Transcript Chapter 11 Water

Chapter
11: Water
© 2010 Pearson Education, Inc.
Why Is Water So Important?

Water is the most abundant substance in the body

Average healthy adult is 45–75% water depending on
• Age
- Percent of water declines with age
• Composition of fat and muscle
- Muscle is ~65% water
- Fat is 10–40% water
• Gender
© 2010 Pearson Education, Inc.
The Composition of the Body
Figure 11.1
Why Is Water So Important?

Water is a polar
molecule
• Excellent
solvent in the
body
• Neutral charge
• Essential in
maintaining
acid-base
balance
© 2010 Pearson Education, Inc.
Figure 11.2
Quick Review

Body is more than 45% water

Muscle tissue has more water than does fat tissue
• Men have more body water than women
• Younger individuals have more body water than older
individuals

Water is polar

Water serves as an acid-base buffer
© 2010 Pearson Education, Inc.
Functions of Water in the Body
You can survive for weeks without food,
but you can survive only a few days without water
© 2010 Pearson Education, Inc.
Functions of Water in the Body

Commonly known as a universal solvent

Polarity allows it to attract charged particles into solutions
and dissolve a variety of other polar substances
• Important to digestion

Helps transport dissolved nutrients and other substances
throughout the body

Blood is composed of water and red blood cells
• Water allows blood to transport oxygen, nutrients, and
hormones to cells
• Water helps transport waste products away from cells to
be excreted
© 2010 Pearson Education, Inc.
Water Helps Regulate Body Temperature
Figure 11.3
Functions of Water in the Body

Lubricates joints, sensitive eye tissues, mouth, and
intestinal tract

Provides a protective cushion, bathing certain organs with
fluid
• During pregnancy the fetus is surrounded by watery
amniotic fluid

Provides a structural component to cells
© 2010 Pearson Education, Inc.
Functions of Water in the Body

Water is essential for most chemical reactions in the body
• During digestion water hydrolyzes the bonds holding
together
- Carbohydrate molecules
- Protein molecules
- Fat molecules
• When smaller molecules combine through condensation
water is formed
© 2010 Pearson Education, Inc.
Quick Review

Water
• Universal solvent
• Transports oxygen and nutrients throughout the body
• Absorbs and releases heat to regulate body temperature
• Acts as a lubricant
• Provides a protective cushion for organs
• Adds structure to cells
• Participates in chemical reactions
- Hydrolysis
- Condensation
© 2010 Pearson Education, Inc.
Maintaining Water Balance

Fluid homeostatis
• Is necessary for
normal reactions
within the cells
• Is maintained by
adaptation to
changes in water
intake and water
loss
• Water balance
Amount consumed = Amount excreted
© 2010 Pearson Education, Inc.
Figure 11.4
Sources of Body Water

Largest source comes from beverages

Food is an additional source
• Except for fats, all food contains some water

Metabolic water – water generated during metabolism
These sources contribute to an average daily intake of
2,550 ml (about 2 quarts)
© 2010 Pearson Education, Inc.
Water Excretion

Majority of fluid is excreted through the kidneys
• More water that is ingested the more urine that is
produced

Excreted through intestinal fluids in the stool
• Dependant on dietary intake of plant fibers and presents
of diarrhea

Evaporated through exhalation and through the skin
• Insensible water loss
© 2010 Pearson Education, Inc.
Water Excretion

Loss through sweat
• Varies based on
- Environmental factors
- Temperature
- Humidity
- Wind
- Sun’s intensity
- Clothing
- Amount of physical activity
© 2010 Pearson Education, Inc.
Water Balance between Fluid Compartments

Body fluid is located
• Intracellular – within
the cells
• Extracellular – outside
the cells
© 2010 Pearson Education, Inc.
Figure 11.5
Electrolytes Participate in Fluid Balance

Electrolytes
• Minerals with electrically charged ions
- Potassium
- Calcium
- Phosphate
- Chloride
- Magnesium
- Sodium
• Help maintain water balance between compartments
- Sodium has greatest effect on fluid balance
© 2010 Pearson Education, Inc.
Electrolytes Participate in Fluid Balance

Osmosis
• Strongest factor influencing water balance between
compartments
• Water moves from a diluted concentration to a more
concentrated area
• Osmolarity of a solution indicates total concentration
© 2010 Pearson Education, Inc.
Osmosis
Figure 11.6
Electrolytes Participate in Fluid Balance

