The Cardiac Cycle
- Created by: Lois
- Created on: 12-12-12 11:56
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- The Cardiac Cycle
- Definition:the sequence of events in one heartbeat
- Three phases in the sequence of contraction
- 1) Filling phase - atria and ventricles are relaxing, internal volume increases and blood flows into the heart.
- Into the atria, through the open atroventricular valves and into the ventricles. This is callled diastole.
- 1) Filling phase - atria and ventricles are relaxing, internal volume increases and blood flows into the heart.
- The sinoatrial node (SAN) is the heart's pacemaker. It is a small patch of tissue that sends out waves
- of electrical excitation at regular intervals to initiate contractions.
- Purkyne tissue is specially adapted muscle fibres that conduct the wave of excitation from the AVN down the septum to the ventricles.
- The need for coordination
- Cardiac muscle initiates its own contraction. So is described as myogenic. The muscle will contract and relax rhythmically.
- The muscles from the atria and the ventricles each have they're own natural frequency of contraction.
- The atrial muscle tends to contract at a higher freguency than the ventricular muscle.
- This property of the muscle could cause innefficient puping (fibrillation) if the contractions of the chambers are not synchronised.
- So the heart needs a mechabism that can coordinate the contractions of all four chambers.
- This property of the muscle could cause innefficient puping (fibrillation) if the contractions of the chambers are not synchronised.
- The atrial muscle tends to contract at a higher freguency than the ventricular muscle.
- The muscles from the atria and the ventricles each have they're own natural frequency of contraction.
- Cardiac muscle initiates its own contraction. So is described as myogenic. The muscle will contract and relax rhythmically.
- How the heart starts
- At the top of the right atrium, near the point where the vena cava enpties blood into tge atrium is the sinoatrial node (SAN).
- This samll patch of tissue generates electrical activity.
- The SAN initiates a wave of excitation at regukar intervals.
- Ib a human, this occur approximately 55-80 times a minute.
- The SAN initiates a wave of excitation at regukar intervals.
- This samll patch of tissue generates electrical activity.
- At the top of the right atrium, near the point where the vena cava enpties blood into tge atrium is the sinoatrial node (SAN).
- Contraction of the atria
- The wave of excitations quickly spreads over the walls of both atria.
- It travels along th membranes of the msucle tissue. As the wave of excitation passes,
- it causes the cariac muscle cells to contract. This is atrial systole.
- It travels along th membranes of the msucle tissue. As the wave of excitation passes,
- At the base of the atria is a disc of tissue thar cannot conduct the wave of excitation.
- So the excitation cannot spread directly to the ventricle walls.
- At the top of the inter-ventricular septum is another node - the atrioventricular node (AVN).
- This is the only route through the disc of non-conducting tissue. The wave of excitation is delayed in the node.
- This allows time for the atria to finish contracting and for the blood to flow down the ventricles before they begin to contract.
- This is the only route through the disc of non-conducting tissue. The wave of excitation is delayed in the node.
- At the top of the inter-ventricular septum is another node - the atrioventricular node (AVN).
- So the excitation cannot spread directly to the ventricle walls.
- The wave of excitations quickly spreads over the walls of both atria.
- Contraction of the ventricles
- After this delay, the wave of excitation is carried awway from the AVN and dpwm specialised conducting tissue.
- This is the Purkyne tissue and it runs down the inter-ventricukar septum.
- At the base of the septum, the wave of excitation spreads out over the walls of the ventricles.
- As the excitation spreads upwards from the base (apex) of the ventricles, it causes the muscles to contract.
- This means that the ventricles contract from the base upwards, pushing blood u[p to the major arteries at the top of the heart.
- As the excitation spreads upwards from the base (apex) of the ventricles, it causes the muscles to contract.
- At the base of the septum, the wave of excitation spreads out over the walls of the ventricles.
- This is the Purkyne tissue and it runs down the inter-ventricukar septum.
- After this delay, the wave of excitation is carried awway from the AVN and dpwm specialised conducting tissue.
- 2) Atrial contraction - Heartbeat starts when atria contracts. Both right and left atria contract together.
- Three phases in the sequence of contraction
- 1) Filling phase - atria and ventricles are relaxing, internal volume increases and blood flows into the heart.
- Into the atria, through the open atroventricular valves and into the ventricles. This is callled diastole.
- 1) Filling phase - atria and ventricles are relaxing, internal volume increases and blood flows into the heart.
- Small increase in pressure created helps push blood into the ventricles.
- This stretches the walls of the ventricles and ensures they are full of blood.
- Contraction of the artia is called atrial systole. Once the ventricles are full they begin to contract.
- Blood fills the atroventricular valve flaps casuing them to snap shut. Preventing blood returning to the atria.
- Contraction of the artia is called atrial systole. Once the ventricles are full they begin to contract.
