1. Blood Vessels and Circulation
Chapter 21
C h a p t e r 21
Blood Vessels and Circulation

2. Pressure and Resistance
Total capillary blood flow directly related to cardiac output
Is determined by:
pressure and resistance in the cardiovascular system
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3. Pressure and Resistance
Figure 21–8 An Overview of Cardiovascular Physiology
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4. Pressure and Resistance
Pressure (P)
The heart generates P to overcome resistance (R)
Absolute pressure less important than pressure gradient
The Pressure Gradient (P) is the difference in P’s
Circulatory pressure has pressure gradient
It is the difference between:
Pressure at the heart
Pressure at peripheral capillary beds
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5. Pressure and Resistance
Flow (F)
Is proportional to the pressure gradient (P) divided by R
F= P / R
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6. Pressure and Resistance
Measuring Pressure
Blood pressure (BP)
Arterial pressure (mm Hg)
Capillary hydrostatic pressure (CHP)
Pressure within the capillary beds
Venous pressure
Pressure in the venous system
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7. Pressure and Resistance
Circulatory Pressure:
∆P across the systemic circuit (about 100 mm Hg)
Circulatory pressure must overcome total peripheral R
R of entire cardiovascular system
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8. Pressure and Resistance
Total Peripheral “R” affected by 3 factors:
Vascular R
Due to friction between blood and vessel walls
Depends on vessel length and vessel diameter:
adult vessel length is constant
vessel diameter varies by vasodilation/vasoconstriction... (R increases exponentially as vessel diameter ________)
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9. Pressure and Resistance
Viscosity
R caused by molecules and suspended materials in a liquid
Whole blood viscosity is about 4 x water
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10. Pressure and Resistance
Turbulence
Swirling action that disturbs smooth flow of liquid
Occurs in heart chambers and great vessels
Atherosclerotic plaques cause abnormal turbulence
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11. Pressure and Resistance
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12. Pressure and Resistance
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13. Pressure and Resistance
Cardiovascular Pressures:
Systolic pressure
Peak arterial pressure during ventricular systole
Diastolic pressure
Minimum arterial pressure during diastole
Pulse pressure
Difference between systolic pressure and diastolic pressure
Mean arterial pressure (MAP)
MAP = diastolic pressure + 1/3 pulse pressure
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14. Pressure and Resistance
Normal/Average BP= 120/80
Abnormal BP:
Hypertension - Abnormally high BP
greater than 140/90
Hypotension - Abnormally low BP
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15. Pressure and Resistance
Larger arterial walls have elastic rebound
Stretch during systole
Recoil to original shape during diastole
Keep blood moving during diastole
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16. Pressure and Resistance
Figure 21–9
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17. Pressure and Resistance
Pressures in Small Arteries and Arterioles affected by distance
MAP and pulse pressure decrease with distance from heart
Blood pressure decreases as multiple branches arise
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18. Pressure and Resistance
Figure 21–10 Pressures within the Systemic Circuit
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19. Pressure and Resistance
Venous Pressure and Venous Return
Low pressure exists in venous system
2 actions improve venous return:
Muscular compression of peripheral veins:
compression of skeletal muscles pushes blood toward heart (through one-way valves)
The respiratory pump in thoracic cavity:
inhaling decreases thoracic pressure (draws air/blood toward lungs)
exhaling raises thoracic pressure (forces air/blood away from lungs)
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20. Pressure and Resistance
Capillary Pressures and Exchange
Vital to homeostasis
Moves materials across capillary walls by
Diffusion (from concentration gradient)
Filtration (from hydrostatic pressure)
Reabsorption (from osmosis)
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21. Pressure and Resistance
Figure 21–11 Capillary Filtration
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22. Pressure and Resistance
Interplay between Filtration and Reabsorption:
Hydrostatic pressure
Forces water out of solution
Osmotic pressure
Pulls water into solution
Both control filtration and reabsorption through capillaries
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23. Pressure and Resistance
Net Hydrostatic Pressure:
Is the difference between
Capillary hydrostatic pressure (CHP)
And Interstitial fluid hydrostatic pressure (IHP)
Pushes water and solutes...
