Renal function: excretory system

Published on February 29, 2024   16 min
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Hello, and welcome back to The Fundamentals of Human Physiology. My name is Jessica Briffa and I'm a postdoctoral fellow in the Department of Anatomy and Physiology at the University of Melbourne in Melbourne, Australia. I'll be delivering a series of four lectures on kidney function, where we'll cover the basic functions of the kidney in the first two lectures, and then go on to the mechanisms of sodium and water reabsorption in the last two lectures.
Similarly to what Charles has done in his lectures, I've also included these stop and think questions throughout my lectures with the aim to help you track how you're doing and set up some ideas for future questions and activities. Let's think about this basic principle in kidney function as I run down the timer and then I'll give you the answer. What is urine mostly made of? If you consider that the kidneys main function is to filter waste products from the blood and balance your body's fluids, you'll appreciate that urine is mostly comprised of plasma. This is because blood filtration leads to a mass movement of water and solutes from the plasma into the renal tubule, which goes on to form urine. Approximately 20% of plasma volume is filtered at any given time, which equates to around 180 litres of fluid being filtered by the kidneys daily. While this is produced by the filtration of blood, no blood is typically present in the urine unless there's an underlying health condition. The mechanisms by which this occurs will be described in more details in subsequent slides.