fluid electrolyte

• Body fluid


  Substance, usually a liquid, that is produced by the body and consists of water and dissolved solutes
• Body fluid compartments


  • Intracellular fluid (ICF)
  • Extracellular fluid (ECF)
• Intracellular fluid (ICF)


  • Two-thirds of total body fluid, the fluid within cells
• Extracellular fluid (ECF)


  • One-third of total body fluid, outside cells and includes all other body fluids
• Components of extracellular fluid (ECF)

  • Interstitial fluid (80% of ECF)
  • Blood plasma (20% of ECF)
  • Lymph
  • Cerebrospinal fluid
  • Synovial fluid
  • Aqueous humor
  • Vitreous body
  • Endolymph
  • Perilymph
  • Pleural fluid
  • Pericardial fluid
  • Peritoneal fluid
• Plasma membrane


  • Selectively permeable barrier that allows some substances to cross but blocks the movement of other substances
• Blood vessel walls


  • Divide the interstitial fluid from blood plasma, only capillaries are thin and leaky enough to permit exchange of water and solutes
• Fluid balance


  When the required amounts of water and solutes are present and are correctly proportioned among the various compartments
• Water makes up 45-75% of total body mass, depending on age, gender, and amount of adipose tissue</b>
• Infants have the highest percentage of water, up to 75% of body mass
• Lean adult males have about 60% water, lean adult females have about 55% water
• Processes allowing exchange of water and solutes among body fluid compartments

  1. Filtration

  2. Reabsorption

  3. Diffusion

  4. Osmosis
• Osmosis is the primary means of water movement between intracellular fluid and interstitial fluid
• Fluid balance is closely related to electrolyte balance
• Sources of body water gain

  • Ingested liquids (1600 mL)
  • Moist foods (700 mL)
  • Metabolic water (200 mL)
• Routes of body water loss

  • Urine (1500 mL)
  • Insensible perspiration (400 mL)
  • Sweat (200 mL)
  • Exhaled water vapor (300 mL)
  • Feces (100 mL)
• Dehydration


  Decrease in volume and increase in osmolarity of body fluids
• Thirst center


  • Area in the hypothalamus that governs the urge to drink
• Decreased blood volume


  Decreased blood pressure
• Increased blood osmolarity


  Stimulates osmoreceptors in hypothalamus, increases thirst
• Antidiuretic hormone (ADH)


  Hormone that promotes water reabsorption in the kidneys, decreasing urine output
• Increased blood osmolarity


  Increases ADH release
• Decreased blood volume or pressure

  Increases ADH release
• Aldosterone


  Hormone that increases sodium reabsorption in the kidneys, conserving fluid volume
• Atrial natriuretic peptide (ANP)

  Hormone that promotes sodium and water excretion in the urine, decreasing fluid volume
• Increased blood volume


  Increases release of ANP
• Movement of water between body fluid compartments

  1. If extracellular fluid becomes hypertonic, water moves from cells into extracellular fluid by osmosis, causing cells to shrink

  2. If extracellular fluid becomes hypotonic, water moves from extracellular fluid into cells by osmosis, causing cells to swell
• Increase in osmolarity of extracellular fluid


  Can occur after eating a salty meal, causes net movement of water from cells into extracellular fluid, can lead to cell shrinkage and neurological issues if prolonged
• Decrease in osmolarity of extracellular fluid

  Can occur after drinking a large volume of water, causes net movement of water from extracellular fluid into cells, can lead to cell swelling and neurological issues if severe (water intoxication)
• Solutions given for intravenous or oral rehydration therapy (ORT) include a small amount of table salt (NaCl)
• Enema


  Introduction of a solution into the rectum to draw water (and electrolytes) into the colon osmotically, increases peristalsis to evacuate feces
• Excessive use of enemas, especially in young children, increases the risk of fluid and electrolyte imbalances
• Extracellular fluids (plasma, interstitial fluid)


  • Contain many protein anions, which are largely impermeable to capillary membranes
  • Responsible for the blood colloid osmotic pressure
• Intracellular fluid


  • Most abundant cation is K+
  • Most abundant anions are proteins and phosphates (HPO4^2-)
  • Sodium-potassium pumps maintain high intracellular K+ and high extracellular Na+
• Milliequivalents per liter (mEq/L)


  Units used to compare the charge carried by ions in different solutions, gives the concentration of cations or anions
• For ions with a single positive or negative charge, the number of mEq/L is equal to the number of mmol/L
• For ions with two positive or negative charges, the number of mEq/L is twice the number of mmol/L
• Functions of ions in the body

  • Control osmosis of water between fluid compartments
  • Help maintain acid-base balance
  • Carry electrical current for action potentials and graded potentials
  • Serve as cofactors for enzyme activity
• Sodium (Na+)


  Most abundant cation in extracellular fluids, helps maintain osmotic balance and acid-base balance
• Chloride (Cl-)


  Most abundant anion in extracellular fluids, reabsorption is linked to sodium reabsorption