Papillary muscles are small conical, inwardly directed, muscle elevations of the ventricular muscles. They are connected by branching chordae to the edges of the leaflet valves, which act as passive check valves to regulate blood flow from the left atrium to the left and right ventricles. Immediately before the contraction phase of the ventricles, the papillary muscles tighten, thereby tightening the tendon filaments, which prevent the leaflet valves from blowing into the atria.
What is the papillary muscle?
Small conical, inward-pointing, protrusions in the ventricular muscles are called papillary muscles. There are three papillary muscles in the right ventricle and two in the left ventricle. They are connected by branching chordae tendineae to the edges of two leaflets of each leaflet. The leaflet valves act as passive check valves and provide the connection between the atrium and the ventricle. They ensure proper blood flow from the atria to the ventricles and prevent blood from flowing back into the atria during contraction of the ventricular muscles (systole). The leaflet valve of the left heart (mitral valve or bicuspid valve) has two leaflets, while the leaflet valve of the right heart (tricuspid valve) has three leaflets. The papillary muscles contract slightly during the tightening phase of the ventricular muscles, thereby tightening the leaflets so that the leaflets of the two leaflet valves are prevented from leafleting into the atria during pressure buildup in the ventricles.
Anatomy and structure
The right ventricle usually contains 3 papillary muscles, which are recognizable as small conical humps projecting into the ventricular space. Frequently, 4 to 5 papillary muscles can also be discerned in the right ventricle without pathologic findings. In the right ventricle, the papillary muscles arise partly from the septum of the ventricles and partly from the anterior ventricular wall. In the left ventricle, there are 2 more robust papillary muscles arising from the anterior and posterior ventricular walls, respectively. Unlike the papillary muscles of the right ventricle, the papillary muscles of the left ventricle never arise from the septum. Because the papillary muscles develop from the ventricular walls or from the septum, their anatomic structure is very similar to that of the ventricular walls. The myocardium, interspersed with muscle cells, makes up the bulk of the papillary muscles. Towards the inside, the endocardium is attached. Tiny lymphatic vessels can also be identified in the myocardium of the papillary muscles, which are connected to lymphatic collecting vessels outside the pericardium. In each case, the chordae tendineae arise at the tips of the papillary muscles. These are very strong and relatively stiff chordae tendineae with their branched free ends fused to the edges of the leaflet valves.
Function and tasks
The two leaflet valves, the mitral valve in the left heart and the tricuspid valve in the right heart, form the portal of entry to the left and right ventricles, respectively. The two passages between the atria and the ventricles show a relatively large cross-section, since blood must be transported from the atria to the ventricles in a few hundred milliseconds during the relaxation phase of the ventricles (diastole). Between the largest possible cross-section of the orifice and the lightest possible design of the leaflet valves, there is the difficulty that light and thus thin leaflets may not be able to withstand the pressure during systole when closed and may be forced through into the respective atrium, so that blood from the ventricles would be pumped back into the atria. Evolution has developed an ingenious aid to avoid this problem. The thin leaflets of the leaflet valves are “held down” at their edges by the chordae tendineae, so that they cannot be pushed through into the atrium. The main role and function of the papillary muscles is to assist this process by contraction. At the beginning of the systolic contraction phase of the ventricular muscles, the papillary muscles contract so that the chordae tighten and the leaflets of the mitral and tricuspid valves become taut. They then cannot be pushed through into the left and right atria, respectively.From a physical point of view, this transforms the bending forces exerted on the sail flaps into tensile forces that are much easier to withstand by the sails, which are made of collagen proteins.
Diseases
One of the most common diseases and problems is the tearing of a papillary muscle (papillary muscle rupture). Tearing is usually associated with myocardial infarction (heart attack), which leads to breakdown or necrosis of the tissue from which the corresponding papillary muscle originates. The muscle then no longer finds sufficient support at its base. This means that the papillary muscle in question shows a reduction in function up to a complete loss of function. The tendon filaments that originate from the corresponding papillary muscle can no longer tighten. As a result, mitral valve regurgitation often occurs with varying degrees of severity or prolapse, a pushing through of the corresponding leaflet valve into the atrium, which is usually associated with a severe course. Papillary muscle rupture most commonly occurs in the left posterior myocardium, thus directly affecting the mitral valve in the left heart. Papillary muscle rupture in the right ventricle is observed much less frequently. This means that the tricuspid valve in the right ventricle is also much less frequently affected by this type of insufficiency or by prolapse. Heart attacks caused by occlusion of an artery directly in the papillary muscles are also associated with similar symptoms.
