Salt: The Essence of Life
Multidisciplinary Curriculum for Students
Unit 5: Biology
Why Do Our Bodies Need Salt?
1-2 Class Periods
Overview
This module focuses on the body's need for salt. Its objective is to give the students an awareness of the role that salt plays in the various physiological processes in the human body.
Background
Sodium chloride is essential in the nutritional and physiological processes of all animals, including humans. It is a necessary part of all body tissues and fluids. It is ingested and excreted in the urine, sweat and feces.
The amount and concentration in the body must be maintained within narrow limits, through a large number of physiological mechanisms. These mechanisms control the concentration and secretion of salt so that the amount eliminated balances with the amount taken in with food. If salt concentrations are greatly disturbed and are either too high or too low (usually caused by disease), death may result.
Blood concentration of sodium ion is directly related to the regulation of safe body fluid levels. As blood fluid levels begin to drop, without altering the total amount of sodium, the concentration of sodium increases. When this concentration reaches a certain level, centers in the brain are triggered, acting as a feedback mechanism designed to naturally stimulate thirst and the consequent ingestion of replacement fluids. This will act to once again restore blood fluid and sodium concentration levels to their normal range. Sodium also assists in the re-absorption of water (otherwise excreted) in the kidneys.
Getting Ready
Time: 1-2 class periods depending on depth of research
Materials
Biology or Physiology textbook or encyclopedia, paper, colored pencils
Activity
1. Ask students if they have ever touched their tongue to their arm after sweating, tasted tears, or blood from a cut. What did it taste like? They should respond that it tasted salty.
2. Next, explain to students that their bodies contain approximately 70% water. The human body also has approximately the same salinity as the oceans.
3. Ask students where they think the salt in their bodies comes from.
4. Explain that the regulation of salt in the body is a dynamic and vital process. The kidneys are the major organ that adjusts the level of sodium which is excreted through urine. Ask students how the kidneys regulate the pH of blood by regulating the amount of Na+ in the blood.
5. Provide students with biology texts, physiology texts, and an encyclopedia so they can obtain more information about how the kidneys maintain the balance of sodium in the body. Have students read about the different structures and chemical reactions involved in this process.
6. Students should then make a diagram of the blood-excretory system which balances the amount of salt in the body. Captions should be used to explain the different anatomical features which are responsible for sodium metabolism and regulation.
Assessment
Students can create a bulletin board display of their findings and diagrams. They may also research diseases related to salt deficiencies.
Conclusion
Different combinations of foods with varying amounts of salt cause the kidneys to maintain the correct amount of Na in the blood by regulating the amount of Na excreted. For example, what would the kidneys do if a lot of salty foods were eaten? What would the kidneys do if not enough salt was eaten?
Students can conduct additional research on how problems with ion balances create medical problems such as hypertension and kidney disease.