BSI: Circulation

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re.pitt
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67774
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BSI: Circulation
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2011-02-21 16:20:13
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BSI Circulation
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BSI: Spring 2011, Circulation
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  1. Describe the functional vessels of the circulation.
    • Arteries: Transport of oxygenated blood
    • Arterioles: Act as valves for entry into capillaries
    • Capillaries: Gas and nutrient exchange
    • Venules: Collects blood from capillary
    • Veins: Carry deoxygenated blood back to heart

  2. Which veins actually carry oxygenated blood back to the heart?
    Pulmonary Veins
  3. Why does gas exchange occur in the capillaries?
    The capillaries are only one endothelial layer of cells thick. Therefore, they are thin enough to allow gas exchange to occur.
  4. What is a tunica?
    A tunica, in laymen's terms, is a covering or a layer. Each tunica (or layer) in an vessel has different components to it.
  5. Describe the three tunicas found in arteries.
    • Tunica interna (intima)
    • - Contains lining of simple squamous epithelium (endothelium), basement membrane, and layer of elastic tissue (internal elastic lamina)
    • - The endothelium lines the entire cardiovascular system
    • - Normally, endothelium is the only tissue that contacts blood

    • Tunica media
    • - Thickest layer
    • - Middle layer
    • - Consists of elastic fibers and smooth muscle that extend circularly around the lumen

    • Tunica externa
    • - Outermost layer
    • - Composed mainly of elastic and collagen fibers
    • - In muscular arteries, an external elastic lamina composed of elastic tissue separates the tunica externa form the tunica media

  6. What is another name for the lining of simple squamous epithelium?
    Endothelium, which is found in tunica interna of the arteries.
  7. What is the only tissue that normally comes in contact with blood?
    Endothelium, which is found in Tunica interna of the arteries.
  8. Describe the two types of arteries.
    • Elastic arteries
    • - Arteries with largest diameter
    • - Tunica media contains large amounts of elastic fibers
    • - Help propel blood onward (by recoiling) while ventricles are relaxing

    • Muscular arteries
    • - More smooth muscle in tunica media (which is innervated by SNS)
    • - Fewer elastic fibers
    • - Capable of greater vasoconstriction and vasodilation to adjust blood flow
  9. Which arteries have smooth muscle that is innervated by the SNS?
    Muscular arteries have smooth muscle in the tunica media layer which is innervated by the SNS. This allows vasoconstriction and vasodilation.
  10. What is the purpose of Arterioles?
    Arterioles carry oxygenated blood and empties into capillaries.

  11. What is the purpose of metarterioles?
    Metarterioles are the region of arterioles that have control over blood flow into capillary bed.

  12. What is the purpose of capillaries?
    Capillaries are the site of gas and fluid exchange with the tissues.

  13. What is the purpose of venules?
    Venules receive deoxygenated blood from capillaries.

  14. Describe the three tunicas found in veins
    Veins consist of the same three tunics as arteries.

    • Thinner tunica interna & tunica media
    • - Less elastic tissue and smooth muscle than arteries

    • Thicker tunica externa
  15. What is compliance and which vessels are more compliant?
    Compliance, in laymen's terms, is the ability to be able to stretch, and then recoil back to its original shape.

    Veins much more compliant than arteries.

    Veins are ~24x more compliant compared to an artery

    • Veins can hold more blood: they act as a reservoir
    • Amount of blood that a vessel can hold for each mm Hg pressure rise (Ask Naylor what this sentence means)
  16. What happens if you decrease compliance?
    As you decrease compliance, that can increase Pulse Pressure.

    Compliance can decrease as you age because vessels will get stiffer.
  17. How do veins prevent backflow of blood?
    Veins contain valves to prevent backflow of blood.
  18. What is the primary purpose of the cardiovascular system?
    The purpose of the cardiovascular system is to maintain blood flow to allow for the delivery of oxygen and nutrients to the tissues.
  19. How is Cardiac Output (CO) calculated?
    • CO = MAP / TPR
    • Cardiac Output = (Mean Arterial Pressure) / (Total Peripheral Resistance)
    • These factors are intimately related: you can't change one without affecting the others.
  20. How is Mean Arterial Pressure (MAP) calculated?
    • MAP = CO x TPR
    • Mean Arterial Pressure = (Cardiac Output) x (Total Peripheral Resistance)
    • These factors are intimately related: you can't change one without affecting the others.

