Cardiac structure, conducting system and cardiac cycle Flashcards
How does the Right and Left part of the Heart work?
- RIGHT ATRIUM receives blood from superior and inferior vena cava.
- RIGHT VENTRICLE pumps out blood to the pulmonary trunk to the lungs for oxygenation
- Oxygenated blood comes back to the heart to the LEFT ATRIUM through the Pulmonary veins.
- Veins now carry oxygenated blood. Blood is then given to the LEFT VENTRICLE which pumps oxygenated blood through the AORTA for the blood to reach all the tissues in the body.
Describe the location of the heart
Located in the thoracic cavity in the space between left and right lung called MEDIASTINUM. Between the vertebrae and sternum which helps us to apply CPR.
How does the right side of the heart pump blood
Into a low pressure and low resistance system - also known as PULMONARY CIRCULATION
How does the left side of the heart pump blood
Pumps at equal volume as right side, but at higher pressure, higher resistance and longer system - also known as SYSTEMIC CIRCULATION. Thus why left is more thicker and stronger.
Explain the Specialised Conducting System
- Impulses begin at the SA node located in the Right Atrium.
- Impulses travel down to the AV node. As it travels down the AV node it splits into 3 branches and Bachmann bundle and excite the Left Atrium at the same time as the Right Atrium. The excitation then leads to muscles contracting.
- Impulses then travel through Bundle of HIS and branches off to Right bundle branch (RBB) and (LBB)
4.Small purkinje fibres branch off and transmit impulses to all the ventricular musculature.
Where is the slowest conduction in the Specialised Conducting System and explain why its slow
AV node. Called the AV nodal delay. Impulses going down from the AV node need to be slow as we don’t want the ventricles contracting at the same time as the Atria. (If both atria and ventricles contract at the same time there won’t be enough filling the ventricle or pumping of blood)
Where is the Tricuspid and Mitral Valve located?
Tricuspid - Between RA and RV
Mitral - between LA and LV
Which part of the heart has semilunar valves?
Aorta and Pulmonary Trunk. Consists of 3 semilunar cusps
Describe the structure and function of semilunar valves
Separate ventricles from great vessels
Prevent backward flow of blood
Both
Describe the structure and function of cardiac cells
2 types = myocardial and pacemaker cells
Pacemaker cells generate impulses automatically and rhythmically of cardiac muscle to ensure efficient pumping
99% of heart is made up of contractile cardiac muscle to generate force of contraction produced by heart
What does then SA node do and where is it located
Sets cardiac rhythm (pacemaker) and located in RA. Its the fastest rhythm (70-80/min)
What does AV node do and where is it located
Located at A-V junction. collects impulses and conducts slowly (40-60/min)
Which valves have chord tendineae?
Aortic and pulmonary valve
Whats the name of the fluid filled sac that surrounds the heart
Pericardium
The valve between the left ventricle and the blood vessel leaving the left ventricle is called
Aortic semilunar valve
Explain the Ionic of different phases of ventricular action potential
PHASE 0 RAPID DEPOLARIZATION - When electrical impulse goes to cardiac muscle, sodium gated channels OPEN. Sodium then enters the cell and membrane becomes more positive. This is called depolarisation. Sodium moves in from the ECF to the ICF making it more positive. Membrane potential shoots UP due to lots of sodium influx into the cell.
PHASE 1 BRIEF REPOLARISATION - Sodium channels close and potassium channels open. Potassium efflux occurs because gradient allows movement of forced potassium inside and outside, causing membrane to be negative. Potassium from ICF moves into ECF.
PHASE 2 PLATEAU PHASE - Potassium efflux continues but at the same time calcium channels open and go into the cell. Potassium efflux from inside goes out (Positivity going in, positivity going out). No movement upwards or downwards. Membrane potential is stable due to positive ions moving in at the same time as moving out therefore its going to be depolarised in plateau phase.
PHASE 3 RAPID REPOLORIZATION - Potassium channels open and potassium efflux continues to occur. Voltage gated calcium channels close. Strong outward potassium making the membrane potential more negative reaching its resting stage.
PHASE 4 RESTING PHASE -
Sodium and calcium channels close. Potassium channels slowly close and resting membrane potential is maintained.
Explain step by step the Mechanism of Cardiac Muscle Excitation, Contraction and Relaxation
- Action potential travels along the membrane
- Voltage gated Calcium channels open and enters the cell
- Calcium induces the release through Ryonodine Receptor channels.
- Local release causes Calcium spark and signal
- Calcium ions binds to troponin to initiate contraction
- Relaxation occurs when calcium unbinds from troponin
- Calcium pumped back into Sarcoplasmic Reticulum for storage
- Calcium exchanged with sodium
- Sodium gradient is maintained by Potassium ATPase
What is the role of Calcium
- Calcium causes the plateau phase in ventricular muscle action potential and contraction of ventricular muscle
- Lots of calcium is important for contraction to take place in the cardiac muscle
- Calcium channel blockers e.g Verapamil reduce Calcium
- Catecholamines increase calcium entry
What is ARP
Absolute refractory period. Half of phase 3 till membrane reaches -50mV.
