The Heart

The Heart and Its Structure

  • The heart is a key organ in the circulatory system, responsible for pumping blood throughout the body.
  • It is a muscular organ, roughly the size of a clenched fist, located in the centre of the chest just slightly to the left.
  • The heart is divided into four chambers: two atria (singular: atrium) at the top and two ventricles at the bottom.
  • The right atrium receives deoxygenated blood from the body via the vena cava and pumps it into the right ventricle.
  • The right ventricle then propels this blood to the lungs for oxygenation through the pulmonary artery, which is the only artery in the body carrying deoxygenated blood.
  • The left side of the heart deals with oxygenated blood: the left atrium receives this freshly oxygenated blood from the lungs via the pulmonary vein, then pumps it into the left ventricle.
  • The left ventricle then pushes this oxygen-rich blood out to the rest of the body via the aorta.

The Cardiac Cycle

  • The cardiac cycle refers to one complete heartbeat, where the heart contracts and relaxes to pump blood.
  • The cycle is initiated when the sinoatrial node (SAN), or the heart’s natural pacemaker, sends an electrical signal causing the atria to contract.
  • This is called the atrial systole phase, during which blood is pumped from the atria to the ventricles.
  • The signal then reaches the atrioventricular node (AVN), causing the ventricles to contract, referred to as ventricular systole. During this phase, blood is pumped out of the heart.
  • Finally, the heart relaxes in a phase known as diastole.
  • This sequence of contraction and relaxation constitutes a single heartbeat.

Heart Health and Diseases

  • A variety of factors such as unhealthy diet, lack of exercise, smoking, and high stress can affect heart health.
  • These factors can lead to health conditions such as coronary heart disease, where the coronary arteries become narrowed by a build-up of fatty deposits.
  • This fatty material is called atheroma and can result in angina, heart attacks, or heart failure.
  • It is important to maintain a healthy lifestyle to reduce the risk of heart-related diseases.
  • Regular exercise, a balanced diet, reduced alcohol consumption, and avoiding smoking are all key for maintaining good heart health.

Regulation of Heart Rate

  • The heart rate can be influenced by both internal and external factors.
  • Internally, the heart rate is controlled by the SAN, which adjusts the rate according to the body’s needs.
  • Externally, substances such as adrenaline can increase the heart rate, while acetylcholine can decrease it.
  • The brain also plays a significant role in regulating the heart rate, especially during physical activity, stress, or changes in body temperature.
  • Regular exercise can improve the heart rate and overall cardiovascular fitness, reducing the risk of heart disease.