Unit 10: Water and Electrolytes

Question 1

Functions of Water in the Body:

Answer 1

• Carries nutrients and waste products throughout the body
• Maintains the structure of large molecules such as proteins and glycogen
• Participates in metabolic reactions
• Serves as the solvent for minerals, vitamins, amino acids, glucose, and many other small molecules so that they can participate in metabolic activities
• Acts as a lubricant and cushion around joints and inside the eyes, the spinal cord, and, in pregnancy, the amniotic sac surrounding the fetus in the womb
• Aids in the regulation of normal body temperature, as the evaporation of sweat from the skin removes excess heat from the body
• Maintains blood volume

Question 2

Causes of Fluid-Electrolyte Imbalance:

Answer 2

Normally, the body defends itself successfully against fluid and electrolyte imbalances. Certain situations and some medications, however, may overwhelm the body’s ability to compensate. Severe, prolonged vomiting and diarrhea as well as heavy sweating, burns, and traumatic wounds may incur such great fluid and electrolyte losses as to precipitate a medical emergency.
If fluid is lost by vomiting or diarrhea, sodium is lost indiscriminately. If the adrenal glands oversecrete aldosterone, as may occur when they develop a tumour, the kidneys may excrete too much potassium. Also, the person with uncontrolled diabetes may lose glucose, a solute not normally excreted, and large amounts of fluid with it. Each situation results in dehydration, but drinking water alone cannot restore electrolyte balance. Medical intervention is required.

Question 3

How is acid-base balance maintained?

Answer 3

The body uses its ions not only to help maintain fluid and electrolyte balance, but also to regulate the acidity (pH) images of its fluids. The body must maintain the pH within a narrow range to avoid life-threatening consequences. Slight deviations in either direction can denature proteins, rendering them useless. Enzymes couldn’t catalyze reactions and hemoglobin couldn’t carry oxygen—to name just two examples.
Regulation in the Lungs
Regulation in the Kidneys
Regulation by Buffers

Question 4

Sodium Functions in the body:

Answer 4

• Most abundant cation in the extracellular fluid
• Maintaining fluid balance and acid‑base balance
• Functions in conducting nerve impulses and in control of muscle contraction.

Question 5

Sodium: symptoms of deficiency and excess intake:

Answer 5

Low blood‑sodium level or low blood volume can result from excessive sweating in a hot climate (heatstroke) or as a result of heavy exercise, vomiting, diarrhea, burns, untreated diabetes, hemorrhages, overuse of diuretics for heart failure or kidney disease, use of very low sodium diets, or adrenocortical insufficiency—for example, in Addison’s disease.

Symptoms of sodium deficiency are loss of body weight, muscle cramps, weakness, anorexia, mental apathy, and coma.
High intakes of sodium can be toxic, causing internal hemorrhages, vomiting, peripheral circulatory failure, respiratory depression, and death.

Question 6

Sodium: relationship to blood pressure:

Answer 6

Hypertension, one of the most common chronic diseases in industrialized countries, is a major factor in coronary heart disease, stroke, and renal failure. Evidence indicates that excess sodium intake, in the form of sodium chloride, is a major cause. It is thought that salt‑sensitive or sodium‑sensitive people with a high salt intake are particularly prone to develop hypertension.

Question 7

Sodium: major food sources:

Answer 7

• Main dietary source of sodium (95%) is common salt (sodium chloride)
• Monosodium glutamate (MSG)
• Sodium bicarbonate (baking soda).
• Common salt is 40% sodium and 60% chloride.
• The average intake of salt in Western societies is about 6–10 grams (2.4–4 grams of sodium) daily.

Question 8

Discuss dietary strategies to reduce salt and sodium intake:

Answer 8

Canada’s Food Guide recommends choosing vegetables, fruit, grain products, meats, and alternatives that are prepared with little or no salt.
The recommended intake for sodium is stated as an AI (acceptable intake) of 1500 mg per day. The UL (upper limit) is 2300 mg per day which is contained in approximately 1 teaspoon of table salt.

Question 9

Potassium: Functions in the body:

Answer 9

Potassium is the major cation in the intracellular fluid

• Helps to maintain fluid and acid‑base balance.
• Like sodium, it is important for neuromuscular activity, including that of the heart muscle.
• Promotes cellular growth in protein synthesis and acts as a biological catalyst in energy metabolism.

