Regulation of Heart Rate & Arterial Pressure

Question 1

What is the equation for blood pressure?

Answer 1

BP = CO x TPR

= (SV)(HR) x TPR

Question 2

According to Frank Starling, at a set afterload and inotropic state, increases in preload will cause what?

Answer 2

Increases in stroke volume within a physiological limit.

As increased ventricular filling (preload) causes the cardiac muscle to stretch more, it also increases the force of contraction. UNTIL preloads get too high and cause the sarcomere stretch to exceed optimal length.

Question 3

The heart rate is principally controlled by the ANS.

What happens if you give it atropine? What happens if you give it propanolol? What about both?

Answer 3

Propanolol inhibits sympathetic activity –> decreased HR

Atropine inhibits parasympathetic activity –> increased HR

Inhibiting both allows the heart rate reaches its intrinsic rate

Question 4

The heart responds more quickly (turn on or off) to sympathetic or parasympathetic stimulation?

Which one is more dominant?

Answer 4

Parasympathetic/vagal activity is faster AND dominant. It can block sympathetic activity, reducing the heart rate to below the intrinsic rate

Question 5

Increased sympathetic activity promotes increased contractility. What does this do the Frank Starling curve?

Answer 5

It increases the cardiac output, shifting the curve upwards.

Whereas, parasympathetic activity decreases CO and shifts it downwards.

Question 6

___ released from sympathetic nerve endings stimulates __ receptors to increase contractility.

___ released from vagus nerve terminals stimulates __ receptors to inhibit contractility.

Answer 6

Norepinephrine from sympathetic nerve terminals stimulates B₁-adrenergic receptors –> increase contractility

Ach from vagus nerve terminals stimulates M2 receptors to inhibit contractility

Question 7

How to sympathetic and parasympathetic fibers exhibit negative feedback on each ohter?

Answer 7

Sympathetic fibers release neuropeptide Y, which blocks nvagus nerve signaling

Ach release from the vagus nerve inhibits sympathetic nerve activity.

Question 8

Antidiuretic hormone (ADH) / Vasopressin

Answer 8

• Released by pituitary gland when
  
  • Low bp
  • Increased serum osmolarity
• Promotes
  
  • Water reabsorption by kidneys
  • Vasoconstriction

Question 9

Atrial natriuretic peptide (ANP)

Answer 9

• Released from atrial muscle cells in response to stretch
• Vasodilator to cause peeing

Question 10

Renin-Angiotensin II - Aldosterole System (RAAS)

Answer 10

• Low blood flow to the kidneys –> increase renin in blood
  
  1. Angiotensinogen –renin–>angiotensin I
  2. Ang I –ACE–> Ang II
• Angiotensin II effects:
  
  • Increase blood pressure
    
    • Increase sympathetic activity –> vasoconstriction
    • Vasoconstriction independent of sympathetics
  • Increase water retention
    
    • Increase aldosterone from adrenal cortex
    • Increase ADH/Vasopressin
    • Tubular reabsorption of Na,Cl
  • Excretion of K+

Question 11

baroreceptor reflex

Answer 11

Increased blood pressure stretches receptors in the aortic arch and carotid sinus to activate cardioregulatory and vasomotor centers in the medulla oblongata

–> decrease sympathetics, increase parasympathetics

–> lower HR and blood pressure

Question 12

Whats the first line of defense against low bp?

Answer 12

Baroreceptor reflex - it’s the fastest and tonically active

Sensitive within 60-175mmHg

Also, after a short period of time, it can reset the bp point it maintains

Question 13

Bainbridge (atrial) reflex

Answer 13

Responds to blood volume (central venous pressure)

Increase in central venous pressure activates atrial stretch receptors to increase sympathetic activity and decrease parasympathetic activity –> increase heart rate

At the same time but slower: ANP release + vasopressin decrease will cause peeing to restore normal blood volume.

Question 14

When is bainbridge reflex dominant? When is the baroreceptor reflex dominant?

Answer 14

Increase in central venous pressure (volume loading), the Bainbridge reflex is increases the heart rate

Drop in central venous pressure (volume depletion) inhibits the baroreceptor reflex so HR increases

Question 15

Chemoreceptor reflex

Answer 15

• Receptors in the carotid and aorta sense
  
  • increases in arterial CO₂
  • decreases in pH and O₂
• Drop in sympathetic activity, increased parasympathetic activity reducing cardiac output
• Increased respiratory rate & depth
  
  • The increased lung stretch & hypocapnia will then reverse the reflex to increase cardiac output

Question 16

Timing and range of baroreceptor, chemoreceptor, and RAAS activation

Answer 16

Baroreceptor is the fastest, then chemoreceptors, then RAAS later

Baroreceptor operates under physiological range of bp;whereas, chemoreceptor activation occurs at lower bps