4.5 Kidney disease

The kidneys are two bean-shaped organs, found on either side of the spine, below the ribcage. Each kidney contains approximately 1 million specialised tubes, known as nephrons (Figure 29).

Figure 29 Schematic of a single kidney; here an enlarged nephron is shown, in reality, individual nephrons can only be seen with the aid of a microscope

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On the left is a schematic of the whole kidney showing the different anatomical components, including: the renal capsule (a thin outer membrane), renal cortex, renal medulla, renal pelvis merging to form the ureter. The renal artery and vein are showing entering the kidney just behind the ureter. On the right is a schematic of one of the nephrons, the functional unit of the kidneys.

Figure 29 Schematic of a single kidney; here an enlarged nephron is shown, in reality, individual nephrons can only be seen with the aid ...

The kidneys contribute to the balance of several aspects of body function. As part of the urinary system, the nephrons within the kidneys filter the blood plasma. Blood plasma is the yellowish liquid component of blood. A variety of substances are suspended within plasma, including red blood cells, several types of white blood cell and platelets (involved in blood clotting). The plasma also contains some waste materials or toxins that need to be filtered out from the plasma and removed from the body. The nephrons filter the blood plasma, and regulate the excretion of the filtered substances. The urine produced as a result of this process reflects the role of the kidneys in balancing the composition of the blood plasma and clearing substances such as metabolites and drugs from the body. The kidneys are also involved in the production of various hormones and play an important role in regulating blood pressure.

Chronic kidney disease is a long-term condition, where the nephrons become damaged, leading to a gradual loss of function. If kidney function falls to 10-15% of normal function, dialysis or transplantation are the only treatments available for the patient. It is estimated that currently 7.2 million people in the UK (Kidney Research UK, 2023) and 1 in 10 adults worldwide are believed to suffer from chronic kidney disease (Li et al., 2021).

Dysbiosis has been observed in patients with chronic kidney disease. The relationship between the gut microbiome and kidney disease is complex and is an active area of research. In kidney disease, the damaged nephrons fail to filter plasma appropriately, which changes plasma composition. Research suggests that this may alter the number and diversity of gut microbiota.

Due to the ‘leaky’ gut wall, some products of metabolism and toxins from food pass into the bloodstream and this has been linked to the onset and progression of kidney disease, and increased mortality risk. Conversely, other metabolites from the gut microbiome, such as SCFAs, appear to protect the kidneys and may increase survival rates of chronic kidney disease patients.

Although more research is needed, current understanding of the complex interactions between the gut microbiome and kidney function suggests that there may be the potential for improvements in patient outcomes, based on microbiome-based treatments.