, CLOTTING FACTORS, RBCs, ETC.

32. VEINS CAPILLARIES ? VENULES ? VEINS RETURN BLOOD TO THE HEART FURTHER FROM THE HEART LOWER BLOOD PRESSURE THAN ARTERIES AVERAGE 10 mmHg VS. 100 mmHg NEED NOT WITHSTAND HIGH PRESSURES

33. VEINS THINNER WALLS LESS SMOOTH MUSCLE LESS ELASTIC TISSUE COLLAPSE WHEN EMPTY EXPAND MORE EASILY PRESSURE NOT HIGH ENOUGH TO RETURN BLOOD TO HEART VENOUS VALVES AND MASSAGING ASSIST RETURN

35. VEINS VENULES 15 – 100 mM DIAMETER PROXIMAL END POROUS FLUID EXCHANGE WITH TISSUES GAINS TUNICA MEDIA SMOOTH MUSCLE SPARSE TRIBUTARIES ? VEINS

36. VEINS VENOUS SINUSES ESPECIALLY THIN WALLS LARGE LUMENS NO SMOOTH MUSCLE E.G., CORONARY SINUS OF THE HEART

37. CIRCULATORY ROUTES HEART ?ARTERIES ? ARTERIOLES ?METARTERIOLES ?CAPILLARIES ?METARTERIOLES ?VENULES ?VEINS ?HEART

38. CIRCULATORY ROUTES TYPICAL CIRCULATORY ROUTE HEART ? ARTERIES ? ARTERIOLES ? CAPILLARIES CAPILLARIES ? VENULES ? VEINS ? HEART USUALLY PASSES THROUGH SINGLE CAPILLARY BED EXCEPTIONS?

39. CIRCULATORY ROUTES PORTAL SYSTEM BLOOD FLOWS THROUGH TWO CONSECUTIVE CAPILLARY BEDS E.G. KIDNEYS

40. CIRCULATORY ROUTES ANASTOMOSIS TWO VESSELS (VEINS OR ARTERIES) MERGE WITH EACH OTHER ARTERIOVENOUS ANASTOMOSIS ARTERIAL ANASTOMOSIS VENOUS ANASTOMOSIS

41. CIRCULATORY ROUTES ARTERIOVENOUS ANASTOMOSIS SHUNT ARTERY ? VEIN BYPASSES CAPILLARIES E.G. FINGERS, TOES, EARS, ETC. REDUCE HEAT LOSS MORE SUSCEPTIBLE TO FROSTBITE

42. CIRCULATORY ROUTES ARTERIAL ANASTOMOSIS TWO ARTERIES MERGE PROVIDE ALTERNATIVE ROUTES OF BLOOD SUPPLY TO A TISSUE E.G. CORONARY CIRCULATION, AROUND JOINTS

43. CIRCULATORY ROUTES VENOUS ANASTOMOSIS TWO VEINS MERGE MORE COMMON ALTERNATIVE ROUTS OF DRAINAGE FROM AN ORGAN

45. BLOOD FLOW AMOUNT OF BLOOD FLOWING THROUGH A TISSUE/ORGAN/VESSEL IN A GIVEN TIME E.G., ML/MIN SUPPLIES NUTRIENTS AND OXYGEN TO CELLS REMOVES WASTES FROM CELLS

46. BLOOD FLOW PERFUSION RATE OF BLOOD FLOW PER GIVEN MASS/VOLUME OF TISSUE E.G., ML/MIN/G

47. BLOOD FLOW MUST KEEP PACE WITH METABOLIC RATE OF CELLS NECROSIS (TISSUE DEATH) TOTAL FLOW CONSTANT IN RESTING INDIVIDUAL EQUAL TO CARDIAC OUTPUT FLOW TO INDIVIDUAL ORGANS VARIES CONTINUALLY

