Fluid, Electrolyte and Acid-Base Balance Chapter 27 Fluid, Electrolyte and Acid-Base Balance

≠ Fluid basics ECF ICF interstitial fluid blood plasma cytoplasm ~1/3 ~2/3 different ion compositions different fluid compartments same osmotic concentration

Fluid basics all homeostatic mechanisms monitor the ECF, not the ICF 2. receptors can’t monitor [ion] but can monitor: plasma volume osmotic concentration 3. cells cannot actively move H2O “water follows salt”

Fluid basics 4. [water] and [electrolyte] will rise if gains exceed losses will fall if losses exceed gains

hormone basics 1. ADH (antidiuretic hormone) high blood [osmotic] release H2O conservation in kidney stimulates thirst

hormone basics 2. Aldosterone released in response to: rising [K+] falling [Na+] renin release [Na+], Cl-, H2O reabsorption in kidney

hormone basics 3. Natriuretic hormones released cardiac/brain cells block ADH release block aldosterone release [Na+] and H2O lost to urine

Fluid movements ECF interstitial fluid plasma hydrostatic pressure osmotic pressure colloid hydrostatic pressure

Fluid movements fig 21-12

rapid movement between ICF and ECF is called fluid shift Fluid movements ECF ICF interstitial fluid plasma rapid movement between ICF and ECF is called fluid shift osmotic pressure colloid hydrostatic pressure

Fluid shift ECF ICF If [osmotic]  hypertonic H2O

Fluid shift ECF ICF If [osmotic]  hypotonic H2O

Fluid shift net loss of water dehydration sweating, vomiting, diarrhea ICF and ECF become more concentrated hypernatrimia ADH, renin secretion  thirst, … give hypotonic fluids (H2O)

Fluid shift net gain of water into ECF into ICF  reduce ADH secretion  increase fluid loss

Fluid shift net gain of water water excess (overhydration) drinking a lot injection of hypotonic solution kidney or liver failure excess ADH production  hyponatrimia effects on CNS H2O intoxication

Electrolyte balance electrolyte balance: will affect H2O balance will affect cell functions Na+ most common electrolyte balance problems less common more serious K+

Electrolyte balance Na+ too much  ADH,  retain H2O renin-angiotensinogen  retain Na+, H2O too little  ADH,  lose H2O ANP, BNP  lose Na+, H2O

Electrolyte balance K+ 98% is in ICF balance in ECF is small maintained by secretion in kidney

Electrolyte balance K+ too much severe cardiac arrhythmias too little  and 

100 Keys pg. 1007 “Fluid balance and electrolyte balance are interrelated. Small water gains or losses affect electrolyte concentrations only temporarily. The impacts are reduced by fluid shifts between the ECF and ICF, and by hormonal responses that adjust the rates of water intake and excretion. Similarly, electrolyte gains or losses produce only temporary changes in solute concentration. These changes are opposed by fluid shifts, adjustments in the rates of ion absorption and secretion, an adjustments to the rates of water gain and loss.”

100 Keys pg. 1019 “The most common and acute acid-base disorder is respiratory acidosis, which develops when respiratory activity cannot keep pace with the rate of carbon dioxide generation in peripheral tissues.”