Settler Describe the route a blood cell would take around the body. You have just left the body entering the heart through the Vena cava. You could do this in bullet points on whiteboards
Module 2Exchange and transport 1.2.7 The cardiac cycle
Success Criteria Learning Objectives Understand the cardiac cycle Explain the terms cardiac cycle, diastole, atrial systole and ventricular systole (Grade E - D) Explain how the valves work in the cardiac cycle (Grade C –B) Describe the cardiac cycle with reference to the action of the valves in the heart (Grade B – A)
Starter • Gently press a fingertip on your neck just one side of your windpipe • Each time the heart beats, you should feel the pulse caused by a surge of blood through one of your arteries that goes to your head • If relaxed should feel a pulse roughly every second • The time between each pulse is the length of the cardiac cycle.
Heart valves • AV valve links the atria to ventricles • SL valves link ventricles to pulmonary artery and aorta • Why are valves important? • Stop blood flowing the wrong way • Valves open and close depending on the relative pressure of the heart chambers. High pressure behind a valve forces it open. • Circulatory system_1.wmv • Explain how the valves work in the cardiac cycle • (Grade C –B)
The heart • Heart muscle does not need to be stimulated by a nerve before it will contract. The heart beat originates in the muscle itself and, for this reason, it is described as being myogenic. • There are 2 phases to the beating of the heart: • Contraction (systole) • Relaxation (diastole)
1. Atrial Systole • Heart is full of blood • Contraction of both atria, decreasing volume of chamber and increasing pressure inside chamber • AV valves open, SL valves close • blood flows ventricles • No backflow as veins have valves
2. Ventricular Systole • Atria relax • Ventricles contract (0.1s after atria) • Decrease in volume = Increase in pressure in ventricle • Forces AV valves to close to prevent backflow • Semi-lunar valves open • blood flows from ventricles arteries • Lasts ~0.3 s
3. Ventricular Diastole • Ventricles and atria both relax • High pressure in pulmonary artery & aorta closes SL valves to prevent backflow into ventricles. • Blood returns to heart & atria fills again due to high pressure in vena cava and pulmonary vein. • Increase in pressure of atria, as ventricles continue to relax , their pressure falls below that of the atria and so AV valves open • Blood flows passively into ventricles from atria. • Atria contracts – whole process restarts
The cardiac cycle • Tasks • Describe each stage of the cardiac cycle, referring to the action of the valves in each stage. • Explain the terms cardiac cycle, diastole, atrial systole and ventricular systole • (Grade E - D)
Cardiac cycle • Cardiac cycle - narrated.swf
A B C Changes in pressure in the heart during one heart beat
Describe the cardiac cycle with reference to the action of the valves in the heart • (Grade B – A) Questions • 1. When does the blood start flowing in the aorta? • 2. Are the semi-lunar valves open or closed at point B? • 3.Why is ventricular volume decreasing at point C? • 4. Calculate the heart rate • ANSWERS • 1. Point A ventricles are contracting (AV valves are shut) forcing blood into the aorta • 2. Closed, ventricles are relaxed and refilling, so pressure is higher in the pulmonary artery and aorta forcing SL valves close • 3. The ventricles are contracting, reducing the volume of the chamber • 4. 60/0.8 = 75 beats per minute
Heart Rate –beats/min Purkyne Tissue
Cardiac muscle is myogenic – naturally contracts & doesn’t need to receive impulses Need to coordinate contractions with pacemaker = sino-atrial node (SAN) Control of Heartbeat
1. The SAN sends waves of electrical activity which spread through the muscle of the atria, causing it to contract. (Blood is forced into ventricles) ATRIAL SYSTOLE • Describe how heart action is coordinated with reference to the sinoatrial node (SA), atrioventricular node (AVN) and Purkyne tissue (Grade C –B) 2. The waves of electrical activity reach the AVN . Here there is a slight delay-making sure the atria have emptied before ventricles contract 3. AVN passes activity onto the bundle of His, and these muscle fibres conducted the waves of excitation along the Purkyne fibres. Once the impulses reach the walls of the ventricles they cause the muscles to contract, forcing blood out of the heart VENTRICULAR SYSTOLE 4. The atria relax (atrial diastole), blood enters the atria from the pulmonary veins or vena cava 5. The ventricles relax (ventricular diastole). Bicuspid and tricuspid valves open and blood enters the ventricles from the atria
Electrocardiograms (ECG) Checks heart function using an electrocardiograph, it records the electrical activity of the heart • The heart muscle depolarises (loses electrical charge) when it contracts, and repolarises (regains charge) when it relaxes. • Patches with wires are placed on the patients chest and wires are connected to a monitor. • Electric charges are recorded by an electrocardiograph, as a electrocardiogram/ECG which shows the patients normal heart rhythm.
Electrocardiograms [ECGs](record the electrical activity of the heart) The ST wave is caused during ventricular diastole. (repolarisation of ventricles The P wave is caused by contraction (depolarisation) of atria The QRS complex is caused by contraction (depolarisation) of ventricles. Larger than P due to more muscle. http://anatimation.com/cardiac-cycle/cardiac-cycle.html
Tachycardia – fast heart rate Bradycardia – a slow heart rate Arrhythmia – abnormal heart rhythm Fibrillation – rapid contraction of heart muscles TASK – Identify each ECG and explanation Terms not to be confused by • Interpret and explain ECG traces, with reference to normal and abnormal heart activity • (Grade B – A)
Rapid fire of the SAN, the heart’s natural pacemaker, defined as a rate greater than 100 beats/min in an average adult. Sinus Tachycardia It’s the normal response to exercise, excitement, anxiety and also stimulants, fever, dehydration, hypothermia & shock, hypoxia
Bradycardia Bradycardia occurs when the heart is beating more slowly than fifty to sixty times a minute. The impulses that control a steady heartbeat, are blocked, delayed, or slowed down. It can occur as a result of age, AVN or SVN problems, metabolic disturbances, as a result of taking certain medications, drug abuse, or as a result of a pre-existing heart disease. Trained athletes tend to have slow resting heart rates, and resting bradycardia in athletes is not abnormal if no symptoms.
Sinus Arrhythmia The normal increase in heart rate that occurs during inspiration (when you breathe in).
Ventricular Fibrillation Uncoordinated contraction of the cardiac muscle of the ventricles in the heart. As a result, the heart fails to adequately pump the blood, During ventricular fibrillation, cardiac output drops to nil, and, unless terminated promptly, death usually ensues within minutes.
Settler Describe how the action of the heart is initiated and co-ordinated. In your answer you should use appropriate technical terms, spelt correctly. (5 marks)
Single Circulation – e.g. fish Blood passes through heart ONCE per complete circuit Blood pressure reduced as blood passes through the gill capillaries - slows down flow to the rest of the body Limits the rate of delivery of O2 and nutrients to cells and removal of waste Efficient for the level of activity of fish but not mammals – also fish do not maintain their body temperature – need to respire relatively less compared to mammals Double Circulation – more efficient - e.g. mammals Heart is composed of two separate pumps – right side pumps blood to the lungs to pick up oxygen; the blood is returned to the left side; the left side pumps oxygenated blood rapidly and at high pressure to the body; the blood is returned to the right side Higher level of activity (energy) and need to maintain their body temperature at 370C – through respiration Need to deliver and remove materials to and from cells rapidly – achieved by delivering blood at high pressure to tissues. Pulmonary – oxygenates blood & removes CO2 Systemic – oxygenated blood from lungs pumped rapidly at an increased pressure by the heart Blood passes through heart TWICEper complete circuit