Chapter 11: Water

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 Electrolytes 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