Chapter 10 WATER AND THE ELECTROLYTES

10.1 Water: The Internal Sea Learning objectives Describe the functions of water in the body. Discuss the forces that move water back and forth across cell membranes. Describe how water is lost or gained by the body. Describe the factors that influence water requirements. Describe the effects of dehydration. Describe the effects of water intoxication. 2

Water Essential nutrient that must be consumed for survival. Polar solvent in the body. The polarity of water comes from hydrogen and oxygen. Blood is 90% water. Blood transports oxygen and nutrients to cells and removes carbon dioxide and waste products. 3

Water Functions as a lubricant and cleanser Tears wash away dirt, synovial fluid lubricates joints, saliva assists in chewing, tasting, and swallowing, and spinal fluid protects against shock. Water assists in regulating body temperature by holding onto heat and changing temperature slowly. 4

Water Molecule Solvent: A fluid in which one or more substances dissolve. Solutes: Dissolved substances Polar: Molecule that has a positive charge at one end and a negative charge at the other Electrons: Negatively charged particles Ion: An atom or group of atoms that carries an electrical charge Dissociate: To separate two charged ions 5

Water Molecule Figure 10.1 Figure 10.1 The polar nature of water Electrons in a water molecule, shown as dots, spend more time around the oxygen atom, giving the oxygen side of the molecule a slightly negative charge, and the hydrogen side a slightly positive charge. When sodium chloride is added to water, the positive sodium ion is attracted to the negative pole of the water molecule, and the negative chloride ion is attracted to the positive pole. Figure 10.1

Hydrolysis and Condensation Reactions Figure 10.3 Hydrolysis and condensation reactions The cleavage of the disaccharide maltose into 2 molecules of glucose is a hydrolysis reaction; disaccharide formation is a condensation reaction. Figure 10.3

Water and pH Balance Figure 10.4 Figure 10.4 pH values of common fluids Fluctuations from the normal blood pH range of 7.35-7.45 leads to acidosis (too much acid) or alkalosis (too much base) and, if severe, can be fatal. Figure 10.4 8

Water in the Body About two-thirds of body water is found inside cells (intracellular fluid). Extracellular fluid is found outside the cells. Interstitial fluid consists of lymph, blood plasma, and extracellular fluid. Intracellular fluid has the highest concentration of protein, extracellular fluid has less, and interstitial fluid has the lowest concentration of protein. 9

Water in the Body Extracellular fluid has the highest concentration of sodium and chloride and a lower concentration of potassium. Intracellular fluid has the lowest concentration of sodium and the highest concentration of potassium. The fluid pressure of blood against the blood vessels is blood pressure. 10

Water in the Body Figure 10.5(a) Figure 10.5 Forces that determine the distribution of body water (a) Body water is distributed between intracellular and extracellular spaces. Figure 10.5(a)

Water in the Body Figure 10.5(b) Figure 10.5 Forces that determine the distribution of body water (b) The amount of water in blood and tissues is determined by blood pressure and the force generated by osmosis. Figure 10.5(b)

Osmosis Figure 10.6 Figure 10.6 Osmosis When sugar is sprinkled on strawberries, osmosis draws water out of the strawberries to dilute the concentrated sugar solution on the surface. (Dennis Drenner) Figure 10.6

Need for Water in the Body Compared to Intake Figure 10.7 Water balance To maintain water balance, intake must equal output. This figure approximates the amounts of water from different sources that make up water intake and the amounts of lost water in an adult who is not sweating. Figure 10.7 14

Sources of Water Figure 10.8 Figure 10.8 Sources of water in Canada’s Food Guide food groups Fruits and vegetables, as well as many choices from other food groups, have a high water content. Figure 10.8 15

Thirst Mechanism Figure 10.9 Figure 10.9 Regulation of water intake The sensation of thirst helps motivate fluid intake in order to restore water balance. Figure 10.9 17

Antidiuretic Hormone Assists in Fluid Intake Figure 10.10 Regulation of water loss The kidneys help regulate water balance by adjusting the amount of water lost in the urine in response to the release of antidiuretic hormone (ADH). Figure 10.10 18

Consequences of Dehydration: Urine Colour and Hydration Status Figure 10.11 Urine colour and hydration status The darker an individual’s urine colour, the greater the level of dehydration. Pale yellow urine indicates good hydration. Figure 10.11 19

