The kidneys are responsible for filtering waste from the blood and play a part in managing the body’s fluid balance and blood pressure. To carry out these complex tasks, they rely on regulation from the nervous system. This control system ensures the kidneys can adapt to the body’s changing needs, from conserving water during dehydration to adjusting blood flow. The network of nerves that governs these functions is important for maintaining overall health.
Defining the Renal Plexus
The nerves and ganglia that serve the kidney are collectively known as the renal plexus. In anatomical terms, a plexus is a complex, web-like network of intersecting nerves. The renal plexus specifically refers to this web of nerves and associated ganglia—which are clusters of nerve cell bodies—that is situated in the upper abdomen. This network is positioned around the renal artery, the main blood vessel supplying the kidney, and follows its branches as they extend deep into the kidney tissue.
This arrangement allows the nervous system to communicate directly with the functional units within the kidney. Its primary role is to transmit signals from the central nervous system to the kidney and to send sensory information from the kidney back to the brain.
Anatomy and Origins of Renal Nerves
The renal plexus is an anatomically complex structure with contributions from several different parts of the autonomic nervous system. It is primarily considered an extension of the celiac plexus, a major nerve network in the abdomen, and also receives fibers from the aorticorenal ganglia. These ganglia, including the celiac and superior mesenteric ganglia, serve as relay points for nerve signals traveling to the kidney.
The thoracic and lumbar splanchnic nerves, particularly the least splanchnic nerve, provide significant input. These nerves carry preganglionic sympathetic fibers, which are nerve fibers that originate in the spinal cord and travel to the ganglia. Postganglionic fibers, which travel from the ganglia to the kidney itself, then complete the pathway.
While the renal plexus is dominated by sympathetic nerves, which manage “fight or flight” responses, it also contains some parasympathetic fibers from the vagus nerve. The nerves, numbering fifteen to twenty, travel along the renal artery and its smaller branches to reach their targets within the kidney.
Functional Control of the Kidney
The efferent, or outgoing, nerves of the renal plexus exert control over several kidney functions, primarily through sympathetic stimulation. One of the main roles of these nerves is the regulation of renal blood flow. When the sympathetic nerves are activated, they cause the small arteries within the kidney, known as arterioles, to constrict. This vasoconstriction reduces blood flow into the glomeruli, the kidney’s filtering units, which in turn can decrease the glomerular filtration rate (GFR).
Another function of the renal plexus is to stimulate the release of renin. Nerve signals act directly on specialized cells called juxtaglomerular cells, prompting them to release this enzyme. Renin is a component of the renin-angiotensin-aldosterone system, a hormonal cascade that helps regulate blood pressure throughout the body. By controlling renin secretion, the renal nerves play a part in long-term blood pressure management.
These nerves also influence how the kidney handles salt and water. Sympathetic nerve fibers extend to the renal tubules, the structures responsible for reabsorbing substances from the filtered fluid. Stimulation from these nerves can increase the reabsorption of sodium and water back into the bloodstream. This action helps the body conserve fluids, which is important during times of dehydration or low blood pressure.
Sensory Signaling from the Kidney
The nerve connection to the kidney is a two-way communication system. In addition to the efferent nerves that send signals to the kidney, there are also afferent, or incoming, nerve fibers that transmit sensory information from the kidney to the central nervous system. These sensory nerves act as monitors, providing the brain with real-time updates on the kidney’s status.
These afferent nerves include two main types of receptors. Chemoreceptors monitor the chemical composition of the blood and urine, detecting changes in factors like ion concentration or pH. Mechanoreceptors, on the other hand, detect physical forces such as stretch or pressure within the kidney. For example, an increase in pressure within the renal pelvis, the central collecting part of the kidney, activates these mechanoreceptors.
Pain originating from the kidney, such as that caused by a kidney stone or a significant infection, is transmitted along these afferent pathways. The information travels from the kidney to the spinal cord and then to the brain, where it is perceived as pain, often felt in the flank and abdominal area.