8.5 - The Heart Flashcards
What is the basic structure and function of the heart?
- Made of cardiac muscle
Has coronary artery and inelastic pericardial membrane
- Has septum wall
- inner dividing wall preventing mixing of oxygenated and deoxygenated blood
What is the function of the coronary artery?
Supplies cardiac muscle w/ oxygenated blood
What is the function of the pericardial membrane?
- Surrounds heart
- Keeps heart in fixed position
- Prevents heart from over-distending (filling) with blood
- Lubricates heart to prevent friction with surrounding tissue when beating
- Prevents heart from infection from surrounding organs
Describe the blood flow path in the RHS of the heart.
- Deoxygenated blood enters right atrium from inferior and superior vena cava into right atrium and low pressure
- As blood flows in, pressure builds until tricuspid valve opens > blood flows into right ventricle –once both right atrium and ventricle are full of blood, right atrium contracts - all blood forced to right ventricle
- Right ventricle contracts, tricuspid valve closes and is stopped from going inside out by chordinous tendons (stops backflow)
- Blood pumped into pulmonery artery via semilunar valved to capillary bed in lungs - semilunar valve closes.
Describe the blood flow path in the LHS of the heart.
At the same time as RHS of body…
- Oxygenated blood enters left atrium through pulmonary vein from lungs. - Pressure in atirum builds, bicuspid valve opens - blood enters left ventricle
- Once both L ventricle and atrium are full, atrium contracts - pumps oxygenated blood through
- L ventricle, contracts, pumps oxygenated blood through semilunar valve in aorta and rest of body - semilunary valve closes.
Describe the events of the cardiac cycle.
- Heart is relaxed (diastole) and blood flows into atria
- Atria then contract - atrial systole
- Higher pressure is generated in atria than ventricles
- Blood then flows into ventricles
- Ventricles then contract - ventricular systole
- Higher pressure in ventricles than atria
- Atrioventricular valves close
- Blood flows into aorta and pulmonary artery
- Higher pressure in aorta and pulmonary artery than in ventricles
- Semilunar valves close
Explain valves closing with respect to pressure differences.
If the pressure is higher in the 2nd location as opposed to the first, the valves close e.g. pressure higher in ventricles than atria, atrioventricular valves close
If the pressure is higher in the 1st location as opposed to the second, the valves open e..g pressure in atria than ventricles, AV valves open
In a pressure graph showing ventricles, atria and aorta, what do the points A, B, C (where graphs cross), represent?
A - pressure in ventricle increases > than atria, pushing AV valves closed
B - pressure in ventricles > than aorta, semilunar valves open
C - semilunar valves close as pressure in aorta is higher pushing back the valves close
D - AV open
Describe and explain the heart sounds.
‘Lub-dub’ Lub - atrioventricular valves closing Dub - semulinar valves in aorta and pulmonary artery close
Define myogenic.
Feature of cardiac muscle, has its own intrinsic rhythm, - Prevents body from wasting resources to maintain basic heart rate.
What is the role of the SAN in a heartbeat initiation?
- Sino-atrial node (natural pacemaker) - starts a wave of excitation in the left and right atrium causing them to contract
- Layer of non-conducting tissue prevents excitation from passing to the ventricles and causing them to contract (ensures ventricles only respon to signal from AVN and Bundle of His)
- SAN is embedded in right atrium wall
What is the role of the AVN in a heartbeat?
- Picks up electrical activity from SAN
- AVN imposes slight delay, ensuring the atria have completely emptied and stopped contracting before the ventricles begin
- Then the Bundle of His is stimulated - a bundle of conducting tissue made of Purkyne Fibres
What is the role of the Bundle of His in a heartbeat?
- Splits into 2 branches and conducts excitation to heart’s apex (bottom)
- Purkyne spread through ventricular wall to trigger ventricular contraction
Describe each section of an ECG.
P wave - atrial systole - wave of depolarisation in atrial walls, atria contracts and blood flows into ventricles
Heart rate calculated from interval between P waves
QRS Complex - Ventricular systole - wave of depolarisation in ventricular wall, ventricles contract, and AV valves close
T wave - ventricular diastole
What does each ECG interval represent?
PR - time taken for impulse to travel from atria to ventricles
QT - contraction time
Interval between T of one cardiac cycle and Q of the next is filling time
Define i) tachycardia ii) bradycardia iii) ectopic heartbeat iv) atrial fibrillation
Tachycardia - rapid heartbeat
Bradycardia - slow heartbeat, maybe due to high fitness, severe brady may lead to need for pacemaker
Ectopic heartbeat - extra heartbeat out of rhythm, usually happens once a day.
- has abnormal QRS
- lack of T wave
- gap between extra systole and next cardiac cycle
Atrial fibrillation - e.g. arrhythmia, abnormal heart rhythm. Rapid electrical impulses generated in atria, causes fast contraction (fibrillation). – contraction doesn’t occur properly, only some impulses pass to ventricles so they don’t contract properly.
