Heart Rate Regulation PDF

Heart rate and its regulation Dr. Ghada Elgarawany Assistant Professor of Medical Physiology * www.gmu.ac.ae COLLEGE OF MEDICINE Rules before lectures Review Question Effect of sympathetic stimulation on the heart is ………………………………….. Effect of parasympathetic stimulation on the heart is ………………………………...

Heart rate and its regulation Dr. Ghada Elgarawany Assistant Professor of Medical Physiology * www.gmu.ac.ae COLLEGE OF MEDICINE Rules before lectures Review Question Effect of sympathetic stimulation on the heart is ………………………………….. Effect of parasympathetic stimulation on the heart is ……………………………… Define heart rate. Enumerates the physiological variation of heart rate. List the factor regulating of heart rate. Describe nervous, chemical and physical regulation of heart rate Heart rate Definition: It is the number of heart beats per minute. Normal range: (60-100), average 70 beat/minute Tachycardia = Excess heart rate above 100 beat/minute Bradycardia = decreased heart rate below 60 beat/minute Methods of counting???? Physiological variations of heart rate 1. Age Heart rate is infant average 120/min and decrease to 70 /min at 20 years 2. Sex : Female> male due to less vagal tone 3. Sleep : decreases heart rate 4. Athlete: < 60/min because their heart is stronger and more efficient. 5. Emotions & Exercise: increase heart rate Heart Rate The heart rate is determined by the rate of S.A. nodal discharge. SA nodal discharge is controlled primarily by the autonomic nervous system:  The parasympathetic through vagus nerves decrease the SA nodal discharge and decrease the HR “bradycardia” (vagal tone)  Sympathetic nerves increase the SA nodal discharge and increase the HR. (tachycardia). UNDER RESTINT CONDITIONS, THE VAGAL TONE PREDOMINATES. Regulation of heart rate Nervous Chemical Physical Nervous regulation A- Impulses from higher centers B- Impulses from right side of heart C- Impulses from baroreceptor D- Impulses from other part of body A- Impulses from higher centers 1. Cerebral cortex: Conditional reflex Emotion Voluntary 2. Hypothalamus Anterior hypothalamus stimulates CIC→ bradycardia Posterior hypothalamus stimulates CAC → tachycardia 3. Respiratory center Inspiration (deep) increase HR while expiration (deep) decrease HR (Respiratory sinus arrythmia) B- Impulses from right side of the heart 1. Bainbridge reflex: (indirect) ↑Venous return → ↑ right atrial pressure → stimulation of atrial stretch receptor → ↑ cardiac filling → ↑ Heart rate 2. Bainbridge effect: (increased heart rate due to direct stretch of S.A Node) McDowal's reflex ↓ venous return (as in decreased Arterial blood pressure ) → ↑ heart rate C- Impulses from Baroreceptors  Arterial baroreceptors are stretch receptors present in carotid sinus and aortic arch. Increase ABP →↑discharge of baroreceptors → 1- Stimulation of Cardiac inhibitory center (CIC) → ↑ vagal stimulation → decrease heart rate.  Marey’s Law = Heart rate α 𝟏 𝑨𝒓𝒕𝒆𝒓𝒊𝒂𝒍 𝑩𝒍𝒐𝒐𝒅 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆  Carotid sinus syndrome: Stimulation of carotid sinus (baroreceptors) lead to bradycardia. D- Impulses from other part of body  Oculo-cardiac reflex: Applying pressure on the eyeball → bradycardia.  Visceral pain → bradycardia.  Alam-Smirk reflex: voluntary contraction of the of the skeletal muscle → tachycardia. Chemical regulation Drugs Blood gases Hypoxia (low O2): Hormones mild & moderate → tachycardia Noradrenaline and Sever : bradycardia Adrenaline → tachycardia Hypercapnia (increased CO2): Thyroxine: tachycardia Moderate → tachycardia. Sever : bradycardia Atropine & sympathomimetic: tachycardia Bile salt, morphine &parasympathetic→bradycar dia Physical regulation Increased body temperature ( Fever) →Tachycardia ( 1◦C increases H.R by 10-13 b/m) Decreased body temperature → bradycardia Exposure to cold??? Summary Define heart rate. Enumerates the physiological variation of heart rate. List the factor regulating of heart rate. Describe nervous, chemical and physical regulation of heart rate