The Human heart is a muscular organ about the size of a fist. Its purpose is to pump blood and nutrients to all parts of the body. In the process of delivering Oxygen-rich blood to the organs and tissues, it also removes Carbon (IV) Oxide and other waste products, which will be excreted from the body.
As we all know, tissues in our body require a constant supply of oxygen for normal functioning. A decrease in Oxygen supply will lead to tissue death(Hypoxia). This applies to the heart itself as it is also an organ. In this article, we will discuss the human heart, its functions, and its structure.
The coronary vessels are responsible for supplying blood containing oxygen and nutrients to the heart muscles while getting rid of waste products that may have accumulated.
Anatomy of the Human Heart.
The human heart is made up of four chambers. These chambers include;
- Two upper Atria(Left and Right Atria).
These include the left Atria and right Atria. The right Atria receives blood from the superior and inferior vena cava, before Passing it on to the right ventricle.
The left Atria will receive oxygenated blood from the lungs, before passing it on to the left ventricle.
- lower Ventricles(Left and Right Ventricles).
The right ventricle receives blood from the right Atria. This blood is deoxygenated. It will then pump the blood to the lungs, where oxygenation will occur. The distance from the heart to the lung is not that great, so the right ventricle does not have a lot of bulk muscles, like the left ventricle.
The left ventricle receives oxygenated blood from the left atria, before Pumping it to all body tissues. This distance is greater, thus explaining why this ventricle has a thick bulk of muscle.
Please note that I will be describing the Heart assuming that it is in its Anatomical position to avoid confusion.
The right Atria and the Right ventricle make up the Right Side of the Heart, while the left Atria and the left Atria make up the left side of the Heart. The right side of the Human Heart is separated from the left side by a Septum.
This Septum prevents a mixture of blood from both sides. The Atria receive from outside the heart and drain it to the ventricle, which will then push the blood outside the Heart.
The Heart is protected and anchored by a double-walled Pericardium Sac. The inner part of this Pericardium Sac is called the Serous Pericardium while the outer part is known as the Parietal Pericardium. A fluid known as the Pericardial fluid runs between these two pericardium structures. The function of the Pericardial fluid is to lubricate the Heart, making its contractions and relaxations easier.
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The main function of valves is to prevent the backflow of blood. The Human Heart is made up of four layers:
- Epicardium Layer (Outermost layer).
- Myocardium layer( Muscles of the heart). It contains the muscles responsible for contraction and relaxation.
- Endocardium (Inner layer). Blood is in contact with this part.
Four valves prevent the backflow of blood. These are:
- The Tricuspid Valve.
- The Bicuspid valve (also called the Mitral valve).
- The Aortic valve.
- The pulmonary valve.
The Tricuspid and Mitral valve can collectively be called the Atrioventricular valves. The Aortic and Pulmonary valves can collectively be called the Semilunar valves.
Functions of the Human Heart’s Valves
The Tricuspid valve is located between the right Atria and the Right Ventricle. Its purpose is to prevent the backflow of blood back into the right Atria during the contraction of the Heart.
The Pulmonary Valve prevents the backflow of blood from the Pulmonary Artery back into the right ventricle during the relaxation of the Heart.
The Bicuspid valve, also known as the mitral valve is located between the left Atria and the left ventricle, therefore separating them. The Bicuspid valve prevents the backflow of blood from the left Ventricle back, into the left atria because of the heart contracting force.
The Aortic valve prevents the backflow of blood back into the left ventricle during the relaxation of the Heart’s muscles.
These four valves are anchored to the Hearts Muscles by ” Heartstrings” called Chordae tendineae. The Heart’s contraction and relaxation are controlled by electrical impulses produced by the Sinoatrial (SA) node.
Physiology of the Human Heart
There are two pathways through which the Heart circulates blood. These are;
1. Pulmonary Circulation.
2. Systemic Circulation.
In Pulmonary circulation, deoxygenated(without Oxygen) blood in the Right Ventricle is pushed when the Heart contracts into the Pulmonary Artery, then finally to the lungs via the Pulmonary Valve. The pulmonary Valve will prevent the backflow of blood back into the Right Ventricle. The blood is oxygenated(Oxygen is added) in the lungs and carbon (IV) Oxide is excreted. This blood will then return to the Left Atria via the Pulmonary Vein. That is the end of Pulmonary circulation.
In Systemic circulation, Oxygenated blood is pumped into the aorta by the Heart’s contraction. This is via the Aortic valve. The blood will then travel through the Aorta to the Arterioles, then to the Capillaries – The exchange of Oxygen, Nutrients, and waste products occurs here. Deoxygenated blood from the capillaries moves into the veins back to the heart via the Superior and Inferior Vena Cava.
Blood Supply the Human Heart
The Heart, also being a muscle, requires its Oxygen and Nutrient supply – or else it will die. Therefore blood leaving the Heart via the Aorta diverges into the Left Main Coronary Artery on one side, and the Right coronary artery. These two can also be called Coronary blood vessels. The Left Main coronary artery will divide into the Circumflex artery and the left anterior descending artery. The right coronary artery supplies blood to the right side of the heart, which is smaller because it only pumps to the lungs. The left main coronary artery supplies blood to the left side of the heart, which is more muscular because it pumps blood to a greater distance – The rest of the body.
Nerve Supply to the Heart
The Human Heart’s nerve supply is by the Vagus Nerve (Cranial Nerve X) and sympathetic fibres. The left vagus nerve innervates the AV Node whereas the Right vagus nerve innervates the Sinoatrial node.
The Heart’s Electrical System.
Contraction of the Heart needs to be in a rhythmic manner with both Ventricles contracting uniformly in a coordinated manner. This enables the heart to maintain a steady rate of 60 to 100 beats per minute at rest. The Heart’s conducting system is responsible for this coordination and uniformity. This electrical signal is the one that initiates the contraction of the Heart’s muscles and therefore pumps blood.
A heartbeat occurs in the following sequence ;
- The electrical impulse begins at the Sinoatrial (SA) Node top of the Right Atria near the Vena Cava. We also call the SA node the Heart’s Pacemaker.
- Both atria will contract due to this impulse squeezing blood into the ventricles.
- The Atrioventricular (AV) node will then send an electrical impulse to the ventricles through the Bundle of His. This signal will divide into two signals, one going to the right ventricle, and the other travelling to the left ventricle.
- The ventricles then contract to pump blood out of the Ventricles.
- The Sinoatrial Node will send another electrical impulse and the cycle will begin again.
In the above steps, one cycle will produce a heartbeat.
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