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The function of the kidneys is to maintain the volume and composition of plasma, regulate water, ion and pH levels, retain nutrients and excrete waste, toxins and excess electrolytes. The kidneys achieve these functions via glomerular filtration, solute reabsorption, tubular secretion, water balance and acid-base regulation.

The function of the kidneys is to maintain the volume and composition of plasma, regulate water, ion and pH levels, retain nutrients and excrete waste, toxins and excess electrolytes. The kidneys achieve these functions via glomerular filtration, solute reabsorption, tubular secretion, water balance and acid-base regulation.

The kidneys are paired organs which reside in the left hand side and right hand side of the dorsal abdomen respectively, and they form during [[Developmental Anatomy of the Kidneys and Urinary Tract - Anatomy & Physiology|development]] from the intermediate mesoderm. Their role is to [[Osmosis and Filtration - Anatomy & Physiology|filter]] the blood through the renal corpuscle; this comprises a capillary tuft known as a glomerulus which is surrounded by the Bownam's capsule within the [[The Nephron - Anatomy & Physiology|nephron]], and the movement of fluid and soluble material across these structures forms what is known as the filtrate. The filtrate is then on the whole reabsorbed along the nephron until what is left comprises compounds superfluous to the requirements of the organism. Some compounds, normally fully reabsorbed, are occasionally present in the body in excess - the kidney tubules are able to respond to this excess and excrete such compounds in greater amounts. This is how the kidneys play a major role in the homeostasis of an animal. The kidneys also play a vital role in [[Introduction to Fluid Movement - Physiology |total water balance]], varying their excretion of water in relation to the hydration status of the animal. Medically, the physiology of the kidneys can be manipulted using diuretic drugs, which inhibit the reabsorption of water from the tubules and as a result increase the volume and therefore water loss in the urine.

The kidneys are paired organs which reside in the left hand side and right hand side of the dorsal abdomen respectively, and they form during [[Developmental Anatomy of the Kidneys and Urinary Tract - Anatomy & Physiology|development]] from the intermediate mesoderm. Their role is to [[Osmosis and Filtration - Anatomy & Physiology|filter]] the blood through the renal corpuscle; this comprises a capillary tuft known as a glomerulus which is surrounded by the Bownam's capsule within the [[The Nephron - Anatomy & Physiology|nephron]], and the movement of fluid and soluble material across these structures forms what is known as the filtrate. The filtrate is then on the whole reabsorbed along the nephron until what is left comprises compounds superfluous to the requirements of the organism. Some compounds, normally fully reabsorbed, are occasionally present in the body in excess - the kidney tubules are able to respond to this excess and excrete such compounds in greater amounts. This is how the kidneys play a major role in the homeostasis of an animal. The kidneys also play a vital role in [[Introduction to Fluid Movement - Physiology |total water balance]], varying their excretion of water in relation to the hydration status of the animal. Medically, the physiology of the kidneys can be manipulated using [[The Effects of Diuretics on the Kidneys - Anatomy & Physiology|diuretic]] drugs, which inhibit the reabsorption of water from the tubules and as a result increase the volume and therefore water loss in the urine.

The kidneys receive 25% of cardiac output. From this they filter 20% of the plasma forming a filtrate of which all but 1% is reabsorbed. This equates to the entire circulatory volume being filtered and reabsorbed every 30 minutes. The kidneys respond dynamically to changes in blood pressure and hydration status, using several mechanisms of [[Kidney - Blood Pressure - Anatomy &  Physiology|regulation]] including the [[Important Hormonal Regulators of the Kidney - Anatomy & Physiology#The Renin Angiotensin Aldosterone System (RAAS)| Renin-Angiotensin-Aldosterone system]] which can alter the movement of sodium chloride and water in the vascular system and extracellular spaces.

The kidneys receive 25% of cardiac output. From this they filter 20% of the plasma forming a filtrate of which all but 1% is reabsorbed. This equates to the entire circulatory volume being filtered and reabsorbed every 30 minutes. The kidneys respond dynamically to changes in blood pressure and hydration status, using several mechanisms of [[Kidney - Blood Pressure - Anatomy &  Physiology|regulation]] including the [[Important Hormonal Regulators of the Kidney - Anatomy & Physiology#The Renin Angiotensin Aldosterone System (RAAS)| Renin-Angiotensin-Aldosterone system]] which can alter the movement of sodium chloride and water in the vascular system and extracellular spaces.