1.1.6 describe the cardiac cycle (atrial systole, ventricular systole and diastole); The structure and operation of the mammalian heart related to its function, including the major blood vessels.

● What does a cardiac cycle consists of?

1. Initially the heart is in diastole with the atria and ventricles relaxed.The atrioventricular valves the open, but the semilunar valves are shut. 2. The returning deoxygenated blood from the body enters the relaxing right atrium through the vena cava. 3. The returning oxygenated blood from the lungs enters the relaxing left atrium through the pulmonary veins. At this stage some blood also passes through the open atrioventricular valve into the relaxing ventricles. 4. When the atria are full, their walls contract (atrial systole) pushing blood through the open atrioventricular valve into the relaxed ventricles. Blood cannot pass back into the veins because they contain valves which prevent back flow, and also the contracting of the atrial walls partly closes off the entries of the vena cava and pulmonary veins to the atria. 5. After a short delay, the ventricles contract from the apex upwards, forcing the blood that high-pressure into the arches. At this time the atrioventricular valve slam shut, preventing backflow of blood to the atria, and the semilunar valves open to allow the passage of blood into the arches. 6. When the ventricles relax (diastole) the sudden fall in pressure causes the semilunar valves to slam shut, thus preventing backflow of blood from the arches.

● Why do the atria have thin muscular walls?

● It has thin muscular walls because it receives blood at low pressure and needs to exert relatively little pressure to move the blood into the ventricles (short distance away).

● Describe the thickness of the right ventricle wall and ventricular septum and explain the reason for the thickness.

● It is thick this is because it pumps blood through the lungs and this is a medium distance away from the heart.

● What does the left ventricle push out and from what?

● Most muscular chamber of the heart (more muscular than the heart). Pushes high pressure oxygenated blood to the organs via the aorta.

● How does the heart contract due to these impulses?

● On the right atrium is a structure called the Sinoatrial Node, or the SAN. ○ This bundle of cells acts as a pacemaker controlling the rate of contraction - the heart rate. ○ Stimulation of this node initiates a wave of electrical impulses which spread aross the atria causing atrial systole which pushes blood into the ventricles. ○ Insolation tissue prevents contractions anywhere but the atrium this means that only the atrium will contract. ● The electrical signal in the atria is picked up by a second node, the AtrioVentricular Node (or the AVN) which passes the signal down to the apex of the heart (bottom of the ventricles). ● This is passed through specialised conducting cardiac muscle fibres called the Bundle of His. From the apex, the electrical activity is spread throughout the ventricles along Purkinje fibres. ○ This means that the ventricles contract from the bottom up once they have filled with blood. ● When the ventricles are filled with high-pressure blood The valves close. When the ventricles contract this pushes the blood to an artery.

● What does the right ventricle push out and from what?

● Pushes deoxygenated blood into the lungs through the pulmonary arteries, one to the left and one to the right lung.

● What does the right atrium receive and from what?

● Receives deoxygenated blood from the lower part of the body via the superior and inferior vena cava.

● What does the left atrium receive and from what?

● Receives oxygenated blood from the lungs via the pulmonary vein, one from the left lung and one from the right lung.

● What type of muscle is the heart made up of? How has it been adapted for its function?

● The heart is made up of a unique type of muscle known as cardiac muscle which has special properties. It is myogenic which means it can contract on his own without being stimulated by a nerve.

● Explain the thickness of the left ventricle wall and explain the reason for the thickness.

● The pressure of the blood in the aorta is higher than pulmonary artery it pumps blood throughout the body which is a very long distance The left ventricle must therefore generate more pressure to overcome pressure of aorta Therefore, thicker muscle required in left ventricle

● What blood vessels are there on the left side of the heart?

● The pulmonary vein enters the heart and the aorta leaves the heart.

● What does the heart respond to?

● The sensitivity of the heart is supplied by nerves that control the heart. ○ One nerve speeds up heart rate and another another slows it down. ○ These nerves are controlled by the cardiovascular centre in your brain. The cardiovascular centre is able to respond to the variable levels of carbon dioxide.- This changes with the demands you make on your body, going up as you exercise. ○ Receptors in your blood vessels respond to these changes in the carbon dioxide levels by sending signals to your heart. This nervous control enables your heart to react to situations e.g. exercise or fear, when a faster heart rate is needed, or sleep and relaxation, when the heart needs to slow down. Hormones also afect your heart rate. E.g. adrenaline, produced when you are excited, angry, nervous or scared, speeds up the heart rate.

● What's the difference between the inferior and superior vena cava?

● The superior vena cava receives blood from the head, neck, arms and chest. The inferior vena cava collects the blood from the lower parts of the body.

● What do the tendons do?

● The tendons make sure the valves are not turned inside out by pressure.

● What are the other names for the atrioventricular valves?

● The valves are between the atria and the ventricle. ○ The tricuspid valve it is on the right side and the mitral/ bicuspid valve is on the left side.

● What blood vessels are there on the right side of the heart?

● The vena cava enters the heart and the pulmonary artery leaves the heart.

● What are arterioles?

● The very smallest molecules of the arterial system, furthest away from the heart.

● Why are cardiac muscle cells called myogenic?

● This means that the contract and relax rhythmically to their own accord, without intervention from the nervous system. ○ They can even beat rhythmically if kept outside the body and warm, isotonic, oxygenated saline.

● What are semilunar valves?

● Valves in the blood vessels are collectively called semilunar valves. ○ The pulmonary valve is in the pulmonary artery on the right side and the aortic valve is in the aorta on the right side of the heart. ○ They aid in stopping the back flow of blood into the heart.

● How are valves affected by pressure?

● Valves only open in one direction and only allow blood to flow in one direction. If there is high pressure behind the valve, then the valves are forced open. If the pressure is high above the valve, the valve is then closed.