Lab 3: The Mechanical and Electrical Activity of the Heart (A hodgepodge of the heart vol I

Overview Review of arteries and veins Electrical signaling in the heart –Limb leads and the ECG Mechanics of the heart –Unidirectional Flow –Mechanics of contraction –Pressure and volume changes in the heart Arteries and veins in the cat

Review-Exam in 2 weeks Where is the Circle of Willis located? Where is the popileatal artery? The suprarenal vein collects blood from which organ? The subclavian vein delivers deoxygenated blood to which vein?

Overview Review of arteries and veins Electrical signaling in the heart –Limb leads and the ECG Mechanics of the heart –Unidirectional Flow –Mechanics of contraction –Pressure and volume changes in the heart Arteries and veins in the cat

What causes contraction of an individual muscle fiber? 1. Negatively charged cell in its resting state. 2. Ca ++ gates are closed. Electrical Impulse Depolarization 1. Positively charged cell generates action potential 2. Ca ++ gates are opened providing the Ca ++ required for actin and myosin filaments to contract.

SA node (Pacemaker) Left and Right Atrium AV node (prevents signals from entering to the ventricles via another route) AV bundles (intraventricular septum) Purkinje fibers Ventricles

Electrical Conduction in the Heart

Electrocardiogram Monitors the electrical signals in the heart by applying electrodes to the skin. Each pair of electrodes will reveal information about the electrical activity of a SPECIFIC part of the heart. –3 standard limb leads (bipolar) –3 augmented unipolar limb leads –6 chest leads

3 Standard Limb Leads Std I: right arm  left arm + 0º across the heart Std II: right arm  left leg + 45º across the heart Std III: left arm  left leg + 90º across the heart

3 Augmented Unipolar Limb Leads aVR: left arm – & left leg – right arm + aVL: right arm – & left leg – left arm + aVF: right arm – & left arm – left foot+ Measure directions between 45º and 90º

6 Chest Leads Start at the sternum and go under the armpit around the apex of the heart 3-D view of the heart

Electrocardiogram 1.P wave: atria contracting 2.Atrial depolarization complete 3.QRS wave: firing of AV valve 4.Ventricular depolarization complete 5.T wave: ventricular repolarization 6. Repolarization of ventricles

EKGs

Break for Dynamic Human

Overview Review of arteries and veins Electrical signaling in the heart –Limb leads and the ECG Mechanics of the heart –Unidirectional Flow –Mechanics of contraction –Pressure and volume changes in the heart Arteries and veins in the cat

Unidirectional flow Blood must flow one direction in the heart. The directionality is maintained by the heart valves. –Bicuspid –Tricuspid –Pulmonary –Aortic

Mechanics of heart contraction The four chambers act as 2:2 –Both atria contract together, both ventricles contract together The contraction is controlled by electrical impulses in the heart.

Pressure and Volume Changes in the Heart Pressure (P) and Volume (V) are always moving towards equilibrium –P 1 V 1 = P 2 V 2 In general, if P  then V must  If the volume in your atrium is decreasing, how is the volume in your ventricle changing? –Volume will be increasing

Phases of the Cardiac Cycle Ventricular filling: blood trickles into the atrium and ventricle from the vena cava’s Atrial Contraction Isovolumetric Contraction: atria relax and the ventricles begin to contract Ventricular Ejection: Ventricles contract and blood moves into arteries Isovolumetric Relaxation: Ventricles relax and expand

Pressure and Volume Changes in the Cardiac Cycle V= volume P L = Low pressure P M = Medium pressure P H = High pressure AtriumAV Valve VentricleSL Valve Artery Ventricular Filling P L V  Loose P L V  Closed P H V 

AtriumAV Valve VentricleSL ValveArter y Ventricular Filling P L V  LooseP L V  ClosedP H V  Atrial Contraction P M V  OpenP L V  ClosedP H V 

AtriumAV ValveVent.SL Valve Artery Ventricular Filling P L V  LooseP L V  ClosedP H V  Atrial ContractionP M V  OpenP L V  ClosedP H V  Isovolumetric Ventricular Contraction P L V  ClosedP M V constant ClosedP H V 

AtriumAV ValveVent.SL Valve Artery Ventricular Filling P L V  LooseP L V  ClosedP H V  Atrial ContractionP M V  OpenP L V  ClosedP H V  Isovolumetric Ventricular Contraction P L V  ClosedP M V constant ClosedP H V  Ventricular Ejection P L V  ClosedP H V  OpenP M V 

Atriu m AV ValveVent.SL Valve Artery Ventricular Filling P L V  LooseP L V  ClosedP H V  Atrial ContractionP M V  OpenP L V  ClosedP H V  Isovolumetric Ventricular Contraction P L V  ClosedP M V constant ClosedP H V  Ventricular Ejection P L V  ClosedP H V  OpenP M V  Isovolumetric Relaxation P L V  ClosedP M V constant ClosedP H V 

Overveiw Review of arteries and veins Electrical signaling in the heart –Limb leads and the ECG Valves of the heart –Unidirectional Flow –Mechanics of contraction –Pressure and volume changes in the heart Arteries and veins in the cat and the human heart

Cat Dissection Artery –Aortic Arch –Left Common Carotoid –Descending Aorta –Renal Artery –Superior Mesenteric Artery Veins –Branchiocephalic –Subclavian –External Jugular –Inferior Vena Cava –Renal Vein –Great Saphenous –Femoral –Deep Femoral –Popliteal