Functions of Cardiac Muscle - Understand Its Structure And Location

Cardiac Muscle Explained: Structure and Function

The human heart is one of the marvellous achievements of biological engineering, persistently pumping blood throughout the body to keep it alive. This key organ works around one type of muscle: cardiac muscle.  

Appreciation of its functioning, structure, and locality is important in understanding how the heart works and towards the contribution of the whole mechanism of health. 

What is the Cardiac Muscle? 

Cardiac muscles, more commonly known as myocardium, are involuntary striated muscles found only in the walls of the heart and make up the heart's ability to contract and, hence, pump blood and deliver oxygen and nutrients to tissues and organs in the body. 

Role of Cardiac Muscles 

Some of the primary functions of cardiac muscles include providing for rhythmic heartbeats that pump blood throughout the circulatory system. Such activity is vital in maintaining the flow of oxygenated blood from lungs to other parts of the body, returning deoxygenated blood back to the lungs for re-oxygenation. 

Pumper of Blood 

The heartbeat is a pumping action that is characterized by two main phases: 

Systole: During systole, the cardiac muscle contracts; as a result, blood is ejected from the heart chambers, the ventricles, into the arteries. The left ventricle then pumps oxygen-rich blood into the aorta, which distributes it to the body, while the right pumps deoxygenated blood into the pulmonary artery that leads to the lungs. 

Diastole: The cardiac muscle relaxes during diastole, and due to this relaxation, it allows the chambers of the heart to fill up with blood. Blood from the veins flows into the atria, and the ventricles fill up in readiness for the next contraction. 

Maintaining Heartbeat 

Cardiomyocytes are cells with intrinsic rhythmicity, capable of generating electrical impulses without the need for external stimuli. Otherwise, it will be an element that secures a constant heartbeat. Electrical impulses produced by the natural pacemaker of the heart—the sinastral node—diffuse in all directions throughout the cardiac muscle, setting the contraction and relaxation phases in synchrony. 

Responding to Physiological Demands 

The cardiac muscle responds to changes in the body's needs. An example of this is the way it increases the heart rate during exercise to pump more oxygenated blood to the working muscles. This adjustability allows for homeostasis and the meeting of the overall metabolic demands of the body. 

Structure of Cardiac Muscle 

The cardiac muscle is specially structured to do effectively its important duties. Some of the features that characterize cardiac muscle set it appreciably apart from skeletal and smooth muscle types. 

Striations and Sarcomeres 

Like skeletal muscle, cardiac muscle is striated, meaning that it appears banded or striated under a microscope due to the arrangement of myofibrils. Myofibrils are composed of repeating units known as sarcomeres, the functional contractile units of muscle fibres. Sarcomeres contain thick filaments and thin filaments, whose sliding produces contraction of the muscle. 

Intercalated Discs 

One of the greatest distinguishing features of cardiac muscle is the intercalated discs that allow single cardiac muscle cells to function physiologically as entities. Intercalated discs contain: 

Gap Junctions: These channels allow the passage of ions and electrical impulses directly from one cell to another, thus ensuring the synchronized contraction of the heart muscle. 

Desmosomes: These provide the mechanical strength for holding cells together, preventing them from separating during the forceful contractions of the heart. 

Branched Cells 

Cardiac muscle cells, as noted above, are branching, whereas the cardiac equivalent of skeletal muscle fibers are grouped together in a linear series. With such a large number of cardiac muscle cells contracting, this branching is very helpful in passing the electrical depolarization action potential throughout the network of cells, producing rapid contraction. 

Single Nucleus 

Generally, cardiac muscle cells contain only one centrally located nucleus. Again, in contrast to skeletal muscle fibers that are multucleated, the presence of this single nucleus coordinates cellular activities and helps to keep metabolic activity of the cell in balance. 

Mitochondria 

The cardiac muscle cells are densely populated with powerhouses of the cell, evidenced by the large quantity of mitochondria. Mitochondria synthesize energy (ATP) for the constant contraction of muscle tissue. It follows, then, that with such a density of mitochondria, the heart can pump blood without tiring. 

Location of Cardiac Muscle 

Cardiac muscle is present only in the heart. It makes up the middle layer of the heart wall, that is, the myocardium. There are three layers to the heart wall: 

Endocardium: The inner layer that lines the heart chambers and covers the valves 
Myocardium: The thick, middle muscular layer that provides the heart's contractile force 
Epicardium: The outer layer that is part of the pericardium, the sac which surrounds and protects the heart. 

Chambers of the Heart 

The heart is divided into four chambers: two atria & two ventricles. Cardiac muscle lines the walls of all four chambers, but the thickness of the muscle varies depending on the chamber's function. 

Atria: The walls of the atria are thinner as compared to the ventricles. Blood returning to the heart accumulates in the atria and they pump it to the ventricles. 

Ventricles: The walls of the ventricles are much thicker, especially that of the left ventricle. This thickness is required to pump blood throughout the body. 

Septum 

The interventricular septum consists of a thick wall of cardiac muscle that separates the two ventricles on the left and right sides. It provides separation for the oxygenated and deoxygenated blood in such a way that it remains in the proper circulatory pathway. 

Disorders of Cardiac Muscle 

Different kinds of pathologies can afflict cardiac muscle, thus impairing its normal function and leading to life threats. 

Cardiomyopathy 

Cardiomyopathy is a disease of the heart muscle—also the myocardium—that makes it hard to pump blood. There exist several cardiomyopathies that include the following:– 

Dilated Cardiomyopathy: Weakening of the cardiac muscle and its enlargement reduces its pumping efficiency. 
Hypertrophic Cardiomyopathy: Abnormal thickening of heart muscle consequently creates an obstruction in blood flow that produces difficulties in heart rhythm. 
Restrictive Cardiomyopathy: The scarring or thickening process hardens the heart muscle and reduces its elasticity, which badly affects its filling capacity with blood. 

Myocarditis 

The inflammation of the heart muscle is called myocarditis. It most often results from viral infections that can become responsible for damage to the cardiac muscle and decrease its contractility. 

Heart Failure 

Heart failure occurs when the heart is unable to function properly to deliver sufficient blood volume into the circulation to meet the body's needs. It can be brought about by a number of conditions, including cardiomyopathy, coronary artery disease, and high blood pressure. 

Summary 

Cardiac muscular tissue is an amazing tissue that plays a very vital role in maintaining life because it continuously pumps blood throughout the body. It has a striated structure, intercalated disks, and many mitochondriae that give it the ability to efficiently function.  

Another highly important qualities of cardiac muscle are its flexibility and endurance, which allow it to respond to changing needs of the body. Its location, only in the heart, coupled with an understanding of the function and structure, allows for a good insight into how the heart works and gives an understanding of why the cardiovascular system needs to be kept fit and healthy.