8.5 Heart Flashcards
How does the heart work?
2 pumps that are joined together and work together
–> deoxygenated blood from body flows into the right side of the heart and this gets pumped to lungs
–> Oxygenated blood from lungs returns to left side and is pumped to body
What is the heart made of?
Made of cardiac muscle, which contracts and relaxes in a regular rhythm- does not get fatigued and need to rest like skeletal muscle
Coronary arteries supply the cardiac muscle with oxygenated blood it needs to keep contracting and relaxing all the time
Heart surrounded by in elastic pericardial membranes (prevents heart from over-distending with blood)
How does deoxygenated blood enter the right side of heart
from upper body & head (superior vena cava)
from lower body (inferior vena cava)
–> brought in at low pressure
As the right atrium fills, what happens
Slight pressure builds up until the Atrio-ventricular vale (aka tricuspid/ AV valve) opens
blood passes down into the right ventricle
Once BOTH right atrium and ventricle are filled with blood, what happens?
atrium contracts
–> forces all blood into right ventricle & stretches ventricle wall
What happens to the atrio-ventricular/ tricuspid valve once the right ventricle contracts?
–> as soon as the right ventricle begins to contract, the AV valve closes to prevent back flow (tendinous cord makes sure valves are not turned inside out due to pressure
Once right ventricle contracts fully what happens?
deoxygenated blood is pumped through semilunar valves into the pulmonary artery
At the same time what is happening on the left side of the heart?
oxygenated blood from lungs enters left atrium from pulmonary vein. Pressure in atrium builds, causing the bicuspid valves to open between left atrium and the left ventricle
—> for ventricle also fills with oxygenated blood
Once both left atrium and ventricle are full, what happens?
atrium contracts, forcing oxygenated blood into left ventricle
—> left ventricle contracts and pumps oxygenated blood through semi-lunar valves into AORTA (& around body)
—> as ventricle contracts, tricuspid valve closes to prevent back flow
Why is the muscle wall on the left side thicker?
blood is passed at a higher pressure through left due to oxygen saturation being high
–> left side needs to overcome resistance of aorta and arterial systems of whole body & move blood under pressure to all extremities of body
lungs are relatively close to heart= short distance to pump and so right side only has to overcome resistance of pulmonary circulation
What is the septum?
Septum: inner dividing wall of heart which prevents mixing of deoxygenated and oxygenated blood
How long does one cardiac cycle take?
0.8 seconds
–> atrial systole 0.1 seconds
–> ventricular systole at 0.3 seconds
–> rest is diastole 0.4 seconds
What is diastole?
the heart relaxing (atria & ventricles fill=. volume & pressure increases)
What is systole?
atria and ventricle contraction
–> pressure inside heart dramatically increases & blood is forced out to either lungs or main body
–> volume & pressure of blood are low at end of systole by blood in arteries is at maximum
Cardiac cycle graph: How is aortic pressure represented
Line that never falls below 12kPa (due to recoil action of elastic wall); during atrial systole, the aortic pressure falls slightly
Once semi lunar valves open during ventricular diastole, aortic pressure rises drastically as the ventricle contracts.
At the end of ventricular diastole , the semilunar valve closes and aortic pressure begins to drop
Cardiac cycle graph: How is ventricular pressure represented
Low at first but increases as atria contract & fill ventricle with blood
–> once left AV valve closes during ventricular diastole, pressure increases quickly
Pressure rises above aorta so that the blood is forced into aorta
–> pressure falls once semi-lunar valves close
Cardiac cycle graph: How is atrial pressure represented?
Always low as wall of atria do not produce much force
–> Highest is during atrial systole and drops when AV valve closes
–> Atria fills with blood during diastole= gradual build up of pressure until slight drop when left AV valve opens
Cardiac cycle graph: How is Ventricular volume?
rises as atria contracts
–> ventricle fills with blood but drops suddenly as ventricle is contracted
–> volume increases as AV valve opens
How is the basic rhythm of the heart maintained?
via a wave of electrical excitation
SAN –> AVN –> two branches of purkyne tissue
–> apex –> walls of ventricles
Rhythm of heart: detailed
wave of electrical excitation begins in pacemaker area (sino-atrial node SAN), causing atria to contract and so initiating heartbeat
- Atrio-ventricular node AVN picks up electrical activity and imposes a slight delay before stimulating bundle of His
- bundle of His splits into two branches at the top fo the septum, conducting the wave of excitation to the apex of the heart
- At apex, purkyne fibres spread out to walls of both ventricle. triggering the contraction starting from the apex
(from bottom because it is more efficient at emptying ventricles)
What is a bundle of His?
bundle conducting tissue made up of fibres called purkyne fibres
What is an electrocardiogram
ECG: recording of electrical activity of heart
–> measures tiny electrical differences in skin
What is an electrocardiogram
ECG: recording of electrical activity of heart
–> measures tiny electrical differences in skin
Parts of an ECG?
P wave= electrical activity during atrial systole
QRS complex= electrical activity during ventricular systole
T wave= ventricular repolarisation
Q-T interval= ventricular contraction time
T-P interval= relaxed ventricles filling with blood
Tachycardia
rapid heart beat, over 100 bpm
–> due to exercise, stress or excitement
Bradycardia
heart rate slows down to below 60 BPM
–> many people have this because they are fit
heart block
separation of P wave and QRS complex
–> pacemaker activity and atrial contraction is normal
–> causes delay in conduction between atria and ventricles
hypertrophy
P wave and atrial contraction is normal but
–> QRS complex is distorted due to hypertrophy of one side of the heart
atrial fibrillation
arrhythmia (abnormal rhythm of heart
–> rapid impulses that contract very fast but ntot properly
