1. The kidneys produce two hormones , Calcitriol, the active form of Vitamin D, helps regulate calcium homeostasis and erythropoietin stimulates production of red blood cells.
2. Regulation of Blood pH
2.1. The kidneys regulate blood pH with the help of excretion of excess H+ in the urine or by conserving bi-carbonate ions an important buffer of Hydrogen ion. Normal Blood pH is 7.35 - 7.45.
2.1.1. When blood pH becomes acidic mean less than 7.35, in this metabolic acidosis state, Kidneys secrets hydrogen ion and reabsorb most of the bi-carbonate ions in proximal tubules and distal tubules. Furthermore, kidneys generate new bi-carbonate to compensate acidosis.
2.1.1.1. Metabolic acidosis may occur due to starvation, diabetic ketoacidosis, severe diarrhea, renal failure, renal tubular acidosis and shock. Signs and symptoms includes drowsiness, confusion, headache and coma.
2.1.2. When blood pH of body becomes alkaline means pH greater than 7.45, this stage is called metabolic alkalosis .kidneys excretes Bi-carbonate ions and prevent hydrogen ion excretion. Thus Kidney play an important role in homeostasis.
2.1.2.1. Metabolic alkalosis may results from gastric suctioning, severe vomiting , diuretic therapy or excessive mineralocorticoids Signs and symptoms may have confusion, lethargy, irritability, nervousness etc.
2.2. Blood gas values affect Acid - base balance. Metabolic acidosis or Metabolic alkalosis depends of the value of Bi-carbonate (HCO3-) which is primarily controlled by the kidneys. Normal value of HCO3 is between 21-28 mmol/l.
2.2.1. Metabolic acidosis may occur due to starvation, diabetic ketoacidosis, severe diarrhea, renal failure, renal tubular acidosis and shock. Signs and symptoms includes drowsiness, confusion, headache and coma.
2.2.2. Metabolic alkalosis may results from gastric suctioning, severe vomiting , diuretic therapy or excessive mineralocorticoids Signs and symptoms may have confusion, lethargy, irritability, nervousness etc.
3. Production of Hormone
4. Excretion of Waste
4.1. The kidneys play an important role of excretion of wastes from the body in form of urine. These include ammonia, urea , bilirubin, uric acid, creatinine and other toxins like drugs and environmental toxins.
5. Regulation of ion levels
5.1. Sodium ion balance
5.1.1. Sodium ions are the most abundant extracellular cations. Regulation of Sodium is mainly depends on the osmolarity of extracellular fluids. Kidney absorb most of the sodium at proximal tubules and rest absorb at distal tubules maintained by aldosterone, ADH and ANP.
5.1.1.1. Hyponatremia due to decreased sodium intake or sodium loss due to vomiting , diarrhea or aldosterone deficiency or excessive water intake. Sign and symptoms includes muscular weakness, dizziness, hypotension, mental confusion, stupor and coma.
5.1.1.2. Hypernatremia occurs with dehydration, excessive sodium intake or water deprivation. Sign and symptoms includes intense thirst, hypertension, edema and convulsion.
5.2. Potassium ion balance
5.2.1. Potassium ions (K+) is the most abundant cations in intracellular fluids. Kidney regulates Potassium ion with the help of aldosterone. Aldosterone acts on the renal collecting ducts to regulate Potassium ion in blood plasma.
5.2.1.1. Hypokalemia, a low potassium level may result from excessive fluid loss by diarrhea or vomiting or decrease potassium intake. Signs and symptoms includes muscle fatigue, flaccid paralysis, mental confusion and changes in electrocardiogram.
5.2.1.2. Hyperkalemia occurs due to excessive potassium intake, renal failure, aldosteron deficiency or crushing body injuries. Sign and symptoms includes irritability, nausea, vomiting, muscular weakness and cause death by inducing ventricular fibrillation.
5.3. Chloride ion balance
5.3.1. Chloride ions are the most prevalent anions in extracellular fluids. Kidney regulates chloride ions with the help of anti diuretic hormone(ADH). Processes that increase of decrease renal reabsorption of sodium ions also affect chloride ion because negatively charged always follows possitively charged sodium ion.
5.3.1.1. Hypochloremia may be due to excessive vomiting, water intoxication, congestive heart failure, aldosterone deficiency or due to diuretics. Signs and symptoms includes muscle spasm, tetany or shallow ventilation.
5.3.1.2. Hyperchloremia mau result from dehydration, severe renal failure, aldosterone excess or some drugs. S/S includes lethargy, weakness and rapid deep breathing.
5.4. Calcium ion balance
5.4.1. Calcium ions are an extracellular cation. Kidney regulates calcium ion with the help of Parathyroid hormone which enhances reabsorption of calcium from the glomerular filtrate.
5.4.1.1. Hypocalcemia may be due to increased calcium loss, reduced calcium intake, elevated level of phosphate or parathyroid deficiency. S/S includes numbness and tingling of fingers, muscle cramp, tetany and convulsions.
5.4.1.2. Hypercalcemia may results from hyperthyroidism, excessive intake of Vit.D. and Paget's disease of bone. S/S includes lethargy, anorexia, nausea, vomiting, polyuria, bone pain, confusion and coma.
6. Regulation of Blood Volume and Blood Pressure
6.1. Kidney regulates blood volume and blood pressure by reabsorbing of sodium and water to blood or by eliminating sodium and water in urine maintained by ADH, ANP as well as renal secreting enzyme Renin which activates Renin-angiotension-aldosteron pathway.
6.1.1. Atrial Natriuretic Peptide(ANP) plays a major role in inhibiting the reabsorption of sodium and water by the renal tubules. Therefore, water and salt are lost in the urine which finally decrease the blood volume and eventually decreases blood pressure
6.1.2. The major hormone that regulates water reabsorption is anti-diuretic hormone(ADH) which operates through negative feedback. When the concentration of water in the blood decreases the hypothalamus stimulate release of ADH. ADH acts on distal convoluted tubules as well as collecting ducts to increase the permeability of the tubule cells thus moves water back into the blood.
6.1.3. The most important hormonal regulators of ion reabsorption and secretion are angiotensin II and aldosterone. In proximal convoluted tubules, angiotensin II enhances reabsorption of sodium and chloride. Angiotensin II also stimulates the adrenal cortex to release aldosteron, a hormone which stimulate collecting ducts to reabsorb Na+ and Cl- thus increase blood volume as well as blood pressure.