48. BLOOD FLOW HEMODYNAMICS PHYSICAL PRINCIPLES OF BLOOD FLOW BASED UPON PRESSURE DIFFERENCES (DP) INCREASED PRESSURE DIFFERENCE ? INCREASED FLOW RESISTANCE (R) INCREASED RESISTANCE ? DECREASED FLOW

49. BLOOD PRESSURE EASILY MEASURED SYSTOLIC PRESSURE PEAK PRESSURE DURING SYSTOLE DIASTOLIC PRESSURE PRESSURE DURING DIASTOLE PULSE PRESSURE SYSTOLIC MINUS DIASTOLIC MEASURE OF STRESS ON ARTERIES

50. BLOOD PRESSURE MEAN ARTERIAL PRESSURE (MAP) AVERAGE OF CONTINUOUS READINGS ESTIMATE DIASTOLIC + 1/3 PULSE PRESSURE AFFECTED BY GRAVITY ~62 mmHg IN HEAD ~180 mmHg IN ANKLES

51. BLOOD PRESSURE HYPERTENSION CHRONIC RESTING BP > 140/90 CHRONIC, NOT TRANSIENT CAN WEAKEN SMALL ARTERIES ANEURYSMS HYPOTENSION CHRONIC LOW RESTING BP RESULT OF ANEMIA, BLOOD LOSS, DEHYDRATION, ETC.

52. BLOOD PRESSURE ANEURYSM WEAK POINT IN BLOOD VESSEL PULSATES, MAY RUPTURE PAIN, DEATH RESULT FROM CONGENITAL WEAKNESS TRAUMA INFECTIONS (E.G., SYPHILIS) ATHEROSCLEROSIS AND HYPERTENSION

53. BLOOD PRESSURE ARTERIES DISTEND AND RECOIL ABSORB SOME OF THE FORCE OF THE EJECTED BLOOD REDUCE PRESSURE FLUCTUATIONS MAINTAIN STEADY BLOOD FLOW CONTINUOUS, YET PULSATILE AORTA 120 CM/SEC SYSTOLE AORTA 40 CM/SEC DIASTOLE DOWNSTREAM B.P. & PRESSURE FLUCTUATIONS REDUCED

55. BLOOD PRESSURE EFFECTS OF AGING INCREASE IN BLOOD PRESSURE ARTERIES LESS DISTENDIBLE ATHEROSCLEROSIS STIFFENS ARTERIES

56. RESISTANCE BLOOD PRESSURE AND RESISTANCE AFFECT EACH OTHER BOTH BLOOD PRESSURE AND RESISTANCE AFFECT BLOOD FLOW

57. RESISTANCE PERIPHERAL RESISTANCE RESISTANCE BLOOD ENCOUNTERS IN THE VESSELS RESULTS FROM FRICTION AGAINST VESSEL WALLS PROPORTIONAL TO THREE VARIABLES BLOOD VISCOSITY VESSEL LENGTH VESSEL RADIUS

58. RESISTANCE VARIABLES AFFECTING RESISTANCE BLOOD VISCOSITY MAINLY DUE TO ERYTHROCYTES AND PLASMA PROTEINS INCR VISCOSITY ? INCR RESISTANCE

59. RESISTANCE VARIABLES AFFECTING RESISTANCE VESSEL LENGTH FRICTION IS CUMULATIVE INCR LENGTH ? INCR RESISTANCE

60. RESISTANCE VARIABLES AFFECTING RESISTANCE VESSEL RADIUS INNATE RADIUS DIFFERENCES ALTERATIONS POSSIBLE VASOCONSTRICTION (NARROWING) VASODILATION (WIDENING) INCREASED FRICTION NEAR VESSEL WALL DECR RADIUS ? INCR RESISTANCE

61. RESISTANCE LAMINAR FLOW BLOOD TRAVELS IN SHEETS FASTER NEAR CENTER OF VESSEL LESS FRICTION SLOWER NEAR VESSEL WALLS MORE FRICTION SIMILAR TO WATER FLOW IN RIVERS

