The human heart is a part of the cardiovascular system that is situated in the middle of the chest between the lungs. Its exact location is slightly positioned to the left and behind the sternum (breastbone). The size of the heart is approximately the size of your fist. Its function is to pump blood through the cardiovascular system, which consists of a network of veins and arteries. The heart is also surrounded by the pericardium, which is a double-layered membrane or sac.
There are four chambers of the heart. They are the upper chambers (left and right atria) and the lower chambers (left and right ventricles).
A wall of tissue called septum separates these chambers. The strongest and largest heart chamber is the left ventricle, which pumps oxygen-rich blood all throughout the body. The vigorous contractions of the left ventricle create your blood pressure. Every part of the heart has its own function. However, all parts simultaneously work together to keep blood moving throughout the body.
The right atrium collects unoxygenated blood from the veins and pumps it to the right ventricle, which then pumps the blood to the lungs to provide it with oxygen. This oxygenated blood is received by the left atrium, which pumps the blood to the left ventricle.
There are four valves that regulate the flow of blood through the heart:
1. Tricuspid Valve
This valve regulates blood flow between the right ventricle and the right atrium.
- It closes the upper right atrium that collects blood from the body.
- It allows blood flow from the upper right chamber to the heart’s lower right chamber.
- This valve also prevents the backward flow of blood from the ventricle to the atrium.
2. Pulmonary (Pulmonic) Valve
This valve controls blood flow from the right ventricle to the pulmonary arteries.
- It closes the lower right chamber of the heart or the right ventricle.
- It also allows the pumping of blood from the heart to the lungs through the pulmonary artery.
3. Mitral Valve
The mitral valve allows oxygenated blood that comes from the lungs to pass from the heart’s left atrium to the heart’s left ventricle.
- It closes the upper left chamber of the heart (left atrium) to collect oxygen-rich blood from the lungs.
- It also allows the passage of blood from the left atrium to the heart’s left ventricle.
4. Aortic Valve
The aortic valve allows the passage of oxygen-rich blood from the left ventricle into the aorta, which is the largest artery in the body.
- It closes the heart’s left ventricle before oxygen-rich blood is pumped out to the body.
- It also allows blood to leave the heart and on to the body.
The Heart's Electrical System
The electrical system of the heart regulates the timing of a heartbeat by sending an electrical signal through the heart's tiny muscle cells.
The sinoatrial (SA) node is usually where the electrical signal begins. The SA node is also called the heart's pacemaker, which is located above the right atrium. This electrical signal induces the atria to contract and push blood into the ventricles. The electrical impulse travels to a group of cells in the atrioventricular (AV) node, which is located at the bottom of the right atrium. These cells can slow down the electrical signal, so the ventricles and the atria will not contract at the same time. The signal is then carried along the Purkinje fibers, which are special fibers within the ventricular walls that pass the impulse to the heart and cause the ventricles to contract.
A healthy heart at rest usually beats around 50-99 times every 60 seconds. However, sometimes, people may have more than 100 beats per minute when they exercise, have a fever, are stressed or emotional, and when taking certain medications.
Blood vessels are part of the circulatory system that transport blood all over the human body. The three main types of blood vessels are:
Arteries are blood vessels that carry oxygen-rich blood far from the heart to the body tissues. As they carry oxygen-rich blood farther from the heart, they tend to branch and become smaller and smaller.
Most major arteries branch off from the aorta, which is the largest artery in the body. The artery that carries oxygenated blood from the aorta to the arms, neck, and head is the brachiocephalic artery. Other types of arteries and their functions are:
- Carotid Arteries - These arteries provide oxygenated blood to the neck and head parts of the body.
- Coronary Arteries - These arteries carry nutrient-filled and oxygen-rich blood to the heart.
- Common Iliac Arteries - These large arteries originate from the main blood vessel of the abdominal region called the abdominal aorta. Common iliac arteries are the ones that carry oxygen-rich blood from the abdominal aorta to the feet and legs.
- Pulmonary Artery - This artery carries deoxygenated blood from the right ventricle to the lungs for oxygenation.
- Subclavian Arteries - These arteries supply blood to the arms.
Unlike the arteries, which carry oxygen-rich blood from the heart to all body tissues, veins are blood vessels that return deoxygenated (oxygen-poor) blood from the organs back to the heart. Veins carry waste products that are subject to removal or excretion from the body.
As veins get closer to the heart, they become larger and larger. The large vein that brings deoxygenated blood from the upper part of the body to the heart is called the superior vena cava, while the vein that brings deoxygenated blood from the lower part of the body (abdomen and legs) to the heart is the inferior vena cava.
Other types of veins are:
- Brachiocephalic Veins - These large veins merge to form the superior vena cava.
- Common Iliac Veins - These veins merge to form the inferior vena cava.
- Pulmonary Veins - These veins transfer oxygen-filled blood from the lungs to your heart.
Capillaries are the smallest blood vessels in the body that connect the arteries and veins. Due to their thin walls, carbon dioxide, oxygen, nutrients, and other waste products are able to pass to-and-fro the organ's cells.