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OCR AS Level Physical Education - Cardiac Cycle and Cardiac Conduction System

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Will Chaloner

on 8 January 2016

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Transcript of OCR AS Level Physical Education - Cardiac Cycle and Cardiac Conduction System

Cardiac Cycle and Cardiac Conduction System
Heart Structure
Cardiac Cycle and Conduction System
The Cardiac cycle is brought about by the Cardiac Conduction System, an automatic (Myogenic) sequence of events that is controlled through a series of neural (Brain) processes.

HR and SV are controlled by these neural transmitters, however we will look at this later. Firstly we must break down the two processes in order to understand how they work together
Key Terms
Heart Rate

Stroke Volume

Cardiac Output

Pulmonary Circulation

Systemic circulation
Heart Values Rest and Exercise
Cardiac Cycle
Cardiac Conduction System
The Cardiovascular System
Phase 1: Diastole
- Known as repolarisation or, more simply, relaxation phase
Phase 2: Atrial Systole
- Atria contract forcing any extra blood into ventricles
Phase 3: Ventricular Systole
- Ventricles contract forcing blood out of the aortic and pulmonary valves.
- As the heart relaxes blood begins to fill the atria via the vena cava and the pulmonary vein
- Pressure builds in the atria, causing blood to be pushed through the AV valves into the ventricles
0.5 Seconds
- AV valves forced shut to prevent any backflow into atria
- Aortic and Pulmonary valves shut
- Aortic and pulmonary valves shut
0.1 Seconds
0.2 Seconds
- Heart in relaxation or repolarisation phase
- Myogenic impulse initiated from the SA Node located in the Right Atrium.
- Wave of excitement sent across both atria causing them to contract
- AV node conducts impulse through the bundle of his, through the septum to the apex of the heart
- Impulse travels through ventricle walls via the purkinje fibres
- Both ventricles contract
Phase 1: Diastole
- Known as repolarisation or, more simply, relaxation phase
Phase 2: Atrial Systole
- Atria contract forcing any extra blood into ventricles
Phase 3: Ventricular Systole
- Ventricles contract forcing blood out of the aortic and pulmonary valves.
- As the heart relaxes blood begins to fill the heart via the vena cava and the pulmonary artery
- Pressure builds in the atria, causing blood to be pushed through the AV valves into the ventricles
0.5 Seconds
- AV valves forced shut to prevent any backflow into atria
- Aortic and Pulmonary valves shut
- Aortic and pulmonary valves shut
0.1 Seconds
0.2 Seconds
Conduction System
- Myogenic wave initiated by SA node
Conduction System
- Wave of excitement send across atrial walls causing them to contract
- AV node conducts impulse down bundle of his and through the septum to the apex of the heart
- Impulse travels down ventricle walls via the Purkinje fibres
Conduction System
- Both atria contract
Cardiac Cycle and Conduction System
Neural Factors
Chemoreceptors
Proprioceptors
Baroreceptors
- Detect changes in blood pH

- Increase Sympathetic Activity
- Stretch receptors in tendons (Gorgi Tendon Organ) detect increased muscle stretch.

- Increased frequency of sympathetic
- Detect changes in Blood Pressure and arterial stretch
Intrinsic Factors
Temperature
- Increased body temperature increases speed of nerve impulses
Starling's Law
- Increased venous return = Greater artrial/ventricular stretch.
Causes a larger end diastolic volume (EDV)
- Greater recoil = Smaller end systolic volume (ESV)
Hormonal Factors
Adrenaline
- Adrenaline released in anticipation of exercise.

- Adrenaline travels to the heart via the bloodstream.

- Directly stimulates SA node increasing HR
Heart Rate Control
Parasympathetic (Vagus) Nerve
(Decreases HR)
Sympathetic (Accelerator) Nerve
(Increases speed and strength HR)
Medulla Oblongata
What changes in the body occur at the onset of exercise?
Cardiac Control Centre
(CCC)
Vasomotor Control Centre
(VCC)
Vasomotor Control Centre (VCC)
- Neural, hormonal and intrinsic information sent to VCC (in Medulla)
- Decrease in sympathetic stimulation to arterioles leading to working muscle.
- Increase in sympathetic stimulation to arterioles and Pre capillary sphincters leading to organs
Vasodilation (Redistribution of Q)
Vasoconstriction
Decrease in nerve impulses to arterioles and PCS leading to muscles requiring O2
Precapillary sphincters relax
Arterioles vasodilate allowing greater blood flow to working muscle
Increase nerve impulses to arterioles and PCS leading to organs (areas not requiring O2)
Vasoconstrict arterioles leading to organs decrease in blood flow to muscles
Pre capillary sphincters contract
Vascular Shunt Mechanism
Process by which blood is moved from non essential areas to areas where it is most needed
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