The Heart: Structure, Function and Anatomy

• Cardiovascular system consists of the heart, circulatory system and ECG

Heart Structure and Function

• The heart, a muscular organ in the chest cavity, is covered by the pericardium
• The pericardium is a moist fibrous sac, allowing free movement during contractions
• The purpose of the heart is to function as a pump to produce pressure to flow blood through blood vessels
• The heart has right and left pumps, divided into two-chamber pumps of an atrium and a ventricle
• The right heart pumps blood to the lungs, while the left heart pumps blood through the peripheral organs
• Each atrium is a weak primer pump for the ventricle, which then propels blood
• The right ventricle propels blood through pulmonary circulation
• The left ventricle propels blood through peripheral circulations
• The heart has special mechanisms causing continuous contractions and cardiac rhythmicity
• Cardiac rhythmicity transmits action potentials for rhythmical beats

Heart Anatomy

• RA: right atrium
• RV: right ventricle
• LA: left atrium
• LV: left ventricle
• T: tricuspid valve
• P: pulmonic valve
• M: mitral valve
• A: aortic valve
• SVC: superior vena cava
• IVC: inferior vena cava
• PA: pulmonary artery
• PV: pulmonary veins
• Three layers of the heart wall: epicardium, myocardium, and endocardium

Heart Wall Layers

• Epicardium is the outer layer
• Myocardium is the middle layer, making up the heart’s mass
• Endocardium is the inner layer, lining chambers, valves, and vessels

Heart Valves and Blood Flow

• Venous blood enters the right atrium (RA) via the superior vena cava (SVC) and inferior vena cava (IVC)
• Blood then flows from the RA to the right ventricle (RV) through the tricuspid valve
• Blood leaves the RV through the semilunar pulmonary valve into the pulmonary artery, which distributes it to the lungs for oxygen/carbon dioxide exchange
• Blood returns to the heart from the lungs via the four pulmonary veins which enter the left atrium (LA)
• Blood flows from the LA, across the mitral valve into the left ventricle (LV)
• Blood is expelled through the semilunar aortic valve and into the aorta, which distributes blood into the arterial system
• Atrio-ventricular valves, such as the tricuspid and mitral valves, have chordae tendineae attached to papillary muscles on ventricular walls
• Papillary muscles contract during ventricular contraction thus generating tension to prevent AV valve bulging

Conducting System of the Heart

• S-A node is the pacemaker and is located in the superior lateral wall of the right atrium near the opening of the superior vena cava
• S-A node has the highest intrinsic impulse generation rate at 90/min which determines heart rate
• A-V node has the second highest impulse generation rate at 60/min
• Action potential travels from the SA node through both atria and then through the A-V node into the ventricles
• There is a delay of more than 0.1 second during passage through the AV node, allowing atria to contract ahead of ventricular contraction
• Atria serve as primer pumps for the ventricles
• Ventricles provide major power source for moving blood through the vascular system
• AP (wave of depolarization) from SA to RA and LA is achieved by intranodular and cardiac muscle cells at 1-0.3 m/sec
• Transmission from AVN to Purkinje system occurs at 1.5-4 m/sec

Cardiac Muscle Properties

• Intercalated discs are cell membranes separating cardiac muscle cells, connected in series and parallel
• Gap junctions between cardiac muscle cells have low electrical resistance, facilitating AP spread
• Purkinje fibers' rapid conduction and diffused distribution cause simultaneous depolarization of right and left ventricular cells for contraction

Action Potential Propagation

• AV node propagation of action potential is delayed for about 0.1 second
• The delay allows the atria to contract and empty blood into the ventricles before ventricular contraction

Conducting System Characteristics

• Autorhythmicity: ability to generate action potential spontaneously
• Specialized conducting system: conducts pulses rapidly for simultaneous atrial and ventricular contraction

Action Potentials

• Ventricular muscle fiber action potential averages around 105 millivolts
• Intracellular potential rises from -85 mV to +20 mV during each beat
• The membrane remains depolarized for about 0.2 seconds, exhibiting a plateau followed by abrupt repolarization
• Ventricular contraction lasts 15x longer in cardiac muscle than skeletal

Factors Causing Prolonged Action Potential and Plateau

• Skeletal muscle action potential happens by the opening of fast sodium channels, creating sodium influx
• Cardiac muscle is caused opening fast sodium channels and slow calcium-sodium channels for influx and prolonged depolarization
• Potassium permeability decreases about fivefold post action potential and maintains a resting voltage

