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General Schemaatic of HR Control. Regulation of Cardiac Cycle. Autonomic nerve impulses alter the activities of the S-A and A-V nodes. Overview of short-term control mechanisms. From: Introduction to Cardiovascular physiology. J.R. Levick. Arnold 4th edition (2003). Heart rate.
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Regulation of Cardiac Cycle Autonomic nerve impulses alter the activities of the S-A and A-V nodes
Overview of short-term control mechanisms From: Introduction to Cardiovascular physiology. J.R. Levick. Arnold 4th edition (2003)
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)
Heart rate • Several factorscontribute 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
Heart rate • Several other factorscontribute to regulation of heart rate: • Age • Gender • Female HR higher • Physical fitness • Resting bradycardia • Body temperature • Increase causes SA node to discharge more rapidly
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.
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.
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
Vasopressin • Enhances water retention • Causes vasoconstriction • Secretion increased by aortic baroreceptors and atrial sensors http://www.cvphysiology.com/Blood%20Pressure/BP016.htm
Aortic arch Carotid sinus Nucleus tractus solitarius Cardiac inhibition Vasoconstriction Cardiac stimulation Constriction of veins & arterioles Increased heart rate Increased stroke volume Increased peripheral resistance Increased cardiac output Baroreceptor reflex Blood pressure falls Sensors Neural integration Effectors Increased blood pressure