10.2 Electrolytes: Salts of the Internal Sea Learning objectives: Compare the intake of sodium and potassium in the Canadian diet. Describe the functions of sodium, chloride, and potassium in the body. Describe the criteria used to set the AIs for sodium and potassium. Describe the causes and consequences of electrolyte deficiency. Describe the causes and consequences of electrolyte toxicity. List other electrolytes in the body besides sodium, chloride and potassium. 20

Electrolytes: Sodium, Potassium and Chloride The correct combination and amounts of electrolytes are essential for life. Distribution of electrolytes affects the distribution of water throughout the body. Sodium, potassium, and chloride are the principle electrolytes in body fluids. 21

CCHS collected information on Canadians’ intake of sodium and potassium. Sodium intake was expressed as the percentage of the population consuming above the UL. 90.2% of males (>19 years) above the UL 65.7% of women (>19 years) above the UL A concern is that excessive sodium intake is associated with increased risk for hypertension.

Regulation of Blood Pressure Figure 10.15

10.3 Hypertension Learning objectives Distinguish between essential and secondary hypertension. Describe some of the risk factors for hypertension. Describe the dietary factors that influence blood pressure. Describe how the sodium content of the Canadian diet can be reduced. Describe some dietary strategies for preventing hypertension.

Hypertension Serious public health concern in Canada 20% of adult Canadians have hypertension (140/90 mm or greater) 20% of adult Canadians have pre-hypertension (120/80–139/89 mm) It is estimated that 17% of Canadians do not know they have hypertension.

Hypertension and Diet The lower the amount of sodium in the diet, the lower the blood pressure. Average sodium intake in Canadian diet is 3,400 mg. A reduction in sodium by 1,000 to 1,500 mg will reduce blood pressure in those with and without hypertension. The Sodium Reduction Strategy for Canada recommends that Canadians reduce their sodium intake to less than 2,300 mg/day.

Keeping Blood Pressure in Normal Range Diet and lifestyle are both involved in regulating blood pressure. Maintain a desirable body weight Stay active Limit alcohol consumption Consuming diet described in Canada’s Food Guide or the DASH Diet will also help.

Salt Sensitivity Figure 10.17 Figure 10.17 Salt sensitivity. Salt-sensitive individuals have impaired sodium excretion, which, in combination with a high sodium intake, increases blood pressure.

Summary of study diets

A second trial, DASH-Sodium, compared the effect of the DASH Eating Plan with a control diet (typical American diet) at three different levels of sodium intake, as shown in the table. Source: Sacks, F. M., Svetkey, L. P., Vollmer, W. M., et al. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH Sodium Collaborative Research Group. N. Engl. J. Med. 344:3–10, 2001.

Comparing results of the control and DASH diets.

Summary of the nutrient content claims for salt and sodium on food labels in Canada.

Hypertension and Diet Source: Hypertension Canada. Health Behavior Management: 2014 CHEP Recommendations. Available online at www.hypertension.ca/en/professional/chep/therapy/health-behaviour-management. Accessed June 18, 2014.

Hypertension and Diet

Hypertension and Diet Food labels list the sodium-containing ingredients in the ingredient list. Nutrition Facts panel gives the total amount of sodium in milligrams and as a percentage of Daily Value to help buyers compare food products. Food labels can also include nutrient content claims relating to salt or sodium. Hypertension Canada recommends Canadians consume foods containing 200 mg of sodium/serving but avoid foods that contain more than 400 mg of sodium/serving.

Canadian Potassium Intake Average Canadian diet contains 2,500 to 3,500 mg of potassium/day (well below recommended 4,700 mg/day). Fruits and vegetables are the best source of potassium.

Canadian Potassium Intake Canadians have low potassium intake because they do not meet the Canada’s Food Guide recommended number of servings of fruits and vegetables. Following Canada’s Food Guide and DASH Diet recommendations potassium intake would be 8,000 to 10,000 mg/day.

Dietary Sources of Potassium Figure 10.18 Sources of potassium in Canada’s Food Guide food groups Foods from all Canada’s Food Guide food groups are good sources of potassium, but whole unprocessed foods are the best. Figure 10.18

Summary of Water and the Electrolytes aRecommended intakes for water, sodium, potassium, and chloride are Adequate Intakes (AIs); UL, Tolerable Upper Intake Level; ND, insufficient data to determine a UL. 42

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