We are all aware about the importance of kidneys but the most we recall is its unique shape and that they filter stuff. But there’s more than meets the eye when it comes to the two-bean shaped organs of ours.
The shape of the kidney comes about from evolution. Not only has it been optimized to keep space along the spine, but the inward curve – also known as the hilum – provides a perfect entry and exit point for the arteries and veins to connect to the organ. Internally, each kidney is split into three structural layers, consisting of the outer renal cortex, the inner renal medulla and the urine-connecting renal pelvis. Zoom in a bit further and you will see the structure that carries out the filtration in the kidneys, the nephrons1. Each kidney contains around 1 million nephrons, each one consisting of a dense network of tiny capillaries (glomerulus) and tubes that ensure nutrients and water is absorbed by your body. Along with other structures that aid the kidney.
Despite having numerous parts, the kidney seamlessly combines them together to carry out the seemingly simple task of clearing out toxins and waste from the body. The organ filters approximately 189 Litres of blood every 24 hours, and the kidneys have evolved to ensure the process is efficient enough to clear out waste but not lose any important nutrients3.
The procedure of filtration in the kidneys is carried out by the nephrons; it follows a 4 step pathway: filtration, reabsorption, secretion and excretion. First, blood enters the glomerulus, which acts as a strainer to push water and small molecules into a cup-shaped sac known as the Bowman’s capsule while retaining components such as blood cells and proteins. Next, as the fluid travels down the tubes, essential nutrients, ions and water all are reabsorbed back into the bloodstream. During secretion, the body pumps out any additional wastes, excess acids and unwanted byproducts back into the tubules. Finally, in excretion the leftover byproducts leave the body as urine. Beyond all of this the kidney also produces hormones and regulates the blood pressure.
From the above it is evident that your kidneys go through a lot.. literally. But what happens when one of the parts gets damaged? This aspect of the organ is the most fascinating but also the most terrifying. Because the kidneys work quietly, damage often goes completely unnoticed until the final stages of failure. When that happens, the only options of treatment are either expensive and time-consuming dialysis or an organ transplant; and the healthcare system isn’t exactly drowning in donor kidneys. With kidney disease being one of the leading causes of death worldwide. It is crucial to protect the one pair given to you in your life, by eating a balanced diet, limiting sodium-intake, staying well-hydrated and getting regular health screenings to ensure you and your kidneys are in good health.
Good kidney health starts today.
References:
1Hall, J. E., & Hall, M. E. (2020). Guyton and Hall Textbook of Medical Physiology (14th ed.). Elsevier.
2Seldin, D. W., & Giebisch, G. (Eds.). (2008). The Kidney: Physiology and Pathophysiology (4th ed.). Academic Press.
3National Kidney Foundation (NKF). (2023). How Your Kidneys Work. National Kidney Foundation Official Clinical Guidance.
4Eaton, D. C., & Pooler, J. P. (2018). Vander's Renal Physiology (9th ed.). McGraw-Hill Education.
5Sahay M, Kalra S, Bandgar T. Renal endocrinology: The new frontier. Indian J Endocrinol Metab. 2012 Mar;16(2):154-5. doi: 10.4103/2230-8210.93729. PMID: 22470848; PMCID: PMC3313729.
6Wadei HM, Textor SC. The role of the kidney in regulating arterial blood pressure. Nat Rev Nephrol. 2012 Oct;8(10):602-9. doi: 10.1038/nrneph.2012.191. Epub 2012 Aug 28. PMID: 22926246.
7Alberto Ortiz, Jennifer S Lees, Roser Torra, Vianda S Stel, Anneke Kramer, Patrick B Mark, The updated global burden of chronic kidney disease: one death every 20 seconds, Nephrology Dialysis Transplantation, 2026;, gfag040, https://doi.org/10.1093/ndt/gfag040