  21. What is the driving force for blood flow through the circulation?
    MAP = Mean Arterial Pressure
  22. What is blood pressure?
    Blood pressure is the force exerted on the walls of the blood vessels by the blood.
  23. How does blood flow?
    Blood flows due to a pressure gradient.
  24. Do the pressure gradients in each vessel differ?
    Yes! Pressure gradients not only differ depending on the vessel type, but the pressure gradients also differ depending on whether you are talking about the systemic circulation versus the pulmonary (lung) ciruculation.

  25. What are the pressure gradients in each of the vessels in the systemic circulation?
    • Arteries = 80-120 mmHg
    • - Diastolic = 80
    • - Systolic = 120
    • - Mean (MAP) = DBP + 1/3(SBP-DBP) = 80 + 1/3(120-80) = 93 mmHg

    Capillaries = 17 mmHg (mean)

    Veins and right atrium = 0 mmHg
  26. If using the normal Systolic and Diastolic pressure for a healthy individual, how do you calculate the Mean Arterial Pressure (MAP)?
    Arteries rang in their pressure from 80-120 mm Hg.

    • In a normal healthy individual, the different arterial pressures are as follows:
    • - Diastolic = 80 mm Hg
    • - Systolic = 120 mm Hg

    • Therefore, the MAP can be calculated as follows:
    • Mean (MAP) = DBP + 1/3(SBP-DBP)
    • MAP = 80 + 1/3(120-80)
    • MAP = 93 mmHg
  27. What are the pressure gradients in each of the vessels in the pulmonary circulation?
    Note that the pulmonary circulation is a lower pressure system than the systemic circualation.

    • - Pulmonary artery = 8-25 mm Hg
    • - Capillaries = 7 mm Hg
  28. What is pulse pressure?
    Pulse Pressure is simply the difference between systolic and diastolic blood pressure.
  29. How is pulse pressure calculated?
    • PP = SBP – DBP
    • Pulse Pressure = Systolic Blood Pressure - Diastolic Blood Pressure

    • In a normal healthy individual, the pulse pressure could be calculated as follows:
    • PP = SBP - DBP
    • PP = 120 - 80
    • PP = 40 mm Hg
  30. What two factors can affect Pulse Pressure?
    • Stroke volume
    • - Greater stroke volume results in greater pressure rise with each heart beat

    • Compliance
    • - Lower compliance of artery results in a greater pressure rise with every heart beat
  31. What is the difference between pulsations in the different vessels?
    Pulsations are dampened further down the vascular treearterioles and capillaries do not experience significant pulsations.
  32. What is Total Peripheral Resistance (TPR)?
    TPR is the resistance to blood flow through all of the ARTERIAL vasculature in the body.
  33. When talking about TPR, which vasculature are we referring to?
    TPR refers to ARTERIAL vasculature only...not venous vasculature.
  34. What is another name for Total Peripheral Resistance (TPR)?
    TPR is also referred to as SVR (systemic vascular resistance).
  35. Is most resistance found in arterial or venous vasculature? Why?
    Most of the resistance is in the arterial vasculature compared to the venous vasculature since the venous vasculature is so compliant.
  36. What are the major factors affecting
    MAP = CO x TPR?
    • 1) vessel diameter
    • 2) venous pump
    • 3) respiratory pump
    • 4) Renin-angiotensin-aldosterone system (RAAS)
    • 5) ADH: Anti-diuretic hormone (vasopressin)
    • 6) ANP: Atrial natriuretic peptide
    • 7) Autonomic nervous system (SNS & PNS)
  37. What does vessel diameter affect in the
    MAP = CO x TPR and how does it affect it?
    TPR increases as vessels vasoconstrict (as vessel diameter decreases)

    TPR decreases as vessels vasodilate (as vessel diameter increases)

    • The vessel diameter can be found by the following formula:
    • Resistance = 1/diameter4

  38. What is the formula for finding vessel diameter?
    The vessel diameter can be found by the following formula:

    Resistance = 1/diameter4
  39. How does vasodilation affect TPR?
    Vasodilation will increase vessel diameter and therefore decrease Total Peripheral Resistance (TPR).
  40. How does vasoconstriction affect TPR?
    Vasoconstriction will decrease vessel diameter and therefore increase Total Peripheral Resistance (TPR).
  41. What is the venous pump and what purpose does it serve?
    The venous pump is the rhythmic contraction of skeletal muscle which helps to push blood forward towards the heart.

    Note that valves prevent backflow during relaxation.

  42. Does the venous pump involve smooth muscle or skeletal muscle?
    Skeletal muscle
  43. What is the respiratory pump and what purpose does it serve?
    During inspiration, abdominal pressure increases and intrathoracic pressure decreases.