From __________ to ____________
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24. Pressure and Resistance
Net Colloid Osmotic Pressure:
Is the difference between
Blood colloid osmotic pressure (BCOP)
And interstitial fluid colloid osmotic pressure (ICOP)
Pulls water and solutes…
From __________ into ____________
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25. Pressure and Resistance
Net Filtration Pressure (NFP):
The difference between:
Net Hydrostatic pressure
And Net Osmotic pressure
NFP = (CHP – IHP) – (BCOP – ICOP)
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26. Pressure and Resistance
Capillary Exchange
At arterial end of capillary
Fluid moves from capillary
Into interstitial fluid
At venous end of capillary
Fluid moves into capillary
From interstitial fluid
Transition point between filtration and reabsorption
Is closer to venous end than arterial end
So… capillaries usually filter more than they reabsorb
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27. Pressure and Resistance
Figure 21–12 Forces Acting across Capillary Walls
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28. Pressure and Resistance
Water continuously moves out of capillaries and back into the bloodstream (Fluid Recycling ) via the lymphatic system
Ensures constant plasma and interstitial fluid communication
Accelerates distribution of nutrients, hormones, and dissolved gases through tissues
Transports insoluble lipids and tissue proteins that cannot cross capillary walls
Flushes bacterial toxins and chemicals to immune system tissues
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29. Pressure and Resistance
Capillary Dynamics
Hemorrhaging
Reduces CHP and NFP
Increase _____________of interstitial fluid (recall of fluids)
Dehydration
Increases BCOP
Increases _____________ of interstitial fluid
High BP
Elevated CHP
Increases _____________ into the interstitial fluid
Fluid builds up in peripheral tissues (Edema)
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30. Cardiovascular Regulation
Tissue Perfusion is the blood flow through tissues
Carries O2 and nutrients to tissues and organs
Carries CO2 and wastes away
Is affected by
Cardiac output
Peripheral resistance
Blood Pressure
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31. Cardiovascular Regulation
Cardiovascular regulation changes blood flow to a specific area
At an appropriate time
In the right area
Without changing blood pressure and blood flow to vital organs (Ex: ______________)
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32. Cardiovascular Regulation
Figure 21–13 Short-Term and Long-Term Cardiovascular Responses
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33. Cardiovascular Regulation
Controlling Cardiac Output and Blood Pressure
Autoregulation
Causes immediate, localized homeostatic adjustments
Neural mechanisms
Respond quickly to changes at specific sites
Endocrine mechanisms
Direct long-term changes
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34. Cardiovascular Regulation
Autoregulation of Blood Flow within Tissues-
Adjusted by Peripheral Resistance while CO stays the same
Can cause local vasoconstriction or vasodialation
Triggered by prostaglandins and other “local” factors
Local vasoconstrictors can reduce blood flow by:
Constricting precapillary sphincters
Affecting a single capillary bed
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35. Cardiovascular Regulation
Autoregulation of Blood Flow within Tissues-
Local vasodilators can accelerate blood flow at tissue level if:
low O2 or high CO2 levels
low pH (acids)
nitric oxide (NO) levels high
high K+ or H+ concentrations
chemicals released by inflammation (histamine)
elevated local temperature
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36. Cardiovascular Regulation
Neural Mechanisms
Cardiovascular (CV) centers of the Medulla Oblongata
Cardiac centers:
cardioacceleratory center: increases cardiac output
cardioinhibitory center: reduces cardiac output
Vasomotor center:
vasoconstriction
controlled by adrenergic nerves (NE)
stimulates smooth muscle contraction in arteriole walls
vasodilation:
controlled by cholinergic nerves (ACh)
relaxes smooth muscle
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37. Cardiovascular Regulation
Vasomotor Tone
Maintained by constant action of sympathetic vasoconstrictor nerves
Keeps your blood pressure high enough to get good capillary exchange!
