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 contracting2.Atrial depolarization complete3.QRS wave: firing of AV valve4.Ventricular depolarization complete5.T wave: ventricular repolarization6. Repolarization of ventricles

1

2

3

4

5

6

•

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– P1V1= P2V2

• 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

• PL= Low pressure

• PM= Medium pressure

• PH= High pressure

Atrium AV Valve

Ventricle SL Valve

Artery

Ventricular

Filling PL

V

Loose PL

V

Closed PH

V

Atrium AV Valve

Ventricle SL Valve

Artery

Ventricular

Filling

PL

V

Loose PL

V

Closed PH

V

Atrial Contraction

PM

V

Open PL

V

Closed PH

V

Atrium AV Valve

Vent. SL

Valve

Artery

Ventricular

Filling

PL

V

Loose PL

V

Closed PH

V

Atrial Contraction PM

V

Open PL

V

Closed PH

V

Isovolumetric

Ventricular Contraction

PL

V

Closed PM

V constant

Closed PH

V

Atrium AV Valve

Vent. SL

Valve

Artery

Ventricular

Filling

PL

V

Loose PL

V

Closed PH

V

Atrial Contraction PM

V

Open PL

V

Closed PH

V

Isovolumetric

Ventricular Contraction

PL

V

Closed PM

V constant

Closed PH

V

Ventricular

Ejection PL

V

Closed PH

V

Open PM

V

Atrium

AV Valve

Vent. SL

Valve

Artery

Ventricular

Filling

PL

V

Loose PL

V

Closed PH

V

Atrial Contraction PM

V

Open PL

V

Closed PH

V

Isovolumetric

Ventricular Contraction

PL

V

Closed PM

V constant

Closed PH

V

Ventricular

Ejection

PL

V

Closed PH

V

Open PM

V

Isovolumetric

RelaxationPL

V

Closed PM

V constant

Closed PH

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