Tutor profile: Daphne J.
Subject: SAT II Biology E/M
Describe the flow of oxygenated heart throughout the body.
Blood in the pulmonary arteries is oxygenated by the lungs during gas exchange. Once oxygenated, the blood is returned to the heart via the pulmonary veins. The heart is pushed by the left atria and then the left ventricle. The left ventricle pushes the blood to the aorta, which pushes the blood to the rest of the body.
2. If the average (arithmetic mean) of 5 consecutive odd integers is 3x, what is the median of these 5 integers? (A) (B) x – 2 (C) x – 3 (D) 3x (E) 3
The correct answer is (D) 3x. This is because when an odd number of consecutive numbers is added, the middle number (the median) will always be the average. So in this case, the average = the median = 3x.
How is urine produced in the body? Explain the mechanisms of the bowman's capsule, loop of henle, proximal tubule, distal tubules, and collecting ducts.
Urine is produced in the kidneys. Specifically, it is produced in a nephron, which is the functional unit of the kidney. There are over one million nephrons in the body! The nephron is not only responsible for producing urine but more importantly, to eliminate wastes from the body. In the most simple terms: blood from the body enters the glomerulus, a bundle of capillaries, and is filtered through inside the bowman's capsule. Nutrients such as glucose and ions will enter the filtrate, which will then go through the proximal tubule, loop of henle, distal tubule, and collecting ducts. In the proximal tubule, important substances such as salt and water, ions, and glucose, will be reabsorbed back into the blood. Furthermore, some drugs will be secreted from the blood into the filtrate so it can be excreted from the body. In the loop of henle, there is a counter-current multiplier system that helps in concentrating the urine (making your urine more yellow!). This is to preserve water inside the body. A lot of water is reabsorbed into the bloodstream through aquaporin channels. In the distal tubule, more nutrients including potassium, sodium, and calcium are regulated. The collecting duct is also responsible for further concentrating the urine. This is the final step before the urine is stored in the bladder, and it utilizes urea to make the urine as concentrated as possible. The excretory system is very, very complex, and many hormones and drugs further regulate these different parts of the nephron. This is only a basic overview!
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