Sodium-potassium pump
• Sodium and potassium play a key role in water
concentration inside and outside of the cells
• Healthy cells
- Low concentration of sodium ions
- High levels of potassium inside the cells
• Water is attracted to sodium and moves toward it
• Transports three Na+ ions out of the cell in exchange for
two K+ ions
- Keeps the cell from swelling and bursting
© 2010 Pearson Education, Inc.
Quick Review


Water balance
• Water is consumed and is produced by the body via food,
beverages, and metabolism
EQUALS
• Water excreted through the kidneys, skin, lungs, and
feces
Body water is contained in either
• Intracellular fluid compartments – majority of body
water
• Extracellular fluid compartments
- Interstitial
- Intravascular
© 2010 Pearson Education, Inc.
Quick Review

Osmosis is the process of water moving from an area of
higher concentration to an area of lower concentration
across a cell membrane

Sodium-potassium pump helps maintain electrolyte and
fluid balance inside and outside of cells
© 2010 Pearson Education, Inc.
How Do Water and Sodium Affect Blood
Pressure?

If the body retains too much fluid, blood volume increases
and blood pressure will likely rise

Kidneys help regulate blood volume and electrolyte balance
through tightly controlled hormone signals
© 2010 Pearson Education, Inc.
How Do Water and Sodium Affect Blood
Pressure?

Three hormones and one enzyme work together to
orchestrate the retention and excretion of water and
electrolytes base on blood volume

Hormones
• Antidiuretic hormone (ADH), also called vasopressin
• Angiotensin
• Aldosterone

Enzyme
• Renin
© 2010 Pearson Education, Inc.
ADH

Blood volume drops
• Hypothalamus detects decrease in blood pressure and
increase in concentration of salts
• Thirst mechanism and fluid intake are stimulated
• Hypothalamus stimulates pituitary glands to release
ADH
• ADH stimulates the kidneys to reabsorb water and
decrease urine output
• Blood volume increase and osmolality returns to normal
© 2010 Pearson Education, Inc.
Renin

Blood pressure falls and sodium concentration is reduced
• Renin is secreted by the kidneys
- Enzyme splits off a protein called angiotensin I from
the protein angiotensinogen found in the blood
- In the lungs angiotensin I is converted to angiotensin
II
- Angiotensin II is a powerful vasoconstrictor
© 2010 Pearson Education, Inc.
Aldosterone

Renin-angiotensin system adapts to changes in dietary
sodium intake
• Consume too little sodium
• Osmolality drops in extracellular fluid (ECF)
• Fluid shifts from the blood to the interstitial fluid
• Blood volume and blood pressure decrease
• Angiotenson II triggers the adrenal glands to release
aldosterone

Aldosterone
• Signals kidneys to retain more sodium
• Indirectly leads to water retention
© 2010 Pearson Education, Inc.
Blood Volume Regulates Blood Pressure
Figure 11.8
Quick Review

Changes in blood volume and osmolality
• Body takes actions to maintain homeostasis and return
blood pressure to normal
• Antidiuretic hormone (ADH) and aldosterone direct the
kidneys to reabsorb water and sodium
• Renin increases sodium retention
• Angiotensin II is a vasoconstrictor

These control mechanisms adjust to the changes in dietary
sodium and fluid intake to prevent hypertension
© 2010 Pearson Education, Inc.
How Much Water? What Are the Best
Sources?


Water needs depend on
• Physical activity
• Environmental factors
• Diet
Recommendations
• 80% intake from beverages and 20% from food
• Adult women: approximately 9 cups of fluid per day
• Adult men: approximately 13 cups of fluid per day
• A well-balanced 2,200 kilocalorie diet that includes
beverages at all meals and snacks will provide about 12
cups of water
© 2010 Pearson Education, Inc.
Daily Beverage Recommendations
Figure 11.9
How Much Water? What Are the Best
Sources?

Drinking bottled or tap water, milk, and juices throughout
the day can help meet the body’s needs

Most foods can also contribute to daily water need
• Fruits and vegetables can be 70% or more water by
weight
• Dry grain products provide some water
© 2010 Pearson Education, Inc.
Quick Review

Daily water needs vary according to
• Physical activity levels, environment, diet

Adult women should consume about 12 cups per day
• 9 cups from beverages
• 3 cups from food

Adult males should consume about 16 cups per day
• 13 cups from beverages
• 3 cups from foods

Active individuals will need more water to avoid
dehydration
© 2010 Pearson Education, Inc.
Do Diuretics Like Caffeine and Alcohol
Affect Water Balance?

