L1 The heart and ECG Flashcards
What is the role of the heart?
Pumps blood through many vessels to deliver/remove blood to/from cells
Transports oxygen + nutrients to specific sites
Contains internal mechanisms that regulate blood volume/ pressure
What is the role of the right atrium?
Receives blood from systemic (bodily) circulation
What is the role of the right ventricle?
Delivers blood to pulmonary (lungs) circulation
What is the role of the left atrium?
Receives blood from pulmonary circulation
What is the role of the left ventricle?
Pumps blood to systemic circulation
What is the role of the septum?
muscle that separates left and right of heart
What is the role of the valves?
maintain pressure within parts of the heart and assist in unidirectionality of blood flow
Describe the path of blood flow
Blood enters right atrium through superior + inferior vena cava
Blood travels from right atrium to right ventricle through atrioventricular valve
Blood is pumped from right ventricle to pulmonary artery through semi lunar valve
Blood becomes oxygenated at the lungs
Pulmonary vein delivers oxygenated blood to the left atrium
Blood flows from left atrium to left ventricle though atrioventricular valve
Blood is pumped from left ventricle to aorta through semi lunar valves
Describe the conduction system of the heart
Heart is myogenic signals itself & has autorhytmicity (creates its own rhythm)
Pacemaker cells are found in SAN and AVN these spontaneously fire action potentials
Conduction fibres contain contractile cells allows for Action Potential(AP) to be conducted 4M/S
Pacemaker cells conduction fibres contractile cells pathway of action potential is facilitated by gap junctions between the cells (Inside the intercalated disk)
Intercalated disk also contains desmosomes these are protein fibres that resist mechanical stress between the cells
Describe the initiation of a heart beat
Impulse arrives at SA node
Impulse travels through the conduction fibres to the Av node
AV node transmits AP less rapidly (delay of 0.1s)
Impulse travels through the bundle of his in the interventricular septum
Signals split of though right and left ventricles
Signals travel from the apex of heart (bundle branch) to the purkynje fibres these spread through ventricular myocardium
Describe the activity of pacemaker cells
Found in SAN and AVN fire action potentials spontaneously
There is slow immediate depolarisation (when AP finishes)
Slow depolarisations are known as pacemaker potentials
Pacemaker potential is highly influenced by the permeability of the membrane to Ca2+ ions
Describe the activity of cardiac contractile cells
Found in atria/ventricles cause contraction of the heart
More akin to profile of normal body cells action potential
Depolarisation/ repolarisation is different to pacemaker cells
What is a ECG and how does it work?
ECG is a device that records the spread of electrical current through the heart as a function of time of the cardiac cycle
Body tissues acts a conductor which allows for electrodes to record the electrical activity of the heart relative to diff parts of the body “Einthoven’s triangle”
Right arm, left arm + left leg
What can be seen on a ECG wave?
P wave – atrial depolarisation 0.1 s
QRS complex – ventricular depolarisation 0.06-1.2s
T wave – Ventricular repolarisation 0.12-0.21s
What heart problems can be detected with ECG?
Arrhythmias (abnormal firing from pacemaker cells):
-Too fast (>100 bpm) - Tachycardia
-Too slow (<50 bpm) - Bradycardia
Third degree heart block
-No conduction in AV node leads to dissociation in contraction between atria and ventricles
External depolarisation
-Electrical signals from outside of conduction pathway can cause pre atrial/ventricular contraction (not fatal)
Fibrillations
-Heart is no longer synchronised (deadly but atrial fibrillations are not as deadly (still contract sufficiently)
