Water and the Major Minerals Chapter 12
Water and the Body Fluids • Water constitutes 50-60% of adult body weight • Body composition: ↑ LBM, ↑ water • Females, obese people, elderly ↓LBM • Why them? adipose has lower % water • Water is 75% of LBM
Water and the Body Fluids • Carries nutrients and waste products • Maintains structure of large molecules • Participates in metabolic reactions • Serves as a solvent for minerals, vitamins, aminos, glucose, enzymes, etc • Acts as a lubricant and cushion for joints, amniotic sac, eyes • Aids in regulation of body temperature (sweat) • Maintains blood volume
Water Balance and Recommended Intake • Cellular fluids • Intracellular fluid • Extracellular fluid • Interstitial fluid • Intravascular fluid • Homeostasis- balanced state • Hypothalamus- brain center that controls water balance
Fluid between the cells (intercellular or interstitial) Cell membrane Nucleus Fluid within the cell (intracellular) Fluid (plasma) within the blood vessels (intravascular) Blood vessel
Water Balance and Recommended Intake • Water intake • Influenced by thirst and satiety • Dry mouth, hypothalamus, and nerves • Thirst response lags behind the body’s need for water- don’t wait for thirst before you drink • Dehydration symptoms- see chart • Water intoxication • Symptoms- confusion, convulsion, death
Maybe it’s Not Dementia • Signs and Symptoms of Dehydration • Signs and symptoms of dehydration, like those of many other treatable health conditions, can be virtually identical to senile dementia symptoms, age dementia symptoms and Alzheimers symptoms. Correcting dehydration can allow an older person to return to a full and normal life.
Maybe it’s Not Dementia • The most common signs and symptoms of dehydration include persistent fatigue, lethargy, muscle weakness or cramps, headaches, dizziness, nausea, forgetfulness, confusion, deep rapid breathing, or an increased heart rate. Dehydration is a very serious condition, more than most people realize. Since seniors often have a reduced sense of thirst,dehydration is one of the most frequent causes of hospitalization after age 65.
Case Study Mr. R is an 85 y/o man with advanced dementia who was sent to the ER from his skilled nursing facility for non-responsiveness since the morning nursing shift started about 8 hours ago. The remainder of his past medical history is unknown. Aside from his mental status, his physical exam is remarkable for a HR of 110↑and BP of 100/50. Labs include the following: Na 164↑ (136-144)Cl 126↑ (98-107) BUN 50↑ (10-20) Glucose 98 (70-99) Hct .85↑ (0.42-0.52) K 4.8 (3.5-5.0) HCO3 28 (22-29) Cr 2.6↑ (0.4-1.2)
Criteria for Clinical Diagnosis of Dehydration • For a clinical diagnosis of dehydration to be made, the following minimal criteria must be present: • Suspicion of increased output and/or decreased intake • At least two physiological or functional signs or symptoms suggesting dehydration (e.g., dizziness, dry mucous membrane, functional decline) • A BUN/creatinine ratio of >25:1 ORorthostasis (defined as a drop in systolic blood pressure >20 mmHg on a change in position) OR a pulse of >100 beats/minute OR a pulse change of 10-20 beats/minute above baseline with a change in position
Water Balance and Recommended Intake • Sources • Water • Beverages- less sugary is better • Foods with moisture in them • Condensation reactions • Oxidation of energy-yielding nutrients • Water Dietary Reference Intakes for various groups
Water Loss • Bare minimum excretion each day is ~ 2 cups or 500 mL urine to carry waste • How water is lost • Vapor from lungs, respiratory rate • Sweat from skin, temperature, humidity • Loss in feces • High-sodium (>2400 mg/d) in diet requires additional water to maintain homeostatic salinity (prevent hypernatremia)
More Precise Water Needs • Generally adults need approximately 1 ml of water for 1 kcal of consumed energy, although this amount changes and it depends on sweating, exercise intensity, and can reach up to 1.5 ml/kcal. Water losses in organism also increase during long-lasting illness, vomiting, diarrhea, fever and burn injuries. • Adequate Intake is set for total water, including food
Water Balance and Recommended Intake • Basic health effects • Meet bodily needs • Protect against urinary stones & constipation • Concentration, alertness, short-term memory • 2 qts(L)/d based on typical 2,000 kcal/d diet • Type of water • Hard water has Ca2+ and/or Mg2+ • Soft water has Na+ and/or K+
Tonicity in relation to [Na+] • Hypertonic: ECF with a higher salt concentration than normal body cells so that the water is drawn out of the cells by osmosis to make it isotonic • Isotonic: Solution having the same osmotic pressure [Na+] as blood • Hypotonic: ECF with a lower salt concentration than normal body cells so that water flows into the cells by osmosis to make the ECF more isotonic
Blood Volume and Blood Pressure • Kidneys are central to blood volume and pressure maintenance • Kidney takes orders from: • Antidiuretic hormone (ADH, vasopressin) • Renin • Angiotensin • Aldosterone
A nephron (a working unit of the kidney). Each kidney contains over one million nephrons. Glomerulus Blood vessel 1) Blood flows into the glomerulus, and some of its fluid, with dissolved substances, is absorbed into the tubule. 1 (1) Capillaries of glomerulus Kidney Ureter Tubule Pelvis Bladder 2) Then the fluid and substances needed by the body are returned to the blood in vessels alongside the tubule. 2 (2) To the body Renal artery 3) The tubule passes waste materials on to the bladder. (3) Renal vein To the bladder Kidney, sectioned to show location of nephrons The cleansing of blood in the nephron is roughly analogous to the way you might clean your car. First (1) you remove all your possessions and trash so that the car can be vacuumed. Then (2) you put back in the car what you want to keep and (3) throw away the trash.
