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Lab 3: The Mechanical and

Electrical Activity of the Heart

(A hodgepodge of the heart vol I


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Overview

Review of arteries and veins

Electrical signaling in the heart

Limb leads and the ECG

Mechanics of the heart

Unidirectional Flow

Mechanics of contractionPressure and volume changes in the heart

Arteries and veins in the cat


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Review-Exam in 2 weeks

Where is the Circle of Willis located?

Where is the popileatal artery?

The suprarenal vein collects blood from whichorgan?

The subclavian vein delivers deoxygenated bloodto which vein?


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Overview



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


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What causes contraction of an

individual muscle fiber?

1. Negativelycharged 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.


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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


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Electrical Conduction in the

Heart


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Electrocardiogram

Monitors the electrical signals in the heart byapplying electrodes to the skin.

Each pair of electrodes will reveal informationabout the electrical activity of a SPECIFIC part ofthe heart.

3 standard limb leads (bipolar) 3 augmented unipolar limb leads

6 chest leads


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3 Standard Limb Leads

Std I: right arm

left arm +

0 across the heart Std II: right arm

left leg +

45 across the heart

Std III: left arm

left leg +

90 across the heart


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3 Augmented Unipolar Limb

Leads

aVR: left arm& left leg

right arm +

aVL: right arm& left legleft arm +

aVF: right arm& left arm

left foot+

Measure directions between

45 and 90


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6 Chest Leads

Start at the sternum and go under the armpitaround the apex of the heart

3-D view of the heart


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Electrocardiogram

1.P wave: atria contracting

2.Atrial depolarization

complete

3.QRS wave: firing of AVvalve

4.Ventricular depolarization

complete5.T wave: ventricular

repolarization

6. Repolarization of ventricles

1

2

3

4

5

6


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EKGs


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Break for Dynamic Human


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Overview




Mechanics of the heartUnidirectional Flow


Pressure and volume changes in the heart

Arteries and veins in the cat


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Unidirectional flow

Blood must flow one

direction in the heart.

The directionality is

maintained by the

heart valves.

Bicuspid

Tricuspid

Pulmonary

Aortic


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Mechanics of heart contraction

The four chambers act

as 2:2

Both atria contracttogether, both

ventricles contract

together

The contraction iscontrolled by electrical

impulses in the heart.


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Pressure and Volume Changes in

the Heart Pressure (P) and Volume (V) are always moving

towards equilibrium

P1

V1

= P2

V2

In general, if P then V must

If the volume in your atrium is decreasing, how isthe volume in your ventricle changing?

Volume will be increasing


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Phases of the Cardiac Cycle

Ventricular filling: blood trickles into the atriumand ventricle from the vena cavas

Atrial Contraction

Isovolumetric Contraction: atria relax and theventricles begin to contract

Ventricular Ejection: Ventricles contract andblood moves into arteries

Isovolumetric Relaxation: Ventricles relax andexpand


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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


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Atrium AV

Valve

Ventricle SL Valve Arter

y

Ventricular

Filling

PL

V

Loose PL

V

Closed PH

V

AtrialContraction

PM

V Open PL

V Closed PH

V


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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

Vconstant

Closed PH

V


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Atrium AV Valve Vent. SL

Valve

Artery

VentricularFilling

PLV

Loose PLV

Closed PHV


V

Open PL

V

Closed PH

V

Isovolumetric

VentricularContraction

PL

V

Closed PM

V constant

Closed PH

V

Ventricular

Ejection

PL

V

Closed PH

V

Open PM

V


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Atriu

m

AV Valve Vent. SL

Valve

Artery

Ventricular

Filling

PL

V

Loose PL

V

Closed PH

V


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

IsovolumetricRelaxation

PLV

Closed PMVconstant

Closed PHV


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Overveiw




Valves of the heart

Unidirectional Flow


Pressure and volume changes in the heart

Arteries and veins in the cat and the human heart


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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

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