Cardiovascular system and disease Flashcards
What are the two functions of the heart?
- To pump oxygenated blood to the body tissues
- To pump deoxygenated blood to the lungs to be oxygenated
Label the missing blood vessels
Label the missing parts of the heart
Describe the two interconnecting networks of muscle fibres in the heart
- Called syncitia
- All the muscle around the atria is interconnected and all the muscle around the ventricles is interconnected
- Each syncitium contracts as a unit because once one muscle cell is stimulated the while syncitium contracts
- The syncitia are eletrically insulated from each other by fibrous connective tissue
Describe cardiac muscle compared to skeletal muscle
- Fibres are shorter in length in cardiac muscle
- Fibres are branched in cardiac muscle
- Cardiac muscle fibres are anchored to each other by intercalted discs and have gap jounctions between them to allow action potentials to pass between fibres
- The fibres are autorhythmic
How is cardiac muscle autorhythmic and why is this useful?
- The fibres are self excitable and can spontaneously depolarise and contract
- This feature is useful as it allows the heart to beat continuously even when you’re sleeping
What is the difference in action potential time for cardiac muscle compared to skeletal muscle and what does this result in?
- Action potenial is longer in cardiac muscle (0.25 sec for cardiac muscle)
- This results in a plateau as there is a delay before repolarisation
Describe why there is a plateau in the contraction cycle for cardiac muscle (the break between action potential and repolarisation)
- Calcium ions enter the axon as sodium ioons are being pumped out and this prevents repolarisation
- This is because calcium ions stop the normal movement of potassium ions
- The membrane potential balances out at 0mV
- There is then a delay between the action potwential and repolarisation
How is each contraction of the heart co-ordinated?
- By the pacemaker
- Sinoatrial node
- By having conduction pathways
How does the SA node help to co-ordinate the contrction of the heart?
- It is a bundle of specialised cadiac muscle ceels with have self excitability and autorhythmic depolarisation and set the heart rate based on the nervous system
- It has a rate of 100 action potentials per minute and this is naturally slowed at rest by the vagus nerve to 75 per minute which is the typical resting heart rate
Describe the conduction pathway up to the bundles of his dividing
- Action potential from the SA node causes contraction of the atria
- The action potential reaches the atrioventricular node and enters the bundle of his
- The AV node delays the impulse to allow ventricular filling to occur before contraction of the ventricles
Describe the conduction bathway from the AV node delaying the impulse
- The bundles of his divide into left and right branches of perkinje fibres where speed of conduction is 6 times faster than through ventricle muscle
- This impulse causes the ventricles to contract from the apex up towards the valves
Label the points on the normal ECG
If the SA node failed to function what would happen?
- The AV node would take over as the pace maker of the heart
- The heart rate would be slower
What prevents the valves of the heart opeing back up when pressure is applied?
Cordae tendineae
