Renal function: sodium balance

Published on March 31, 2024   23 min
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Hello and welcome back to The Fundamentals of Human Physiology. My name is Jessica Briffa. Today, we'll be going through the third lecture in the 'Kidney Function' series, which is on sodium balance.
Before we delve into this topic, I have a few stop-and-think questions that are designed as a refresher for the content already covered and to get you started thinking about this topic. First, let's consider the following question. What tubular activity do you think is bigger? As you may recall from the first lecture, reabsorption and secretion occurs throughout the nephron. We also know that 20% of plasma is filtered into the nephron. However, less than 1% of the volume is excreted as urine. It may not be too surprising that reabsorption is a bigger tubular process.
Now that we know that reabsorption is the biggest tubular activity, let's consider the following question. Where do you think tubular reabsorption is of the greatest along the nephron? If you think back to the structure of the nephron, you'll appreciate that the first segment of the tubule that the glomerular filtrate comes into contact with is the proximal convoluted tubule. It is not too surprising that this is a site where the majority of solute and water reabsorption occurs, which is responsible for reabsorbing 50-60% of glomerular ultrafiltrate. The reabsorption that occurs in the proximal convoluted tubules is primarily driven by the reabsorption of sodium ions; a topic which we will expand upon in this lecture.