The Heart 8.5 Flashcards
How the heart works
It pumps blood around the entire body, using two pumps working together. Deoxygenated blood flows through the right side of the heart and is pumped into the lungs. The oxygenated blood then comes back through the left side of the heart and is pumped around the body.
What is the heart made of?
It’s made of cardiac muscle which contracts and relaxes constantly. It doesn’t get fatigued like other types of muscle and can keep going all the time. It is surrounded by an inflexible pericardial membrane which stops it from getting too filled with blood.
Explain how blood is pumped in the body
Deoxygenated blood enters the heart at low pressure through the superior and inferior vena cava where it then enters the right atrium which has thin muscular walls. The blood will build up in the atrium until the tricuspid valve opens so the blood can flow into the right ventricle. When blood has filled both the atrium and ventricle, the atrium will contract and force all the blood into the ventricle, stretching the walls. The ventricle then contracts and the tricuspid valve closes so to prevent backflow. Tendinous chords make sure the valve isn’t flipped inside out by the pressure. As the ventricle contracts, the blood is then pumped up through the semilunar valves which prevent backflow and through the pulmonary artery where it heads to the lungs to be oxidised. At the same time, oxygenated blood will return to the heart via the right and left pulmonary veins and will enter the left atrium. The pressure will build up inside the atrium until the bicuspid valve opens so the blood will flow into the left ventricle. After the atrium and ventricle are both filled, the left atrium will contract and force the blood into the left ventricle where the pressure will build up. The bicuspid valve will close to prevent backflow, so the left ventricle will contract and pump the blood through the semilunar valves which prevent backflow and through the aorta to the rest of the body under high pressure. It will also flow through the carotid arteries to go to the brain.
Why is the left wall of the heart thicker than the right?
The right said of the heart receives deoxygenated blood and also pumps blood to the lungs which are a relatively short distance compared to the left side which has to pump blood around the entire body so is under a lot more pressure. This is why it needs a thick wall to be able to withstand the pressure.
What does the septum do?
It divides the heart in two sections so oxygenated and deoxygenated blood don’t mix together
Cardiac Cycle
This describes the events in a single heartbeat
Diastole
This is when the heart relaxes and occurs when both the atria and ventricles are filled with blood. The pressure inside the heart is building but the pressure in the arteries is low.
Systole
This is when the heart contracts firstly with the atria which is atrial systole and then the ventricles which is ventricular systole. The blood on the right side is pumped to the lungs and the blood on the left side is pumped to the rest of the body. The pressure in the heart is low at the end of systole but the arteries are at their maximum pressure.
What makes the heartbeat sound?
The sound is made by valves closing. The first ‘lub’ is created by the blood in the atrium hitting the tricuspid valve which is closed as the ventricles contract. The second ‘dub’ is caused by the backflow of blood hitting the semilunar valves in the aorta as the ventricles relax.
What makes the heartbeat by itself?
Cardiac muscle is myogenic which means it forms its own rhythm at 60-70 bpm. It’s maintained by electrical excitation instead of a nervous impulse.
What are the stages of electrical activity in the heart?
Sino-atrial node, Atrioventricular node, Bundle of His, Purkyne fibres
Sino-atrial Node (SAN)
It acts as the pacemaker of the heart, it starts a heartbeat by producing a wave of electrical excitation.
It caused the atria to contract which starts the heartbeat. There is a layer of non-conductive tissue so that this doesn’t occur in the ventricles. It is found on the top right corner of the heart where the right atrium is.
Atrioventricular Node (AVN)
This will pick up electrical activity from the SAN and will impose a little delay before stimulating the Bundle of His. The AVN is found at the bottom of the right atrium.
Bundle of His
A bundle of conducting tissues called the Purkyne fibres which are in the septum between the ventricles. It splits into 2 branches and conducts the wave of excitation to the bottom (apex) of the heart.
Purkyne Fibres
When the wave of excitation has gotten to the apex of the heart, the Purkyne fibres that are spread out on both ventricular walls will trigger the contraction of the ventricles. Because the starting at the bottom, it allows more efficient emptying of the ventricles.
