Cardiovascular Fitness

Order of the heart

Cardiac Conduction System

1. Specialised cells in the wall of heart sends electrical impulses to the cardiac muscle → contraction

2. Beat starts in heart muscle (myogenic) with an electrical signal in sinoatrial node

3. Electrical impulse spreads through heart in a wave of excitation

4. Impulse spreads through atria walls, causing them to contract to force blood into the ventricles

5. Impulses passes through the atrioventricular node found in the atrioventricular septum

6. AVN delays transmission of impulse for approx. 0.1 second to enable the atria to fully contract

7. Impulse passes down through some specialised fibres (Bundle of His), located in septum

8. Bundle of His branches out into 2 Bundle branches, then into small branches (purkinje fibres), spread throughout the ventricles causing them to contract

Neural Control Mechanism

Sympathetic nervous system - heart go faster

Parasympathetic nervous system - returns heart to resting level

Consist of central nervous system (brain and spinal cord) and peripheral nervous system (nerve cells that transmit to and from the CNS)

Two systems are co-ordinated by the cardiac control centre (medulla oblongta) - detects CO2 levels

Chemoreceptors

• Found in carotid arteries and aortic arch

• Sense chemical changes. Detect increases in CO2 in blood

• Increase concentration of CO2 in blood stimulates the sympathetic nervous system, heart beating faster

Baroreceptors

• Contain nerve endings that respond to the stretching of the arterial wall (blood pressure)

• Increase blood pressure ← → Decrease in heart rate

• When exercising, they are restricted and do not slow the heart rate down

Proprioceptors

• Muscles, tendons and joints provide information about body position and movement

• When detecting movement/exercise, receptors send an impulse to the SAN to increase heart rate

• Parasympathetic system stimulates the SAN to increase heart rate

Cardiac hypertrophy

Thickening of the muscular wall of the heart

Bradycardia

Resting heart rate is below 60 beats per minute

Stroke Volume

Amount of blood pumped out of heart per beat

Starling’s law

Increased stroke volume means that overall cardiac output will increase

Cardiac output

Amount of blood pumped out of the heart per minute

Stroke volume x beats per minute