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Water and Electrolytes Katrina Krebs Water In a normal adult, water accounts for around 60% of total body weight. Within the body, it is put into two main compartments Intracellular fluid (ICF) Water within cell membranes Extracellular fluid (ECF) All water excluding intracellular water Divided into: Plasma (intravascular fluid (IVF)) Interstitial fluid (ISF) (allows nutrients and metabolic products to move between the cells and blood) Water Sources Beverages (80% of total water intake): All beverages including coffee, soda, and alcohol Caffeinated and non-caffeinated Food (~20% of total water intake): Lettuce, grape fruit, broccoli, and yogurt Metabolism (~300-400 mL per day) Input and output Input: Diet: 2,300 mL Metabolism: 200 mL Output: Urine: 1,400 mL Sweat: 100 mL Feces: 200 mL Insensible loss: 600 mL Diffusion through skin Evaporation from breathing Hydration Recommendations Institute of Medicine (IOM) recommends: Women: 11 cups/day (90 ounces) Men: 16 cups/day (125 ounces) Caffeinated beverages like coffee and tea and alcoholic beverages count as water. Diuretic effect from both caffeine and alcohol, but not enough to make a huge impact on hydration. Water’s Role Essential for life: Solvent Dissolves nutrients in blood and dissolves waste products. Transport Medium Once nutrients and waste products are dissolved, water can transport them into cells or out of the body. Lubricant GI tract, skin, reproductive system, respiratory tract Regulator of internal body temperature High specific heat (hard to change temperature) Evaporative cooling (sweating to release heat) Involved in hundreds of chemical reactions Hydrolysis reactions Condensation reaction (produce 1.5 cups of water per day) Dehydration Lack of sufficient water has a detrimental effect on the body. A 2% decrease of body weight by water loss poses severe issues: Inability to regulate body temperature Mental confusion Decreased muscle function Fatigue Long and short term memory loss At Risk for Dehydration: Children & Elderly— Dehydration symptoms may be severe Dehydration in elderly is sometimes mistaken for dementia. Athletes who perspire a lot Water Toxicity Over consumption of water leading to low sodium in blood Rare Most commonly seen in endurance athletes Causes hyponatremia—low sodium in blood Dilutes the concentration of electrolytes Symptoms: Confusion Seizures Coma Water Regulation Vasopressin or Antidiuretic Hormone (ADH) Synthesized in hypothalamus Stored & secreted by posterior pituitary glands Secretion triggered by: Increased ECF water osmolarity Decreased IVF volume Increases thirst Increases water reabsorption in kidneys ADH attaches to V2 receptors Synthesis of cAMP aquaporins on distal portion of ascending loop of Henle and collecting ducts Aquaporins: water channels Increases Na+ excretion in kidneys Same mechanism as above except with Na+ channels Electrolytes Anions (-) and cations (+) Present in the water compartments of the body In each compartment (mentioned earlier), electrolytes maintain electrical neutrality. Cations in extracellular fluid: Sodium, potassium, calcium, and magnesium Anions in (ECF): Chloride, bicarbonate and negatively charged proteins Maintenance Maintaining electrolyte and pH balance in the body are almost completely regulated by the Kidneys. Kidney’s Role Nephron—the functional unit of the kidney Around 1 to 1.5 million nephrons Excretion starts in the Bowmans’s capsule (a component of the nephron) Glomerulus (the capillary network in Bowman’s capsule) Act as a filter for: Water, electrolytes, metabolic waste products, glucose, and amino acids. Filtered substances are known as glomerular filtrate. Most glomerular filtrate substances need to be used by the body Tubular reabsorption (active or passive) Sodium (Na+) Sodium: 30% located on surface of bone crystals Remainder is found in the extracellular fluid Primarily the plasma 93% of cations in body Sources: Added salt (NaCl) 1 tsp= 2,300 mg of sodium Processed foods Canned soups, meats, condiments, canned vegetables Low amts in milk, and lower amts in meat, fish poultry, and vegetables Na + Absorption 95%-100% of ingested sodium is absorbed Three pathways for absorption: 1. Na+/glucose cotransport system *Most important* Involves a carrier on the apical membrane Requires glucose 2. Electroneutral Na+ and Cl- cotransport system Sodium uptake requires chloride 3. Electrogenic sodium absorption In colon Serum concentrations are highly regulated (~135-145 mEq/L) by: Aldosterone, atrial natriuretic hormone, and vasopressin Sodium’s Role Maintenance of fluid balance Regulating osmotic pressure Increased sodium increases ECF volume and blood pressure Nerve Transmission and muscle contraction Part of the Na+/K+ ATPase pump Exchange of Na+ for K+ and hydrolysis of ATP= nerve conduction Sodium Excretion: Excess excreted through kidneys and sweat Deficiency: Not common Abundance of sodium in food Extreme sweating—at risk More than 3% decrease of body weight Over hydration with little sodium consumption Symptoms Nausea, vomiting, muscle cramps, shock and coma Sodium Regulation During low blood pressure and hyponatremia, Aldosterone is secreted from the adrenal glands, which decreases sodium excretion. Renin-Angiotension-Aldosterone System (RAAS) is discussed later. How much? Adequate Intake (AI) 1,500 mg Tolerable Upper Intake Level (UL) 2,300 mg Avg. American consumes between 3,000-5,000 mg of sodium each day. Assessment of Nutriture 24-hour urinary sodium excretion Most often measured Ion-selective electrode potentiometry Measures Na+ like pH meter measures protons Potassium (K+) Intracellular cation 95-98% of potassium is found within cells Sources: Unprocessed foods Fruit: apricots, avocados, mangos, bananas, cantaloupe