Biology: The Heart

The Structure of the Heart

The human heart is a muscular organ responsible for pumping blood around the body through the circulatory system.
Structurally, the heart is divided into four compartments: two atria on the top and two ventricles at the bottom.
The heart’s walls are made up of cardiac muscle tissue known as myocardium.
The heart is enclosed by a sac known as the pericardium, which offers protection and reduces friction during heart contractions.

Deoxygenated blood flows into the heart through veins. Specifically, the superior and inferior vena cava deliver blood to the right atrium.
From the right atrium, blood is pumped into the right ventricle which then sends the blood to the lungs via the pulmonary artery for oxygenation.
Oxygenated blood returns to the heart into the left atrium via the pulmonary veins.
The left ventricle pumps the oxygenated blood through the aorta to the rest of the body.
The cycle then repeats.

Heart valves ensure that blood flows in the correct direction and prevent backflow.
The tricuspid valve is located between the right atrium and right ventricle, while the mitral valve is between the left atrium and left ventricle.
The pulmonary and aortic valves, situated at the outlets of the right and left ventricles respectively, control blood flow from the heart to the lungs and rest of the body.

The cardiac cycle refers to the sequence of events that occur when the heart beats.
Typically, there are three stages: atrial systole (contraction of atria), ventricular systole (contraction of ventricles), and diastole (resting phase).
Each cycle causes the heart to pump blood, ensuring continuous provision of oxygen and nutrients to cells, and disposal of waste materials from cells.

Your heartbeat is regulated by an electrical system within the heart tissue known as the cardiac conduction system.
The sinoatrial node (SA node) is the heart’s natural pacemaker. It initiates an electrical signal that causes the atria to contract.
This signal then travels to the atrioventricular node (AV node) which relays the electrical impulses to the ventricles causing them to contract.
The rate and rhythm of the heartbeat can also be influenced by external factors such as exercise, stress, and hormones.

Coronary heart disease is a condition where the coronary arteries, which supply oxygen-rich blood to the heart muscle, become narrow due to a build-up of fatty materials.
Congenital heart disease refers to structural problems with the heart present at birth.
Heart failure is a condition where the heart is unable to pump blood around the body effectively.
Arrhythmias are heart rhythm problems that occur when the electrical impulses to the heart that coordinate heartbeats are not working properly.