Transcript FLUID, ELECTROLYTES, ACID/BASE BALANCE

FLUID, ELECTROLYTES, ACID/BASE
BALANCE - PHYSIOLOGY {ST1}
BY RANJEET RAMAN
 I. Fluids of the Body
 A.Fluid Compartments
 1.intracellular fluid compartment - within the cells
themselves (about 25L or 40% of body weight)
 2.extracellular fluid compartment outside the cells (about
15L or 20% of body weight) a.plasma - fluid portion of the
blood (3 L) b.interstitial fluid - fluid bathing all cells and
tissues of body (12 L)
 Total body water volume = 40L or about 60% of body
weight
 B.Fluid Composition
 1.nonelectrolytes - no electrical charge (glucose)
2. electrolytes - dissociate into ions (NaCl) 3.milliequivalents
per liter (mEg/L) - measure of number of charges in 1 liter
of solution
 concentration of ion (mg/L)
 mEq/L = x# charges per ion
 atomic weight of ion
 C.Extracellular vs. Intracellular Fluids
 1.extracellular - high Na+ and high Cl 2.intracellular - low Na+ and low Cl-
 D.Fluid Movement between Compartments
 1.plasma -> interstitial -> plasma & lymphatics 2.Oxygen,
glucose -> into cells 3.Carbon Dioxide, nitrogenous wastes> out of cells 4.ECF <====> ICF depends on NaCl in the
ECF
 II.Water Balance
 A.Overview of Water Balance
 1.intake - 90% ingested water; 10% metabolic water
2.output - 60% urine; 28% lungs/skin (mucosa); 12%
sweat/feces 3.water need - trigger thirst & release of ADH
 B.The Thirst Mechanism
 decrease in plasma volume OR increase in osmolarity à
excitation of hypothalamic thirst center à sensation of
thirst C. Regulation of Water Output
 1.obligatory water loss - lungs, sweat, feces 2.regulation of
water - kidneys (ADH -> Na+)
 D.Disorders of Water Balance
 1.dehydration - water loss -> water intake a.bleeding, burns,
sweating, diuretics 2. hypotonic hydration - too much water
or Na+ 3.edema - accumulation of water in interstitial space
 III.Regulation of Sodium (Na+) Balance
 A.Sodium (Na+) - 90% of solutes in the ECF; most
important and prevalent of all electrolytes B. Aldosterone released by adrenal cortex (renin-angiotensin)
 1.released in response to:
 a.decrease in blood pressure
 b.decreased osmolality of filtrate
 c.sympathetic stimulation of juxtoglomerular cells
 2.function - increase Na+ reabsorption at distal tubule
 a.water will follow if ADH makes the distal tubule permeable
to water
 C.Baroreceptors
 1.located in carotid arteries and aorta
 2.respond to changes in stretch due to blood pressure
 a.blood pressure increases à
 hypothalamic stimulation à
 sympathetics to kidneys decrease à
 increased GFR (water removed)
 b.blood pressure decreases (same path as above) ----> ----> 
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---> lower GFR (water retained)
D.Antidiuretic Hormone (ADH)
1. released from the posterior pituitary
2.responds to osmoreceptors in the hypothalamus
a.decrease in osmo of ECF à
decreased release of ADH à
less permeability of distal tubule to water à more water
released into urine
 b.increase in osmo of ECF à
 increased release of ADH à
 more permeability of distal tubule to water à
 less water released into urine
 E.Atrial Natriuretic Factor (ANF)
 1.released by cell of heart atria under high B.P.
 2.reduces blood pressure and blood volume by INHIBITING
nearly all events that promote vasoconstriction and
Na+/water retention.
 F.Steroid Hormones
 1.estrogen - increases resorption of Na+ in distal convoluted
tubule 2.glucocorticoids (cortisol) - increases resorption of
Na+ in the distal tubules
 IV.Regulation of Potassium (K+) Balance
 A.Importance of K+
 1.K+ is primary CATION (+) within cells 2.K+
abnormalities cause changes in Resting Mem Pot (neurons,
cardiac muscle especially)
 B.Renal Control of K+ Levels
 1.10-15% constantly lost in urine
 2.most resorption occurs in Proximal Tubule 3.regulation changing amount SECRETED into urine in the collecting
tubules
 a.low K+ ----> less secretion (intercalated cells in collecting
tube can reabsorb more) b.high K+ -----> more secretion
 C.Factors Controlling K+ Secretion
 1.tubule cell intracellular K+ level - when low, secrete less;
when high, secrete more 2.aldosterone level - K+ secreted:
 Na+ reabsorbed a.increase aldosterone -> more K+
secretion b. decrease aldosterone -> less K+ secretion 3.pH
- K+ and H+ compete for antiport with Na+ a. lower pH
(high H+) -> less K+ secretion b. higher pH (low H+) ->
more K+ secretion
 V.Regulation of Calcium (Ca++) Balance
 A.Importance of Ca++
 1.bone is the "reservoir" of most Ca++ in the form of
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Calcium Phosphate (Ca++ with PO4-2)
2.primary physiological roles (already covered):
a.at the muscle and neuron synapse
b.essential for blood clotting process
c.very critical in heart rhythms
 B.Ca++ Regulation: Parathyroid Hormone (PTH) &
Calcitonin
 1.parathyroid hormone (PTH) - chief control when Ca++
begins to DECREASE too low
 a.bones - Ca++ and PO4-2 release to blood b.small intestine
activates Vitamin D which is essential for Ca++ resorption
c.kidneys - Ca++ reabsorbed (but PO4-2 excreted)
 2.calcitonin (thyroid gland) - released when Ca++ begins to
INCREASE too high
 a.inhibits Ca++ release from bone, increases actual
formation of Calcium Phosphate in bone