    This change in pressure leads to increased venous return due to pressure gradient.
  44. What is the purpose of the Renin-angiotensin-aldosterone system (RAAS)?
    Activation of RAAS increases blood pressure.
  45. What are the "players" involved in the RAAS?
    • Renin (enzyme)
    • Angiotensin II (hormone)
    • Aldosterone (hormone)

  46. What two things will stimulate the RAAS system by stimulating Renin?
    Two things will stimulate Renin and therefore the RAAS system:

    • 1) decreased stretching of blood vessels (specifically arterioles)
    • 2) activation of the SNS (which makes sense because the SNS will be activated when BP drops)
  47. What will cleave Angiotensinogen to Angiotensin I?
    Renin, which is released from the kidney, cleaves Angiotensinogen to Angiotensin I.

  48. Where is Renin released from?
    Renin is released from the kidney.
  49. What cleaves Angiotensin I to Angiotensin II?
    Angiotensin Converting Enzyme (ACE) cleaves Angiotensin I to Angiotensin II.

  50. Where is Angiotensin Converting Enzyme (ACE) released from?
    ACE comes from the lungs.
  51. What are the consequences of Angiotensin II?
    • Angiotensin II will effectively have several consequences to increase arterial pressure:
    • - increase further stimulation of the SNS
    • - increase contractility
    • - directly affects the kidney to increase renal retention of salt and water
    • - promote vasoconstriction
    • - allow for release of Aldosterone which is released from the cortex in the adrenal glands

  52. What are the consequences of Aldosterone?
    Aldosterone (like Angiotesin II) directly affects the kidneys for renal retention of salt and water for the purpose of increasing overall blood pressure.
  53. Where does Aldosterone come from?
    Aldosterone is released from the cortex of the adrenal glands.
  54. Describe the sequence of events that happens when the RAAS system is activated.
    • 1) Two things stimulate the release of Renin from the kidneys:
    • - decreased stretching of blood vessels (specifically arterioles)
    • - activation of the SNS (due to decreased BP)

    2) Renin will cleave Angiotensinogen into Angiotensin I.

    3) Angiotensin I will be converted by the Angiotensin Converting Enzyme (ACE) found in the lung to Angiotensin II.

    • 4) Angiotensin II will then effectively have several consequences to increase arterial pressure:
    • - increase further stimulation of the SNS
    • - increase contractility
    • - directly affects the kidney to increase renal retention of salt and water
    • - promote vasoconstriction
    • - allow for release of Aldosterone which is released from the cortex in the adrenal glands

    5) Aldosterone also directly affects the kidney for renal retention of salt and water.

    6) Angiotensin II can be inactivated by the Angiotensinase enzyme.

  55. What are the two subtypes of angiotensin II receptors and where are they found?
    • AT1: brain, kidney, myocardium, peripheral vasculature, adrenal glands
    • AT2: adrenal medullary tissue, uterus, brain (does not influence blood pressure)
  56. Which Angiotensin II receptor does NOT influence blood pressure?
    AT2 does not influence blood pressure.
  57. What does Angiotensin II do?
    Angiotensin II causes the kidneys to retain salt & water.
  58. How does Angiotensin II act?
    Angiotensin II causes the kidneys to retain salt & water in two ways:

    • 1) Acts directly on kidneys to cause salt and water retention.
    • 2) Angiotensin II causes adrenal glands to secrete aldosterone. The aldosterone in turn increases salt and water reabsorption by kidneys.
  59. What are the three major consequences of
    Angiotensin II?
    • Angiotensin II causes vasoconstriction
    • Angiotensin II increases contractility of the heart
    • Angiotensin II stimulates the SNS
  60. What does ADH stand for?
    Antidiuretic Hormone (also known as vasopressin)
  61. When is ADH released and from where?
    ADH is released from the posterior pituitary gland in response to decreased blood volume and/or changes in osmolarity.
  62. Will an increase or decrease in osmolarity stimulate ADH?
    Recall ADH is released in response to decreased blood volume or changes in osmolarity for the purpose of promoting water retention.

    Therefore, an increase in osmolarity (higher salt content, less fluid) would increase ADH because the blood would be more concentrated.