Vegetables: leafy green vegetables, winter squash Legumes, nuts and seeds Yogurt and milk Absorption >85% of potassium from diet is absorbed Absorbed in the small intestine & colon Actively or passively (concentration dependent) Diffuses from enterocyte through basolateral membrane K+ Channel Transport into nonintestinal cells occurs actively Na+/K+ ATPase pump Stimulated by insulin and some catecholamines Potassium’s Role Electrolyte balance PH balance Contraction of: Cardiac, smooth, and skeletal muscle Nerve excitability Interaction with other Nutrients Decreases calcium excretion from urine Consuming potassium citrate reduces: Bone turnover High bone turnover is commonly seen with high sodium diets. Excretion Most excreted from the kidneys (90%) Small amount in feces 80% of glomerular filtrate is reabsorbed Deficiency Does not occur due to dietary reasons Most often seen in people with: Extreme fluid loss Severe vomiting and diarrhea On medications for high blood pressure Cause high excretion of potassium in the urine Refeeding syndrome Causes Hypokalemia (low serum concentrations) <3.5 mEq/L Symptoms: Muscle weakness, irritability, glucose intolerance, irregular heart beat, hypercalciuria Toxicity Hyperkalemia Seen in people with: Renal impairments Symptoms: Irregular heart beat Cardiac arrest *Potassium supplements should only be used under the advisement of a doctor Too much or too little can cause death How Much? Adequate intake (AI): 4,700 mg per day (Age 14+) No UL has been established for food sources, only for supplements Average American intake ~ 3,300mg Even if consuming a diet high in fruits and vegetables DASH diet Boiling depletes potassium—roast or steam vegetables Assessment: Serum potassium levels (3.5-5.0 mmol/L) Ion-selective electrode potentiometry Sodium & Potassium Regulation Renin-Angiotension-Aldosterone System (RAAS) Renin is released by granular cells of the juxtaglomerular apparatus of the kidney. Stimulated by a decrease in pressure sensed by the baroreceptors. Renin hydrolyzes angiotensinogen (synthesized in the liver) to angiotensin I. Angiotensin I is converted into angiotensin II by ansiotensinconverting enzyme. Hypertension drugs act on this enzyme. Angiotensin II: Vasoconstricter, reduces glomerular filtrate, stimulates thirst, vasopressin and aldosterone synthesis and release. Aldosterone increases Na+ ion channels on the apical membrane and Na+--K+ pumps in the basolateral membrane. Increases water and Na+ retention. “Diets containing foods that are good sources of potassium and low in sodium may reduce the risk of high blood pressure and stroke”. Sodium & Hypertension Reducing the consumption of sodium decreases blood pressure . In both hypertensive and normotensive subjects, a decrease in both blood pressure and urinary excretion of sodium occurred when individuals had moderate decreases of sodium intake. Sodium increases Ca+ excretion, which is linked to hypertension. Potassium & Hypertension High intake of potassium has been associated with lowering both systolic and diastolic blood pressure. Potassium increases Na+ excretion and decreases excretion of calcium and magnesium. Increases vascular smooth muscle relaxation and decreases platelet aggregation and arterial thrombosis. DASH Diet Dietary Approaches to Stop Hypertension Diet to help prevent high blood pressure Reduce sodium intake and increase nutrients such as potassium magnesium and calcium Also follows dietary recommendations to prevent diabetes, osteoporosis, stroke, heart disease and cancer DASH Cont… The 2,000 calorie DASH diet includes: Grains: 6-8 servings per day Whole grains—higher in nutrients and fiber than refined Vegetables: 4-5 servings per day Tomatoes, carrots, leafy greens, broccoli Fruit: 4-5 servings per day Strawberries, blueberries, peaches, pears Leave skin on when possible—fiber Dairy: 2-3 servings a day Low-fat or fat free Lean meat, poultry, and fish: 6 servings or less per day Trim fat when possible Nuts, seeds, and legumes Lentils, almonds, peas Oils and Fats: 2-3 servings a day Limit saturated fats and avoid trans fats Tips to Reduce Sodium Intake Foods incorporated into the DASH diet are naturally low in sodium. Tips: 1. Use sodium free spices and herbs to season foods. 2. Rinse off canned foods (rinse canned beans, corn, peas etc.). 3. Purchase “low-sodium”, “no salt added” or “sodium free” products. 4. Avoid adding extra salt to food. References Cool it down: five water-rich foods to keep you hydrated. Eat Right. http://www.eatright.org/public/slideshow.aspx?id=6442470873#6. Accessed October 4, 2013. DASH diet: healthy eating to lower your blood pressure. Mayo Clinic. http://www.mayoclinic.com/health/dash-diet/HI00047/NSECTIONGROUP=2. Updated May 15, 2013. Accessed October 4, 2013. Drinking enough water. WebMD. http://www.webmd.com/a-to-z-guides/drinking-enough-water-topicoverview?page=2. Updated January 27, 2011. Accessed October 13, 2013. Gropper SS, Smith JL. Water and Electrolytes. In: Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism. 6th ed. Belmont, CA: Wadsworth; 2013. Home remedies for high blood pressure that really works. Health clop. http://www.healthclop.com/homeremedies-high-blood-pressure/. Revised October 1, 2013. Accessed October 14, 2013 McGuire M, Beerman KA. The Major Minerals and Water. In: McGuire M, Beerman KA. Nutritional Sciences: From Fundamentals to Food. 3rd ed. Belmont, CA: Wadsworth; 2013. Soong J. What counts as water? How to stay hydrated. WebMD. http://www.webmd.com/parenting/features/healthy-beverages. Revised September 9, 2011. Accessed October 10, 2013.. The urinary system. Napa Valley College. http://www.napavalley.edu/people/briddell/Documents/BIO%20105/_START_HERE_CH26_LECTURE.pdf. Accessed October 14, 2013.
