L13 - Physiology of circulation

• What is the volume of blood flowing through a vessel called?

  Blood flow
• What does total blood flow equal?

  Cardiac output (CO)
• What is blood pressure measured in?

  mmHg
• From where to where does blood flow based on pressure gradient?

  From high pressure to low pressure
• What is resistance in the cardiovascular system related to?

  Blood viscosity, vessel length, vessel diameter
• What does the equation ΔP = Pin – Pout represent?

  The pressure gradient in blood flow
• How does blood viscosity affect resistance?

  Resistance increases with higher viscosity
• What primarily affects blood viscosity?

  RBC number and plasma protein concentration
• How does vessel length relate to resistance?

  Resistance increases with longer vessel length
• What is the main determinant of resistance in blood vessels?

  Vessel diameter (radius)
• What happens to resistance if the radius of a vessel decreases?

  Resistance increases significantly
• What factors affect blood flow in vessels?

  • Pressure gradient (ΔP)
  • Resistance (R)
  • Blood viscosity
  • Vessel length
  • Vessel diameter
• Where is systemic blood pressure highest?

  In the aorta
• What happens to blood pressure as blood flows through the circulatory system?

  It declines until reaching 0 mmHg
• What is systolic pressure?

  Maximum arterial pressure during contraction
• What is diastolic pressure?

  Minimum arterial pressure during relaxation
• What is mean arterial pressure (MAP)?

  Pressure propelling blood to tissues
• How is MAP calculated?

  MAP = $\frac{2}{3} P_{diastolic} +$$\frac{1}{3} P_{systolic}$
• What is capillary blood pressure range?

  35 to 16 mmHg
• Why is capillary blood pressure low?

  To protect capillaries from rupture
• How does venous blood pressure compare to arterial blood pressure?

  Venous blood pressure is low and not pulsatile
• What are the mechanisms for controlling blood pressure?

  • Acute mechanisms (neural)
  • Chronic mechanisms (hormonal)
  • Peripheral resistance
  • Cardiac output
  • Blood volume
• What does cardiac output (CO) equal?

  CO = SV × HR
• What affects stroke volume (SV)?

  Blood volume also affects stroke volume
• What is total peripheral resistance (TPR)?

  Resistance for the systemic circuit
• What primarily affects TPR?

  Arteriole diameter
• What is the role of baroreceptors?

  They respond to changes in blood pressure
• Where are baroreceptors located?

  In carotid sinus and aorta
• What is the baroreflex?

  A negative feedback loop regulating BP
• How does the sympathetic nervous system affect heart rate?

  It increases heart rate and stroke volume
• What does the renin-angiotensin-aldosterone system do?

  It regulates blood volume and pressure
• What does atrial natriuretic peptide (ANP) do?

  It decreases blood volume and pressure
• What are the control mechanisms for regional circulation?

  • Intrinsic (local) mechanisms
  • Extrinsic (neural/hormonal) mechanisms
  • Act on arterioles and pre-capillary sphincters
• What do metabolically active tissues produce to increase blood flow?

  Metabolites that stimulate vasodilation
• What local factors can stimulate vasodilation?

  Compounds like nitric oxide and histamine
• What happens to arterial blood pressure (BP) when it decreases?

  Baroreceptor firing decreases
• What is the relationship between arterial BP and baroreceptor firing?

  Decreased BP leads to decreased baroreceptor firing
• What does MAP stand for in blood pressure control?

  Mean Arterial Pressure
• How is MAP calculated?

  MAP = CO × TPR
• What does CO represent in the MAP equation?

  Cardiac Output