[Biology Form 5] Human Heart

1. State the function of human heart.
   It pumps blood throughout the body.
   
   
2. Everything in heart seems to come in fours:
   There are four main blood vessels in the heart. Name the blood vessels labelled A, B, C and D in the diagram, and state their functions.
   
   
   
   
   A: Aorta - transports oxygenated blood to all parts of the body from the left ventricle of the heart.
   
   B: Pulmonary artery - transports deoxygenated blood to the lungs from the right ventricle of the heart.
   
   C: Pulmonary vein - transports oxygenated blood from the lungs to the left atrium of the heart.
   
   D: Vena cava - brings in deoxygenated blood from all parts of the body to the right atrium of the heart.
   
   
3. There are four chambers: left atrium, right atrium, left ventricle and right ventricle. Explain why the left ventricle has the thickest muscle wall.
   (Tip: Where does it pump its blood to? Does it undergo high pressure?)
   It must be able to withstand very high pressure because it pumps blood to all parts of the body.
   
   
4. There are four main valves: bicuspid valve, tricuspid valve and two semi-lunar valves. State their function.
   (Tip: All valves ensure a one-way flow of blood)
   
   • Bicuspid valve - prevents the backflow of blood between the left ventricle and the left atrium.
     
     
   • Tricuspid valve - prevents the backflow of blood between the right ventricle and the right atrium.
     
     
   • Semi-lunar valves - while one of them prevents the backflow of blood between the left ventricle and aorta, the other prevents it between the right ventricle and the pulmonary artery.
     
     
5. There are four structures involved in the beating of the heart: sinoatrial node (SAN), atrio-ventricular node (AVN), bundle of His and Purkinje fibres. State the functions of the SAN and AVN.
   (Tip: The two nodes act like batteries and generate electrical impulses that cause the cardiac muscles to contract)
   The two nodes act like batteries to produces electrical impulses that cause the cardiac muscles to contract.
   
   
6. The pacemaker of a patient's heart fails to function. An electronic pacemaker is used to replace the original pacemaker. Explain how this works.
   (Tip: Think about the function of the SAN - the electronic pacemaker has the same function)
   The electronic pacemaker generates electrical impulses that make the cardiac muscles contract and the heart beat.
   
   
7. Compare the rate of blood flow in blood vessels A and D.
   (Tip: Which of the blood vessels is an artery or a vein? Which undergoes more pressure? So, in which of them will blood flow more and at a greater speed?)
   
   • A, the aorta, is the largest artery and undergoes very high pressure. So, in it, blood flows at a greater speed.
   • D, the vena cava, the largest vein, does not undergo as much pressure. Thus, in it, blood flow is slower.