The Circulatory System

In this episode, we learn about the Circulatory system, focusing on its key players, the pathway of blood throughout the body, blood types, hemoglobin dissociation curves, hormones affecting blood pressure, and more! If you have any questions, suggestions, or corrections, please email themcatquizshow@gmail.com

Transcript

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SPEAKER_03 0:03

See what you I don't know who you are. I don't know where you are. But you may want to start changing your ways. Or changing your name.

SPEAKER_04 0:30

Thanks for the intro, Pat Collins. Welcome everyone to the MCAT quiz show. I'm Plankton, and joining me today, as always, is my favorite host, Issa Huck. Let's not waste any time and get right into the episode. But first, if you haven't listened to the intro episode yet, make sure you do that first. So today's topic is the circulatory system. Isa, are you ready to start with the first question?

SPEAKER_01 0:58

Yep, thanks for the intro, Plankton. Let's get started. Round one. Fight. Okay, the first questions will be dealing with the deoxygenated blood pathway. So the first question is the right atrium receives deoxygenated blood from the body through what? And this would be the vena cava. Right? It would be the superior and the inferior vena cava. So the right atrium pumps deoxygenated blood through which valve to reach the right ventricle?

SPEAKER_00 1:37

And this would be called the tricuspid valve. Are the atria or ventricles more muscular?

SPEAKER_01 1:48

And this would be the ventricles. So why is that? Well, for this episode, definitely look up a picture of the circulatory system, the heart in particular, and know where everything is. But you can see that the atria are just pumping the blood to the ventricles, right? It's a short distance. But the ventricles are pumping blood to the lungs and the entire body. So they have to generate a significantly higher pressure. So you know they're doing more work, they have to be more muscular. So related to that, the next question is is the left or right ventricle more muscular? And this would be the left ventricle. Because the right ventricle is pumping blood to the lungs, which are nearby, but the left ventricle is pumping blood throughout the entire body. So just intuitive. It's about workload demand. So for all these questions, when I'm asking them to you, try your best to visualize the heart in your head. Okay, the right ventricle pumps the deoxygenated blood through the pulmonary valve to reach which artery? So that would be the pulmonary artery, right? Pulmonary meaning lungs. So it's going to be pumps through the pulmonary valve to the pulmonary artery. We want to get that blood to the lungs to oxygenate it. So we're talking about arteries and veins. Which one flows away from the heart and which one flows towards the heart? I like the saying A for away. So arteries start with the letter A, so they'll be flowing away from the heart. Therefore, veins are flowing towards the heart. So think A for away. Okay, now let's ask some questions about the oxygenated blood pathway. What part of the heart receives oxygenated blood from the lungs through the pulmonary vein? And that would be the left atrium. The left atrium pumps oxygenated blood through which valve to reach the left ventricle? And that would be the mitral valve, aka the bicuspid valve. The left ventricle pumps oxygenated blood through which valve to reach the aorta? And that would be the aortic valve. And that would be through the arterioles. And then it leaves as deoxygenated blood through what? After it enters the capillaries, it's leaving through the venules. Okay, let's just recap really quick. I want you to walk me through the pathway of deoxygenated blood entering the heart and going through all the different steps and then leaving the heart as oxygenated blood. I'll give you 10-15 seconds. If you need more time, just pause, think about it, and visualize it.

SPEAKER_00 5:21

Okay, time starts now. Okay, hopefully that was enough time. If you need more time, just pause it.

SPEAKER_01 5:42

Just a quick visual. So walk me through it. Hopefully you're saying the steps before I do, so I'll give you a chance. What's the first step? Well, we have oxygen poor blood returning from the body, and it's entering the heart via the superior and inferior vena cava. Good, that's step one. Okay, step two. After the blood goes through the vena cava, it's now entering the right atrium. Okay, so that's that upper right quadrant of your heart. That's the first chamber to receive blood. Now what's step three? Well, the blood is gonna pass through the tricuspid valve to the right ventricle.