62. RESISTANCE LAMINAR FLOW LARGER VESSELS GREATER FRACTION OF BLOOD IN CENTER SMALLER VESSELS GREATER FRACTION OF BLOOD NEAR VESSEL WALLS RESISTANCE = CONSTANT / RADIUS4 FLOW RATE = CONSTANT * RADIUS4

64. REGULATION OF BLOOD SUPPLY VASOCONSTRICTION WIDESPREAD VASOCONSTRICTION RESULTS IN INCREASE IN BP RESULTS IN INCREASED PERFUSION LOCALIZED VASOCONSTRICTION INCREASES RESISTANCE IN AREA REDIRECTS BLOOD FROM ONE ORGAN TO ANOTHER

67. REGULATION OF BLOOD SUPPLY LOCAL CONTROL AUTOREGULATION REACTIVE HYPEREMIA VASOACTIVE CHEMICALS ANGIOGENESIS

68. REGULATION OF BLOOD SUPPLY LOCAL CONTROL AUTOREGULATION INADEQUATE BLOOD FLOW ? BUILDUP OF WASTE PRODUCTS ? VASODILATION STIMULATED ? INCREASED BLOOD FLOW

69. REGULATION OF BLOOD SUPPLY LOCAL CONTROL REACTIVE HYPEREMIA BLOOD SUPPLY CUT OFF, THEN RESTORED INCREASED BEYOND NORMAL LEVEL OF FLOW E.G., AFTER COMING IN FROM COLD POSSIBLY DUE TO BUILDUP OF WASTE PRODUCTS

70. REGULATION OF BLOOD SUPPLY LOCAL CONTROL VASOACTIVE CHEMICALS RELEASED BY PLATELETS, ENDOTHELIAL CELLS, ETC. E.G., HISTAMINE STIMULATES VASODILATION E.G., PROSTACYCLIN STIMULATES VASOCONSTRICTION

71. REGULATION OF BLOOD SUPPLY LOCAL CONTROL ANGIOGENESIS GROWTH OF NEW BLOOD VESSELS LONG-TERM CHANGE E.G. REGROWTH OF UTERINE LINING FOLLOWING MENSTRUATION E.G., MUSCLES OF ATHLETES E.G., ARTERIAL BYPASSES AROUND CORONARY OBSTRUCTIONS

72. REGULATION OF BLOOD SUPPLY NEURAL CONTROL VASOMOTOR CENTER OF MEDULLA OBLONGATA NERVE FIBERS CAN STIMULATE VASOCONSTRICTION IN MOST BLOOD VESSELS CAN STIMULATE VASODILATION IN CARDIAC AND SKELETAL MUSCLE

73. REGULATION OF BLOOD SUPPLY NEURAL CONTROL THREE AUTONOMIC REFLEXES BAROREFEXES CHEMOREFLEXES MEDULLARY ISCHEMIC REFLEXES

74. REGULATION OF BLOOD SUPPLY NEURAL CONTROL BAROREFLEXES RESPONSE TO D IN BLOOD PRESSURE D DETECTED BY BARORECEPTORS PRESENT IN AORTIC ARCH AND IN OTHER ARTERIES ABOVE HEART NEGATIVE FEEDBACK RESPONSE

77. REGULATION OF BLOOD SUPPLY NEURAL CONTROL CHEMOREFLEXES RESPONSE TO D IN BLOOD CHEMISTRY ESPECIALLY pH, [O2], [CO2] D DETECTED BY CHEMORECEPTORS PRESENT IN AORTIC ARCH AND IN OTHER ARTERIES ABOVE HEART ADJUST RESPIRATION STIMULATE VASOCONSTRICTION INCREASE BP ? INCREASE PERFUSION

