Function of the heart

Synonyms

Heart sounds, heart signs, heart rate, medical: Cor

Introduction

The heart ensures the blood circulation of the whole body through constant contraction and relaxation, so that all Oragne is supplied with oxygen and nutrients and decomposition products are removed. The pumping action of the heart takes place in several phases.

Heart action

In order for the heart to pump the blood so effectively that it flows through the entire body, it must be ensured that all heart muscle cells work together in a coordinated manner within the cardiac cycle. In principle, this control functions by means of an electrical impulse that is generated in the heart itself, then spreads through the muscles and leads to an ordered action (contraction) in the muscle cells. This only works because all cells are electrically conductive and connected to each other.

The work cycle/heart function (filling the heart with blood and expelling the blood into the circulation) is divided into 4 phases that run regularly one after the other: Relaxation and filling phase (together: diastole) and tension and expulsion phase (together: systole). At physical rest, the duration of diastole is 2/3 of a heart cycle (approx. 0.6 sec), systole is 1/3 (approx.

0.3 sec). If the heart rate increases (and thus the length of a cardiac cycle decreases), this is due to increased shortening of the diastole. The terms of the individual phases refer to the condition of the heart chambers, as they handle the much more important part of the heart’s work.

They run simultaneously on the right and left. The individual phases in detail:

• Tensioning phase: When the heart is filled with blood, the muscle cells of the ventricles begin to contract and increase the pressure inside the heart cavity (isovolumetric work), but without contracting, since all heart valves are closed. The pressure in the ventricle is higher than in the atrium, therefore the sail valves are closed.

  Also in the executing vessels (right: pulmonary artery = truncus pulmonalis, left: aorta) the blood pressure is higher than the pressure in the ventricle, therefore the pocket valves are also closed.

• Expulsion phase: The chamber muscles constantly increase the pressure in the chamber (tensing) until it exceeds the blood pressure of the vessels performing the expulsion. At this moment, the pocket valves open and the blood flows from the chambers into the performing vessels. The pressure that now prevails is called the systolic blood pressure (the higher value when measuring blood pressure, approx.

  120mmHg). As blood is ejected from the chamber, the volume and thus the pressure decreases. This process continues until the pressure in the chamber falls below the pressure in the performing vessels (diastolic blood pressure – the lower of the two measured values, approx.

  80mmHg). Once this point is reached, the pocket valves are passively closed again (by the apparently reversing blood flow), and systole is terminated. A total of 60-70 ml was expelled from the heart, which corresponds to an ejection fraction of 50-60% of the total blood in the ventricle.

• Relaxation phase: During this phase, the heart muscle cells slacken, whereby all heart valves are closed due to the pressure differences to the inflow path (atria) and expulsion path.
• Filling phase: Due to the closed sail flap, the blood from the atrium could no longer enter the chamber, so that more blood has now collected here.

  As soon as the pressure in the atrium exceeds the pressure of the (relatively empty) chamber, the filling phase begins and the blood can flow back into the chamber. Filling is facilitated by the relaxation of the chamber muscles. The chamber relaxes and returns to its original position.

  Since the blood in the heart no longer changes its position, the sail valves now literally turn over the blood that previously collected on the closed sail valves. This mechanism is called the valve level mechanism and explains why after the first third of the filling phase 3⁄4 of the chamber filling is already reached – and thus why one can also accept a shortening of the filling phase without a large loss of effectiveness. At the end of the filling phase there is a supporting contraction of the atrial muscles to force the remaining amount of blood into the chamber.