- This stretches the walls of the ventricles and ensures they are full of blood.
- Three phases in the sequence of contraction
- 3) Ventricular contraction - All four heart valves are closed. The walls of the ventricles contract. This is called ventricular systole.
- This raises the pressure in the ventricles very quickly.
- The contraction starts at the apex (base) of the heart so this pushes the blood upwards towards the arteries.
- The semilunar valves open and blood is pushed out of the heart. The contraction only last for a short time.
- Then the ventricle walls relax allowing the heart to fill up again.
- The semilunar valves open and blood is pushed out of the heart. The contraction only last for a short time.
- The contraction starts at the apex (base) of the heart so this pushes the blood upwards towards the arteries.
- This raises the pressure in the ventricles very quickly.
- The sound of the heart
- The Cardiac Cycle
- Definition:the sequence of events in one heartbeat
- The sinoatrial node (SAN) is the heart's pacemaker. It is a small patch of tissue that sends out waves
- of electrical excitation at regular intervals to initiate contractions.
- Purkyne tissue is specially adapted muscle fibres that conduct the wave of excitation from the AVN down the septum to the ventricles.
- The need for coordination
- Cardiac muscle initiates its own contraction. So is described as myogenic. The muscle will contract and relax rhythmically.
- The muscles from the atria and the ventricles each have they're own natural frequency of contraction.
- The atrial muscle tends to contract at a higher freguency than the ventricular muscle.
- This property of the muscle could cause innefficient puping (fibrillation) if the contractions of the chambers are not synchronised.
- So the heart needs a mechabism that can coordinate the contractions of all four chambers.
- This property of the muscle could cause innefficient puping (fibrillation) if the contractions of the chambers are not synchronised.
- The atrial muscle tends to contract at a higher freguency than the ventricular muscle.
- The muscles from the atria and the ventricles each have they're own natural frequency of contraction.
- Cardiac muscle initiates its own contraction. So is described as myogenic. The muscle will contract and relax rhythmically.
- How the heart starts
- At the top of the right atrium, near the point where the vena cava enpties blood into tge atrium is the sinoatrial node (SAN).
- This samll patch of tissue generates electrical activity.
- The SAN initiates a wave of excitation at regukar intervals.
- Ib a human, this occur approximately 55-80 times a minute.
- The SAN initiates a wave of excitation at regukar intervals.
- This samll patch of tissue generates electrical activity.
- At the top of the right atrium, near the point where the vena cava enpties blood into tge atrium is the sinoatrial node (SAN).
- Contraction of the atria
- The wave of excitations quickly spreads over the walls of both atria.
- It travels along th membranes of the msucle tissue. As the wave of excitation passes,
- it causes the cariac muscle cells to contract. This is atrial systole.
- It travels along th membranes of the msucle tissue. As the wave of excitation passes,
- At the base of the atria is a disc of tissue thar cannot conduct the wave of excitation.
- So the excitation cannot spread directly to the ventricle walls.
- At the top of the inter-ventricular septum is another node - the atrioventricular node (AVN).
- This is the only route through the disc of non-conducting tissue. The wave of excitation is delayed in the node.
- This allows time for the atria to finish contracting and for the blood to flow down the ventricles before they begin to contract.
- This is the only route through the disc of non-conducting tissue. The wave of excitation is delayed in the node.
- At the top of the inter-ventricular septum is another node - the atrioventricular node (AVN).
- So the excitation cannot spread directly to the ventricle walls.
- The wave of excitations quickly spreads over the walls of both atria.
- Contraction of the ventricles
- After this delay, the wave of excitation is carried awway from the AVN and dpwm specialised conducting tissue.
- This is the Purkyne tissue and it runs down the inter-ventricukar septum.
- At the base of the septum, the wave of excitation spreads out over the walls of the ventricles.
- As the excitation spreads upwards from the base (apex) of the ventricles, it causes the muscles to contract.
- This means that the ventricles contract from the base upwards, pushing blood u[p to the major arteries at the top of the heart.
- As the excitation spreads upwards from the base (apex) of the ventricles, it causes the muscles to contract.
- At the base of the septum, the wave of excitation spreads out over the walls of the ventricles.
- This is the Purkyne tissue and it runs down the inter-ventricukar septum.
- After this delay, the wave of excitation is carried awway from the AVN and dpwm specialised conducting tissue.
- The Cardiac Cycle
- The lup-dup sound made by the heart is made by the valves closing: -the first sound, lub, is made by the atrioventricukar valves closing as the ventricles start to contract.
- The sound of the heart
- The second sound, dub, is made by the semilunar valves closing as the ventricles start to relax.
- The atrioventricular valves snap shut, so this noise is louder than the closing semilunar valves, which shut because blood is accumulating in their pockets.
- The sound of the heart
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