Sodium channels in their inactivated state. Prevents summation and tetany. Ensures filling chambers
What are pacemaker potentials
Spindle shaped. Unsteady resting membrane potential.
Ionic basis
Explain step by step the mechanism of Pacemaker potential
- Potassium channels closed. Opening of funny channels
- T type channel opens where calcium influx takes place. Funny channels close at -55mV
- Calcium channels open (L type channels)
- Closure of T type calcium channels
- Potassium channel opens
What is the role of Sympathetic and Parasympathetic activity
Sympathetic - increases heart rate by increasing and sodium influx through funny channels
Parasympathetic - decreases heart rate by increasing potassium efflux (means membrane becoming more hyper polarised - more negative). Takes long time to reach threshold due to less calcium.
What is Ectopic pacemaker
When cardiac tissue develops a faster rhythm than SA node.
Can produce an extra heartbeat
Always caused by heart disease e.g anxiety, caffeine, nicotine.
What is Sinus Arrhythmia
During inspiration, HR is higher. during expression your HR is lower
What happens when myocardial cell is stretched
Allows more calcium to enter and increase the force of contraction
What does action potential in cardiac contractile cell cause
Opening of L- type channels
In condition known as heart block, what happens?
Electrical signals from SA node never reach ventricles, so contraction of atria is not coordinated with the contraction of the ventricles
What is the term for heart rate of 125bpm
Tachycardia
What happens when heart is in fibrillation
effective pumping of the ventricles ceases because the myocardial cells fail to work as a team and brain cannot get adequate oxygen
What is the Cardiac Cycle
Period of time from beginning of one ventricular or atrial contraction to the beginning of next (all events that take place in one heartbeat)
How is length of cardiac cycle measured
ECG recording - calculating r-r interval 60/HR (beats/min)
Name the electrical events in cardiac cycle
Depolarisation and repolarisation of cardiac chambers
Name the mechanical events of cardiac cycle
Pressure changes in chambers
Volume changes in chambers
Valvular closures making heart sounds (1st & 2nd)
Pressure changes in great vessels
Explain step by step the phases of Cardiac cycle
VENTRICULAR SYSTOLE -
Isovolumetric ventricular contraction: depolarisation of ventricles. They then contract and rise in pressure closes AV valves producing 1st heart sound
Rapid ventricular ejection: Ventricular pressure increases. SL valves open. Blood rejects rapidly. Ventricular pressure reaches max level. Pressure in great vessels and ventricular volume decreases
Reduced ventricular ejection:
Last phase of ventricular systole. Ventricular pressure starts failing as large volume is ejected. Ventricles eject at lower rate and pressure in great vessels also start falling. End systolic volume of blood remains in ventricles (systole).
Prodiastole: R AND L ventricle pressure fall below the aortic & pulmonary artery pressures leading to closure of SL valves. This produces the 2nd heart sound
Isovolumetric ventricular relaxation: AV valves not open yet. Ventricular pressure falls very steeply. Ventricular pressure still exceeds atrial pressure
Rapid ventricular filling:
AV valves open & blood flows to ventricles
Blood flow rapid due to high pressure gradient
Rapid flow produces 3rd heart sound
Maximal filling occurs and ventricular volume increases
Ventricular pressure remain low as ventricles are relaxing
Reduced ventricular filling (diastasis): Longest phase
Blood flow is less due to low pressure gradient. Atrial & ventricular pressures become equal at end of this phase
Atrial systole: Last phase. Spread of next cardiac impulse causes depolarisation of atria (marked P wave in ECG)
Both atria contract
Small volume of blood fills into ventricles producing 4th heart sound
Ventricular volume reaches EDV
Ventricles ready for next systole
What is EF and how do you measure it
Fraction of EDV ejected in 1 heart beat. SV/EDV. To find % = X by 100.
Normal EF = 50-60% at rest.
Increase in EF = positive in inotropic effect
Decrease in EF = negative inotropic effect
What happens at each heart sound
S1 - closure of AV valves
S2 - closure of SL valves
S3- First rapid filling
S4- atrial contraction
Name all the Auscultatory areas on the body
Aortic area - right side (2nd intercostal space)
Pulmonic area - left side (2nd intercostal space)
Tricuspid area - left side (4th intercostal space)
Mitral area - left side (5th intercostal space)
What happens in cardiac cycle at high heart rate
Duration of cardiac cycle decreases
Systolic and diastolic time decrease (diastolic decreased more)
Diastasis phase decrease more
Very high rates (as in ventricular tachycardia) enroach on diastole & filling reduced resulting in decreased SV (may lead to hypotension)