Role of Atria and Pumping Effectiveness

• Atria act as primer pumps, increasing ventricular pumping effectiveness by 20 per cent
• Most conditions can prevail should the heart continue to operate without this extra 20 per cent effectiveness
• It is normally capable of pumping 300 to 400 per cent more blood required
• The difference is unseen unless person exercises, triggering heart failure

Cardiac Cycle Phases

• Ventricular contraction (systole)
• Ventricular relaxation (diastole)
• Each beat depends on changes in blood volume, pressure, as well as closure and opening of heart valves
• The events in the RV and LV is the same, except that the pressure in the RV is smaller than the LV
• Superior vena cava collects veins from head and upper body
• Inferior vena cava collects veins from legs and lower torso

Ventricular Events during Systole and Diastole

Pressure Changes in Aorta

• During systole, the aortic pressure increases reaching a maximum value of 120 mmHg which is systolic
• During the diastolic at the end of diastole, the aortic pressure decreases reaching a minimum value of 80 mmHg

Distole vs Systole

• Diastole involves ventricular relaxation, allowing the ventricles to passively fill with blood from the atria through atrio-ventricular valves
• The right atrium receives venous blood through the superior vena cava (SVC) and inferior vena cava (IVC)
• The left atrium receives oxygenated blood through the four pulmonary veins
• At the end blood is ejected into the ventricles
• Systole signifies ventricular contraction, ejecting blood into the aorta and pulmonary artery through aortic and pulmonary valves
• At the atrio-ventricular valves are closed, blood continues to enter

Mechanical Events of the Cardiac Cycle

• Ventricular systole: atria systole, isovolumic contraction phase, rapid ejection phase, reduced ejection phase
• Ventricular diastole: isovolumic relaxation phase, rapid filling phase, slow filling phase (diastasis )

Cardiac Cycle Phases

• Atrial Contraction (Phase 1): Increase pressure within the atria chambers and forces more blood through open atrio-ventricular (AV) valves
• AV valves are open, while semilunar valves are closed
• Isovolumetric Contraction (Phase 2): Ventricular pressure rises sharply, causing A-V valves to close
• The ventricle builds its pressure to push the semilunar valves, there is no emptying
• It is an isometric contraction that is occurs during increasing muscle tension that causes little or no changes to length
• Rapid Ejection (Phase 3): Initial, and is caused by the aortic and pulmonary arteries
• Ejection occurs when the intra-ventricular pressures surpass pressuries
• Reduce Rejection (Phase 4): Arotic/Pulmonary vales open AV vales remain closed The rate of blood flow exceeds rate of aorta. Aoritic pressure reduces and makes the 2nd heart sounds.
• The aortic calve closers mark the end of ventricular systole, and an onest to diastole. The dicrotic notch has an incisura from the aoritic valve
• Isovolumetric Relaxation (Phase 5): Ventricular relaxation begins, causing ventricular pressures to decrease
• arterial pressure decreases and aortic and pulmonary valves are snapped closed causing isovolumic ot isometric relaxation
• Rapid filling (Phase 6): Major Stage of ventricles filling When the av valve open blood flows in the ventricle, which is happening because aterial pressure is higher making the valve open
• - Reduced filling Phase (7):* Followed by Diastasis, bloods come from Rt Atrium filling and is coming from the System blood circulating And the Bloods form the lung flows into it Atrium then goes to the ventricles
• First third: rapid filling
• Middle Third: Small amount of blood coming from veins, passed though artia ad goes to the ventricle
• Last Third giving truct to the filing, during hear
• An A wave is cause from antail Contraction 4/5 mm hg

End-Diastolic, Systolic Volume , as well as Stroke Volume

• Normal filling increases each ventricle's to about 110-120 milliliters from the end-diastolic volume
• Decreased volume is called strokes
• Ends is called End-volums sysotlic. The is call the fraction and about 60%
• Strongly Contract ends to be just around 10 to 20 MLs
• 150-180 Mls is high normal volume. Then the volume as the strike will be higher
• 150 is too Much,
• 1 militer is 39 MLs
• 1 milli liter is 100MLs
• Systolic is too much,
• During Systolic the pressure reaches mm Hg, which is systolic
• In heart of heart and other parts, what ever happening on left will effect the right