Question 10

Potassium: relationship to blood pressure:

Answer 10

Potassium intake of most people is low, and this is also associated with above normal blood pressure and hypertension.

Question 11

Potassium: major food sources:

Answer 11

Unprocessed whole foods, such as fruit, vegetables, and whole grains

Question 12

Fat storage, however, requires little water, which is why obese individuals have less total body water in proportion to their weight than do muscular athletes, and have more difficulty in cooling themselves during hot weather or when they have a fever. TRUE OR FALSE?

Answer 12

TRUE

Question 13

Describe Water Balance

Answer 13

The loss of water through the kidneys, lungs, feces, and skin is balanced by the intake of water from liquids and food and by metabolic water produced during energy metabolism (water balance). Since there is no water storage per se in the human body, water losses must be replaced daily. The regulation of water intake and excretion is related directly to electrolyte balance in body fluids. Fluid balance refers to the balance between water inside and outside body cells, but water balance and fluid balance are often used interchangeably.

Question 14

Define Electrolyte

Answer 14

Electrolytes are charged ions produced when a salt, acid, or base dissociates in water. These charged particles are capable of conducting an electric current.

Question 15

Define Cation

Answer 15

Cations are positively charged ions

Question 16

Define Anion

Answer 16

Anions are negatively charged ions

Question 17

Explain Cations and Anions in the fluid of the body

Answer 17

In any electrolyte solution, the number of cations is balanced by the number of anions, so that electroneutrality is maintained. Sodium is the major cation and chloride the major anion in the extracellular fluid. In the intracellular fluid, the major cations are potassium and magnesium, and the major anions are phosphate and proteins.

Question 18

Define Water Intoxication

Answer 18

Water intoxication, on the other hand, is rare but can occur with excessive water ingestion and kidney disorders that reduce urine production. The symptoms may include confusion, convulsions, and even death in extreme cases. Excessive water ingestion (10 to 20 litres) within a few hours dilutes the sodium concentration of the blood and contributes to a dangerous condition known as hyponatremia. For this reason, guidelines suggest limiting fluid intake during times of heavy sweating to between 1 and 1.5 litres per hour

Question 19

Define pH

Answer 19

pH is the unit of measure expressing a substance’s acidity or alkalinity.

Question 20

Regulation by Buffers

Answer 20

Bicarbonate (a base) and carbonic acid (an acid) in the body fluids, as well as some proteins, protect the body against changes in acidity by acting as buffers—substances that can neutralize acids or bases. Carbon dioxide, which is formed all the time during energy metabolism, dissolves in water to form carbonic acid in the blood. Carbonic acid, in turn, dissociates to form hydrogen ions and bicarbonate ions. The appropriate balance between carbonic acid and bicarbonate is essential to maintaining optimal blood pH. Figure 11-9 presents the chemical reactions of this buffer system, which is primarily under the control of the lungs and kidneys.

Question 21

Regulation in the Lungs

Answer 21

The lungs control the concentration of carbonic acid by raising or slowing the respiration rate, depending on whether the pH needs to be increased or decreased. If too much carbonic acid builds up, the respiration rate speeds up; this hyperventilation increases the amount of carbon dioxide exhaled, thereby lowering the carbonic acid concentration and restoring homeostasis. Conversely, if bicarbonate builds up, the respiration rate slows; carbon dioxide is retained and forms more carbonic acid. Again, homeostasis is restored.

Question 22

Regulation in the Kidneys

Answer 22

The kidneys control the concentration of bicarbonate by either reabsorbing or excreting it, depending on whether the pH needs to be increased or decreased, respectively. Their work is complex, but the net effect is easy to sum up. The body’s total acid burden remains nearly constant; the acidity of the urine fluctuates to accommodate that balance.

Question 23

Potassium: symptoms of deficiency or excess intake

Answer 23

Deficiency usually results from abnormal conditions that cause excessive loss of body fluids, such as vomiting, diarrhea, diuresis (production of abnormally large amounts of urine, such as in diabetic acidosis), and prolonged malnutrition. Symptoms of deficiency are muscular weakness, mental apathy, and cardiac arrhythmia or failure.
If injected into blood, potassium can stop the heart from beating. Special care must be exercised when using a salt substitute containing potassium chloride, especially by people with kidney failure. Symptoms of potassium toxicity include mental confusion, numbness of extremities, poor respiration, weakening of heart action, and vomiting.