The Heart Flashcards
What are the functions of the cardiovascular system ?
- distribution of nutrients
- support for metabolism (transportation of oxygen and carbon dioxide and metabolic waste products)
- distribution of water and electrolytes
- transportation and distribution of hormones
What is the arrangement of the cardiovascular system ?
- the heart has 4 chambers and has a unidirectional flow of blood
- the blood in the systemic vascular beds runs in parallel
- the pulmonary circulation of blood runs in series
What is the role of the valves ?
they prevent backflow of blood and ensure unidirectional flow
Why is the muscle on the left side of the heart greater in volume than on the right side of the heart ?
The left ventricle contracts more powerfully in order to supply blood all around the body whereas the right side of the heart only supplies blood to the lungs
What is the cardiac output at rest ?
~ 5 litres per minute
What is the formula to calculate cardiac output ?
cardiac output = heart rate x stroke volume
What is stroke volume ?
the amount of blood leaving the heart per beat (ml per beat)
Where is the sinoatrial node located ?
in the right atrium
What is the role of the sinoatrial node ?
- it is the natural pacemaker of the heart
- it generates the spontaneous rhythm of the heart by sending electrical impulses into the atrioventricular node and then down into the bundle of his and down to the septum where the impulses are then sent up the ventricles
How does the SAN generate the spontaneous rhythm ?
The resting membrane potential of the SAN is not stable and is constantly depolarising
threshold is then reached and then repolarisation begins
the action potential generates the electrical impulses
What does the ECG trace show ?
It represents electrical activity in the whole heart
What does the P wave on the ECG show ?
depolarisation of the atria
What does the QRS complex on the ECG show ?
depolarisation of the ventricles
What does the T wave on the ECG show ?
repolarisation of ventricles (ventricles are relaxing and filling)
What does the PR interval on the ECG complex show ?
it shows the speed of conduction from the atria to the ventricles through the atrioventricular node
What does the QT duration on the ECG complex show ?
it shows the electrical activity taking place in the ventricles - depolarisation and repolarisation of the ventricles
How can the heart rate be modified ?
- autonomic nervous system (sympathetic and parasympathetic)
- circulating hormones e.g. acetylcholine
What does parasympathetic stimulation do to the heart rate ?
It decreases the frequency of action potentials and slows the heart rate
What does sympathetic stimulation do to the heart rate ?
It increases the frequency of action potentials and increases the heart rate
How does a cardiac ventricular action potential differ from a nerve action potential ?
The cardiac ventricular action potential incudes a plateau phase where the net movement of calcium ions out of the cell is equal to the inwards movement of potassium ions
What is calcium-induced calcium release ?
It is when calcium ions move into a cell and cause calcium ions to be released from intracellular stores and this is important in EC coupling of cardiac myocytes
How is contraction of the heart coordinated ?
- contraction is highly organised
- atrial contraction is followed by ventricular contraction
- relaxation is also coordinated to allow filling
What is systole ?
contraction of chamber and ejection of blood
What is diastole ?
relaxation and filling
Briefly describe the cardiac cycle
1) Atrial systole
2) Isovolumic contraction of the ventricles
3) Ventricular ejection
4) Isovolumic relaxation of the ventricles
5) Passive ventricular filling
What is isovolumic contraction ?
It is when the valves are closed so the volume is not changing but the pressure is increasing
How can stroke volume be modified ?
- intrinsic control : degree of stretch of cardiac muscle - this is what returns to the heart from the venous end (Starling’s law)
- extrinsic control : sympathetic stimulation (modulation of calcium ion availability)
