From the Guidelines
Renal physiology is the study of how the kidneys function in the body, playing crucial roles in filtering blood, regulating fluid balance, controlling electrolyte levels, maintaining acid-base balance, and producing hormones that affect blood pressure and red blood cell production. The kidneys are vital organs that contain about one million functional units called nephrons, which filter blood through a process involving glomerular filtration, tubular reabsorption, and tubular secretion 1. This filtration system processes about 180 liters of fluid daily, with most being reabsorbed and only 1-2 liters excreted as urine. Understanding renal physiology is essential for diagnosing and treating kidney diseases, managing fluid and electrolyte disorders, and addressing conditions like hypertension and diabetes that can impact kidney function.
Key Components of Renal Physiology
- Glomerular filtration rate (GFR) is the best measure of overall kidney function in health and disease, with a normal level varying according to age, sex, and body size 1.
- Kidney damage can be diagnosed without knowledge of its cause, with persistent proteinuria being the principal marker of kidney damage, and an albumin-creatinine ratio greater than 30 mg/g in untimed urine samples considered abnormal 1.
- The kidneys play crucial roles in regulating blood pressure through the renin-angiotensin-aldosterone system, producing erythropoietin to stimulate red blood cell production, and activating vitamin D for calcium absorption.
Clinical Significance of Renal Physiology
- Chronic kidney disease (CKD) is defined as either kidney damage or decreased kidney function for 3 or more months, with a GFR level less than 60 mL/min per 1.73 m2 representing loss of half or more of the adult level of normal kidney function 1.
- Acute kidney injury (AKI) is a common cause of hospital admission for patients with heart failure, and can be detected through routine laboratory measurements, with earlier detection allowing for earlier intervention and potentially increased chance of prevention or amelioration 1.
- Understanding renal physiology is essential for managing fluid and electrolyte disorders, and addressing conditions like hypertension and diabetes that can impact kidney function, with regular monitoring of renal function and adjustment of prescribed drugs potentially preventing or delaying adverse outcomes 1.
Recent Guidelines and Recommendations
- The National Kidney Foundation practice guidelines for chronic kidney disease recommend early detection and treatment of CKD, with a definition of CKD that includes either kidney damage or decreased kidney function for 3 or more months 1.
- The ACR Appropriateness Criteria for renal failure recommend a thorough history, physical examination, and laboratory analysis of blood and urine for patients with AKI or CKD, with renal biopsy indicated for differentiation of nephritic and nephrotic syndromes 1.
From the Research
Overview of Renal Physiology
Renal physiology refers to the study of the functions and processes of the kidneys, which play a crucial role in maintaining the body's internal environment. The kidneys perform several major functions, including:
- Eliminating toxins produced by cellular or xenobiotic metabolism 2
- Regulating the homeostasis of the internal environment 2, 3, 4, 5
- Playing a hormonal role, producing erythropoietin, calcitriol, and renin 2, 3
Structure and Function of the Nephron
The nephron is the basic structural and functional unit of the kidney, composed of a glomerulus and a tubule. The glomerulus acts to filter the blood, producing an ultrafiltrate that enters the tubule, where reabsorption and secretion occur to produce the final urine 3, 4, 5. The processes of filtration, reabsorption, and secretion are essential for maintaining the body's balance of water, minerals, electrolytes, and hydrogen ion concentration, as well as eliminating toxic substances 3, 4, 5.
Regulation of Body Fluid and Solutes
The regulation of body fluid and solutes is governed by the processes of filtration, reabsorption, and secretion. Unwanted fluid and substances are excreted from the body as urine 4, 5. The renal proximal tubule plays a critical role in solute reabsorption, including the reabsorption of glucose, a critical source of energy for the body 6.
Importance of Renal Physiology
Understanding renal physiology is essential for understanding the various disorders that can affect the kidney. The kidneys are highly vascularized organs that are responsible for maintaining the body's internal environment, and dysfunction can lead to pathophysiological conditions such as diabetes and acidosis 2, 6.