SPEAKER_00 6:34

Good. Okay, what is step four?

SPEAKER_01 6:39

The right ventricle is going to pump the blood towards the lungs. So your right ventricle is that lower right quadrant. It's gonna pump the blood towards the lungs, and that is gonna pass through which valve? I'll pass through the pulmonary valve or the pulmonic valve into the pulmonary artery.

SPEAKER_00 7:04

Okay, what's next?

SPEAKER_01 7:07

Well, the pulmonary artery is gonna carry the deoxygenated blood to the lungs. Perfect. Okay, how about step seven? Well, the lungs are going to oxygenate the blood. So the blood's gonna pick up oxygen, it's gonna release carbon dioxide. Okay, how about step eight? So the pulmonary veins are going to return the oxygenated blood to the left side of the heart. It's going to enter the step 10 would be sorry, step nine would be the left atrium. It's gonna enter the left atrium, that upper left quadrant. It's gonna receive that oxygenated blood from the lungs. So now it's sitting in the left atrium. What's gonna happen now? So step 10, the blood's gonna pass through the mitral or bicuspid valve into the left ventricle, that lower left quadrant. So now it's sitting in the left ventricle. What is step 11? Well, that left ventricle is going to pump oxygenated blood to the body. How is it gonna do that? It's gonna pump it through the aortic valve. Good. Passing it through the aortic valve into the aorta. So I guess step 13 is now the aorta is going to distribute the blood to the rest of the body. Okay, that was really, really good. That's the heart itself. It's pretty intuitive when you think about it. Essentially, let's just get the blood into the lungs and let's get the blood out. Okay, and after it gets pumped through the aorta, we know it's going to go next into arterioles, then it's gonna pass into capillaries, good. Gas exchange is gonna happen there, then it's gonna go to the venules, then the veins. So the order is the arteries, arterioles, capillaries, venules, veins. Okay, and all that may be complicated, so if that was difficult for you, look up a diagram, it's gonna make a lot of sense. Okay, let's move on. Let's talk about electrical conduction. So, can you tell me the order of electrical conduction through the heart?

SPEAKER_00 9:53

There's four different parts.

SPEAKER_01 9:59

So the signal is gonna start at the sinoatrial node, we like to call it the SA node for short. What happens after that? The signal travels to the AV node or the atrioventricular node, and after that, to the bundle of HISS, and after that, the Purkinje fibers. Good. So sonoatrial node, SA node, AV node, bundle of HISS, Purkinje fibers. During what phase of the cardiac cycle are the atrioventricular valves open, meaning that blood travels from the atria to the ventricles? And this phase is called diastole. And what about the phase when atrioventricular valves are closed, meaning blood travels from the ventricles to the arteries? And that would be called systole. So whenever you hear someone's blood pressure, and they always say, you know, diastolic over systolic, that's what they're referring to. Blood in the arteries are mostly oxygenated, except for which artery. And that would be the pulmonary artery. So why is that the case, right? We think that AOA, that's our term for identifying arteries, but we also usually think that arteries are oxygenated blood and veins are deoxygenated. But one of the exceptions is the pulmonary artery. We're sending deoxygenated blood away from the heart to the lungs. So therefore, blood in veins are mostly deoxygenated, except for which vein? And that would be the pulmonary vein, right? And that's going to be your oxygenated blood coming back to the heart. Can you tell me the other exception to this rule? Where arteries are oxygenated and veins are deoxygenated. And that would be the umbilical artery in fetal circulation, because that carries deoxygenated, waste-rich blood from the fetus to the placenta. So that's one of the other exceptions. Remember, lungs is an exception, and the umbilical artery. Okay, next question. Fluid leaks out of capillaries due to which pressure? This is called the starling pressure. Shout out the sounds of the lamps, Clarice Starling. Okay, so let's talk about the starling pressure. It has a strong or weak hydrostatic pressure and a strong or weak oncotic pressure. So the starling pressure has a strong hydrostatic pressure and a weak oncotic pressure.

