intro to cardiology.pdf

Capillaries: where exchange of things occur Congenital disorders that lead to no closure of ovales which allows for mixture of blood which does not matter to a fetus because their source of oxygen is from the placenta. But once the fetus is born, the respiratory system takes hold and if you do not c...

Capillaries: where exchange of things occur Congenital disorders that lead to no closure of ovales which allows for mixture of blood which does not matter to a fetus because their source of oxygen is from the placenta. But once the fetus is born, the respiratory system takes hold and if you do not close that hole, the heart will work extra hard to meet metabolic needs. This is rate of flow when you are doing nothing. If heart rate increases, cardiac output can get very close to 20L/min. Although the brain is not the largest organ, it has high energetic demand. A lot of blood goes to kidney because they are involved in maintenance of chemical balance of the blood Cardiac System is a closed system so there is no leakage. The amount of blood that leaves the heart has to match the blood that comes back. Exceptions including when CO increases during exercise. So when we are exercising, 15–20L/min is pumped even though we do not have that much blood. This is done by the venous system. Majority of blood is in the veins so when you do physical exercise, the increase in sympathetic activity will squeeze the veins and allow for increase in venous return. How much blood is there in the avg individual? A: 5L of blood. So the heart is pumping all of the blood in your body per minute. Electrical events first occur in pacemaker cells. The stimulus generated in the SA node is conducted through modified cardiomyocytes. Stimulus is delivered to the contractile muscle cells. So muscle cells depolarize and repolarize. There is a refractory period before the next stimulus. Automaticity: If you take the heart out of a living person, and the heart is placed in bucket of water with salts and sugars, the heart will continue beating on its own even though its separated from the body. The heart does not need stimulus from nervous system for it to do what it needs. Pacemaker cells are modified cardiac cells not neurons. Excitability: This is where the refractory period becomes important because it ensures that the heart will contract with one heartbeat and fully relax before the next heartbeat. If you take skeletal muscle and increase frequency of stimulation, you will get tetany contraction but you wouldn’t want the heart to do this. If the heart remained contracted, the heart would not be able to pump blood. Conductivity: Allows for AP to be propagated to actual muscle cells. The heart works as functional syncytium which means that the heart (even though it is built from billions of individual cells), is made of these cells which are connected to each other through gap functions. Na+ gradient is roughly 10-15x more concentrated outside than inside. K+ is 30-40x more concentrated inside than outside. Ca2+ is 1000x more concentrated outside than inside Different parts of the heart have different action potentials. For example in the atrium, there is less of a plateau. The phases for the contractile cells are different from the pacemaker cells. The RMP is different. So contractile cells are at roughly -90mV. RMP for pacemaker cells is debatable but it is roughly around-60mV. These cells have different ion channels that allows them to work in a particular way. There’s potassium leaving the cell but ca2+ entering the cell which gives the shape of phase 2 The sodium channels do not close, they actually inactivate! I K+ channels have slow kinetics. When Ca2+ channels close, K+ channels remain open. r Didn’t mention this here Phase 0 does not rely on Na+ channels but on voltage gated channels; however it is not as fast as in contractile cells Funny channels are no selective, nonspecific cation channels. Funny channels tend to be open all the time so the cycle occurs immediately again. Funny channels drive the automaticity of the heart. They enable immediate regeneration of pacemaker potential as soon. Refractory period is 250 ms which allows time for ion movements that will enable cells to be restimulated with the next cycle. In other words, for the heart to function properly, as phases need to occur in that same exact sequence. Long refractory period allows cells to fully repolarize before it can depolarize again. This will ultimately allow cell to move ca2+ into the cell and out of the cell before it can start this process again. Overall, cardiac muscle will be able to filly relax before it can contract. Systole involves pumping of blood out of heart and before it can pump blood again, it needs to fill with blood before it can pump again. Junction that holds cells together to allow heart cells to remain attached to each other despite the force applied to them. Intercalated disc shape through electron microscopy symons yggation If something happens to impair the SA node, the heart will still be able to contract? Yes. But will it contract at the same rate? No. The AV node will be next but the heart will have a slower rate. Activity of pacemaker cells is subjected to input from autonomic nervous system. Parasympathetic reduces action potential through hyperpolarization mechanism an adrenaline norad