Exam 4 - Electrolytes 1 Flashcards
Total body water volume
40 L, 60% of body weight
Intracellular fluid volume (inside the cell)
25 L, 40% of body weight
Extracellular fluid volume
15 L, 20% of body weight
Interstitial fluid volume
outside of blood system and cell
12 L, 80% of ECF
Plasma volume (inside the blood system)
3 L, 20% of ECF
Water movement
water moves easily between COMPARTMENTS AND ACROSS MEMBRANES
Losing water through sweat and replacement
- water loss (sweating)
- sweat glands produce perspiration by capillary filtration
- blood volume and pressure drop: osmolarity rises
- blood absorbs tissue fluid to replace loss
- intracellular fluid diffuses out of cells to replace lost tissue fluid
How is water acquired in the body?
Preformed water and metabolic water
Preformed water
ingested in food and drink
Metabolic water
by-product of:
- aerobic metabolism
- dehydration synthesis
Dehydration
DECREASED blood volume and pressure
INCREASED blood osmolarity
Mechanisms of regulating water intake: osmoreceptors in hypothalamus are stimulated by:
- Angiotensin II (produced in response to decreased BP)
- increased ECF osmolarity
Mechanisms of regulating water intake: responses
- ADH produced
- CEREBRAL CORTEX is notified of conditions to create SENSE OF THIRST
- SALIVATION IS INHIBITED because sympathetic signals are sent to salivary glands (source of “dry mouth” when preparing to give a speech)
Long term inhibition of thirst
Rehydration of blood (decrease blood osmolarity)
Short term inhibition of thirst
Act quickly but only last for 30-45 minutes
- cooling and moistening of mouth
- distention of stomach and intestine
Routes of water loss
- urine
- feces
- expired breath
- sweat / cutaneous transpiration
Respiratory loss of water
increases w/ cold, dry air or heavy work
Perspiration loss of water
increases w/ hot, humid air or heavy work
Obligatory water loss
- breath
- sweat / cutaneous transpiration
- feces
- minimum urine output (400 mL/day)
Mechanisms of regulating water output
Controlling Na reabsorption
- as Na is reabsorbed or excreted, water follows
Action of ADH
- AQUAPORINS (membrane proteins in renal collecting ducts to channel water back into renal medulla) are synthesized in response to ADH
Mechanisms of ECF volume regulation
Increased blood pressure in right atrium > Increased ANH > increased Na excretion and increased water loss result in decreased BP
Decreased BP > kidney releases renin > Angiotensinogen > Angiotensin I > Angiotensin II > increased aldosterone secretion > increased Na and water reabsorption results in increased BP
What do kidneys compensate well for?
they compensate well for EXCESSIVE fluid intake, but not for INADEQUATE intake
(no matter how much fluid you overly take in, your body can maintain the same amount of around 5L)
Volume depletion (hypovolemia)
- Decreased total body water
OSMOLARITY NORMAL because FLUIDS AND ELECTROLYTES ARE LOST IN ROUGHLY EQUAL PROPORTIONS
How does hypovolemia occur?
- hemorrhage
- severe burns
- chronic vomiting
- diarrhea
Dehydration
- loss of RELATIVELY MORE WATER than solute
- decreased total body water
OSMOLARITY INCREASES
Sources of dehydration
- lack of drinking water
- diabetes
- profuse sweating
- diuretics
What are the most serious effects of hypovolemia and dehydration
- circulatory shock
- neurological dysfunction
- death
Volume excess
- both Na and water retained, ECF is ISOTONIC
- source includes aldosterone hypersecretions
Hypotonic over-hydration
- MORE WATER THAN Na RETAINED or ingested, ECF is HYPOTONIC
EX: drinking water instead of Gatorade after exercise
What are the most serious effects of volume excess and hypotonic over-hydration?
pulmonary and cerebral edema
Sequestration problems
Overall body volume is ok but fluid is not properly distributed among the compartments
most common form of sequestration problems
edema w/ fluid accumulation in the interstitial spaces
Other examples of fluid sequestration problems
Hematomas
- hemorrhage into tissues
- blood is therefore lost to circulation
Pleural effusions
- several liters of fluid may accumulate in some lung infections
Functions of Na
- membrane potentials
- accounts for 90-95% of OSMOLARITY of ECF
- Na-K pump creates a gradient for COTRANSPORT of other solutes (e.g. glucose) and also generates heat
- NaHCO3 has major role in buffering pH
Primary concern of Na homeostasis
excretion of dietary excess
- 0.5 g/day needed, typical diet has 3 to 7 g/day
Hormonal mechanisms that enhance dilution or excretion of Na
ADH
- released when Na level increases causing kidneys to reabsorb more water w/o retaining more Na
ANP (atrial natriuretic peptide)
- released when atria are stretched causing kidneys to excrete more Na and H20 thus decreasing Na and volume
Hypernatremia
plasma volume > 145 mEq/L
Frequent cause of hypernatremia
IV saline administrations
Hypernatremia effects/results
- water retention
- hypertension
- edema
Hyponatremia
plasma volume < 130 mEq/L
Hyponatremia effects/results
Excess body water (relative to sodium) as might occur in SIADH (syndrome of inappropriate antidiuretic hormone) - excessive release of ADH