SPEAKER_00 13:24

So what is hydrostatic pressure and what is oncotic pressure?

SPEAKER_01 13:31

So let's start with hydrostatic pressure. That is pressure that pushes fluid out of the capillaries into the tissues driven by blood pressure. So it's pushing fluid out of the capillaries, hydrostatic. Oncotic pressure is what? That is a type of osmotic pressure that pulls fluid back into the capillaries, driven by proteins like albumin. So hydrostatic pressure pushes fluid out, oncotic pressure pulls fluid in. So you can see that these are opposing forces. And they regulate fluid movement across the capillary walls. Collectively, they're known as the starling pressures. If that makes sense. Since veins have lower pressure than arteries, what feature do they need to prevent backflow of blood? And that would be valves. So, because of that lower pressure, and if you didn't have valves, you think how would the blood get back to the heart? It's because they have these valves. And the arteries don't have these valves in the same way that the veins do. Okay, let's talk about the contents of blood. 55% of blood is what? Give you a hint. It is an aqueous solution made up of mostly water, salts, and proteins. And this is known as plasma. So that means that 45% of blood is what? And I give you a hint, some things are erythrocytes, leukocytes, platelets. These are all obviously cells. Anytime you see the word or the prefix or suffix site, that means cells. So we have 55% plasma and 45% cells. The percent of blood cells in the bloodstream is referred to as the what? And that would be called the hematocrit. Hematocrit. That's the percent of blood cells in the bloodstream. Tell me what the three portal systems are. And that would be the hypophaseal, the hepatic, and the renal portal system. Can you please tell me what portal systems are composed of? And they're composed of two capillaries that blood travels through before returning to the heart. And these are two distinct capillary beds, and they're in series rather than in parallel. So they're arranged sequentially.

SPEAKER_00 16:28

What are red blood cells also known as?

SPEAKER_01 16:34

And that would be erythrocytes. Red blood cells are responsible for transporting oxygen and carbon dioxide through the use of a protein called what?

SPEAKER_00 16:47

That's called hemoglobin. Damaged red blood cells get destroyed by which organ? And that is the spleen. New red blood cells are made by what? That is the bone marrow.

SPEAKER_01 17:08

Red blood cells have what type of shape? If you can describe it, that'd be good, but the term is called biconcave. Kind of looks like little donuts. And why is it a biconcave shape? And that's because it increases surface area for gas exchange and it helps them fit through tight areas. Each molecule of hemoglobin has how many polypeptide chains, each with its own heme group. That would be four polypeptide chains. So if you picture a molecule of hemoglobin, there's four separate chains, and they each have their own heme group. So there'd be four heme groups as well. Hemoglobin is an allosteric protein, meaning binding at one site affects the other sites. What is that called? When binding at one site affects the other sites, and this is called cooperative binding. So essentially, when you bind that first site, the next site is easier to bind, and so on. So the fourth one would be the easiest to bind. When hemoglobin is deoxygenated, it is in what state? And this is called the tense state. So deoxygenated hemoglobin is in the tense state. And what could you say about the affinity for oxygen in the tense state? And that would be low. So it has a low affinity for oxygen in the tense state. So how about then when hemoglobin is oxidized? What is that state called? And that's called the relaxed state. And intuitively, this has what affinity for oxygen in the relaxed state? And that would be a high affinity for oxygen. On the hemoglobin disassociation curve, what is on the x-axis and what is on the y-axis? Tough question. If you can imagine this curve on your head, hemoglobin disassociation. So on the x-axis, we have the O2 pressure. So x-axis has a bottom line there. And then on the line on the left, our y-axis, that is the oxygen affinity. So look up a picture of this hemoglobin disassociation curve because it's important to kind of understand how this mechanism works. So your next question is based on the hemoglobin dissociation curve, when there is high O2 pressure, hemoglobin's affinity to oxygen is what? So we have high O2 pressure. High O2 pressure means that hemoglobin's affinity to oxygen is high. We have lots of oxygen. Hemoglobin's gonna really want oxygen. But when there's low O2 pressure, you could guess that hemoglobin's affinity to oxygen is low. So it's not a direct linear line. So that's why I'd say look it up. But essentially, it's kind of a sigmoidal, kind of an S shape. So it starts off low, slowly increases, then it really increases high at a fast rate, and then it kind of levels off and plateaus. I'm pretty sure that's called sigmoidal. In the tissue, a molecule called what takes oxygen from the hemoglobin due to its higher affinity for oxygen. So we're in the tissue, and this molecule that's taking the oxygen from hemoglobin is called myoglobin. Myoglobin. And what does the myo prefix mean?