Alcoholic drinks, regular coffee, and tea contribute to total
water intake

Alcohol and caffeine are considered diuretics
• Contribute to water loss
• Overconsumption can upset fluid balance
© 2010 Pearson Education, Inc.
Caffeine

Mild diuretic that blocks the action of ADH in the kidneys

Research unable to confirm that this mild diuretic actually
results in dehydration

Caffeine doesn’t cause a significant loss of body water
over the course of the day compared to noncaffeinated
beverages

Tolerance to diuretic effects develops over time
© 2010 Pearson Education, Inc.
Alcohol

Inhibits ADH

Can induce urination as quickly as 20 minutes after
consumption

Can be dehydrating

Effects electrolytes, especially potassium

Older drinkers are less effected than younger drinkers

To prevent dehydration
• Reduce alcohol consumption
• Drink water after consuming alcohol
© 2010 Pearson Education, Inc.
Diuretic Medications Can Help Treat
Hypertension

First line of treatment for hypertension
• Often pharmaceutical diuretics
- Promote diuresis by inhibiting the reabsorption of
sodium
- Increased sodium excretion increases fluid excretion
- Reduces blood volume and lowers blood pressure

Some diuretics increase potassium loss and the risk of
hypokalemia
© 2010 Pearson Education, Inc.
Quick Review

Moderate caffeine intake does not affect fluid balance

Alcohol reduces the effects of ADH and can cause
dehydration

Pharmaceutical diuretics are prescribed to reduce
hypertension

Pharmaceutical diuretics may cause electrolyte imbalances
© 2010 Pearson Education, Inc.
Effects of Too Much Water

Water intoxication
• Rare in healthy individuals who consume a balanced diet
• Drinking fluid too fast without adequate sodium
replacement depletes sodium and increases the rate of
urine production
- Results in hyponatremia
• Can cause swelling in the brain
- Fatique
- Confusion
- Disorientation
© 2010 Pearson Education, Inc.
Effects of Too Little Water

Dehydration can result from
• Not drinking enough water
• Losing excessive amounts of water due to diarrhea,
vomiting, high fever, or use of diuretics
• As little as a 2% loss of body water can trigger
- Loss of short-term and long-term memory
- Lower attention span and cognition
- Reduced ability to maintain core temperature
- Increase risk of urinary tract infections and fatigue

Consequences of dehydration can be severe for children,
elderly, and athletes
© 2010 Pearson Education, Inc.
Thirst Mechanism Signals Dehydration

Thirst is often the first
sign of dehydration

Urge to drink is important
in preventing dehydration
and restoring water
balance

Less circulating blood can
lead to
 Reduced blood pressure
 Hypotension if severe
enough
Figure 11.11
Thirst Mechanism Signals Dehydration

Hypovolemia and hypotension can
• Reduce cardiac output
• Impair digestion
• May cause fainting and blacking out

When dehydrated
• Water is depleted from extracellular fluid and
intracellular fluid
© 2010 Pearson Education, Inc.
Monitor Water Intake to Avoid
Overhydration and Dehydration

Measure body weight before and after long bouts of
vigorous physical activity or labor and note changes
• If weighs less after an activity the change is due to loss
of body water
• If weight gain is noted overhydration is likely
- Consume less fluid before next activity
© 2010 Pearson Education, Inc.
Monitor Water Intake to Avoid
Overhydration and Dehydration

Urine color can be used to assess hydration
• Individuals who are dehydrated produce less urine due to
the release of ADH
• With dehydration urine is more concentrated and darker
in color
• Darker urine indicates possible need to increase fluid
intake
© 2010 Pearson Education, Inc.
Putting It All Together

Water is
• A universal solvent
• The main component of fluids in which all reactions
involving the energy-producing nutrients take place in
the body
- Vitamins and minerals aid in these chemical reactions

Nutrients work in conjunction with water to meet metabolic
needs

Consuming a wide variety of foods from all food groups,
with an emphasis on maintaining sufficient fluid intakes, is
the best diet prescription to meet the body’s needs for
carbohydrate, proteins, fat, vitamins, minerals, and water
© 2010 Pearson Education, Inc.