Analysis of Kidney Filtration Using a Simple Filtration System

Practical 2: Observation of mammalian kidney model and tissue slides. Analyzing kidney filtration using simple filtration system

Introduction:
Kidney is part of mammalian's body endocrine system. Every mammals have a pair of kidneys that is located at the middle back of the body and symmetrically beside the spine and below the rib cage. A kidney approximately 0.5% of the organism body weight. Every kidney will receive huge amount of blood to enable them to perform important task. The base unit of kidney is called a nephron that contains all the basic filtering cells of kidney. ( How your kidney works)
Kidney is very important to a mammal's body. Without a normal functioning kidney, the organism's blood vessels will be full of waste product as kidney's function is to filter waste products from the blood stream. Both kidneys receive oxygenated blood from the renal artery which contains oxygen and waste product. Both kidneys than will filter the blood contents. All the waste product such as urine is being expelled from the blood and excreted out through the urethra in the urinary system. The remaining of the blood will than leave the kidneys through renal vein which doesn't contain oxygen as oxygen has being used up by the kidneys to produce ATP. In return, the renal vein is cleaned.
A normal kidney has 3 layers. The outermost layer is called the cortex. The function of cortex is simply by producing ammonia to titrate the acidity of urine. (Ask.com-Science) Next layer will be medulla. Medulla is the area that is responsible for maintaining blood, salt and water in the body as nephrons are located here to reabsorb water according to the demand of water needed by the body. The last layer is the pelvis. The major function of this renal pelvis is to act as a funnel for urine to flow until the ureter.
A failed functioning kidney is very harmful for the organism. The organism may suffer and external medical assistance is required to keep the organism alive.
Objective:
To observe and identify all the major components of the kidney and how they work and carry out an experiment to give an idea about how kidney works by comparing filtered and unfiltered solutions.

Materials:
Microscope, Mammalian kidney model, Kidney nephrons slide, Whatman filter paper, Conical flask, Filter funnel, Biuret solution, Benedict's solution, Iodine in potassium iodide solution, Test tubes.

Procedures:
a) Observation of major structures in a mammalian kidney
1) Kidney model is observed and various important structures in the kidney that is vital for osmoregulation is identified.
2)All the main structures are drawn and labelled. The position of nephrons and tubules are indicated.
b) Examination of tissue slides under a microscope
1)A prepared horizontal or transverse section of mammalian kidney slide is observed.
2)The slide is held up and to be examined under a lens. The demarcation between cortex and medulla is noted.
3) The cortex is examined under low power. Bowman's capsule, tubules and capillaries are noticed.
4)The cortex is then examined under high power.
5)The medulla is observed and examined under high power.
6) High power drawing for each section of cortex and medulla is prepared.
c) Analyzing kidney filtration
1) 1ml of 1% of protein, 1% of glucose, starch and water are prepared and labelled in 4 different test tubes.
2)1ml of Biuret solution is added to the test tube labelled protein.
3)1 ml of Benedict's solution is added to the test tube labelled glucose. The test tube is placed in a water bath in 100 degree celcius for 5 minutes and is being shaken.
4)1 drop of iodine in potassium iodide is added into the test tube labelled starch.
5)Steps 2-4 is repeated for test tube 4.
6)The test solutions are discarded and test tubes are rinsed.
7)4.0ml of the previous solutions are prepared.
8)Filter paper on a Buchner funnel and a conical flask is prepared. All the contents of each test tubes are poured to the filter paper. The filtered solution is collected in the conical flask.
9)Steps 2-4 are repeated onto the filtrate.
10) Observations are recorded.

Results:
A)

B)

C)
Tube Number
Colour Intensity
(before filtration)
(- : no presence, + : least intense, ++ : intense, +++ : most intense)
Colour Intensity
(after filtration)
(- : no presence, + : least intense, ++ : intense, +++ : most intense)
1
(Biuret)
++
+

2
(Benedict’s)
++
+
3
(Iodine)
+++
++
4
(All 3)
No colour change
No colour change

Discussion:
A) A cross-section of a model kidney was observed. The main components of the kidney were identified. First of all, the renal artery and vein are clearly seen. The renal artery is the big red artery that is going into the kidney. It carries oxygen and waste products ready to be filtered. The arteries branch out to arterioles and then further into capillaries. Then they join back together to form venules and the venules join together to form the renal vein (the big vein blue in colour) which leaves the kidney and has no oxygen or waste products since they have been filtered out by the kidney nephrons.