78. REGULATION OF BLOOD SUPPLY NEURAL CONTROL MEDULLARY ISCHEMIC REFLEX RESPONSE TO INADEQUATE PERFUSION IN BRAINSTEM INCREASE HEART RATE & CONTRACTION FORCE INDUCE WIDESPREAD VASOCONSTRICTION INCREASE BP ? INCREASE PERFUSION

79. REGULATION OF BLOOD SUPPLY HORMONAL CONTROL ANGIOTENSIN II VASOCONSTRICTIVE HORMONE INCREASE BP ? INCREASE PERFUSION ANGIOTENSINOGEN ? ANGIOTENSIN I CONVERSION STIMULATED BY RENIN KIDNEYS PRODUCE RENIN IN RESPONSE TO LOW BP ANGIOTENSIN I ? ANGIOTENSIN II CONVERSION STIMULATED BY ACE (ENZYME) ACE PRESENT IN LUNGS ACE INHIBITORS TREAT HYPERTENSION

80. REGULATION OF BLOOD SUPPLY HORMONAL CONTROL EPINEPHRINE / NOREPINEPHRINE VASOACTIVE HORMONES BIND TO a-ADRENERGIC RECEPTORS ON SMOOTH MUSCLE OF MOST BLOOD VESSELS VASOCONSTRICTION INCREASE BP ? INCREASE PERFUSION BIND TO b-ADRENERGIC RECEPTORS ON BLOOD VESSELS OF SKELETAL MUSCLE AND CORONARY BLOOD VESSELS VASODILATION INCREASED BLOOD FLOW TO HEART & MUSCLES

81. CAPILLARY EXCHANGE CAPILLARIES SITES OF EXCHANGE BETWEEN BLOOD AND SURROUNDING TISSUES ROUTES OF EXCHANGE PASSAGE THROUGH FENESTRATIONS PASSAGE THROUGH INTERCELLULAR CLEFTS PASAGE THROUGH ENDOTHELIAL CELL CYTOPLASM

83. CAPILLARY EXCHANGE MECHANISMS OF EXCHANGE DIFFUSION TRANSCYTOSIS FILTRATION REABSORPTION

84. CAPILLARY EXCHANGE DIFFUSION MOST IMPORTANT MECHANISM MOVEMENT DOWN CONC GRADIENT IMPORTANT FOR O2, CO2, STEROID HORMONES THROUGH PLASMA MEMBRANE GLUCOSE, ELECTROLYTES, ETC. THROUGH CHANNELS / CLEFTS / FENESTRATIONS NOT IMPORTANT FOR PROTEINS, ETC. (TOO BIG)

85. CAPILLARY EXCHANGE TRANSCYTOSIS MOVEMENT THROUGH EPITHELIAL CELLS ENDOCYTOSIS, THEN EXOCYTOSIS IMPORTANT FOR FATTY ACIDS ALBUMIN SOME HORMONES (E.G., INSULIN)

86. CAPILLARY EXCHANGE FILTRATION CAPILLARY PRESSURE ~30 mmHg AT ARTERIAL END TISSUE PRESSURE ~-3 mmHg FLUID LEAVES AT ARTERIAL END REDUCED, BUT NOT PREVENTED BY ONCOTIC PRESSURE

87. CAPILLARY EXCHANGE ONCOTIC PRESSURE TISSUE FLUID HAS FEWER SOLUTES THAN BLOOD OSMOTIC FORCE PUSHING FLUID INTO CAPILLARIES CANNOT OVERCOME PRESSURE DIFFERENCES AT ARTERIAL END OF CAP. CAN OVERCOME PRESSURE DIFFERENCES AT VENOUS END OF CAPILLARIES

88. CAPILLARY EXCHANGE REABSORPTION CAPILLARY PRESSURE ~ 10 mmHg AT VENOUS END TISSUE PRESSURE ~-3 mmHg ONCOTIC PRESSURE OVERWHELMS PRESSURE DIFFERENCE FLUID ENTERS AT VENOUS END

