The heart

The Heart

Structure and Function

  • The heart is a muscular organ that functions as a pump to circulate blood around the body.
  • The heart is divided into four chambers: two atria (singular: atrium), and two ventricles.
  • The atria receive blood returning to the heart from the body and lungs, acting as reservoirs before blood is pumped into the ventricles.
  • The ventricles are heavily muscular chambers that pump blood out of the heart to the lungs and to the rest of the body.
  • The chambers are separated by a wall of muscle called the septum to prevent oxygen-rich and oxygen-poor blood from mixing.

Valves

  • To maintain a one-way flow of blood through the heart, a series of valves are present.
  • The atrioventricular (AV) valves (the bicuspid valve on the left and tricuspid valve on the right side of the heart) open to allow blood to flow from the atria to the ventricles and prevent backflow when the ventricles contract.
  • The semi-lunar valves at the base of the aorta and the pulmonary artery also prevent backflow of blood into the ventricles after pumping.

Coronary Circulation

  • The heart muscle, or myocardium, has its own network of blood vessels — the coronary arteries.
  • These arteries branch off from the aorta, supplying oxygen-rich blood to the myocardium.
  • Coronary veins collect the deoxygenated blood and nutrients from the myocardium and drain into the right atrium, completing the circulation.

Cardiac Muscle

  • The heart is made of a special kind of muscle tissue called cardiac muscle.
  • Unlike other muscle tissue, cardiac muscle is auto-rhythmic, meaning it can generate its own contractions without signals from the nervous system.
  • This contractile activity is coordinated by specialised cells known as pacemaker cells, which initiate the electrical signals causing the heart muscle to contract.

Myogenic Contraction

  • Contractions of the heart are initiated from within the heart itself, a phenomena known as myogenic contraction.
  • The sinoatrial node (SAN) located in the wall of the right atrium acts as the heart’s own pacemaker, setting the rhythm of the heartbeat.
  • The electrical impulses from the SAN first cause the atria to contract and then stimulate the atrioventricular node (AVN), which transmits the impulses to the ventricles, causing them to contract after a short delay.

Heart Conditions and Health

  • Understanding the heart’s structure and function provides insight into the pathologies that can affect heart health, such as heart attack (myocardial infarction), stroke, heart failure, valvular heart disease, and arrhythmias.
  • Lifestyle choices such as a balanced diet, regular exercise, avoiding tobacco and limiting alcohol intake can significantly reduce the risk of developing heart disease.
  • Treatments for heart conditions can include medication, lifestyle changes, surgical procedures and, in some cases, the use of medical devices like pacemakers.