chapter 11: water

© 2010 Pearson Education, Inc.

Chapter 11: Water


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

Figure 11.1

The Composition of the Body

© 2010 Pearson Education, Inc. Figure 11.2

Why Is Water So Important? Water is a polar

molecule• Excellent

solvent in the body

• Neutral charge• Essential in

maintaining acid-base balance


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


Functions of Water in the Body

You can survive for weeks without food,but you can survive only a few days without water


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

Figure 11.3

Water Helps Regulate Body Temperature


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


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


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


Amount consumed = Amount excreted

Figure 11.4

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


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)


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


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. Figure 11.5

Water Balance between Fluid Compartments Body fluid is located

• Intracellular – within the cells

• Extracellular – outside the cells


- Calcium- Chloride- Sodium

Electrolytes Participate in Fluid Balance Electrolytes

• Minerals with electrically charged ions- Potassium- Phosphate- Magnesium

• Help maintain water balance between compartments- Sodium has greatest effect on fluid balance


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

Figure 11.6

Osmosis


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


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


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


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


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


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


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


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

Figure 11.8

Blood Volume Regulates Blood Pressure


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


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

Figure 11.9

Daily Beverage Recommendations


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


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


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


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


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


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


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


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


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

Figure 11.11

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


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


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


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


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

chapter 11: water

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