1. Waste excretion in urine
1.1. Excess ions sodium, potassium, calcium, magnesium, chloride, bicarbonate, phosphates and ammonium
1.2. Metabolic wastes- urea, creatinine, uric acid,nitrogenous waste
1.3. Drug metabolites- most pharmacological agents are eventually excreted from the body through the kidneys, many are detoxified in the liver first.
1.4. Metabolites of hormones for example human chorionic gonadotrophin in the urine in the early stage of pregnencies.
2. Erythropoietin production
2.1. This Hormone is produced by erythropoietin producing cells of the kidney to maintain normal red cell count and prevention of anemia.
2.1.1. Erythropoietin is stimulated by hypoxia and inhibited when the hypoxia is corrected, thus its production is controlled by the negative feedback principle
3. pH balance
3.1. The pH scale is a logarithmic scale(range1-14)that measures the concentration of free hydrogen ions in a fluid. This scale reciprocal when pH is low, hydrogen ions is high. Normal pH is between 7.35-7.45
3.1.1. Kidney controls the acid base balance by controlling the bicarbonate ions concentration in the body.
3.1.1.1. When plasma bicarbonate concentration is normal(25mmol) then all of the filtered bicarbonate is reabsorbed in the proximal tubule.
3.1.1.2. When the plasma bicarbonate concentration is higher than normal then excess bicarbonate is lost in the urine or undergoes bicarbonate trapping where bicarbonate ion is reserved in the blood and excretion excess hydrogen ions.
3.2. The rise in hydrogen ion concentration(acidosis is corrected by kidney by secreting the excess hydrogen into the urine and in the process generating further bicarbonate for reabsorption into the plasma. Fall in hydrogen ion concentration(alkalosis) in the body fluids is corrected by kidney by reducing the amount of hydrogen ion secretion in the urine
4. potassium , aldosterone is the only hormone involved in the control potassium content in the body
4.1. Small increase of extracellular potassium directly stimulates adrenal cortex to produce aldosterone which affects the distal tubule of the nephron to secrete potassium into the urine.
4.2. When the aldosterone level falls, the reverse occurs and less potassium is secreted and is controlled by negative feedback system.
5. Fluid volume balance
5.1. ADH-is a secreted by the posterior pituatry gland and ADH receptors and found in collecting ducts of kidney tubulers.
5.1.1. When there is raise in plasma osmolality, water is reabsorbed into the blood, diluting the plasma and reducing osmolality to normal.
5.1.2. A fall in plasma osmolality leads to decrease in ADH secretion by negative feedback. ADH receptors are found in collecting ducts of kidney tubules.
5.2. Aldosterone is a steroid hormone secreted from the adrenal cortex of the kidney and effects the distal tubule of the nephrons. Secretion of aldosterone is regulated by peptide, angiotensin II
5.2.1. When more aldosterone is secreted the more sodium is reabsorbed and therefore water reabsorbed.
5.3. Atrial natriuretic peptide-is released from cardiac atrial cells in response to an increased atrial stretch.
5.3.1. ANP inhibits aldosterone secretion by adrenal cortex, reduce renin release by kidney and reduction of ADH the posterior pituitary to reduce the fluid volume by excreting sodium and water
6. Electrolytes balance
6.1. Calcium is important in the extracellular fluid in controlling nerve and muscle conduction.
6.1.1. calcium reabsorption occurs depending on the level of circulating parathyroid hormone.
6.2. Phosphates is important in buffer system to maintain the plasma pH and exits in equilibrium with calcium
6.2.1. When plasma phosphate level is low the filtered phosphate is reabsorbed in the early proximal tubule and if it is high, it is excreted in the urine.
6.3. magnesium also an important intracellular cation involved in energy storage and production.
6.3.1. Similar to calcium, increase in PTH increase tubular reabsorption of magnesium.
7. Blood pressure control
7.1. Macular densa in the wall of distal tubule make contact with cells in the endothelium of the arteriales which release a hormone called renin, this is called juxtaglomerular apparatus which maintain a constant blood flow through tubule feedback mechanism.
7.1.1. Renin acts via the renin angiotensin system to produce both local vasoconstriction of the efferent arteriole increasing GFR and also peripheral vasoconstriction to increase arteral blood pressure.