regulation of blood flow

• What is the driving force of tissue perfusion?

  Arterial blood pressure
• What happens if blood pressure is too low?

  Brain blood flow and kidney filtration fall
• What occurs if blood pressure is too high?

  Pathological damage occurs in many tissues
• What is the formula for mean arterial pressure (MAP)?

  MAP = CO x TPR
• How can blood pressure be varied?

  By varying cardiac output or resistance
• How is blood flow analogous to electrical current?

  Blood flow follows Ohm's law principles
• What does Ohm's law state?

  V = IR
• What is the pressure gradient equation in blood flow?

  ΔP = flow (Q) x resistance (R)
• What does Darcy's law state about flow?

  Q = ΔP ÷ R
• How does flow vary with pressure gradient and resistance?

  Proportional to pressure gradient, inversely to resistance
• What is the baroreceptor reflex responsible for?

  Short-term control of blood pressure
• Where are baroreceptors located?

  In the walls of the aortic arch and carotid sinus

  
• What are the central relays in the baroreceptor reflex?

  Cardiovascular centres in the brain stem
• What happens when blood pressure drops?

  Less stretch of arteries decreases baroreceptor firing
• What is the effect of decreased baroreceptor firing?

  Decreased vagal outflow, increased sympathetic outflow
• What leads to increased vascular tone?

  Increased sympathetic nervous system activity
• What is the result of increased cardiac output and total peripheral resistance?

  Increase in mean arterial blood pressure
• How long does the baroreceptor reflex last?

  About 1-2 days before resetting
• What is involved in long-term blood pressure regulation?

  Fluid regulation and the renin-angiotensin system
• What defines hypertension?

  Systolic >140 mmHg or diastolic >90 mmHg
• What is Grade II hypertension?

  Over 160/100 mmHg
• What should be done if "white-coat hypertension" is suspected?

  Record 24-hour ambulatory pressures
• What are the main components of systemic pressures and blood pressure control?

  • Systemic and pulmonary pressure
  • Baroreceptor reflex
  • Hypertension
• What are the intrinsic and extrinsic responses in vascular tone regulation?

  Intrinsic responses:

  1. Mechanical stimuli (stretch and shear)
  2. Endothelial regulation and metabolites

  Extrinsic responses:

  1. Systemic regulation (nerves & hormones)
• What is vascular tone?

  The constriction applied across vessels
• What happens to arteries at rest?

  They are slightly constricted
• What is the effect of constriction on blood flow?

  Decreases radius, increases resistance, decreases flow
• What is the effect of dilatation on blood flow?

  Increases radius, decreases resistance, increases flow
• What is arterial tone a balance of?

  Constrictors and dilators acting on smooth muscle
• What is the distribution of cardiac output and oxygen consumption in tissues?

  • Liver/GI: 25% CO, 30% O2
  • Kidney: 20% CO, 20% O2
  • Skeletal Muscle: 20% CO, 20% O2
  • Brain: 13% CO, 18% O2
  • Other: 10% CO, 14% O2
  • Heart: 4% CO, 2% O2
• How does vascular tone respond to factors?

  It responds to intrinsic and extrinsic factors
• What is the myogenic response in smooth muscle?

  Smooth muscle constricts when stretched
• What contributes to the basal tone of arteries?

  Myogenic response stabilizes flow and prevents excessive perfusion
• What role does the vascular endothelium play?

  Releases paracrine factors affecting smooth muscle
• What are some vasodilators released by the endothelium?

  Nitric oxide (NO) and prostacyclin (PGI2)
• What are some vasoconstrictors released by the endothelium?

  Endothelins (ET), Ang II, and thromboxane (TxA2)
• What is nitric oxide (NO) produced by?

  Nitric oxide synthase (NOS) enzymes
• What are the effects of nitric oxide (NO)?

  Vasodilator, anti-thrombogenic, anti-atherogenic
• What increases nitric oxide production?

  Shear stress and agents like ACh, histamine
• What happens with an unhealthy endothelium?

  Endothelial dysfunction leads to atherosclerosis