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Renal System II

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University of Toronto St. George
Christopher Perumalla

Maintenance of an internal constancy is essential for life This is called homeostasis Some systems exert mechanisms on the body to maintain this internal environment constant while other systems are themselves involved in maintaining one or more aspects of the internal environment constant For example the endocrine system and the nervous system exert mechanisms on various systems of the body to keep certain aspects of the internal environment constant The endocrine system does this by releasing hormones and the nervous system does this by releasing neurotransmitters In addition to this there are other systms such as the respiratory system and the renal system that are responsible for maintaining certain aspects of the internal environment constant The respiratory system is responsible for maintaining the internal concentration of oxygen and CO2 constant The renal system on the other hand is involved in the homeostatic regulation of water and various ions in the blood Functions of the Renal SystemHomeostasisKidneys perform many vital fucntions and failure of kidneys leads to death Fluid balance Maintaining fluid balance is important in two ways Firstly it leads to maintenance of proper osmolarity Osmolarity is the measure of the concentration of solute molecules in a solution The body integrates kidney functions with behavioral drives such as thirst to maintain blood osmolarity at a value that is closer to 300 mlosmoles Secondly kidneys also contribute to maintenance of proper plasma volume By doing this they contribute significantly to the long term regulation of arterial blood pressure Ionic Composition Kidneys also aid in keeping the concentration of key ions such as sodium potassium calcium magnesium chlorite bicarbonate etc within the normal range by balancing dietary intake with urinary output This is very important because even slight changes in the ionic concentration can produce profound effectspH regulation pH is determined by the concentration of hydrogen ions Maintenance of appropriate pH levels is important for survival Therefore there are several mechanisms that are geared to maintaining and regulating the hydrogen ion concentration If the ECF becomes too acidic for example kidneys remove hydrogen ions and conserve bicarbonate which acts as a bufferWhen the ICF becomes too alkaline kidneys remove bicarbonate and conserve hydrogen ion Although kidneys do not correct pH disturbances as rapidly as lungs kidneys play a significant role in the homeostasis of blood pHExcretionKidneys excrete two types of substances metabolic end products and foreign compounds that have entered the body Metabolic Waste Kidneys excrete urea a nitrogenous waste that is chiefly found in the liver as a byproduct of protein metabolism Since proteins metabolism increases during injury of trauma to the tissue urea production also increases Uric acid is an end product of nucleic acid Uric acid is constantly produced in the body Occasionally plasma uric acid concentrations can significantly increase resulting in uric acid crystals precipitating in joints and thereby increasing inflammation and painful swelling of joints This can cause a pathology called Gaut Creatinine is produced by the catabolism of creatine phosphate an energy storage molecule in the muscle tissue that donates phosphate to ADP resulting in the formation of ATP There is a constant amount of creatinine that is produced and needs to be excreted Urobilirubin is a metabolyte of hemoglobin molecule Urobilirubin gives urine its characteristic yellow color If these wastes accumulate in the body they can become toxic especially to the brain For this reasons they need to be eliminated and kidneys play a major role in doing this Foreign Compounds Kidneys excrete drugs food additives artificial sweetner etc pesticides etcHormonal Secretes Erythropoietin
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