Heart Anatomy + Diseases to Know for the USABO
In this article, I will cover various heart diseases that are important to know for the USABO and other biology competitions/examinations.
But first: a really quick basic review. Here is a schematic of the heart:
1) tricuspid valve
2) pulmonary artery
3) pulmonary vein
4) bicuspid valve
5) aorta
6) vena cava
Hopefully this basic structure makes it easier to understand this beast:
This diagram is basically the same as my schematic, except with a few extra details. Of note are the superior vs inferior vena cavae (one brings in blood from the upper body, and one from the lower), right and left pulmonary arteries/veins (which send/receive blood to the right/left lungs), and the pulmonary/aortic semilunar valves (which regulate blood passage between the RV-->pulmonary artery and LV-->aorta).
The heart utilizes this intricate system of tubes and compartments to pump blood around the body. This GIF summarizes the pumping mechanism pretty well:
Read this to learn more about the heart pump pattern, specifically in the context of the electrocardiogram (a diagnostic tool): https://www.sixfootscience.com/brain-snips/understanding-and-interpreting-the-electrocardiogram.
On to the diseases!
First is left ventricular hypertrophy. Hypertrophy refers to an increase in muscle size. So, the LV increases in muscle mass. This is often a result of hypertension (high blood pressure), which can be caused by excess sodium in the blood (hypernatremia). This can also be a result of overtraining/too much exercise, as the heart is pumping a lot of blood very quickly during exercise, so the muscle grows to adapt to this training. However, if the LV muscles get too large, the ventricle gets stiff and eventually loses pumping capabilities. For this reason, this condition is also known as "athlete's heart" or "hypertrophic cardiomyopathy."
Another disease is atherosclerosis, which is stiffening of arteries due to plaque buildup. (This differs from arteriosclerosis, which is just a narrowing, not yet stiffening, of arteries due to plaque buildup.) Plaque is composed of various fatty/clotting/cholesterol-y substances. High blood pressure contributes to erosion of artery walls, and this induces inflammatory pathways. Additionally, infective conditions such as endocarditis (pathogenic infection of the blood vessel lining/endocardium ruining heart valves) put the heart in an inflammatory state, facilitating plaque formation. Fatty molecules, collagen/elastin, and clotting substances replace the dead tissue, resulting in a region that is much more stiff than before. This stiffness prevents blood flow in arteries.
Stroke refers to blockage in the arteries that supply blood and nutrients to the brain. Brain cells die if they don't get nutrients for even a little bit of time, so stroke can cause permanent brain damage (neurons don't divide - the dead cells can't be replaced). Peripheral artery disease refers to blockage of arteries in the legs due to plaque buildup, which can eventually kill off leg tissue. Angina pectoris describes the condition of coronary artery blockage due to plaque buildup; angina presents with chest pain. The coronary arteries supply blood to the heart muscles to keep them pumping (every muscle needs a blood supply to get nutrients and keep working). Angina is a common indicator of future myocardial infarction (heart attack). More immediately, heart attacks present with left arm pain; the reason heart attack pain is in the left arm rather than the chest is because of referred pain - nerve networks are connected such that an issue in the heart is felt in the arm. Heart attacks result from inability of heart pumping; left untreated, this can cause complete cessation of heart pumping action. This is known as cardiac arrest, which is way more severe than a heart attack. Fortunately, atherosclerosis can be made a bit better using a stent, which is shown in the video below:
You can't put a stent in every artery though, and atherosclerosis is a systemic condition. Additionally, stents don't work for embolisms, which are broken-off bits of plaques floating around in the blood that can get stuck in arteriole/skinny artery/capillary tubes and block blood flow. Embolisms can also be any discontinuity in the blood that can impede flow, such as an air bubble. A pulmonary embolism is an example of an embolism where the pulmonary artery (the one between the right ventricle and the lungs) gets blocked by something (usually from a leg vein or something) and impedes breathing/gas transport to and from the blood.
Another disease is congestive heart failure, which results from weakened ventricular muscles from high blood pressure. This hypertension stretches the muscle too much, and the muscle cross-bridges are too far apart to be functional (read more about cross-bridge cycling here). The inability to pump results in edema, which is a local pileup of fluid due to stagnant blood and extra time for fluid leakage into the extracellular space.
Here are some resources to learn more about these diseases:
Atherosclerosis - https://en.wikipedia.org/wiki/Atherosclerosis#Pathophysiology.
Congestive heart failure - https://en.wikipedia.org/wiki/Heart_failure#Pathophysiology.
CHF and edema: https://pubmed.ncbi.nlm.nih.gov/8156185/.
Another cool one: rheumatic heart disease - https://www.hopkinsmedicine.org/health/conditions-and-diseases/rheumatic-heart-disease.
