General Schemaatic of HR Control

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General Schemaatic of HR Control
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Regulation of Cardiac Cycle
Autonomic nerve impulses alter the activities of
the S-A and A-V nodes
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Overview of short-term control mechanisms
From Introduction to Cardiovascular physiology.
J.R. Levick. Arnold 4th edition (2003)
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Heart rate

• Autonomic regulation (medullary CV center)
  Receives input from higher brain centers and
  variety of sensory receptors
• Proprioceptors
• Chemoreceptors
• Baroreceptors
• Sympathetic output ?HR and contractility
• Parasympathetic impulses
• ? HR
• Little effect on contractility
• (does not innervate ventricular myocardium)

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Heart rate

• Several factors contribute to regulation of heart
  rate
• Chemical regulation
• Cardiac activity depressed by
• Hypoxia
• Acidosis
• Alkalosis
• Hormones
• Catecholamines and thyroid hormones increase HR
  and contractility
• Cations
• Alterations in balance of K, Na and Ca2 alter
  HR and contractility

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Heart rate

• Several other factors contribute to regulation of
  heart rate
• Age
• Gender
• Female HR higher
• Physical fitness
• Resting bradycardia
• Body temperature
• Increase causes SA node to discharge more rapidly

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PNS

• Vagus nerve (via ACh) ? HR by ? slow inflow of
  Na and Ca and by ? the subsequent outflow of
  potassium (K).
• Acts at SA and AV nodes.
• May treat SNS-driven heart attack by gagging or
  massage of carotid arteries ? activate vagal
  reflexes ? PNS counteracts SNS.

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The Cardiovascular Stress Response

• Get the heart to beat faster ? SNS tone, ? PNS
  tone
• Norepinephrine (NE) and epinephrine (Epi) ? slow
  inflow of Na and Ca ? increase rate of
  re-excitation in SA node.
• This ? Ca also increases contractility.
• SNS terminals also excite AV node and whole
  myocardium enhances contractility everywhere.

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Summary of long term BP control

• Cardiac output and BP depend on renal control of
  extra-cellular fluid volume via
• Pressure natriuresis, (increased renal
  filtration)
• Changes in
• Vasopressin
• Aldosterone
• Atrial natiuretic peptide

• All under the control of altered cardiovascular
  receptor signaling

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Vasopressin

• Enhances water retention
• Causes vasoconstriction
• Secretion increased by aortic baroreceptors and
  atrial sensors

http//www.cvphysiology.com/Blood20Pressure/BP016
.htm
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Baroreceptor reflex
Blood pressure falls
Sensors
Neural integration
Effectors
Increased blood pressure