the heart Flashcards
explain where oxy/deoxy blood flows in the heart
- deoxygenated blood flows into right side of the heart and then to the lungs
- oxygenated blood from lungs returns to left side of the heart
what is the heart made from
myogenic cardiac muscle
what artery supplies the heart
coronary artery supplies oxygenated blood
what is the heart surrounding by and what do they do?
inelastic pericardial membranes - prevent over-distending
what is meant by ‘over-distending with blood’
when pressure in blood vessels is too high for a long period of time
which side of the heart has thicker muscular walls?
the left side
why does the left side of the heart have thicker muscular walls than the right?
- right side has to pump blood a relatively short distance
- left has to provide sufficient force to overcome resistance of the aorta and arterial systems to move blood under pressure to all extremities of the body
what is the septum?
the inner dividing wall of the heart
what is the role of the septum?
prevents mixing of deoxygenated and oxygenated blood
what is a heart murmur
when there is a hole in the septum of the heart
what causes a heart murmur?
- septum does not fully develop until after birth
- blood is oxygenated by the placenta, not lungs (in fetus)
- blood in the heart is very similar so mixes freely
- days after birth, septum closes to ensure separation of blood
- a gap in the septum after the first few weeks of life is a murmur
how long does the cardiac cycle last in adults?
0.8s
what happens during diastole?
the heart relaxes - atria and then ventricles fill with blood, volume and pressure of blood builds as the heart fills, but arterial pressure is at a minimum
what happens during systole?
the atria contract (atrial systole), followed by the ventricles (ventricular systole)
- pressure inside the heart increases dramatically as blood is forced to the lungs (right) and to main body circulation (left)
- volume and pressure of blood in heart are low at end of systole, pressure in arteries is at a max.
what creates the ‘lub’ sound in the cardiac cycle?
blood is forced against atrio-ventricular valves as ventricles contract
what creates the ‘dub’ sound in the cardiac cycle?
backflow of blood closes the semilunar valves in the aorta and pulmonary artery as ventricles relax
what is meant by myogenic?
it has its own intrinsic rhythm by initiating its own electrical impulses
why does the heart have an average rhythm? what is it?
prevents body wasting resources by maintaining the basic heart rate - 60bpm
what 3 factors can affect heart rate?
- exercise
- excitement
- stress
explain how the basic rhythm of the heart is maintained
- sino-atrial node (SAN) begins wave of electrical excitation - causes atria to contract - non-conducting tissue prevents excitation passing into the ventricles
- electrical activity is picked up by atrioventricular node (AVN) that imposes slight delay before stimulating bundle of His
- bundle of His splits into two branches and conducts wave of excitation to apex
- purkyne fibres at apex spread through ventricle walls, spread of excitation stimulates ventricle contraction (starting at the apex)
what does the SAN do?
initiates electrical impulses to start atrial systole/contractions
what does the AVN do?
delays the signal from the SAN - allows atria to contract fully to allow blood to complete flow into ventricles
what is the bundle of His composed of?
purkyne fibres
what does the bundle of His do?
transmits impulses from AVN to apex of the heart
