1. The Heart’s External Anatomy & Conduction System

2. Atria (R & L) contract simultaneously
Heart at rest
Blood flows from large veins into atria
Passive flow from atria into ventricles
Atria (R & L) contract simultaneously
Blood forced into ventricles
Ventricles (R & L) contract simultaneously
Atrioventricular valves close  “lubb” sound
Blood forced into large arteries
Ventricles relax
Semilunar valves close  “dub” sound

3. Pericardium Membrane sac Surrounds the heart Protection Anchors
Contains serous fluid
HEART
Pericarditis
inflammation of the pericardium decreases serous fluid causing painful adhesions interfering with heart movements
A 2 layered bag the outer layer is called the fibrous pericardium and the serous pericardium
The fibrous pericardium anchors the heart to surrounding structures like the diaphragm and the sternum.
The serous pericardium secrets a fluid contained within the pericardium allows the heart to beat easily in a relatively frictionless environment
Pericarditis is when the pericardium becomes inflamed causing the layers of the sac to stick to each other and interfere with heart movemnts
Pericardium

4. Heart Wall
Epicardium (outside) – visceral layer of the serous pericardium.
Myocardium (muscle) – cardiac muscle layer forming the bulk of the heart.
Endocardium (within) – endothelial layer of the inner myocardial surface.
Remember “visera” means internal part of a structure or the organs
The bulk of the walls of the heart is the myocardium which consists of thick bundles of cardiac muscle twisted and whorled into ringlike arrangements. This is the layer that actually contracts
The endocardium is a thin membrane that lines the heart chambers.
Endocarditis is inflammation of this lining – what sorts of problem could this cause?

5. Cardiac Muscle Specialized muscle cells Involuntary Striated
Cushioned by endomysium
Joined by intercalated discs
Cardiac muscle cells are branching cells that are joined by special junctions called intercalated discs, this along with the spiral arrangement of the muscle bundles allow heart activity to be closely coordinated.
Why is it important the muscles of the heart be coordinated?
The cardiac muscle cells are set up to be fatique resistant by having large mitochondria and having the ability to burn both sugar and fat for energy
Cardiac cell metabolism
Areobic
Large mitochondria
Organic fuels: fatty acids & glucose
Fatigue resistance

6. Coronary Arteries Branch off aorta above aortic semilunar valve
Left coronary artery
supplies left atrium and left ventricle
Anterior interventricular artery
supplies both ventricles
Right coronary artery
supplies right ventricle
Posterior interventricular artery

7. Coronary Veins Collects wastes from cardiac muscle
Drains into a large sinus on posterior surface of heart called the coronary sinus
Coronary sinus empties into right atrium

8. The heart beats because of the spread of electrical impulses to the heart muscle, causing it to contract.

9. Cardiac Conduction System
Cardiac muscle tissue exhibits autorhythmicity = generates its own stimulation.
This is possible because of an internal cardiac conduction system which can initiate and distribute electrical impulses.

10. Cardiac Conduction System
Comprised of interconnected structures
Sinoatrial node
Atrioventricular node
Atrioventricular Bundle
Bundle Branches
Purkinje Fibres

11. Sinoatrial (SA) Node Natural Pacemaker Upper RA Neuromyocardial cells
Sympathetic & parasympathetic
Sympathetic ↑HR
Parasympathetic ↓HR

12. Atrioventricular (AV) Node
Junction of atria and ventricles
Spread of depolarisation - from atrial myocardium
Delay 0.15 seconds
Time atria to expel blood
Time for ventricular filling
Protection to ventricles
Less autonomic nervous control than SA node
Sympathetic ↑conduction time
Parasympathetic ↓conduction time
Atrioventricular
node

13. Linked to the nervous system
The cardiovascular center of the medulla oblongata connects to the SA & AV nodes directly via the vagus nerve (cranial nerve 10) as well as thru the spinal cord.
Sensory information is sent to the cardiac center of the medulla which can illicit a parasympathetic response directly or a sympathetic response thru the spinal cord/
Nervous control from the cardiovascular center in the medulla
Sympathetic impulses increase heart rate and force of contraction
parasympathetic impulses decrease heart rate.
Baroreceptors (pressure receptors) detect change in BP and send info to the cardiovascular center

14. Depolorization Depolarization begins in sinoatrial (SA) node
The heart is autorhythmic
Depolarization begins
in sinoatrial (SA) node
Spread through atrial myocardium
Results in myocardial contration of the atria
Delay in atrioventricular (AV) node
To the Bundle of His
AKA atrioventricular bundle
The heart is autorythmic – it can carry impulses

15. Depolorization Entire musculature depolarizes quickly
The heart is autorhythmic
Separates into 2 main
branches left & right
Located in the interventricular septum
Left bundle – antero-superior division
Right bundle – postero-inferior division
Bundle branches divide - small, dense network of conduction tissue called the Purkinje Fibers
Entire musculature depolarizes quickly

16. Electrocardiogram
Variations in electrical potential radiate from the heart
ECG records electrical events in the heart.

17. P wave QRS complex T wave P-Q interval Q-T interval
P-P = one cardiac cycle
P-Q = time for atrial depolarization
Q-T = time for ventricular depolarization
T-P = time for relaxation
P wave
Depolarization of atria
Followed by contraction
QRS complex
3 waves (Q, R, & S)
Depolarization of ventricles
T wave
Repolarization of ventricles
P-Q interval
Time atria depolarize & remain depolarized
Q-T interval
Time ventricles depolarize & remain depolarized

18. SA node Represented on the ECG as P wave
QRS
SA node Represented on the ECG as P wave
AV node conduction is represented on the ECG as the PR Interval
The Bundle Branch and purkinje fibre depolarisation constitutes ventricular depolarisation Represented on the ECG as the QRS
Atrial repolarisation occurs within the QRS & therefore is masked
Ventricular repolarisation is represented on the ECG as a T wave

19. 1) atrial depolarization begins 2) atrial depolarization
complete (atria contracted)
3) ventricles begin to
depolarize at apex;
atria repolarize (atria relaxed)
4) ventricular
depolarization complete
(ventricles contracted)
5) ventricles begin to repolarize at apex
6) ventricular repolarization complete (ventricles relaxed)