Water Balance – 50 Informal Points Introduction



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Water Balance – 50 Informal Points

Introduction

Bill’s friends throw a summer picnic to celebrate his 40th birthday. Bill spends the day playing touch football and chasing around after his kids. It’s almost 100°F outside and he is doing what he can to stay cool. Cold beer seems to work so he drinks many over the course of the day. Other than running to the bathroom all afternoon, Bill feels fine. But the next morning when he wakes up, he feels awful. He’s nauseous, dizzy and wishing he had stuck to water at the party. He wonders what is causing this horrific hangover.


Water balance is key to human survival. If you have ever competed in a vigorous athletic event or have been out in the heat for too long a time, you have probably experienced the signs and symptoms of dehydration. You become weak, nauseous, and may even pass out. Your body’s urinary system is designed to help you conserve water, but if no new water is coming in and your body is losing water through exercise or sweat, a balance cannot be maintained. The volume of urine that we excrete is a reflection of how much fluid and salt our bodies have to spare. Your body will give you warning signs, but sometimes they come a bit too late!
Like most processes in the body, water balance is regulated by hormones. These chemical messengers help control how much water is retained or removed from the body. In fact, your endocrine system, your nervous system, and your urinary system work together to signal thirst and to effectively manage a water shortage. In this activity, you will explore how the body monitors water levels and calls the kidneys into action. Your job is to help Bill understand how the events of the day affected his ability to maintain homeostasis. Why is poor Bill feeling so bad? What has happened to the water balance in his body? How does this lack of water link to his symptoms and how can he find some relief? Explore the feedback loops in the body that work to keep a water balance and investigate how substances such as alcohol can directly affect the release of hormones.

Procedure

  1. Research the area of the brain that senses and controls thirst. The sensation of thirst and your body’s ability to maintain a proper water balance are controlled by communication between the nervous system, the endocrine system and the urinary system.

    • Area of brain that controls thirst: ______________________________

  2. Review effects of vasopressin (antidiuretic hormone (ADH)) on water balance in the blood by the monitoring of blood pressure. Use the figure below to help write a 2-3 paragraph essay describing how the renin-angiotensin feedback loop raises blood pressure when it is too low. You may either type this or hand write it on separate paper.



  1. Use the figure and your essay to help create a negative feedback loop that shows how your body uses ADH to maintain a water balance.

  • Start by thinking about how the brain detects high or low levels of sodium or water in the blood.



  • Your feedback loop descriptions should include the following words: thirst, ADH, hypothalamus, neuron, pituitary gland, nephron, kidney, urine, reabsorption, osmoreceptors.



  • Your feedback loop should show the involvement of the nervous system, the endocrine system and the urinary system in restoring a water balance. Make sure to reference key regions in the brain, specific glands and their target organs as well as indicate how the nephron is affected.



  • You may need to do a bit of additional research to include all the necessary key terms and fully understand the physiology.



  • Create your feedback loop a Body system organizer to show where each step is taking place in the body.

  1. Continue to research the effects of alcohol on ADH and your body’s water balance and answer the following questions about Bill.

    • Why did Bill keep running to the bathroom?

Alcohol is a diuretic. Alcohol also reduces the production of a hormone called vasopressin, which tells your kidneys to reabsorb water rather than flush it out through the bladder. With the body's natural signal switched off, the bladder is free to fill up with fluid.

    • What is happening to his body since he is producing so much urine?

Bill is becoming increasingly dehydrated.

    • How are changed in the ADH hormone linked to Bill’s symptoms?

Alcohol also reduces the production of a hormone called vasopressin, also known as ADH (anti-diuretic hormone), which tells your kidneys to reabsorb water rather than flush it out through the bladder. With the body's natural signal switched off, the bladder is free to fill up with fluid.

  1. Note that another hormone, aldosterone, helps maintain a water balance. However, the way in which this hormone works differs from the mechanism of ADH. Research the way in which aldosterone affects the nephron. Make sure to reference the effect of aldosterone on electrolytes and note the gland that is responsible for the release of the hormone. Describe in the space below:


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