Blood Clotting
1. idea that there is a cascade of events (leading to blood clotting) ;
2. thromboplastin (starting the cascade);
3. conversion of prothrombin into thrombin
4. Idea that {thromboplastin/thrombin} is an enzyme 5. Conversion of fibrinogen into fibrin;
6. Formation of mesh of {fibres/fibrin}
7. requirement of {calcium ions/ Ca2+ / vitamin K} ;
The Cardiac Cycle is made up of 3
Stages
1. Atrial systole
2. Ventricular systole
1. Atrial Systole
• Both the atrial walls contract
• Blood is forced through the atrio-ventricular valves into the ventricles
2.
2. Ventricular Systole
• The thick muscular walls of the ventricles contract from the bottom upwards increasing the pressure of the blood and forcing it out of the heart. Blood
rushes upwards into the aorta and pulmonary artery through the semi lunar valves.
3. Ventricular Diastole
• This is the stage where the ventricles relax.
• As the muscles relax, the pressure in the ventricles drops.
• The high pressure blood in the arteries would flow back into the ventricles, but the semi-lunar valves prevent this by snapping shut.
• Atrial Pressure - the major bump in the black
curve “a” indicates an increase in pressure –
this is when the atria
contract
• When pressure in the atria is greater than in the
ventricles the A/V valve opens. When the
pressure in the atria is lower than in the
ventricles the A/V valve closes.
Atrial Pressure Curve
Ventricular Pressure Curve
(colour over this curve in blue)
• Ventricular Pressure - increases a little when the atria
contract as blood is being forced into the ventricles (small bump).
• The pressure increases a great deal at the ventricles
• When pressure in the ventricles is greater than the aorta, the semi-lunar valves open.
• When the pressure in the ventricles is lower than the pulmonary artery and aorta, the semi-lunar valve
Ventricular Volume Curve
(colour over this curve in red)
• Ventricular volume increases to a
maximum
as
the atria contract forcing blood into the
ventricles.
• Ventricular volume decreases as blood is being
forced out by ventricles contracting.
• Ventricular volume increases when heart is in
Properties of the Heart
• The heart muscle is myogenic – it can beat by itself • The heart beat starts at the SAN (known as the
pacemaker)
1. The SAN sends out electrical impulses over the atria causing them to contract
2. The electrical impulse is picked up by a second node known as the AVN (atrioventricular node)
3. After a short delay the electrical impulse is passed down specialized conducting fibres known as the
bundles of His - in the wall (septum) between the left and right ventricles
•This short delay at the AVN is important as it allows
the blood time to flow from the atria into the
4. The bundles of His (or Purkinje fibres) take the excitation wave to the base of the ventricles
5. The excitation wave passed through the wall to the base of the ventricles causing them to contract.
•This ensures that the ventricles contract from the
Electrocardiograph
•How fast your heart is beating
•Whether the rhythm of your heartbeat is steady or irregular
An Electrocardiograph
• P wave – contraction of the atria
• QRS - complex – caused the contraction
(depolarization) of the ventricles
Electrocardiograph
• An electrocardiogram is a machine that
records the electrical activity of the heart.
• The heart muscle depolarises when it
contracts and repolarises (regains charge)
when it relaxes.
Tachycardia
• Exercise
• Anxiety, pain, fear • Hypotension
• Over active thyroid
Brachycardia – slow heart rate
• Normal finding in fit, athletic individuals • Drug effect e.g. beta blockers
• Hypothermia
Fibrilliation
• Fibrillation – a very irregular heart beat. The atria and ventricles lose their rhythmn and stop
contracting properly. It can result in chest pain and fainting and can also lead to a lack of pulse and