unknown 21:24

Right?

SPEAKER_01 21:24

Like for example, a myocyte or myopathy. Myo is a relationship to muscle. So that's why we said that in the tissue, the myoglobin is the molecule that's taking the oxygen from the hemoglobin. And it has a higher affinity to oxygen than hemoglobin. Because if it didn't have a higher affinity to oxygen than hemoglobin, then it would be hard for that myoglobin to take that oxygen and use it for the tissues. So when you're exercising, what does um what happens to the hemoglobin dissociation curve? It shifts. In what direction does it shift? And exercise causes a right shift. So if we look at our normal sigmoidal S-shaped curve, exercise is going to put it in the right direction. It's going to shift it over, tad to the right. Okay? A right shift on the hemoglobin dissociation curve means the affinity for oxygen is higher, the same, or lower. So that right shift means that the affinity for oxygen is lower. Okay. So that means that you need a higher O2 pressure to get the same amount of hemoglobin affinity to oxygen. Fetal hemoglobin causes what kind of shift in the hemoglobin dissociation curve? And that would be a left shift. And a left shift on the curve means the affinity for oxygen is higher, lower, or the same. And that would be higher. So let's just think this through, right? When you are exercising, you want your tissues, your muscles to get oxygen, right? So we're essentially lowering our affinity for oxygen from hemoglobin so that it's easier for myoglobin to take up that oxygen. If the hemoglobin affinity was really high, it would be hard to get that oxygen into our tissues. But for fetal hemoglobin, we are moving that shift to the left. And now it's easier for hemoglobin to bind the oxygen. Why is that? And this is because the shift is allowing the fetus to effectively extract oxygen from maternal blood in the low oxygen environment of the placenta. Right? So think that through, look up a graph of the hemoglobin dissociation curve, and understand what happens for right shift and left shift. Okay, next question. The antigens for red blood cells are what type? So are they like, you know, dominant, they recessive, are they co-dominant? Are they incomplete dominant? These antigens for red blood cells are co-dominant. Okay? There's one exception. And that is what? And that is the O antigen for blood types. And this O antigen is what? Is it dominant, recessive, codominant, incomplete dominant? Anything else you can think of? So O is recessive. So everything else, all other antigens are co-dominant, but O is recessive. Those with the A antigen can donate blood to who? So if you have the A antigen, you can donate blood to those who have the A and AB antigens. If you have the A antigen, you can receive blood from who? You can receive blood from the A and O antigens. Okay. If you have the B antigen, you can donate blood to who? Hopefully this makes sense. It's starting to make sense. Remember we said for A, I apply that same logic to B. So the B antigen can donate blood to those with the B and AB antigens. And they can receive blood from who? Those with the B antigen. They can receive blood from those with the B and O antigens. Those with the A B antigen can donate blood to who? They can donate only two other A B antigens. But those with the A B antigen can receive blood from who? They can receive blood from A, B, AB, and O. And how about those with the O antigen? They can donate blood to who? It's pretty easy now. They can donate blood to anyone. A, B, A, B, or O. And those with the O antigen can receive blood from who? Only other O antigens. So based on that, the A B antigen is known as what? You have the A B dan antigen. You are the universal recipient, right? We said that AB can receive blood from anyone. And the O antigen is known as what? And that would be the universal donor. For red blood cells, those with the RH factor are denoted with what? What's like the symbol for the RH factor if you have it? You'd be called positive. And those without it are called negative. So can individuals with the Rh factor donate to those without the Rh factor? So if you have the RH factor, can you donate to someone without it? No, you cannot. No, you cannot. Can individuals with the Rh factor donate to those with the Rh factor? And that would be yes. You donate to others with the Rh factor. The only thing you can't do is if you have the RH factor and donate to those without the Rh factor. But if you don't have the Rh factor, you can still donate to others with the Rh factor. So based on that, what is our real universal donor? We said it was O, right? But what is the real universal donor? That would be O negative. O antigen, but without the Rh factor. Okay, so how do you remember this? How do you kind of get your mind around who's a donor, who's a recipient? Well, I just like to think in my head, I made these kind of two characters. And don't apply this logic to actual people who have these blood types. It's just a way for me to remember it. So I think that if you donate blood, you know, you're a great, great person, you're a hero. So I have a little mind map, and I have my O antigen, especially the O negative, being the biggest hero. Because Oantigen is just giving their blood, you know, to everyone and anyone. They are such a selfless hero. And then as you go down this line, you get less and less selfless. So you become less and less of a hero. So on the full other end of the spectrum, I'm not dogging on anyone who has this blood type, this is a way for me to remember it. But on the other end of the blood type spectrum is A B positive. Because A B positive can only donate to A B positive. That's it. So they're very limited in their donations. So if A B positive is the weakest hero and O negative is the strongest hero, it's pretty easy for you to fit everything in between. Right? So everything in between. If you're A B, you can't really donate to anyone, and if you're positive, you can't donate to many people. But if you're O, you donate to a lot of people, and if you're negative, you can donate to a lot of people, and then A and B are in the middle. Alright? They're respective to each, because A can donate to A and A B, and B can donate to B and A B. Okay, hopefully that makes sense. If it didn't, just look up a quick graph, it's not too hard to understand. Okay, what is another name for white blood cells?