    For example, think of it in terms of exercising. When you exercise, you sweat and therefore you lose overall body fluid. Therefore, there will be less blood volume which makes what blood you have more concentrated (ie an increase in osmolarity). Therefore, ADH would be stimulated to act on kidneys to promote the retention of water.
  63. Where does ADH come from?
    ADH is released from the posterior pituitary gland.
  64. What is the purpose of releasing ADH?
    ADH will act directly on the kidneys to promote the retention of water.
  65. What is the overall consequence of ADH?
    • ADH increases blood pressure by:
    • - Causing vasoconstriction
    • - Acting on kidneys to promote retention of water
  66. What does ANP stand for?
    Atrial natriuretic peptide
  67. When is ANP released and from where?
    ANP is released by cells of atria in response to stretch.
  68. What is the overall consequence of ANP?
    • ANP decreases blood pressure by:
    • - Causing vasodilation
    • - Acting on kidneys to promote loss of salt and water in urine
  69. Which two chemical hormones are exact opposites?
    • ADH: increases overall blood pressure
    • ANP : decreases overall blood pressure
  70. What two systems is the Autonomic Nervous System (ANS) composed of?
    • SNS: Symapthetic Nervous System
    • ANS: Autonomic Nervous System
  71. What is the primary role of the SNS in the circulatory system?
    The SNS plays a role in controlling circulation.
  72. What does the SNS innvervate?
    • The SNS innervates the heart and all vessels except:
    • - capillaries
    • - precapillary sphincters
    • - metarterioles
  73. Does the SNS innervate capillaries?
    • No. The SNS innervates the heart and all vessels except:
    • - capillaries
    • - precapillary sphincters
    • - metarterioles
  74. What is the overall consequence of the SNS?
    The SNS increases heart rate and contractility.
  75. What is the primary role of the ANS in the circulatory system?
    • The ANS plays very small role in controlling blood flow and circulation since majority of blood vessels are not innervated by PNS.
  76. What does the PNS innervate?
    The PNS innervates the heart.
  77. What is the overall consequence of the PNS?
    The PNS decreases heart rate and decreases contractility slightly.
  78. What system regulates the ANS?
    The vasomotor center regulates the ANS.

  79. What are the three receptors that send information to the vasomotor center?
    • Baroreceptors
    • Chemoreceptors
    • Atrial and Pulmonary Stretch Receptors
  80. What are Baroreceptors?
    Baroreceptors are stretch receptors located in walls of large arteries (carotid artery and aortic arch).

  81. What pressure do Baroreceptors function optimally in?
    Baroreceptors function optimally in the range of 60-180 mm Hg.
  82. How do baroreceptors work?
    If arterial pressure increases, stretching of baroreceptors causes vasodilation and decreases heart rate and contractility.

    If arterial pressure decreases, stretching of baroreceptors is reduced and therefore causes vasoconstriction and increases heart rate and contractility.

  83. What is the importance of Baroreceptors?
    Baroreceptors reflexes are important for rapid changes in BP and reducing variation in BP throughout the day.

    Baroreceptor reflexes are not important in long-term regulation because they reset in 1-2 days.
  84. What are Chemoreceptors?
    • Chemoreceptors are found in carotid bodies (a small "body" of tissue rich in capillaries) and aortic bodies and sense:
    • 1) a decrease in O2 content
    • 2) an increase in CO2 and H+ content.
  85. Compare chemoreceptors to barocreceptors.
    Chemoreceptors are similar to baroreceptors. However, chemoreceptors work at a much lower pressure than baroreceptors. Also, baroreceptors can increase or decrease BP, whereas chemoreceptors only function to increase BP.

    Chemoreceptors will regulate breathing, ventilation and respiration
    , but some information is also sent to increase blood pressure when a decrease in blood pressure is detected.
  86. What pressure do chemoreceptors function in?
    Chemoreceptors function at lower blood pressures (<80 mmHg)
  87. How do chemoreceptors work?
    If blood pressure decreases, blood flow decreases through chemoreceptors. They become stimulated and excite the vasomotor center resulting in increased blood pressure.
  88. What are atria and pulmonary artery stretch receptors?
    Atria and pulmonary artery contain stretch receptors that are low pressure receptors optimal for detecting changes in pressure in low pressure areas.
  89. What is another name for atria and pulmonary artery stretch receptors?
    Low pressure receptors
  90. What is the importance of atria and pulmonary artery stretch receptors?
    Atria and pulmonary artery stretch receptors are important in minimizing changes in pressure in response to volume changes.
  91. Give an example of receptors in action that send information to the vasomotor center.
    Example: if infuse 300 ml of blood into a dog, the blood pressure only rises ~15 mm Hg. However, if denervate baroreceptors, blood pressure rises 40 mm Hg. If denervate baroreceptors and low pressure receptors, blood pressure rises 100 mm Hg.
  92. Out of all the receptors, which are most important in the lives of healthy normal individuals?
    Baroreceptors
  93. What is the body sensitive to with all of the reflexes active?
    With all of the reflexes active, the body is sensitive to pressure changes in a full range of pressures.

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