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kidney dissection - Kidney Structure _ Function

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					Kidney Structure & Function
Introduction

Kidneys are paired organs which are located close to the dorsal (back) wall of the
abdominal cavity, on either side of the spine. Their function is to filter metabolic
wastes, such as urea and excess ions, from the blood. In doing so, the kidneys
maintain the pH of the blood and regulate the water balance of the body.
The basic structural unit of the kidney is the nephron. The human kidney consists
of approximately one million nephrons. The glomeruli, the sites of blood filtration,
along with the Bowman’s capsules and collecting tubules, the sites of urine
production, are located in the cortex. The loop of Henle extends down into the
medulla. The longer the loop of Henle, the thicker the medulla and the more
efficient the reabsorption of water is. This results in a more concentrated urine.


Part A               Kidney Structure
Aim

To identify the main structural components of a mammalian kidney.

Materials

      Mammalian kidney (eg sheep kidney)
      Scalpel
      Forceps
      Dissecting board
      Disposable gloves

Procedure

      Place the kidney on the dissecting board. Examine its external features. It
       should be possible to locate and identify three tubes entering or leaving
       the kidney.
      Using your textbook to help you, draw a labelled diagram of the external
       features of the kidney.
      Use a scalpel to cut the kidney in half lengthways by making an incision
       just to one side of the tubes. Examine each of the cut surfaces. Try to
       identify the internal structures shown in Figure 1.
      Draw a labelled diagram of the internal structures of the kidney. Include
       comments about the differences in appearance of the cortex and the
       medulla.
      Dispose of your dissected kidney in the appropriate manner.
       Dispose of your gloves and wash your hands.




Discussion Questions

   1.   How did you distinguish between the renal artery and the renal vein?
   2.   Which area of the kidney contains the glomeruli and Bowman’s capsules?
   3.   In which part of the kidney does the majority of water reabsorption occur?
   4.   What is the function of the ureters?




Part B               Kidney function and water loss

Aim

To investigate the relationship between kidney structure and the concentration of
urine produced by mammals that live in different environments.

Procedure

Read the following information and then answer the questions.

The control of water loss is very important for terrestrial (land) mammals. A study
was done on nine species of mammals in which biologists measured the
concentrations of urea and ions in the urine of each species. They also
measured the relative thickness of the medulla in the kidneys of each species.
The data they obtained is shown in Figure 2. The nine species tested are
represented by letters of the alphabet.

Discussion Questions

   5. Describe the general relationship observed by biologists between the urea
      concentration and medullary thickness.
   6. Consider specifically mammals a and g. Using the data to support your
      choice, which of these mammals would you consider to be most capable
      of surviving in a desert environment?
   7. How would the kidney of the mammal you have just selected make it
      suitable for survival in the desert?
   8. What other adaptations might such a mammal have to enable it to live in
      the desert?




Figure 2. The relationship between the concentration of urea and the thickness of
the medulla in various mammalian kidneys.
Answers to discussion questions

  1. The renal artery is the larger blood vessel as the kidney needs a rich
     blood supply to carry out its role of filtration
  2. The cortex.
  3. In the medulla, as this is where the loop of Henle extends into therefore
     the collecting ducts are located here.
  4. The ureters transport urine from the kidneys to the bladder for storage.
  5. The thicker the medulla the greater the concentration of urea and ions in
     the urine produced.
  6. Mammal g would be most suited to living in a desert environment because
     it produces a more concentrated urine. This means that more water is
     being reabsorbed into the body, enabling greater conservation of water in
     a desert environment.
  7. The kidney of mammal g would have a longer loop of Henle, and therefore
     a thicker medulla, which enables greater reabsorption of water resulting in
     the production of concentrated urine.
  8. This mammal may also have a light coloured coat that reflects heat, an
     insulating coat of fur to keep the heat out, a low surface area:volume ratio,
     or fat tissue may be concentrated in a particular region so that it doesn’t
     interfere with heat loss (as seen in camels).

				
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