Kidney_Renal_Activity

Background: During prolonged exercise of a sub maximal intensity, the body becomes hot due to an increase in muscle contractions. In response to this, sweating occurs and evaporates from the skin resulting in an increase in water and sodium loss from the body. To counteract this process, the kidney has evolved a control mechanism whereby water and sodium is conserved and the kidneys decrease the rate of urine production. When water is ingested it is rapidly absorbed by the intestine diluting the blood. This is detected by osmoreceptors in the hypothalamus which reduces the anti-diuretic hormone, ADH, by the pituitary gland. The kidneys respond to this drop in hormone by increasing the production of urine i.e. les water is reabsorbed. Aims: The main aim of this experiment was to investigate the interaction between water consumption and prolonged sub maximal exercise on kidney function. The main observations of the study focused on changes in urine production and its pH, osmolality, Na+ and K+ content alongside changes in skin and core body temperature. Methods: 80 ppts in groups of 4 were divided into 2 subjects and 2 experimenters. Subjects then allocated exercise or control condition. It was important that subjects came to the lab in a normally hydrated state. All subjects were then given a code letter to label urine samples with. Both control and exercise Subjects emptied their bladders before ingesting 1000mls (1 litre) of water at which the time was noted. Non-clothed weights were recorded immediately and repeated after 1 hour and 2 hours. The control and exercise subjects produced urine samples every 20mins for the next 2 hours. The exercise subject took part in 1 hour of sub maximal intensity exercise on a cycle ergometer ( suggested workloads being 120 watts for females and 150 to 180 watts for males) followed by a 1 hour recovery period. Skin temperature at the surface of the thigh and aural temperature (indicator of core temperature) were taken every 5 minutes for the first 20 minutes of each hour and then every 20 minutes on both control and exercise subjects. Experimenters tested each urine sample for measurements of urine volume (m/L), urine pH and urine osmolality (mOsmoles/L) via a handheld osmometer. Urine Na+ and K+ concentrations in mmol/L were provided via the flame photometer. It was important the urine samples were diluted 1:200 necessary for calibration of instrument readings. The mass of Na+ and K+ in each sample was calculated in mg by multiplying concentration in mg/L by volume (L) of the sample. Results: After 60 minutes the control group produced an average of 214ml whereas the exercise group produced an average of 44.3ml of urine. Exercising subjects showed a sharper decrease in pH level with exercise averaging at 5.98 for 60 mins compared with 6.6 for controls. Exercise ppts averaged at 330 (mOsmoles/L) after 60 minutes compared to 110 (mosmoles/L) for controls. Na+ levels in both controls and exercise ppts showed a decrease until 60 mins. K+ levels in both groups similarly showed a delayed rise after 60 moins of exercise. K+ levels in urine were significantly higher in exercise subjects. Skin temperature showed similar trends in both control and exercise ppts steadily increasing and then sharply decreasing after 60 mins after exercise had stopped. Skin temperature then continued to rise. Core temperature showed a significant rise in exercise ppts but decreased rapidly after 60 mins of exercise. A larger decrease in weight was shown in exercise subjects. Conclusion: During sub maximal exercise blood is redistributed to tissues with the greatest immediate demand i.e. skeletal muscles, and away from areas with les demand for oxygen i.e. kidneys. A decrease in renal blood flow, caused by compensatory renal arteriolar vasoconstriction, causes this reduction in urinary output. Exercise causes sweat loss which disrupts the electrolyte balance of Na+ and CL- with less water available to dilute it increasing the acidity of urine. Alongside this is an increase in metabolites produced during exercise such as Nitric oxide. As a result of this increase in the number of dissolved particles per unit of water in the urine e.g. Na+, osmolality also increases in exercise subjects. During exercise excessive sweating causes a decrease in Na+ and water which in turn reduces plasma volume. This triggers the release of rennin inhibiting GFR and increasing Na+ and water reapsortion back into the blood and hence a reduction in excretion. Na+ excretion was expected to increase in controls compared with exercise ppts during the first 60 mins due to an increase in plasma volume triggering a release in ANP. However volumes of urine were a common occurrence throughout the experiment which affected the results. Na+ increased after exercise had stopped as sweating came to a stop i.e. more water was retained and the Na+ balance was restored. K+ levels also increase during exercise decreasing the plasma volume levels. Aldosterone is secreted and in response potassium excretion is increased. Q: Under hypoxic conditions i.e. acute sub maximal exercise, the kidneys produce and secrete erythropoietin (EPO). This cytokine is produced by peritubular fibroblasts of the renal cortex and triggers the increased production of red blood cells hence expanding blood volume levels. Plasma volume is regulated by the extracellular fluid (ECF) which is increased as a result of thirs as well as changes in total circulating proteins, primarily albumin. During exercise circulating protein levels increase causing an osmotic pull resulting in more fluid being retained in the blood.