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Class Activities |
Chapter 46: Excretion And Osmotic Balance |
1. Relevance of Topic
The importance of the excretory system is mainly seen in analyzing its various dysfunctions, and in realizing that animals cannot survive unless waste is properly filtered from their blood and eliminated from the body.
Many chemicals affect the regulation of the excretory system; humans experiment with common diuretics such as caffeine and alcohol on a daily basis, sometimes with serious results.
Medical issues surrounding renal dialysis and kidney transplants are regularly in the news and could be brought into discussions when covering this chapter.
2. Continuity
Another major system of all animals is the excretory system.
The next chapter covers digestion and intake of food and excretion of waste is intimately associated with this activity.
3. Demonstration Activities
Text section 46.1
1. Show Figure 46.1 and stress the fact that all animals store the carbon skeletons of amino acids and excrete the amino groups in some form or other.
2. Give examples of groups of animals that have representative methods of excretion.
3. Include mention of some adaptations that allow terrestrial animals to control water loss in connection with excretion adjustments (Figure 46.2).
Text section 46.2
1. Show Figure 46.3 and stress that all excretory systems share a common structure.
Text section 46.3
1. Show Figure 46.4 and discuss how the sodium pump works and the role it plays in the elimination of waste.
2. Discuss generally the role of epithelia as a boundary membrane in this system.
3. Discuss the famous Ussing experiment that showed that epithelium was a functional analog for the distal convoluted tubule of the kidney.
Text section 46.4
1. Show Figure 46.7 and, if possible, dissect a previously frozen cockroach before class and pin out the Malpighian tubules to show their location at the end of the hindgut.
Text section 46.5
1. Show Figure 46.8 and discuss the fact that kidneys are paired; ask the students to propose ideas on the adaptive significance of this.
2. Using a model of the kidney, a preserved specimen, or a fresh specimen from a slaughterhouse, illustrate the major anatomical features of the kidney.
3. Show prepared microscope slides of kidney tissue sections, including the cortex, medulla, glomerulus (Figure 46.10), and Bowman's capsule.
4. Discuss pathology in the vertebrate kidney, and current methods for treatment, including dialysis and organ transplant.
Text section 46.6
1. Using Figure 46.11, discuss the loop of Henle, the vasa recta and the countercurrent system they form.
2. Show Figure 46.12 and discuss in detail the function of each section of the loop of Henle.
Text section 46.7
1. Use Figures 46.13 and 46.14 to discuss how the vertebrate body regulates blood pressure and osmolarity.
2. Include a discussion of the use of diuretics and mention the effects of caffeine and alcohol on this system.
Text section 46.8
1. Show Figure 46.15 to illustrate the concepts of blood pH, acidosis, and alkalosis, and how the nephron can rapidly rectify each of these situations.
Text section 46.9
1. Show Figure 46.16 and differentiate between osmoregulators and osmoconformers.
2. Ask students which of these they are.
3. Discuss the excretory system of freshwater fish and ask students to explain how fish regulate water balance and also how they maintain the proper salt concentrations in their blood.
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