Download 241L3

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?
Electrical
Impulse
Depolarization
1. Negatively
charged cell in its
resting state.
2. Ca++ gates are
closed.
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
1
3.QRS wave: firing of AV
valve
4.Ventricular depolarization
complete
5.T wave: ventricular
repolarization
6. Repolarization of ventricles
3
5
6
2
4
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
Atrium AV
Valve
Ventricular PL
Filling
Loose
Ventricle SL
Valve
PL
V
V
•
•
•
•
V= volume
PL= Low pressure
PM= Medium pressure
PH= High pressure
Artery
Closed PH
V
Atrium AV
Ventricle SL Valve Arter
Valve
y
Ventricular
Filling
PL
V
Atrial
PM
Contraction
V
Loose
PL
V
Open PL
V
Closed
PH
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 PL
Ventricular
V
Contraction
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
Atriu
m
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
Relaxation
PL
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