Low volume/pressure (thick ECF) • Hypothalamus stimulates pituitary gland to release ADH • Water-conserving hormone • Stimulates kidneys to reabsorb water (conserve water, decrease urinary output) • Also triggers thirst to pour water into body • Drink water + retain water = higher blood volume, but isotonic blood is priority
Blood Volume and Blood Pressure • Kidney cells release Renin • Another water-conserving hormone • Enzyme released by kidney cells when blood pressure is low • Kidneys reabsorb sodium • Water retention follows sodium absorption • Angiotensin • Renin hydrolyzes angiotensinogen to angiotensin I • Convert to active form – angiotensin II
Blood Volume and Blood Pressure • Aldosterone • Released from adrenal glands • Release stimulated by angiotensin II • Signals kidneys • Excrete potassium • Retain sodium • Retain water
The kidneys respond to reduced blood flow by releasing the enzyme renin. The hypothalamus responds to high salt concentrations in the blood by stimulating the pituitary gland. Renin Renin converts angiotensinogen From the liver to angiotensin I. Angiotensin I The lungs, kidneys, and brain activate angiotensin I to angiotensin II. Angiotensin II Angiotensin II causes the blood vessels to constrict, raising pressure. Angiotensin II stimulates release of aldosterone from the adrenal glands and ADH from the pituitary gland. Aldosterone ADH Aldosterone signals the kidneys to excrete potassium, which causes the blood vessels to constrict. Aldosterone signals the kidneys to retain sodium, increasing blood volume. ADH signals the kidneys to retain water, which increases blood volume.
Fluid and Electrolyte Balance • Fluid balance • Two-thirds inside the cells • One-third outside the cells • Dissociation(separation) of salt into electrolytes • Sodium – cation [Na+] • Chloride – anion [Cl-] • [Na+] [Cl-] in solution conduct electricity
Chemical symbols: •K = potassium •P = phosphorus •Mg = magnesium •S = sulfate •Na = sodium •Cl = chloride Outside the cells Cell membrane K Mg Na S P Cl Within the cell Key: Cations Anions Blood vessel
Fluid and Electrolyte Balance • Electrolytes attract water • Water molecules have net charge of zero • Water follows electrolytes • Electrolytes predominantly outside of cell • Sodium and chloride • Electrolytes predominantly inside of cell • Potassium, magnesium, phosphate, sulfate • Selectively permeable membranes
Cl– Na+ Na+ Cl– The negatively charged electrons that bond the hydrogens to the oxygen spend most of their time near the oxygen atom. As a result, the oxygen is slightly negative, and the hydrogens are slightly positive (see Appendix B). In an electrolyte solution, water molecules are attracted to both anions and cations. Notice that the negative oxygen atoms of the water molecules are drawn to the sodium cation (Na+), whereas the positive hydrogen atoms of the water molecules are drawn to the chloride ions (Cl–).
A B A B A B Water can flow both ways across the divider, but has a greater tendency to move from side A to side B, where there is a greater concentration of solute. The volume of water becomes greater on side B, and the concentrations on side A and B become equal. Now additional solute is added to side B. Solute cannot flow across the divider (in the case of a cell, its membrane). With equal numbers of solute particles on both sides of the semipermeable membrane, the concentrations are equal, and the tendency of water to move in either direction is about the same. Stepped Art
Dietary Salt and Water Balance Salt attracts water to dilute it, increasing volume, hence pressure
Fluid and Electrolyte Balance • Proteins regulate fluid movement • Attract water • Transport proteins in cell membranes • Passage of ions across cell membranes • Sodium-potassium pump • Regulation of fluid and electrolyte balance • Two sites • GI tract • Kidneys
Fluid and Electrolyte Imbalance • Causes of electrolyte imbalance • Prolonged vomiting or diarrhea • Heavy sweating • Burns • Traumatic wounds • Some medications • An imbalance can result in a medical emergency
Fluid and Electrolyte Imbalance • Solutes lost depend on why fluid is lost • Vomiting or diarrhea – sodium • Tumor development – potassium • Replacing lost fluids and electrolytes • Plain cool water and regular foods • Special replacement fluids like ORT • ½ c water, 4 tsp. sugar, ½ tsp. salt
Acid-Base Balance • Regulation of acidity • Narrow pH range to avoid life-threatening consequences • Denaturation of proteins like enzymes for rxn’s, hemoglobin to oxygenate tissues • Concentration of hydrogen ions • High hydrogen concentration [H+]–acidic • Low hydrogen concentration [H+] –basic
Normal and abnormal pH ranges of blood pH of common substances 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Basic Concentrated lye 8.00 Death Alkalosis Household ammonia Baking soda 7.45 Pancreatic juice Normal Blood 7.35 pH neutral Water Milk Urine Coffee Acidosis Orange juice Vinegar 6.8 Lemon juice Gastric juice Death Battery acid Acidic
Acid-Base Balance • 3-system body defense against pH fluctuation • Buffers in blood • Bicarbonate • Carbonic acid • Respiration in lungs • Excretion in kidneys • Bicarbonate
pH Regulation by Lungs • Use energy → • H+ released • pH↓ as H2CO3↑ • respiration rate↑ • H2CO3↓ from • CO2 excretion↑ • until there’s homeostasis