1. Chapter 11: Water

2. 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

3. The Composition of the Body
Figure 11.1

4. Why Is Water So Important?
Water is a polar molecule
Excellent solvent in the body
Neutral charge
Essential in maintaining acid-base balance
Figure 11.2

5. 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

6. Functions of Water in the Body
You can survive for weeks without food, but you can survive only a few days without water

7. 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

8. Water Helps Regulate Body Temperature
Figure 11.3

9. 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

10. 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

11. 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

12. 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
Figure 11.4

13. 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)

14. 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

15. Water Excretion Loss through sweat Varies based on
Environmental factors
Temperature
Humidity
Wind
Sun’s intensity
Clothing
Amount of physical activity

16. Water Balance between Fluid Compartments
Body fluid is located
Intracellular – within the cells
Extracellular – outside the cells
Figure 11.5

17. Electrolytes Participate in Fluid Balance
Minerals with electrically charged ions
Potassium
Phosphate
Magnesium
Help maintain water balance between compartments
Sodium has greatest effect on fluid balance
Calcium
Chloride
Sodium

18. 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

19. Osmosis
Figure 11.6

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. Blood Volume Regulates Blood Pressure
Figure 11.8

29. 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

30. 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

31. Daily Beverage Recommendations
Figure 11.9

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

42. 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

43. 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

44. 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

45. 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

46. 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