Awatif B. Al-Backer Function of the nerve innervations in the heart (Sympathetic or Parasympathetic): Alteration of the basic rhythm of the heart
Conduction in heart
Heart Properties Heart Properties “Heart muscle is syncitium” Contractility Automaticity Rhythmicity Conductivity Excitability
Conduction of impulses in the heart Heart conduction Heart conduction
ANS supply of heart SympatheticParasympathetic Receptorb1M2 TransmitterAdrenalineAch Synthetic agonistIsoprenalineMethacholine Effect +ve inotropic, +ve chronotropic -ve inotropic & -ve chronotropic MOA + Gs protein→ + adenylyl cyclase→↑ cAMP→↑ calcium →contraction + Gi protein→ - adenylyl cyclase→↓cAMP→↑K & ↓calcium →hyperpolarization Blocker Propranolol “non-selective” Esmolol, Atenolol “selective” Atropine N.B. -Isoprenaline is more potent than adrenaline on the isolated heart -Atropine can cause bradycardia followed by tachycardia
Other agents that influence the heart function 1. Histamine: Receptor: H2 MOA: ↑ cAMP →↑calcium → contraction Antagonist : Ranitidine & Cimitidine Action: + ve inotropic & + ve chronotropic Note: H2R in the stomach & the heart while H1R present all over the body.
Continue 2. Methylxanthines: Examples: Theophylline, Caffeine & Theobromine MOA: 1- Phosphodiesterase enz. Inhibitors. 2- Inhibition of adenosine receptors Action: + ve inotropic & + ve chronotropic
3. Serotonin:- Receptors: 5HT2 Example: Serotonin MOA: Bind to 5HT2 leading to increase cAMP & increase Ca. Blocker: Ketanserine Action: + ve inotropic & + ve chronotropic Continue
Direct acting drug Direct acting stimulant: E.g. calcium chloride (Cacl2) Direct acting depressant: E.g. potassium chloride (Kcl)
Experiment N Isoprenaline Propranolol Isoprenaline N Dil. nicotine Conc.nicotine Dil. nicotine N Ach Atropine Ach N Cacl 2 N Kcl Color key: Agonist Antagonist Normal N
CONCLUSION The receptors on the heart are: 1. Stimulatory: B1, H1, & 5HT2 2. Inhibitory: M2, & Nn
Determination of heart rate Example: * Speed= 1square/sec, * Number of beat/sq=6 beats/square Calculate the HR (beat per minute)? 6 beats 1 sec. x 60 sec x = 60*6 = 360 BPM