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Evaluation of Urine and Plasma for Kidney Function

Info: 2679 words (11 pages) Essay
Published: 8th Feb 2020 in Biology

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 “The kidneys are essential for homeostasis (maintaining a constant internal environment) of the body’s extracellular fluids”. (Mcb.berkeley.edu, 2018). There are two kidneys, and they achieve homeostasis via many crucial functions, primarily the regulation of the ion and water content in the body. They monitor the extracellular fluid, to ensure there is sufficient quantity to keep the blood flowing to vital organs. This is done using the renin-angiotensin system or RAS. The enzyme renin is released if blood volume or sodium levels in the blood are low, and also if potassium is high. It works to increase blood volume, (and therefore blood pressure), and sodium levels to maintain the correct levels. (Ukrocharity.org, 2018). The kidneys control the osmolarity of the extracellular fluid through a complex of tiny functional units called nephrons (figure 2), which regulate the ion concentrations and pH in the blood plasma. The kidney also produces the hormone Erythropoietin (EPO), which promotes the formation of red blood cells by the bone marrow. (Siamak N. Nabili, 2018). Blood is filtered by the glomeruli and then follows a pathway of tubules through the nephron, which reabsorb and secrete ions and water, ensuring the levels match requirements. The kidney’s importance cannot be overestimated as it also has a role in bone development and metabolism, by regulating calcium and phosphate.


  1. To increase our understanding of kidney anatomy, by dissecting and examining a kidney. This assists us in identifying key parts of the kidney in relation to the function, most importantly ion and water balance and urine production.
  2. To increase our understanding of the efficiency of the kidney to filtrate, reabsorb and secrete, in order to maintain homeostasis. By examining urine and plasma samples we can compare the levels of solutes to evaluate the functionality of the kidney.
  3. To identify contributing factors to kidney failure and the methods that may be used to correct this.


 As instructed in the BIO2103 Practical Manual and Exercises (Kennedy, 2018), we firstly examined the external features of the sheep’s kidney, prior to dissecting the kidney. Next we conducted a comparison of plasma and urinary solute concentrations. We used a pH-Fix kit to find the concentration of Hydrogen Ions, proteins and glucose. By comparing the pad colours with the colour ranges on the pH-Fix kit we could estimate the pH in the urine and blood plasma. We used a Multistix Kit, to estimate the solute concentration for protein and glucose by comparing pad colours with colour ranges on the side of the container.  We did this for both urine and blood plasma. Finally we determined the amount of sodium and potassium in the urine and blood plasma.  We did this by obtaining a NA+LAQUA twin kit.  We placed approximately 0.3ml of the urine sample onto the LAQUAtwin electrode. After testing the urine we rinsed the sensor with milliQ water.  We then repeated the process for the plasma solution but firstly we diluted the plasma 1:5 with RO water so that the reading would be more accurate.  The reading then had to be multiplied by 5 to account for the dilution.  Next we used the same process to test the sodium levels, this time using a k+ LAQUA twin kit.  There was no need to dilute the solution, therefore no need to multiply the results.


Figure 1:  Dissected Kidney

The diagram shows the renal artery and vein, by which blood enters and exits the kidney.  The ureter takes the urine to the bladder.  The nephron (figure 2), crosses over the medulla and the cortex of the kidney.  This is important for the reabsorption and secretion of substances.  Each renal pyramid filters the urine into the renal calyx.

Figure 2: Nephron of the kidney

Blood enters the kidneys via the renal artery and is filtered by the glomeruli. The filtrate follows a pathway of tubules through the nephron. Substances are filtered out of the blood at the glomerulus, but the body still requires many of these. These are reabsorbed at the proximal convoluted tubule (figure 2). Water follows via osmosis. The filtrate then passes through the loop of Henle, which creates a concentration gradient in the medulla of the kidney via the countercurrent multiplier. As the fluid passes through the descending limb, water flows out (the walls are permeable to water).  This creates a more dilute fluid outside of the tubule, which causes salt to follow as it proceeds through the ascending limb.  Water balance is controlled by hormones (Aldosterone and Anti Diuretic Hormone) in the distal convoluted tubules. (Sciencing.com, 2018)

TABLE 1.  Plasma and Urinary Concentrations of Solutes.


Plasma Conc.

Urine conc.

Hydrogen ions 





 1 g/L



 10,000 mg/l or 55 mMol/L


Sodium (ppm)



Potassium (ppm)



Figure 3: Solute concentrations of urine and plasma samples.


