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State of equilibrium in the internal environment of the body, naturally maintained by adaptive responses that promote healthy survival.
- 50-60% in adult
- more in men (more lean body mass)
- less in elderly (less ""
- Infants: 70-80%
Two major fluid compartments in body
- Intracellular--intracellular fluid
- Extracellular--interstitial fluid
Function of water in body
- 1. Transporting nutrients, electrolytes, O2 to cells
- 2. Transporting waste away from cells
- 3. Regulation of body temp
- 4. Lubricates joints and membranes
- 5. Medium for food digestion
How much does water weigh?
1 liter of water = 2.2 lb or 1 kg
substances whose molecules dissociate, or split into ions, when placed in water
- Electrically charged particles
- Cations: positively-charged ions: sodium (Na+), potasium (K+), calcium (Ca+), magnesium (Mg+)
- Anions: negatively-charged ions: sodium bicarbonate (HCO3-), chloride (Cl-), phosphate (PO4-).
Main cations/anions in extracellular fluid
'"" in intracellular fluid?
- ECF= Na+, Cl-
- ICF= K+, PO43-
movement of molecules from area of high concentration to area of lower concentration. No energy required. Stops when equilibrium is reached. (ex: gases-oxygen, nitrogen, CO2 and urea). Membranes must be permeable to teh diffusing substance.
Simple diffusion (no energy required), from area of high to low concentrations, but requires carrier molecule to take place.
- Molecules move against the concentration gradient. Energy required.
- Ex: Sodium-Potasium Pump--maintains the difference in concentrations of Na+ outside cell and K+ inside cell with help from ATP. (Na+ moves out of cell and K+ moves into cell).
Movement of water between two compartments separated by semi-permeable membrane. Water can move freely, but solutes cannot. Water moves from area of low concentration of solute to area of high concentration (to balance solute concentration). Stops when equal or when hydrostatic pressure prevents more movement in.
- Measures the osmotic force of solute per unit of weight of solvent (mOsm/kg or mmol/kg). Describes fluids inside of body.
- Test typically used to evaluate the concentration of plasma to urine.
Normal plasma osmolality
- 275-296 mOsm/kg.
- Higher means concentation of particles is too great or that the water content is too little (water deficit)
- Value less mean too little solute for amount of water or too much water for the amount of solute (water excess).
Normal urine osmolality
100-1300 mOsm/kg depending on fluid intake and amoutn fo antidiuretic hormone (ADH) in circulation adn the renal response to it.
- Iso--same osmolality
- Hypo--Solutions in which teh solutes are less concentrated than the cells
- Hyper--solutions with solutes more concentrated than cells
- ECF adn ICF are isotonic normally.
- force wtihin a fluid compartment:
- In blood vessels, HP is the blood pressure generated by contraction of heart=
- decreases to 40 mm Hg at arterial end of capillary, only 10 mm Hg at venous end of capllary bed.
Major force that pushes water out of vascular system.
- Colloidal osmotic Pressure: osmotic pressure exerted by colloids in solution. Major colloid pressure in vascular system is protein. Proteins attract water, pulling fluid from tissue space to vascular space.
- Normally 25 mm Hg in plasma
Antidiuretic Hormone:synthesized in hypothalmus and stored in posterior pituitary gland. Regulates water balance.
Power of a solution to draw water. The more concentrated a solution, the more water it will draw--it has high osmotic pressure
Respiratory mechanisms to restore pH (acid/base balance)
- Lungs control body's carbonic acid supply via carbon dioxide retention or removal. When serum is too acidic (pH is low), lungs remove CO2 through raid, deep breathing. This makes less CO2 available for carbonic acid, which is used to raise pH, so the pH is .
- If to alkali (pH is high), lungs conserve CO2 with shallow respirations so more CO2 is available for NaHCO3 (sodium bicarbonate), which raises the pH.
To determine if respiratory or metabolic acidosis or alkalosis:
- 1. Determine pH (is it higher or lower than normal?)
- 2. Examine PCO2 and HCO3 values.
- If the PCO2 is affected, then it's respiratory.
- If the HCO3 is affected, then it's metabolic.
PCO2 normal values
- Normal= 35-45 mm Hg
- < 35 = too little acid (respiratory acidosis)
- > 45 = too much acid (respiratory alkalosis)
If respiratory, the renal system must compensate for abnormal pH (takes up to 3 days).
- Normal = 22-26 mEq/l
- <22 = too little base (metabolic acidosis)
- > 26 = too much base (metabolic alkalosis)
If metabolic, then respiratory system must compensate (faster)
If pH and only one value are abnormal.
If the pH and one ABG is abnormal, w/ the second ABG starting to change and the pH starting to move toward normal.
Occurs when pH has returned to normal range and both other ABGs are abnormal.
How do vital signs reflect info about fluid, electrolyte and acid/base balance?
- Temp-increased body temp increases loss of body fluids, hypernatremia, temps rise b/c less fluid for sweating. In uncomplicated fluid volume deficit, body temp decreases
- Pulse: tachycardia in fluid volume deficit. Dysrhythmias from K, Ca, Mg imbalances. Fluid status affects pulse volume
- REspiratory rate: alterations in breathing may be cause of acid-base imbalances or a compensation mechanism
- Blood pressure: rises and falls with fluid volume; affected by electrolytes. High sodium increases hypertension. High K and Mg may lower BP.