07: Blood Pressure Regulation

Question 1

Outline the sequelae of hypertension.

Answer 1

Question 2

What is blood pressure and what are its factors?

Answer 2

Blood pressure is the outward pressure of blood against vessel walls.

Product of blood flow from the heart and inward resistance of blood vessel walls.

Question 3

How do you calculate blood pressure?

Answer 3

BP = CO x TPR

CO = SV x HR

Question 4

What factors regulate cardiac output?

Answer 4

• Filling pressure (volume)
  
  • Sodium retention
• Heart rate
  
  • Sympathetic = ↑
  • Parasympathetic (vagus) = ↓
• Force of contraction
  
  • Sympathetic = ↑

Question 5

What factors regulate vascular resistance?

Answer 5

• Vasoconstriction
  
  • Norepinephrine ↑
  • Angiotensin ↑
  • Nitric oxide ↓
• Structural changes
  
  • Vascular remodeling/hypertrophy

Question 6

What two major systems regulate blood pressure, and how?

Answer 6

1. Autonomic Nervous System (ANS)
   
   • ​​Via brain, sympathetic nerves, adrenal glands
   • ↑CO & TPR
   • ↑renin release from kidneys (promotes angiotensin –> ↑BP)
   • Feedback loop via baroreceptors
2. Renin-Angiotensin-Aldosterone System (RAAS)
   
   • ​​Via kidney, blood stream, adrenal glands
   • ↑Na⁺ and H₂O retention and TPR
   • Feedback loop in kidneys

Question 7

Outline the baroreceptor reflex to increased arterial pressure.

Answer 7

Question 8

How are catecholamines synthesized, where are they released from, and what is their role in blood pressure regulation?

Answer 8

• Dopa (in sympathetic nerve terminal) –> dopamine –> **norepinephrine **(released by sympathetic nerves) –> epinephrine (released by adrenal glands)
• ↑sympathetic response (vasoconstriction, ↑HR)

Question 9

Describe the synthesis of angiotensin II.

Answer 9

• **Prorenin **(from juxtaglomerular cells) converted into renin and secreted from kidney into blood.
• Renin converts angiotensinogen (secreted by liver) into angiotensin I.
• Angiotensin-converting enzyme (ACE) (found in lungs, kidney) converts angiotensin I into angiotensin II.

Question 10

Describe the role of angiotensin II

Answer 10

• Adrenal cortex:
  
  • Stimulate synthesis/secretion of aldosterone
  • Aldosterone acts on **renal distal tubule **and collecting duct
  • ↑Na⁺reabsorption into blood (↑ECF volume and blood volume –> ↑CO)
• Arterioles: vasoconstriction (↑TPR)
• Kidney: stimulates Na⁺-H⁺ exchange in renal proximal tubule and ↑Na⁺ & HCO₃^- reabsorption (↑CO)
• Hypothalamus:
  
  • ↑Thirst, water intake
  • Stimulates antidiuretic hormone (ADH) (increase water reabsorption in collecting ducts –> ↑CO; causes vasoconstriction –> ↑TPR)
• Heart:
  
  • ↑contractility, ventricular hypertrophy

NB: To fulfill actions, must acto on AT₁ subtype receptors.

Question 11

What stimulates renin secretion?

Answer 11

• Decreased renal perfusion (sensed by mechanoreceptors)
• Decreased sodium
• Sympathetic activation

Question 12

Outline the RAAS response to a decrease in arterial pressure.

Answer 12

Question 13

Other than the ANS and RAAS pathways, what mechanisms regulate blood pressure?

Answer 13

1. Chemoreceptors in carotid and aortic bodies
   
   • Sense ↓ PO2, ↑CO2
   • Sense ↓pH
   • Affect sympathetic vascoconstrictor centers
2. Central (medullary) chemoreceptors
   
   • Sense changes in PCO2 or pH
   • Affect outflow of medullary brain centers
3. Antidiuretic hormone
   
   • Stimulated by angiotensin II, increases in serum osmolarity
   • From posterior lobe of pituitary gland
   • **V1 receptors **(vascular smooth muscle)
     
     • Vasoconstriction (↑TPR)
   • V2 receptors (renal collecting ducts)
     
     • ↑water reabsorption
4. Cardiopulmonary (low-pressure) baroreceptors
   
   • Respondd to increased pressure in veins, atria, and pulmonary artery
   • ↑blood volume –> ↑venous/atrial pressure –> baroreceptor activation
     
     • ↑atrial natriuretic peptide (ANP) secretion –> relax smooth muscle –> vasodilation and ↓TPR; vasodilation of kidney –> ↑Na & H2O excretion
     • ↓ADHB
     • Renal vasodilation (via inhibition of sympathetic vasoconstriction in renal arterioles)
     • Increased heart rate
       
       • Info from atrial receptors –> vagus nerve –> nucleus tractus solitarius
       • Bainbridge reflex: ↑CO –> increased renal perfusion –> ↑Na+ & H2O excretion

Question 14

What pathologies cause hypertension?

Answer 14

• CNS
  
  • ↑basal sympathetic tone
  • Abnormal stress response
  • Abnormal response to signals from baroreceptors
• Pressure/volume receptors
  
  • Desensitization
• Kidney
  
  • ​RAA dysfunction
  • Ion channel defects
• Adrenal
  
  • Catecholamine leak or malregulation
• Blood vessel
  
  • ​Functional
    
    • ↑Endothelin production (vasoconstrictors)
    • ↓NO secretion
    • Channel defects
    • Hyperresponsiveness to catecholamines
  • Structural
    
    • Exaggerated medial hypertrophy