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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