Name ____________________________
Water Balance – 50 Informal Points
Introduction
Bill’s friends throw a summer picnic to celebrate his 40 th 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.
3. 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.
o Start by thinking about how the brain detects high or low levels of sodium or water in the
blood.
o Your feedback loop descriptions should include the following words: thirst, ADH,
hypothalamus, neuron, pituitary gland, nephron, kidney, urine, reabsorption,
osmoreceptors.
o 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.
o You may need to do a bit of additional research to include all the necessary key terms and
fully understand the physiology.
o Create your feedback loop a Body system organizer to show where each step is taking
place in the body.
4. 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.
5. 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:
Aldosterone also causes water to be reabsorbed along with sodium; this increases blood
volume and therefore blood pressure. Thus, aldosterone indirectly regulates blood
levels of electrolytes (sodium, potassium and hydrogen) and helps to maintain the blood
pH.
6. In the space below, create a Venn diagram that compares and contrasts the action of the two hormones
ADH and aldosterone.
7. Return to your Maniken® and use clay to create an adrenal gland. Use images you find on the Internet to
help you locate this gland and design and build a replica. Find the pituitary gland you built earlier in the
year. Both of these glands help maintain the body’s water balance.
8. Use the Internet to research answers to the questions listed below.
o The kidneys themselves also serve as an endocrine gland. What hormones are produced
by the kidney and what function do they serve? What other human body system do these
hormones regulate?
Hormones that are produced by the kidney are Erythropoietin, which is the vital hormone for
the production of red blood cells (regulate cardiovascular system), Calcitriol, which is vital for calcium
homeostasis (regulate Skeletal system), and acts to raise plasma calcium levels, and Renin, which
forms a vital part in the renin-angiotensin-aldosterone system, a complex system of hormones and
enzymes which raise blood pressure when stimulated by hypotension.
o Describe the role of at least two other organs or structures that help the body deal with an
influx of alcohol.
The liver metabolizes the alcohol using an enzyme known as alcohol dehydrogenase to break
down the alcohol into acetate, where it is further broken down into carbon dioxide and water.
The kidney handles the excess, diluted urine caused by the diuretic effect of alcohol.
Conclusion Questions
1. Would blood ADH levels be higher or lower than normal in a person who just completed a three mile run
without drinking any water? Explain.
The blood level of ADH would be higher than normal after a 5km run, due to loss of body
water in sweat, since ADH is anti-diuretic and the person is trying to conserve as much
water as possible.
2. Is the ADH feedback loop an example of positive or negative feedback? Explain.
Negative because the opposite is attempting to happen. ADH is attempting to conserve water to increase
blood volume and raise blood pressure when the blood pressure is too low. Hypotension is currently in
place, so blood pressure is trying to increase.
3. How did the events of Bill’s day impact his body’s ability to conserve and balance water?
Bill became dehydrated because ADH (vasopressin) was suppressed by the alcohol, causing his
homeostasis to become out of whack since he was releasing more water than he should have, causing
him to become increasingly dehydrated.
4. Explain the role of sweating in the body. What effect did sweating have on Bill’s water balance?
Sweating causes a person to lose water and salt, causing them to become dehydrated if they are not taking in
enough water and salt to make up for this loss. This also contributed to Bill’s dehydration and subsequent
hangover.
5. How could Bill have prevented his horrible hangover? Explain.

Limited the amount of alcohol he drank; drink water instead of alcohol or at least switch between
alcohol and water

Not ran around so much so that there would have been less sweating

Drink Gatorade to replenish both water and electrolytes

Find cooler shelter reduce sweating
6. Diuretics are often prescribed to treat high blood pressure. Given the name of the class of drug, how do
you think diuretics affect the kidney, the fluid and electrolyte balance in the body and overall blood
pressure?
Diuretics cause the kidneys to remove more sodium and water from the body,
which helps to relax the blood vessel walls, thereby lowering blood pressure.
7. Explain how drinking too much water can throw off the electrolyte balance in your blood. How does this
imbalance specifically affect the nervous system and the muscular system? Hint: Think back to what
happens at the plasma membrane for a nervous signal to be communicated and to the ions that are
required for muscle contraction.
This is EXTERMELY rare:
Water intoxication is the extreme result of a bodily imbalance between electrolytes (the minerals in
your blood and body fluid that carry an electric charge) and water, a condition called "hyponatremia."
Chemically speaking, an electrolyte is any substance that ionizes, i.e. gains or loses an electron or
electrons, when dissolved in a solvent like water. A classic example is table salt, chemical formula NaCl,
which dissociates into a positively charge sodium ions and negatively charged chloride ions when
dissolved in water.
In severe cases of hyponatremia, the kidneys – which help, among other things, to regulate water and
electrolyte levels in the body – become overwhelmed. At rest, under normal conditions, your kidneys
are a supremely efficient filtration system.
Consume water at a faster rate than the kidneys can process it, however, and the excess is driven by
osmosis to regions of the body with high electrolyte concentration, beginning with the blood and
eventually seeping into the salt-rich interiors of cells throughout the body. The cellular influx of water is
manifest as swelling known as edema; the cells of your body become turgid, ballooning and distending
with their newly acquired water weight.
8. Explain how a shortage of water affects the health of your cells. Make sure to use words such as osmosis,
hypertonic solution, hypotonic solution, or isotonic solution in your answer.
Cell size responds to tonicity. Osmosis is the passive movement of water across a cell membrane.
When body cells are in isotonic solutions the net movement of water is zero, creating a healthy, stable cell.
This means the amount of water moving into the cell matches that of the amount of water moving out of
the cell.
When body cells are in hypertonic solutions the net movement of water is out of the cell, causing it to shrink
and shrivel. This is bad because the internal components of the cell will not have enough water to function
properly. This can be reversed and typically is not as harmful as hypotonic solutions.
When body cells are in hypotonic solutions the net movement of water is into the cell, causing it to expand.
This could be deadly if it happens to swell so large that it bursts.