Homeostasis - kidneys
The kidneys and water balance is a nice topic to teach. Students have direct experience of the process and can observe changes depending on their own water intake. It is satisfying when students understand processes so directly related to their own physiology.
Part of the topic deals with kidney dialysis and transplants. Care should be taken in this area as some sensitive issues are touched upon. It is not beyond possibility that some class members may have direct experience through a family member or friend. Likewise, fatal accidents can often be the source of donor kidneys and this should be remembered.
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Links and Resources
This animation and video show students the structure and function of the kidneys. It also describes dialysis and kidney transplants.
Students can use the animation as a self-study activity once the topic of the kidneys and their broad function has been introduced. Alternatively, it makes a good revision activity once the topic has been completed.
Depending on the detail required by your course specifications, students can be given a framework of headings so that they can focus onto the relevant sections of the animation. They could make their own notes on the topic, which will help them develop skills in interpreting and summarising information. Supply diagrams for annotation.
There is a good section on dialysis. Ask students to consider the dialysis solution and explain its composition.
A kidney dissection is readily carried out in the laboratory. The video shows how to carry out the procedure effectively, or alternatively it can be used in place of a dissection. It is worth viewing the video as it shows the blood vessels and ureter. These are normally missing kidneys obtained from a butcher.
With any dissection, it is beneficial to be sensitive to students’ feelings. Reassurance may be gained by informing students that the animal that the kidneys were taken from was not killed specifically for that purpose. Be aware of cultural objections to handling tissues from certain animals. It may be worth talking to students prior to the lesson so that any concerns can be raised and any permissions from parents granted.
If students genuinely do not want to be involved, they can have alternative activities arranged for them.
A Catalyst article which describes the structure and function of the kidneys. Students can read the whole article.
There is a good diagram which shows the structure of a kidney tubule and relates it to the processes of filtration and reabsorption. This is quite a tricky concept as students are told that kidneys ‘filter’ the blood. Intuitively, this is a one-way process. Reabsorption suggests something else.
Students can be challenged to write three stories that tell the routes through the kidney and beyond of:
• a water molecule destined to be excreted from the body;
• a molecule of urea (from excess protein);
• a sugar molecule.
You can use these stories to check if the students have understood the process of filtration, followed by reabsorption.
One section of the article describes the control of urine production via ADH. Students could produce flow diagrams to illustrate the control pathways that happen when the body has too much, or too little water.
The activities in this resource take a closer look at renal dialysis, peritoneal dialysis and kidney transplants.
The first activities can be used to revise kidney structure and function. These activities need not be done they have recently been covered.
There is a good information sheet on dialysis and transplants. This can be used as the basis of a comprehension activity. Have students produce suitable questions and swap them amongst the class. These can then be peer marked. The answers can be discussed and misconceptions addressed.
A final activity looks at how transplant patients are chosen. This is a good activity to get students thinking about the broader implications of the procedure. How would they decide?
Remember to be sensitive to any class members, friends or family who may have kidney failure or indeed who may have been involved in the type of accident from which many donor tissues are obtained.
These materials contain a wide range of activities but the ones relating to the kidneys can be found in section 5, starting on page 60.
There are two good activities that help students to understand how the kidneys work and how dialysis works.
The first activity sees students modelling the filtration of the blood. Using a mesh or net, students see how large molecules and blood cells cannot be filtered whilst smaller solute molecules can be.
It is worth stressing where this process is happening in the kidney and also that the useful molecules are subsequently reabsorbed.
A second activity uses Visking tubing and a sample of made up ‘blood’ to model dialysis. This will help students to get a grasp of a process that they would otherwise be unable to view. It will help to make it less abstract. A subsequent activity focusses onto what happens in a renal dialysis machine.
Students’ understanding of dialysis can be tested at this point. In the experiment, glucose and salt enter the dialysis fluid. This would then be discarded. How does this compare to a real dialysis machine? What is the composition of the dialysis fluid? How is it adjusted to make sure that useful substances like glucose and salt are not taken out of the blood? After all, the body needs to keep these. It is just the urea that the dialysis machine is designed to remove. This leads to a good discussion about diffusion and concentration gradients.