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For my STEAM project I chose the objective: Know the anatomy of kidneys and general function of the renal cortex, medulla, and pelvis. I chose to focus on the effects of CKD on the renal medulla. For my project, I made a stuffed kidney from felt.
The kidneys are essential organs responsible for filtering blood, removing waste products, and maintaining fluid and electrolyte balance. Each kidney comprises three main regions: the cortex, medulla, and pelvis. Understanding the anatomy and function of these regions in the kidney is crucial to comprehending how chronic kidney disease (CKD) affects renal health, particularly the medulla. (Anatomy and Physiology Section 25.4)
The renal cortex is the outer layer of the kidney, containing the glomeruli and convoluted tubules, which are vital for filtering blood and initiating urine formation. Beneath the cortex lies the renal medulla, composed of pyramid-shaped structures known as renal pyramids. These pyramids house the loops of Henle and collecting ducts, which play a significant role in concentrating urine and conserving water. The innermost region, the renal pelvis, acts as a funnel, collecting urine from the collecting ducts and channeling it into the ureter for excretion.
The renal medulla is integral to the kidney’s ability to concentrate urine. It contains the loops of Henle and collecting ducts, which establish a concentration gradient through a countercurrent exchange mechanism. This gradient allows for the reabsorption of water and solutes, enabling the production of concentrated urine. The medulla operates in a relatively low-oxygen environment, making it particularly susceptible to hypoxic injury. (Anatomy and Physiology Section 25.4) (Eddy)
Chronic kidney disease is characterized by a gradual decline in kidney function over time. While CKD primarily affects the glomeruli in the cortex, the medulla is not spared from its detrimental effects. The medulla’s low oxygen environment makes it vulnerable to hypoxia, especially as CKD progresses. Hypoxia in the medulla can lead to cellular injury, inflammation, and fibrosis, impairing its ability to concentrate urine. This impairment results in symptoms such as polyuria (increased urine output) and nocturia (frequent urination at night). (Mayer Brezis and Rosen) (Schnaper)
Furthermore, CKD-induced damage to the medulla can disrupt sodium and potassium handling, leading to electrolyte imbalances. The thick ascending limb of the loop of Henle, located in the medulla, is responsible for reabsorbing sodium and chloride. Damage to this region can result in salt wasting and contribute to hyponatremia (low sodium levels). Additionally, impaired potassium secretion in the collecting ducts can lead to hyperkalemia (elevated potassium levels), posing serious health risks.
The medulla’s susceptibility to hypoxic injury in CKD is further exacerbated by the loss of peritubular capillaries, which reduces oxygen delivery to the tissue. This capillary loss, combined with increased oxygen demand due to hyperfiltration, creates a vicious cycle of worsening hypoxia and tissue damage. Over time, this leads to tubulointerstitial fibrosis, further compromising medullary function and accelerating the progression of CKD. (Mayer Brezis and Rosen)
In conclusion, the renal medulla plays a crucial role in urine concentration and electrolyte balance. Chronic kidney disease adversely affects the medulla by inducing hypoxic injury, inflammation, and fibrosis, leading to impaired urine concentration and electrolyte handling. Understanding these effects is essential for developing strategies to preserve medullary function and slow the progression of CKD.
References:
- Mayer Brezis, and Seymour Rosen. “Hypoxia of the Renal Medulla — Its Implications for Disease.” The New England Journal of Medicine, vol. 332, no. 10, 9 Mar. 1995, pp. 647–655, https://doi.org/10.1056/nejm199503093321006. Accessed 23 Apr. 2023.
- Eddy, Allison A. “Progression in Chronic Kidney Disease.” Advances in Chronic Kidney Disease, vol. 12, no. 4, Oct. 2005, pp. 353–365, https://doi.org/10.1053/j.ackd.2005.07.011. Accessed 12 Mar. 2019.
- Schnaper, H. William. “Remnant Nephron Physiology and the Progression of Chronic Kidney Disease.” Pediatric Nephrology, vol. 29, no. 2, 29 May 2013, pp. 193–202, www.ncbi.nlm.nih.gov/pmc/articles/PMC3796124/, https://doi.org/10.1007/s00467-013-2494-8.
- Anatomy and Physiology 2e. Openstax, 2022, Section 25.1-25.10.
Hayley’s STEAM project focuses on the effects of Chronic Kidney Disease (CKD) on the Renal Medulla. She explains that the kidneys are very important organs and are responsible for filtering blood, removing waste products, and maintaining fluid and electrolyte balance. There are three main parts of the kidneys, the cortex, medulla, and pelvis. The renal cortex is the outer most part of the kidney, and has glomeruli and convoluted tubules, which are crucial for filtering blood and initiating urine formation. The renal medulla is found under the cortex and have renal pyramids. Renal pyramids house the loops of Henle and collecting ducts, which are vital in concentrating urine and conserving water. The inner most part is the renal pelvis, which acts as a funnel as it collects urine from the collecting ducts and channeling it into the ureter for excretion. She explains that CKD is characterized by a gradual decline in kidney function over time. While CKD affects the glomeruli in the cortex mostly, the medulla is also at risk to its devastating effects. As CKD progresses, the medulla’s low oxygen environment makes it more vulnerable to hypoxia. Hypoxia in the medulla can lead to cellular injury, inflammation, and fibrosis, decreasing its ability to concentrate urine. CKD can also disrupt sodium and potassium handling, leading to electrolyte imbalances. Hayley also states that “The medulla’s susceptibility to hypoxic injury in CKD is further exacerbated by the loss of peritubular capillaries, which reduces oxygen delivery to the tissue”, showing once again how detrimental CKD can be to the kidneys, especially the renal medulla, as well as the body as a whole. She made a stuffed kidney out of felt which showed the parts of the kidney she talked about in her written piece, which helped as a reader give a visual on the different parts of the kidney and where in the kidney was mostly effected.