Animals: Circulatory System - The Heart

Animals: Circulatory System - The Heart

  • The heart is a key organ in the circulatory system, facilitating the transport of oxygen, nutrients and waste materials around the body.

  • Structurally, the heart is divided into four chambers: two at the top called atria and two at the bottom called ventricles.

  • Blood flow in the heart follows a specific pathway. Oxygen-poor blood from the body flows into the right atrium, then moves into the right ventricle.

  • From the right ventricle, blood is pumped to the lungs through the pulmonary artery as part of the pulmonary circulation.

  • In the lungs, blood releases carbon dioxide and absorbs oxygen during respiration. This oxygen-rich blood returns to the heart, entering the left atrium.

  • The oxygen-rich blood then moves down into the left ventricle, which pumps it into the aorta, from where it travels throughout the body - this circuit is known as systemic circulation.

  • Between each chamber and major blood vessel, there are valves which prevent backflow of blood. The tricuspid valve is found between the right atrium and ventricle, and the mitral or bicuspid valve lies between the left atrium and ventricle.

  • The semilunar valves (pulmonary and aortic) are found at the entrances of pulmonary artery and aorta and they also prevent backflow of blood.

  • The heart rate, commonly referred to as the “pulse”, denotes the number of times the heart beats per minute. Factors like hormones, temperature, and exercise can alter the heart rate.

  • Muscle tissue in the right atrium, known as the sinoatrial node (SAN), regulates heart beat. It initiates an electrical impulse that spreads over the atria, making them contract.

  • The atrioventricular node (AVN), located between the atria and ventricles, then receives this impulse. After a brief delay to allow the atria to empty, it sends the impulse to the ventricles, causing them to contract.

  • During rest, the coronary arteries supply the heart muscle (myocardium) with blood. Blockages in these arteries can lead to heart attacks.

  • The heart’s muscular walls, particularly the left ventricle, allow it to forcefully pump blood around the body.

  • This function is crucial for the sufficient delivery of oxygen and nutrients to body cells, and for the efficient removal of waste products such as carbon dioxide.

  • Understanding heart structure and function is fundamental in the study of biology, particularly for those interested in human health and disease.