B) In this section of the experiment, a light microscope was used to observe the main components of the kidney. It was possible to identify the Bowman’s capsule, glomerulus, the thick and thin sections of loop of Henle and the collecting duct. The Bowman’s capsule is the first part of the nephron and it wraps almost all of the capillaries and in there is a mesh of capillary networks called the glomerulus. This is where ultrafiltration takes place. This process filters out everything that is present in the capillaries except for red blood cells and some plasma proteins. The wall of the Bowman’s capsule is thin to ease the diffusion process. All the filtrates then go into the Bowman’s capsule then they pass through the proximal convoluted tubule. The proximal tubule is the portion of the duct system of the nephron of the kidney which leads from Bowman's capsule to the loop of Henle. Here almost all of the water and salt is reabsorbed. Then the filtrate now moves on to the loop of Henle where even more salt and water and some nutrients are reabsorbed. Finally the filtrate moves to the collecting duct where the remaining water is reabsorbed.

C) This experiment was carried out to demonstrate how the kidney works. A solution of protein, glucose, starch and distilled water were tested. The protein solution was tested with biuret solution, the glucose with Benedict’s solution and starch with iodine in potassium iodide. All solutions gave positive test results: the biuret solution turned purple, Benedict’s solution turned brick red and iodine in potassium iodide turned blue-black. The same test was repeated with the same solutions but this time, the protein, glucose and starch solutions were filtered before being tested. They all gave the same positive results except this time, all the colors were lighter. This is due to some proteins, glucose and starch molecules being left as residue on the filter paper. As for water, filter water doesn't make any difference as the original test, water is just a control for the experiment.

Questions:
1) Among the tested substance, which of the compounds passed through the filter paper?
Ans: All of them passed through the filter paper.

2) Was there a difference in the intensity of the colour that was observed from your initial tests? If so, why? If not, why? Suggest a method to quantify your method.
Ans: Yes there was a difference in colour intensity. For example, the protein solution albumin. After being filtered, some protein molecules were left behind on the filter paper and thus there were not as many protein molecules available to react with the biuret solution so the purple color isn’t as dark as the unfiltered solution. The same thing happened with glucose and starch.

3) Explain why some of the compounds did not pass through the filter paper.
Ans: The molecules were too big to pass through the pores in the filter paper.

4) What is the function of test tube 4?
Ans: To act as a control.

5) How does the filtration in this activity resemble the activity of the kidney?
Ans: Both the kidney and filter paper allow some substances to pass through and prevent others from passing through.

6) Explain the difference in the roles played by the different tubules present in the nephron structure of a kidney.
Ans: Proximal convoluted tubule join the bowman's capsule and Loop of Henle while distal convoluted tubule join loop of Henle with collecting duct. Proximal convoluted tubule helps to regulate pH and ion whereas distal convoluted tubule regulates salt, water and organic solutes.

7) Why do mammals need to get rid of their excretory products?
Ans: Excretory products are very harmful to mammals. The products need to be excreted because there are insoluble. No enzyme can combine with the excretory products or break it down into simpler or less harmful substance. The only option left is to release it out of the body.

References:
1)How your kidney works- Craig Freudenrich, Ph.D
Available at http://science.howstuffworks.com/life/human-biology/kidney1.htm
<Access date: 2nd February 2104>

2)Ask.com-Function of cortex, medulla and pelvis
Available at http://www.ask.com/question/kidney-cortex http://www.ask.com/question/function-kidney-renal-pelvis http://www.ask.com/question/function-of-renal-medulla
<Access date: 2nd February 2014>

3) Reabsorption and Secretion Along the Loop of Henle - Anatomy & Physiology.
Available at: http://en.wikivet.net/Reabsorption_and_Secretion_Along_the_Loop_of_Henle_-_Anatomy_%26_Physiology
<Access date: 3rd February 2014>

4) Encyclopaedia Brittanica – Loop of Henle
Available at: http://global.britannica.com/EBchecked/topic/347799/loop-of-Henle
<Access date: 3rd February 2014>