The heart - Lecture

In the Mediastrinum

The Mediastrinum is is the area from the sternum to the vertebral column and between the lungs

Apex (means top part)- directed downwards and to the left

Base - directed upward and to the right

Anterior surface - under the sternum and ribs

Inferior surface - rests on the diaphragm

Left and Right border - faces the left and right lung

The heart sack

Dense irregular connective tissue membrane

Protects, anchors and prevents overstretching of the heart

Thin delicate membrane

• Made of 2 layers:
• Parietal layer - attached to the fibrous
• Visceral layer (epicardium) - attached to the wall of the heart

Pericardial Cavity with Pericardal Fluid between the Parietal and Visceral layers  - it is used for lubrication

Thin walled receivers of blood from the body and lungs that empty into the ventricles

Thick walled pumps of blood to lungs and body

Parietal layer of serous pericardium

1- Epicardium- visceral layer of serous pericardium

2- Myocardium - cardiac muscle layer is the bulk of the heart

3- Endocardium - chambers lining and valves cover

2

• 1- Contractile Cardiac Muscle
• It makes up of 99% of the muscle
• Make all the Myocardium muscle
• Produce contractions of the heart chambers

• 2- Auto-rhythmic Cardiac Muscles
• It makes up of 1% of the muscle cells
• Specialized muscle cells that are self-excitable like nerves
• Form the heart pacemaker
• Form the Conduction System through the heart muscles

• Striated
• Branched
• Intercalated Discs
• Involuntary
• Aerobic

Heartbeat is Intrinsic (internal) because it has its own pacemaker that starts each beat

It is the pacemaker that starts each heartbeat by spontaneously depolarizing at the speed of the heart rate producing the normal sinus rhythm.

Resulting action potential (cardiac impulse or signal) spreads through the conduction system into the contractile cardiac muscle cells

• 1- Sinoatrial (SA) Node - Pacemaker
• Automatically depolarizes and produce the cardiac impulse

• 2- Atrioventricular (AV) Node
• Receives electrical impulse from SA node, delays it for a very short time then sends it into the atrioventicular bundle.

3- AV Bundle (of His) receives signal from AV node

• 4- Right and left Bundle Branches
• Formed by division of AV bundle
• Send signal to each ventricle

5- Purkinje Fibers spread signal throughout ventricles

In the Atrioventricular (AV) Node

P wave - atrial deploarization

• QRS complex - ventricular depolarization
• (the bigger the heart the bigger the QRS wave)
• T wave - ventricular re-polarization

P-Q interval - time for the signal to travel from SA node to AV bundle

• Q-T interval - time for both ventricular depolarization and re-polarization
• (problems with the purkinje fibers or muscle fibers)

Each impulse produces one cycle by depolarization and repolarization of the heart muscle producing

Systole - Heart muscles contraction phase

Diastole - Heart muscles relaxation phase

Is the amount of blood ejected by the heart in one minute

The amount of blood ejected by the heart in each beat. (S.V.)

Number of heart beats in one minute (H.R.)

Cardiac output = (S.V.) x (H.R.)

End Diastolic Volume

Amount of blood in the Ventricles at the end of the Diastole phase

Preload increases, stroke volume increases

Diastolic Blood Pressure in the Aorta and the Pulmonary Trunk

Afterload decreases, stroke volume decreases

Contraction force of the cardiac contractile muscles

Neutral control is done by the Cardiac Centers in the Brain

Acceleratory - Sympathetic Impulss

Nor-epinephrine - increases heart rate

Acetylcholine  - decreases heart rate

A heart rate above 100 beats/min.

A heart rate below 60 beats/min.

A means none

Cardiac standstill, no contraction

Narrowing of the coronary arteries

Decreased blood flow to the tissues

Inflammation of the pericardium

Chest pain due to heart problem

Loss of living heart muscle cells

Thickening of the arterial walls

hardening of arteries

Irregularity of heart rhythm

Reduced ability of the heart to pump blood