90. CAPILLARY EXCHANGE FILTRATION AND REABSORPTION FLUID LEAVES CAPILLARY AT ARTERIAL END ~85% OF FLUID REENTERS CAPILLARY AT VENOUS END CAPILLARIES ARE LARGER AND MORE NUMEROUS AT VENOUS END ~15% REENTERS RETURNED VIA LYMPHATIC SYSTEM

91. CAPILLARY EXCHANGE EDEMA EXCESS FLUID IN A TISSUE ACCUMULATION CAUSED BY INCREASED CAPILLARY FILTRATION REDUCED CAPILLARY REABSORPTION OBSTRUCTED LYMPHATIC DRAINAGE

92. CAPILLARY EXCHANGE CAUSES OF EDEMA INCREASED CAPILLARY FILTRATION CAUSES (E.G.) INCREASED CAPILLARY B.P. INCREASED CAPILLARY PERMEABILITY CONGESTIVE HEART FAILURE POOR VENOUS RETURN INSUFFICIENT MUSCULAR ACTIVITY KIDNEY FAILURE ? HYPERTENSION

93. CAPILLARY EXCHANGE CAUSES OF EDEMA REDUCED CAPILLARY REABSORPTION CAUSES (E.G.) BLOOD ALBUMIN DEFICIENCY REDUCED ONCOTIC PRESSURE LIVER DISEASES (LESS ALBUMIN) HYPOPROTEINEMIA (LESS ALBUMIN)

94. CAPILLARY EXCHANGE CAUSES OF EDEMA OBSTRUCTED LYMPHATIC DRAINAGE ~15% OF FLUID LOST IS RETURNED VIA LYMPHATIC SYSTEM OBSTRUCTION OR REMOVAL INTERFERES WITH THIS RETURN

95. VENOUS RETURN FLOW OF BLOOD BACK TO THE HEART MECHANISMS OF VENOUS RETURN PRESSURE GRADIENT THORACIC (RESPIRATORY) PUMP CARDIAC SUCTION SKELETAL MUSCLE PUMP GRAVITY

96. VENOUS RETURN PRESSURE GRADIENT MOST IMPORTANT FORCE IN VENOUS RETURN VENULE PRESSURE ~15 mmHg VENA CAVAE PRESSURE ~ 4.6 mmHg BLOOD FLOW TO THE HEART FAVORED BY DP

97. VENOUS RETURN THORACIC (RESPIRATORY) PUMP INFERIOR VENA CAVA SPANS ABDOMINAL AND THORACIC CAVITIES DURING INHALATION THORACIC PRESSURE DROPS ABDOMINAL PRESSURE INCREASES FLOW OF BLOOD FROM ABDOMINAL TO THORACIC CAVITY PROMOTED

98. VENOUS RETURN CARDIAC SUCTION DURING VENTRICULAR SYSTOLE CHORDAE TENDINEAE PULL AV VALVE CUSPS TOWARD VENTRICLES ATRIAL SPACE SLIGHTLY INCREASED BLOOD DRAWN INTO ATRIA

99. VENOUS RETURN SKELETAL MUSCLE PUMP VEINS SURROUNDED AND SQUEEZED BY SKELETAL MUSCLES BLOOD SQUEEZED OUT VALVES SIMILAR TO SEMILUNAR VALVES INSURE UNIDIRECTIONAL FLOW

101. VENOUS RETURN GRAVITY BLOOD IN HEAD AND NECK SIMPLY FLOWS DOWNHILL

102. VENOUS RETURN EFFECTS OF EXERCISE INCREASED CARDIAC OUTPUT INCREASED BLOOD PRESSURE BLOOD VESSEL DILATION INCREASED FLOW RATE INCREASED RESPIRATORY RATE ENHANCED THORACIC PUMP MUSCLE CONTRACTIONS ENHANCED SKELETAL MUSCLE PUMP