Chapter 26 Fluids, Electrolytes, Acid-base
Chapter 26 Fluids, Electrolytes, Acid-base
Water
* 50 – 75 % of body weight
* universal solvent
* ICF = intracellular fluid 2/3 of body water
* ECF = extracellular fluid
* blood plasma
* tissue fluid interstitial fluid
* lymph vessels lymph
* meninges CSF
* joints synovial fluid
solutes
* electrolytes dissociate into ions
* non-electrolytes
* glucose
* proteins
* lipids
water flow
* exchange between ECF’s and ICF
* continuous mixing of body fluids
* water movement :
* osmosis
* towards high solute concentration
* towards high osmolarity (all solutes)
* any change in solute concentration leads to water flow
* filtration
water volumes
* water intake = water output
* 1o intake = beverages
* also food metabolic water
* 1o output = urine
* also sweat respiratory
* constant osmolality 285 – 300 mOsm / L
hypothalamic regulation
* osmoreceptors - osmolarity of blood
* ( osmolarity ( conserve water get water
* ( osmolarity ( lose water
* oral receptors - dry mouth
* less filtration means less saliva
renal regulation
* juxtaglomerular cells ( plasma volume
* renin-angiotensin stim hypothalamus thirst centers
need more water
* hypothalamus
* thirst get water behavior change
* ADH conserve water
* kidney
* make less urine
* ( filtration
* concentrate urine
* ADH ( H20 reabsorbed
* aldosterone doesn’t change osmolarity
too much water
* hypothalamus
* ( thirst , ADH
* kidney
* makes more urine
* ( filtration
* ANP ( urine , but doesn’t change osmolarity
Electrolytes
* dissociate in water
* ions + ions = cations - ions = anions
* functions: osmolarity acid – base balance tissue / organ functions
cations
* Na+ sodium ECF nerve, muscle osmolarity
* K+ potassium ICF nerve, muscle
* Ca++ calcium bones, teeth nerve (NT release) muscle contraction cardiac conduction blood clotting
* Mg++ magnesium bone ATP
anions
* Cl- chloride ECF HCl
* HCO3- bicarbonate buffer system CO2 transport
* HPO4-- phosphate ICF bones, teeth DNA, RNA, ATP phosphate buffer
* proteins - buffers plasma osmolarity
sodium
* most abundant cation in ECF
* 142 mEq/L
* accounts for most osmolarity of plasma and ECF
* ECF concentration rarely changes
* water follows salt
* no Na receptors have been found
* regulation tied to osmolarity blood pressure (volume)
sodium regulation
* kidney reabsorbs 90% Na+ w/o hormonal control
* aldosterone increases Na reabsorption
* stim: renin-angiotensin increased K+ concentration in ECF ACTH (minimal)
* ANP decreases Na reabsorption inhibits ADH
* sympathetic = pressure diuresis afferent arteriole dilation ( GFR increase urine and Na loss
sodium regulation – part 2
* estrogen like aldosterone ( Na rebsorb “retain water”
* progesterone blocks aldosterone Na excreted
* corticoids ( Na and water reabsorption edema
potassium
* main cation ICF
* affects resting membrane potential
* high K+ in ECF cells depolarize lose excitability
* acidosis H+ cause K+ to leave cell hyperpolarization
potassium balance
* renal control
* 10-15 % lost in urine regardless of need
* K+ secreted in collecting ducts
* ( in ECF / plasma ( secrete
* aldosterone ( K+ secreted
* stim: ( K+ in ECF / plasma renin-angiotensin
* Addison’s hyperkalemia
* diuretics possible hyperkalemia
calcium
* functions bones , teeth clotting secretions 2nd messenger nerve muscle contraction
* hypocalcemia tetany
* hypercalcemia inhibits neurons (( Na permeability)
calcium regulation
* blood levels important, not bone
* renal PCT reabsorption (diffusion)
* PTH parathyroid hormone ( blood Ca
* bone ( Ca to blood
* small intestine ( Ca absorption
* kidney ( reabsorption (DCT)
* calcitonin ( blood Ca
* ( Ca deposition to bone
Acid – Base , pH
* pH = parts hydrogen
* acid increases H+ proton donor
* base decreases H+ proton acceptor
* in blood :
* increased pH alkalosis > 7.45
* decreased pH acidosis < 7.35
the pH problem
* pH ~ free H+ ions
* most bodily functions are affected by pH changes !
* H+ concentration affects:
* protein functions (3D shape depends on H bonds)
* enzymes
* Na+ and K+ concentrations
acid – base homeostasis
* buffer systems fastest weak, short term
* respiratory mechanisms slower (few minutes) stronger 75% effective
* renal mechanism slowest (several hours) strongest long term
buffer systems
* buffer = weak acid or weak base
* buffer system = weak acid + weak base
* strong acid + buffer ( weak acid
* strong acid + weak base ( weak acid
* strong acid + weak base ( weak acid + salt
* strong base + buffer ( weak base
* strong base + weak acid ( weak base
* strong base + weak acid ( weak base + water
3 buffer systems
* bicarbonate system
* blood and ECF
* phosphate system
* kidney , ICF
* protein system
* ICF
bicarbonate buffer system
* bicarbonate ion HCO3-
* weak acid carbonic acid H2CO3
* weak base sodium bicarbonate NaHCO3
* strong acid + weak base ( weak acid + salt
* HCl + NaHCO3 ( H2CO3 + NaCl
* strong base + weak acid ( weak base + water
* NaOH + H2CO3 ( NaHCO3 + H2O
phosphate buffer system
* weak acid sodium dihydrogen phosphate Na H2PO4
* weak base sodium monohydrogen phosphate Na2HPO4
* strong acid + weak base ( weak acid + salt
* HCl + Na2HPO4 ( Na H2PO4 + NaCl
* strong base + weak acid ( weak base + water
* NaOH + Na H2PO4 ( Na2HPO4 + H2O
protein buffer system
* amino acid = weak acid and a weak base
* amino group = weak base NH2
[pic]
* carboxyl = weak acid COOH
[pic]
respiratory mechanism
* ( respiratory rate causes ( blood pH
* ( blood pH ( ? respiratory rate
* ( blood pH ( ? respiratory rate
* compensates for metabolic causes of pH imbalance by rate of CO2 exhaled
renal mechanism
* “ultimate acid-base regulatory organ”
* can buffer any pH imbalance lactic acid uric acid ketones
* H+ and HCO3- secretion / reabsorption
* low blood pH ( H+ excretion ( HCO3- reabsorption
* hi blood pH ( H+ excretion ( HCO3- reabsorption
* wide range of urine pH
acid-base imbalances
* respiratory caused by respiratory problem
* respiratory acidosis poor CO2 exchange respiratory disease
* respiratory alkalosis hyperventilation
* metabolic caused by non-respiratory problem
* metabolic acidosis diarrhea lactic acid (exercise) ketosis (diabetes)
* metabolic alkalosis antacids constipation
* kidney diseases
note :
* respiratory mechanism
* will compensate for metabolic and renal causes
* can’t compensate for respiratory causes
* renal mechanism
* will compensate for metabolic and respiratory causes
* can’t compensate for renal causes
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