SPEAKER_00 30:12

These are called leukocytes.

SPEAKER_01 30:15

How about platelets?

SPEAKER_00 30:17

Give me another name for those.

SPEAKER_01 30:21

They are called thrombocytes. The final product of the coagulation cascade is what?

SPEAKER_00 30:32

And this would be called fibrin. And what does fibrin do?

SPEAKER_01 30:39

Fibrin forms a mesh that seals blood clots. In a hot environment, what occurs with your blood vessels and what happens to the speed of the blood? So in a hot environment, basodilation is gonna occur. These vessels are gonna dilate, and the velocity of blood is going to decrease. Okay, so it's gonna get bigger, it's gonna decrease speed. And what is this doing? Why is this happening? This is helping the body release heat through the larger surface area. Okay, because it's a hot environment. So, how about a cold environment? Use that same logic. What's happening to our vessels? What's happening to the speed? So there's vasoconstriction occurring, and the velocity of blood is increasing. What's that doing? That's helping the body conserve heat to the smaller surface area. So we can use a formula, maybe you'll see it in the physics section, planning to do podcast episodes on that in the future. But that formula is A1B1 equals A2V2. And that's related to the area and speed.

SPEAKER_00 32:07

Okay. What is the equation for the ideal gas law?

SPEAKER_01 32:14

And this is P V equals N R T. I'm sure you guys have all heard this, high school physics. But I don't like giving formulas without saying what those actually mean. Because a formula is useless if you can't use it based on information in written form. So tell me what the letters in P V N R T um equals NRT mean. So P is the pressure in atmospheres, ATM.

SPEAKER_00 32:47

V is what?

