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Kidneys and nephrons functions

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________________ ________________ ________________ Kidneys and nephrons functions ________________ ________________ Introduction Kidneys are located on the posterior wall of the abdomen and protected by lower ribs. They are supplied by blood, which is transported from aorta through renal arteries, and filtered blood will be transported back through renal veins (Bradley & Calvert 2011). A kidney consists of outer cortex, inner medulla and renal pelvis, where urine is hold and passed to ureter and then to the bladder (Bradley & Calvert 2011). Osmoregulation is controlled by kidneys (electrolytes and fluid levels in the body). Kidneys are also responsible for excretion of urea (nitrogenous waste) (Bradley & Calvert 2011). Electrolytes and body fluid levels are very important for functioning cells and tissues. Even slight changes in plasma potassium can cause heart failure and paralysis and kidneys regulate this (Bradley & Calvert 2011). The fluids and electrolytes from plasma are going through filtration and then appropriate level will be reabsorbed into blood to keep sufficient plasma level. The process of reabsorption is achieved by hormonal control (Bradley & Calvert 2011). Kidneys are also responsible for the removal of the waste nitrogen, which is the product of proteins breakdowns (Bradley & Calvert 2011). Any dysfunctions of kidneys can be fatal as homeostatic state will be interrupted, therefore it is important to understand the mechanism of this important organ (Bradley & Calvert 2011). ...read more.


At the lower part of the loop of Henle, the tubular and interstitial fluids obtain osmolarity of 1200 mosmol, around 4 times higher then the plasma (Bradley & Calvert 2011). The gradient is achieved because ascending limb does not allow water to pass through, but moves sodium to ascending limb, therefore solute concentration increases (Bradley & Calvert 2011). The filtrate then moves from the ascending limb to distal tubule, where sodium and water continues to be removed (Bradley & Calvert 2011). Excretion of sodium is controlled by aldersterone, a hormone which production occurs in adrenal gland, when Na+ions level is low (Bradley & Calvert 2011). If sodium absorption increases, water also increases. The final excretion of water occurs in collecting ducts, which are connected with renal medulla directed to renal pelvis (Bradley & Calvert 2011). Because they move through the renal medulla, it passes through high osmolarity at the lower part of loop of Henle (Bradley & Calvert 2011). Epithelium cells of colleting ducts consist water channels- aquaporins that speeds up movement of water out of the duct and into interstitial fluid (Bradley & Calvert 2011). Aquaporins are more permeable to water then urea, therefore urea will be more concentrated in the urine (Bradley & Calvert 2011). ...read more.


(2012) [Online]. Kidneys are also responsible for production of hormones that may have an effect on functions of other systems such as a particular hormone obtained from kidneys will initiate production of erythrocytes, where another hormone obtained from kidneys will maintain blood pressure and calcium levels National Kidney Foundation. (2012) [Online]. As mentioned above homeostasis of water and electrolytes depends on kidney function National Kidney Foundation. (2012) [Online]. If renal filtration would not take place, blood plasma?s range point would change dramatically National Kidney Foundation. (2012) [Online]. However, without cardiovascular system, which is responsible for maintenance of blood pressure, the kidneys would not be able to process blood plasma (Thibodeau & Patton 2007). For that reason both urinary and cardiovascular mechanisms are dependent on each other respectively (Thibodeau & Patton 2007). Urinary system is also interdependent on nervous because nerve reflexes control urinary functions. Also endocrine system interacts with urinary functions as regulation of urinary system take place outside the kidney by endocrine hormone production (Tortora & Derrickson 2007). The kidneys removes nitrogen waste and unwanted metabolic acids from blood plasma, which was formed sue to chemical reactions in almost every cell in the body (Tortora & Derrickson 2007). They can also remove toxins and other substances that can be found in the blood via respiratory or digestive tracts (Tortora & Derrickson 2007). ...read more.

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