1. regulate arterial blood pressure / maintenance of extracellular fluid volume balance
1.1. when extracellular fluid (ECF) volum is high
1.1.1. atrial natriuretic hormone from the heart reduce sodium and fluid reabsorption in the kidneys
1.2. when extracellular fluid (ECF) volum is low
1.2.1. activation of Renin-Angiotensin- Aldosterone System, due to decreased renal blood flow
1.2.1.1. renin is secreted in the kidney -> renin acts on angiotensinogen to produce angiotensin I -> angiotensin I converted to angiotensin II in lungs
1.2.1.1.1. vasoconstriction
1.2.1.1.2. secretion of the hormone aldosterone which increases the reabsorption of sodium and water into the blood and excrete potassium at renal tubules
1.2.2. antidiuretic hormone (ADH) increase the reabsorption of water by altering the permeability of the distal convoluted tubule and collecting duct in kidney
2. regulation of glucose
2.1. by releasing glucose into the circulation via gluconeogenesis
2.1.1. Insulin suppresses glucose release in kidney
2.1.2. catecholamines stimulate the release of renal glucose
2.2. by uptaking glucose from the circulation to satisfy its energy needs (reabsorption)
2.3. by reabsorbing glucose from the glomerular filtrate
3. electrolytes balance
3.1. sodium homeostasis
3.1.1. sodium is reabsorbed by active transport mechanisms in the proximal tubule (most of the reabsorption occurs here)
3.1.1.1. reabsorption of sodium in the distal convoluted tubule is stimulated by aldosterone and ADH (fine-tuning reabsorption)
3.1.1.1.1. sodium is reabsorbed by active transport mechanisms in the proximal tubule (most of the reabsorption occurs here)
3.1.1.2. renal reabsorption of sodium is inhibited by atrial natriuretic peptide.
3.1.2. sodium excretion in kidney is largely regulated based on the total extracellular fluid volume
3.2. chloride homeostasis
3.2.1. the ability of the nephrons to reabsorb chloride maintains the serum (and ECF) chloride concentration within a narrow range
3.2.1.1. the proximal tubule reabsorbs the majority of the filtered chloride. The distal tubule and collecting duct play an important role in this balance
3.2.2. the quantity of chloride excreted into the urine varies from day to day depending on whether the kidneys are trying to conserve or eliminate chloride
3.3. potassium homeostasis
3.3.1. kidney is primarily responsible for maintaining total body K+ content by matching K+ intake with K+ excretion
3.3.1.1. potassium is freely filtered by the glomerulus. The bulk of filtered K+ is reabsorbed in the proximal tubule and loop of Henle, such that less than 10% of the filtered load reaches the distal nephron
3.3.1.2. potassium secretion begins in the early distal convoluted tubule and progressively increases along the distal nephron into the cortical collecting duct
3.4. calcium homeostasis
3.4.1. more than 95% of filtered calcium is reabsorbed along the renal tubules
3.4.2. biologically active Vitamin D which augments gastrointestinal calcium absorption is mainly converted in kidney
3.4.3. The fine regulation of calcium excretion occurs in the distal convoluted tubules and connecting tubules
3.5. phosphate homeostasis
3.5.1. phosphate is filtered at the glomerulus then reabsorbed almost exclusively in the proximal tubule
4. waste management
4.1. metabolic waste
4.1.1. renal nitrogen excretion / nitrogen balance
4.1.1.1. urea
4.1.1.1.1. amino acids may also be metabolized through the liver to form urea, which is then excreted in the urine
4.1.1.2. ammonia
4.1.1.2.1. ammonia excretion accounts for the majority of basal bicarbonate generation and changes in ammonia excretion are the primary response to acid-base disorders
4.1.2. uric acid homeostasis
4.1.2.1. serum uric acid levels mainly depend on uric acid synthesis and its renal excretion
4.1.2.1.1. the majority of uric acid is excreted by the kidney following the filtration, reabsorption, and secretion processes
4.1.2.1.2. factors influencing renal uric acid excretion are: high sodium intake, electrolyte disorders, extracellular fluid volume, acid-base balance, urinary pH, Insulin resistance
4.1.3. creatinine excretion
4.1.3.1. creatinine is removed from the blood chiefly by the kidneys, primarily by glomerular filtration, but also by proximal tubular secretion
4.1.3.1.1. if the filtration in the kidney is deficient, creatinine blood levels rise.
4.1.3.2. little or no tubular reabsorption of creatinine occurs
4.2. drug metabolites
4.2.1. most metabolites of pharmacological agents are eventually excreted from the body through the kidneys by
4.2.1.1. glomerular filtration
4.2.1.2. secretion
4.3. regulation of body fluid osmolality
4.3.1. the ability of the kidneys to excrete all the body’s excess solutes in varying amounts of water by concentrating or diluting the urine is essential for maintaining a constant body osmolality
5. acid-base homeostasis
5.1. because of their capacity to definitively eliminate acids without consumption of physiological buffers and their ability to generate novel bicarbonate, the kidneys are the organ which controls long-term acid-base
5.1.1. when ECF pH is excessively low
5.1.1.1. the kidneys resorb all of the filtered bicarbonate, actively secrete hydrogen ions, and generate novel ECF bicarbonate, thus slowly raising ECF pH
5.1.2. when ECF pH is excessively high
5.1.2.1. the kidneys can excrete large amounts of filtered bicarbonate and reduce hydrogen ion secretion, thus slowly reducing ECF pH