SPEAKER_01 32:50

V is the volume in liters. How about small n? Small N is the moles.

SPEAKER_00 33:00

How about R, big R?

SPEAKER_01 33:05

And big R is the ideal gas constant. And usually this is 8.314 um joules over moles times Kelvin. And how about the T? What does the T stand for? Big T in the equation. And that is the temperature in Kelvin. So P pressure, V volume, and moles are ideal gas constant and T temperature. How about Boyle's law?

SPEAKER_00 33:42

What does Boyle's law mean? First of all, what is Boyle's law? And secondly, what is the formula? So let's start with the formula. What is the formula for Boyle's law?

SPEAKER_01 33:55

Boyle's law is P1 V1 equals P2 V2, where P is pressure, thank you, and V is volume. What is Boyle's Law showing? It's showing that pressure and volume are inversely proportional to each other when moles and temperature are kept constant. So just think pressure, volume inversely proportional. I always like my balloon example when I think about physics, especially these laws. So we have our balloon. If we have a super massive balloon, big volume, is our pressure going to be big or small? Our pressure will be smaller because it's inversely proportional. Let's say we have a tiny balloon, tiny volume, our pressure will be bigger, inversely proportional. And that's obviously when our moles and temperature are kept constant. Okay, now I'm going to go over a few review questions. So if you listen to past episodes, you may have heard these already. And this is a great opportunity for you to test your memory, test your understanding of different topics and how they relate to other topics. So, what is the only cell type in the human body without a mitochondria? And those are red blood cells. Does ADH or aldosterone change osmolarity? And that would be ADH. Does ADH or aldosterone transport water? That would again be ADH. Does ADH or aldosterone transport salt? This time it would be aldosterone transporting salt? Does ADH or aldosterone increase blood pressure? Bit of a trick question, but that is both. Does ADH or ANP decrease blood pressure? This one should be easy. Well it's ANP because ADH is increasing our blood pressure. So AMP will be decreasing. And does ANP or aldosterone change osmolarity? And neither of them do. Neither of them change osmolarity. Does ANP or aldosterone transport salt? And that would actually be both. So write out a little table, compare these three hormones because they're very important in renal physiology, in the circulatory system physiology. But, you know, to recap, uh, if we look at the effect of ADH, ADH is coming from our hepathalamus and posterior pituitary, it's increasing blood pressure, it's water being transported directly from the kidney to the blood, and it's changing osmolarity. That was ADH, antidiuretic hormone. If we move on now to aldosterone, aldosterone is the located in the adrenal cortex, it's increasing blood pressure, it's transporting sodium, and the water is following it. It's not transporting water directly, it's transporting sodium, and it's maintaining osmolarity. And then ANP, atrial naturid peptide, located in the heart, or all these locations is where it's actually like originating, I guess. Uh the effect is it's lowering blood pressure, ANP. It's transporting sodium, and then water is following the gradient, similar to aldosterone, and ANP is maintaining osmolarity as well. So if you need to write those out, look up a diagram. Know those hormones very well. And quick tip if you ever see the word vasopressin, that's the same thing as antidiuretic hormone. ADH is another word for it. And our final question of the episode I know it's been a long episode, guys, so thanks for staying with me. What is the name for the peptide hormone responsible for making red blood cells? And this is erythropoietin. So that was a lot. That was a lot of stuff to go through through the circulatory system. I did more of an in-depth explanation for some concepts that I felt were good to know, easy to understand. But that's it for me for this episode. You know, once again, I hope you enjoyed. I hope you learned something new or reinforced your current understanding. And as always, please feel free to email me if you have any questions, corrections, or suggestions. And with that, I will pass the mic back to Plankton for a final message.

SPEAKER_04 39:05

Thanks, Isa. I learned a lot from this episode. If you guys also benefited from this podcast, please feel free to leave us a review as it helps us reach more students. And for all the listeners out there, you got this. Cause like you guys, I went to college.