Kidney disease contributes significantly to the global burden of disease, both in developing and developed countries. The Centers for Disease Control and Prevention estimate that in the United States, more than 10% of people 20 years of age and older (more than 20 million individuals) have chronic kidney disease. In addition, many more people suffer from acute kidney injury and other forms of kidney disease annually. Thus, clinicians of all specialties will encounter patients with renal disorders, and it behooves us to be aware of the various risk factors and causes of kidney disease. This is particularly important because with early detection and appropriate management, most forms of kidney disease can be treated to prevent or at least slow the rate of progression to kidney failure or other complications.
The kidneys serve a crucial role in filtering blood, and a wide range of diseases of other organ systems and systemic diseases may be manifested in the kidney. For example, renal disease is a prominent presentation of long-standing diabetes mellitus and hypertension and of autoimmune disorders such as systemic lupus erythematosus.
A particular challenge is that patients are typically asymptomatic until relatively advanced kidney failure is present. There are no pain receptors within the substance of the kidney, so pain is not a prominent presenting complaint, except in those renal diseases in which there is involvement of the ureter (eg, nephrolithiasis) or the renal capsule (eg, renal cell carcinoma). In early stages of kidney disease, patients may have only abnormalities of urine volume or composition (eg, presence of red blood cells and/or protein). Later, they may manifest systemic symptoms and signs of lost renal function (eg, edema, fluid overload, electrolyte abnormalities, anemia). Depending on the nature of the renal disease, they may progress to display a wide range of chronic complications resulting from inadequate renal function.
The kidneys play multiple roles in the body, including blood filtration, metabolism and excretion of endogenous and exogenous compounds, and endocrine functions. Perhaps most significantly, the kidneys are the primary regulators of fluid, acid–base, and electrolyte balances in the body, and this remarkable pair of organs maintains homeostasis across a broad array of dietary and environmental changes. An understanding of each of these roles is required to illuminate the pathophysiologic basis behind the many manifestations of kidney disease.
NORMAL STRUCTURE & FUNCTION OF THE KIDNEY
ANATOMY, HISTOLOGY & CELL BIOLOGY
A remarkable attribute of the kidneys is their ability to maintain homeostasis while functioning under a broad range of environmental water and salt availabilities. For example, the kidneys have the capacity to excrete free water in freshwater fish, widely varying amounts of water and solute in humans, and an extremely concentrated urine in the kangaroo rat, ...