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38. Cardiovascular Regulation
Reflex Control of Cardiovascular Function
Cardiovascular centers monitor arterial blood
Baroreceptor reflexes:
respond to changes in blood pressure
Chemoreceptor reflexes:
respond to changes in chemical composition, particularly pH and dissolved gases
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39. Cardiovascular Regulation
Baroreceptor Reflexes
Stretch receptors in walls of
Carotid sinuses: maintain blood flow to brain
Aortic sinuses: monitor start of systemic circuit
Right atrium: monitors end of systemic circuit
When blood pressure rises, CV centers
Decrease cardiac output
Cause peripheral vasodilation
When blood pressure falls, CV centers
Increase cardiac output
Cause peripheral vasoconstriction
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40. Cardiovascular Regulation
Figure 21–14 Baroreceptor Reflexes of the Carotid and Aortic Sinuses
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41. Cardiovascular Regulation
CNS Activities and the Cardiovascular Centers
Thought processes and emotional states can elevate blood pressure by cardiac stimulation and vasoconstriction
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42. Cardiovascular Regulation
Hormones and Cardiovascular Regulation
Hormones have short-term and long-term effects on cardiovascular regulation
E and NE from suprarenal medullae stimulate cardiac output and peripheral vasoconstriction
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43. Cardiovascular Regulation
Antidiuretic Hormone (ADH)
Released by neurohypophysis (posterior lobe of pituitary)
Elevates blood pressure
Reduces water loss at kidneys
ADH responds to:
Low blood volume
High plasma osmotic concentration
Circulating angiotensin II
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44. Cardiovascular Regulation
Angiotensin II
Responds to fall in renal blood pressure
Stimulates
Aldosterone production
ADH production
Thirst
Cardiac output
Peripheral vasoconstriction
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45. Cardiovascular Regulation
Erythropoietin (EPO)
Released at kidneys
Responds to low blood pressure, low O2 content in blood
Stimulates red blood cell production
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46. Cardiovascular Regulation
Natriuretic Peptides
Atrial natriuretic peptide (ANP)
Produced by cells in right atrium
Brain natriuretic peptide (BNP)
Produced by ventricular muscle cells
Respond to excessive diastolic stretching
Will lower blood volume and blood pressure
And reduce stress on heart
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47. Cardiovascular Regulation
Figure 21–16a The Hormonal Regulation of BP and BV
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48. Cardiovascular Regulation
Figure 21–16b The Hormonal Regulation of BP and BV
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49. Cardiovascular Adaptation
Blood, heart, and cardiovascular system
Work together as unit
Respond to physical and physiological changes (for example, exercise, blood loss)
Maintains homeostasis
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50. Cardiovascular Adaptation
The Cardiovascular Response to Exercise
Light exercise
Extensive vasodilation occurs:
increasing circulation
Venous return increases:
with muscle contractions
Cardiac output rises:
due to rise in venous return (Frank–Starling principle) and atrial stretching
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51. Cardiovascular Adaptation
The Cardiovascular Response to Exercise
Heavy exercise
Activates sympathetic nervous system
Cardiac output increases to maximum:
about 4 x resting level
Restricts blood flow to “nonessential” organs (e.g., digestive system)
Redirects blood flow to skeletal muscles, lungs, and heart, skin
Blood supply to brain is unaffected
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52. Cardiovascular Adaptation
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53. Cardiovascular Adaptation
Exercise, Cardiovascular Fitness, and Health
Regular moderate exercise
______ total blood cholesterol levels
Intense exercise
Can cause severe physiological stress
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54. Cardiovascular Adaptation
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55. Cardiovascular Adaptation
The Cardiovascular Response to Hemorrhaging
Entire cardiovascular system adjusts to
Maintain blood pressure
Restore blood volume
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56. Cardiovascular Adaptation
Shock
Short-term responses compensate after blood losses of up to 20% of total blood volume
Failure to restore blood pressure results in shock
Organ systems start to fail
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57. Cardiovascular Adaptation
Vascular Supply to Special Regions
Blood Flow to the Brain is top priority due to high oxygen demand
When peripheral vessels constrict, cerebral vessels dilate, normalizing blood flow to brain
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58. Cardiovascular Adaptation
Stroke
Also called cerebrovascular accident (CVA)
Blockage or rupture in a cerebral artery
Maybe due to aneurism rupture
Stops blood flow to brain
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59. Cardiovascular Adaptation
Blood Flow to the Heart
Through coronary arteries
Oxygen demand increases with activity
Rising Lactic acid and low O2 levels
Dilate coronary vessels
Increase coronary blood flow
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60. Cardiovascular Adaptation
Heart Attack (Myocardial Infarction/MI)
A blockage of coronary blood flow
Can cause:
Angina (chest pain)
Tissue damage
Heart failure
Death
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61. Cardiovascular Adaptation
Blood Flow to the Lungs
Regulated by O2 levels in alveoli
High O2 content in alveolus
Vessels dilate, _______ cap exchange
Low O2 content in alveolus
Vessels constrict, _______cap exchange
Shunts blood to other O2rich alveoli
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62. Aging and the Cardiovascular System
Cardiovascular capabilities decline with increasing age
Age-related changes occur in:
Blood
Heart
Blood vessels
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63. Aging and the Cardiovascular System
3 Age-Related Changes in Blood
Decreased hematocrit
Peripheral blockage by blood clot (thrombus)
Pooling of blood in legs
Due to venous valve deterioration
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64. Aging and the Cardiovascular System
5 Age-Related Changes in the Heart
Reduced maximum cardiac output
Changes in nodal and conducting cells
Reduced elasticity of cardiac (fibrous) skeleton
Progressive atherosclerosis
Replacement of damaged cardiac muscle cells by scar tissue
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65. Aging and the Cardiovascular System
3 Age-Related Changes in Blood Vessels
Arteries become less elastic
Pressure change can cause aneurysm
Calcium deposits on vessel walls
Can cause stroke or infarction
Thrombi can form
At atherosclerotic plaques
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