The levels recorded were not those of a functional kidney. We can see that the protein content of the blood was very low.  A normal level would be at least 35-55g/L.  The kidney reabsorbs protein (keeping the osmosis gradient of blood constant).  Protein is also important for muscle and bones and acts as a buffer for acidic pH.  Low protein is known as hypoproteinemia. (Stacy Sampson, 2018). This may help to explain why the pH is not in a normal range and is acidic. The pH should be around 7.4.  Acid base balance is important and it is maintained primarily by secretion of hydrogen ions (in acidosis) together with the reabsorption of bicarbonate ions. (Courses.lumenlearning.com, 2018)

Urine pH is in the normal range and there is no protein in the urine, however as acid or alkaline urine is an important mechanism to maintain constant body pH, we should expect the urine to be slightly more acidic to keep the plasma levels at homeostasis (Rnceus.com, 2018)

The glucose levels are excessively high, around 10 times the normal range.  This suggests that there is diabetes present.  There is no glucose in the urine, which is normal.  The sodium levels are slightly lower than the 135-145 m/Eq/L.  (2750ppm converts to 120.57 m/Eq/L).  This is known as hyponatremia but it could just be from excessive exercise and sweating, or vomiting. (Healthline, 2018). The potassium levels are in the normal range in the blood plasma, but very high in the urine. This could be explained by certain medication or health conditions like diabetes acidosis. Normal blood levels of potassium are critical for maintaining normal heart electrical rhythm. Both low blood potassium levels (hypokalemia) and high blood potassium levels (hyperkalemia) can lead to abnormal heart rhythms. The net secretion of potassium takes place in the distal tubule and the collecting ducts. (Melissa Conrad, 2018). The accuracy of the results was limited by the approximate estimation of the pH and the glucose and protein concentrations.   A pH meter would be a better tool to accurately ascertain the correct pH level.   Also, diluting the plasma solution and then multiplying by 5 could be have affected the accuracy of the reading.  The tests were only conducted once on one concentration of urine and plasma.  It would be unclear as to what the activity of the person was at this time.  For example, eating and fasting would have opposite affects on the glucose levels and exercise would cause the kidney to reabsorb more salts and water.  The tests should have been conducted over a period of time and with different samples from different times.  It is also unclear how old the urine samples were, which could have limited the results. 

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Because of the vital functions the kidneys perform, they may be susceptible to conditions such as kidney failure or Chronic Kidney Disease (CKD).  If one kidney stops working the second kidney can continue to function adequately alone. If for some reason the second kidney stops working then the blood can no longer be filtered and another mechanism has to be used.  This is called dialysis.  Dialysis removes excess water, solutes and toxins from the blood via heamodialysis (blood) or peritoneal dialysis.  During heamodialysis a needle slowly removes blood and transfers it to a machine called a dialyseror dialysis machine. The machine uses to membranes to act as filters and a special liquid called dialysate. The membranes filter waste products from your blood, which are passed into the dialysate fluid. (Nhs.uk, 2018). During peritoneal dialysis, fluid is pumped into the peritoneal cavity in your abdomen.  The fluid enters and leaves through a catheter, which stays in place permanently.  The waste from the blood is drawn into the fluid through a membrane in your abdomen and then removed from your body.  It can be performed manually or through a machine. (National Kidney Foundation, 2018). Dialysis doesn’t always have to be permanent.  If the kidneys are not in total failure, they can recover. One of the risk factors in CKD is obesity. A body mass index between 18.5 and 25 kg/m2 is considered by the World Health Organization (WHO, 2018) to be normal weight, a BMI between 25 and 30 kg/m2 as overweight, and a BMI of >30 kg/m2 as obese. Obesity increases the prevalence of nephrolithiasis (kidney stones) and cancer in the kidneys. (Kovesdy, L. Furth and Zoccali, 2017).  In addition higher visceral adipose tissue (fat around your internal organs) is associated with a higher prevalence of abnormal levels of the protein called albumin in your urine. “However the exact mechanisms whereby obesity may cause CKD remain unclear, and the fact that most obese individuals never get CKD suggest an increase in weight alone is not sufficient enough to induce kidney damage.  Some of the real consequences could be as a result of downstream comorbid conditions like diabetes or hypertension”. (Kovesdy, L. Furth and Zoccali, 2017). The insulin resistance of diabetes may lead to nephrolithiasis and the early stages of acidosis. In addition, there is the requirement to increase the filtration rate to meet higher metabolic demands. This increases the intraglomerular pressure and can damage the kidneys. (Kovesdy, L. Furth and Zoccali, 2017).


The kidney is one of the most important organs in our body and is vital for homeostasis, which is vital for life. The kidney maintains a constant ion and water content in the body via a series of tubules and nephrons that perform highly complex functions.  The kidney regulates this through hormonal control and osmolarity.  The importance of salt reabsorption and secretion is of primary importance as it affects the amount of water in the blood and therefore blood pressure.  In our sample salt levels were low and this would affect blood pressure.  The pH in our sample combined with the very high level of glucose, would be detrimental to health.  It would be necessary to repeat this samples over a period of time, when all external factors are disclosed.


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  • nhs.uk. (2018). How it’s performed. [online] Available at: https://www.nhs.uk/conditions/dialysis/what-happens/ [Accessed 6 Sep. 2018].
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