B3.2 The Cardiac Cycle PDF 2025 (OCR)

First Exams 2025 B3.2 The Cardiac Cycle Theme: Form and Function Level of Organisation: Organisms HEART BEAT Statement(s) and Objective(s): B3.2.16: Stages in the cardiac cycle. State the cause of each of the two sounds of the heartbeat Describe the stages of the cardiac cycle Expla...

First Exams 2025 B3.2 The Cardiac Cycle Theme: Form and Function Level of Organisation: Organisms HEART BEAT Statement(s) and Objective(s): B3.2.16: Stages in the cardiac cycle. State the cause of each of the two sounds of the heartbeat Describe the stages of the cardiac cycle Explain the pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle State the cause of systolic and diastolic pressure Define myogenic contraction. Define cardiac cycle. Outline the role of the pacemaker cells in the sinoatrial node. Describe the propagation of the electrical signal from the sinoatrial node through the atria and ventricles. Explain the flow of blood during atrial and ventricular systole and diastole. Define systolic and diastolic blood pressure. State the cause of systolic and diastolic blood pressure. State the cause of each of the two From the IB sounds of the heartbeat The heart sounds (“lubb-dupp, lubb-dupp”) are made when sets of valves within the heart close in response to pressure changes. The first heart sound (“lubb”) is caused by the closure of theFrom atrioventricular valves at the start of ventricular systole. the IB The second heart sound (“dupp”)is caused by the closure From of the semilunar valves at the start of ventricular diastole the IB HL Content Only From B3.2.16: Stages in the cardiac cycle the IB Application of skills: Students should understand the sequence of events in the left side of the heart that follow the initiation of the heartbeat by the sinoatrial node (the “pacemaker”). Students should be able to interpret systolic and diastolic blood pressure measurements from data and graphs. HL Content Only Control of the Cardiac Cycle The medulla oblongata has two nerves connected to the sinoatrial node of the heart. The nerves control the rate at which the heart beats ❓ Explain how the heartbeat is initiated and coordinated. HL Content Only Control of the Cardiac Cycle Cardiac muscle is myogenic, as it contracts without stimulation. The sinoatrial node (pacemaker) controls the rate of heart beat. The sinoatrial node initiates an action potential (electrical signal) which rapidly spreads across the atria, causing atrial systole (contraction). A layer of fibrous tissue prevents the action potential from travelling directly to the ventricles. There is a pause before the signal reaches the ventricles, so that the four chambers do not contract at the same time. The action potential travels to the ventricles via the atrioventricular node. HL Content Only Control of the Cardiac Cycle The action potential travels down the Purkinje fibers to the apex of the heart. The action potential travels up the walls of the ventricles, initiating ventricular systole from the apex, pumping all of the blood out of the ventricles. ❓ Label structures 1 to 5 on the diagram of the heart. All structures are involved in the initiation Control of Heart Rate and control of heart beat. HL Content Only The Cardiac Cycle Systole is the contraction of heart muscles. Diastole is the relaxation of heart muscles. ❓ Explain the cardiac cycle for the left side of the heart. HL Content Only The Cardiac Cycle The left atrium and left ventricle are in diastole. Most of the blood flow directly through the atrium to the ventricle. An action potential from the sinoatrial node causes the left atrium to enter systole. Pressure increases in the atrium as it contracts, forcing all of the blood into the ventricle. An action potential from the atrioventricular node causes the ventricle to enter systole. As the ventricle contracts, pressure increases in the ventricle, causing the atrioventricular valve to close, as pressure is higher in the ventricle than the atrium. HL Content Only The Cardiac Cycle The high blood pressure in the ventricle increases until the semilunar valve opens and blood moves into the aorta. The ventricle enters diastole, and pressure in the ventricle decreases. When pressure is greater in the aorta than the ventricle, the semilunar valve closes. When pressure in the ventricle is lower than the atrium, the atrioventricular valves open. From the IB  From the IB Atrial Systole Ventricular Systole Atrial and Ventricular Diastole What is occuring at each From number on the graph? the IB 4 1 - A very slight increase in 3 pressure during the atrial systole. 2 - Ventricular systole begins with a massive increase in pressure - this forces the AV 1 2 valve closed. The only pathway for the blood to follow is through the aorta. 3 - Very shortly thereafter, the pressure in the aorta spikes from the blood flow. 4 - Everything relaxes as blood flows back into the atria.  From the IB Go here for an interactive view of the cardiac cycle. HL Content Only Measuring Blood Pressure Blood pressure measurements include two pressure measurements: Systolic pressure, caused by ventricular systole. Diastolic pressure between ventricular contractions. Describe how sound is used to From the IB measure blood pressure The sound of blood pulsing through the brachial artery can be heart with the use of a stethoscope and sphygmomanometer. Describe how sound is used to From the IB measure blood pressure Blood pressure is measured in arteries using a sphygmomanometer. (veins do not have sufficient pressure to be easily detected). The sphygmomanometer is a blood pressure cuff (sleeve) that cuts off circulation to a region (typically the brachial artery in the arm). The pressure of the cuff is slowly released until a pulse can From be audibly detected with a stethoscope (systolic pressure). the IB