Water and Electrolyte Balance Flashcards
Total body water (TBW) is about 42L. ______ of body weight in healthy adult males. ______ of body weight in healthy adult females.
60%, 50%
________ have the highest percentage of TBW until the age of ______
infants, 2
TBW declines with ________
aging
TBW ______ as fat percentages ______
declines, increase
2/3 of TBW is ____________ which consists of fluid contained with all of the cells in the body. What is it regulated by?______% of body weight/28L
intracellular fluid volume (ICFV)
It is regulated by proteins and organic compounds in ICF and solutes that move between compartments.
40%
1/3 of TBW is ____________, all fluids outside of the cell. This is broken down into 3 additional categories which are what?
Extracellular Fluid Volume (ECFV)
- Interstitial fluid volume = 3/4 ECFV
***15% of body weight/10L - Plasma/Vascular volume = 1/4 ECFV
***4% of body weight/3.5L - Transcellular volume = typically inconsequential/1L
***Increases in this compartment called third-spacing
When looking at electrolytes/water we can only measure ________ most of the time.
plasma (1/4)
What are fluid requirements?
Usually require 35 ml/kg/day or 100mL per 100 kcal metabolized
Dissolving and eliminating metabolic wastes
Loss of fluid is relatively stable. It increases during which factors?
- fever states
- diarrhea
- sweating a lot
- certain renal diseases
- significantly increased respiratory rate
- wounds
- increases in metabolic rate
What are sources of fluid gain?
liquid, in food, water generated in metabolic processes
What are sources of fluid loss?
renal (obligatory urine output), GI tract, insensible losses (skin, lungs)
___________ is the primary barrier to movement between compartments. ________ substances pass directly by dissolving into the lipid layer.
cell membrane, lipid soluble
Water passes through by ________ through ______ protein channels
osmosis, aquaporin
Ions require active transport such as the _____________
Na+/K+ ATPase
Osmosis
movement of water across a semi-permeable membrane
Generates a pressure called osmotic pressure
Diffusion
movement of particles along a concentration gradient (charged or uncharged particles)
-Molecules are in constant motion
-Move from area of higher to lower concentration
Transfer of water between vascular space and interstitium occurs at a capillary level. It is controlled by 4 forces:
- Capillary filtration pressure/capillary hydrostatic pressure: pushes water out of capillary and into interstitial space
- Capillary colloidal osmotic (oncotic) pressure: pulls water back into capillary
- Interstitial fluid (hydrostatic) pressure: opposes movement of water out of capillary (pushing water into interstitium)
- Tissue colloidal osmotic pressure/interstitial oncotic pressure: pulls water out of capillary into interstitial spaces
_________ is the unit of measure for the amount of a substance. It is used as a way to express amounts of reactants and products in chemical reactions.
moles.
i.e. 2 H2 + 02 = 2 H20 (2 moles of H2 and 1 mole of O2 will react to form 2 moles of water)
What are osmoles?
-number of moles of solute that contribute to the osmotic pressure of a solution
-Depends on dissolution in solution
i.e. NaCl dissolutes in serum creating 1 mole of Na+ and 1 mole of Cl- where as glucose does not dissolve and remains one mole.
What is osmotic activity?
the force that nondiffusable particles exert in pulling water from one side of a membrane to another
-Expressed in osmolarity/osmolality
-Influenced by number of particles NOT size or weight
Osmolarity/osmotic concentration
measure of solute concentration, number of osmoles of solute per liter of solution
Osm/L
Allows the measurement of the osmotic pressure of a solution
Determines how the solvent will diffuse across a semipermeable membrane
Osmolality
measures the body’s water/electrolyte balance
Osm/kg
_______ is often used for fluids outside the body
osmolarity
slide 10 (look at notes section)
Tonicity
the effect that the osmotic pressure of a solution with impermeable solutes exerts on cell size due to water movement across the cell membrane
Determined by effective solutes that cannot penetrate the cell membrane
i.e. glucose
In water balance regulation, what does the need for increased volume stimulate?
stimulates thirst mechanism to increase water ingestion. Conscious sensation of the need to drink fluids high in water content
ADH Increases in water reabsorption by the kidneys controlled primarily by ___________: Antidiuretic hormone
ADH/Vasopression
ADH is produced by the ______ and released by ________
hypothalamus, posterior pituitary
ADH controls ________ of water by kidneys
reabsorption
What are the 2 vasopressin receptors ?
V1 in smooth muscle causes vasoconstriction
V2 in tubular cells of collecting ducts increases permeability of the collecting duct to water by influencing aquaporins
What is ADH regulation stimulated by?
- Osmoreceptors that sense increases in serum osmolality
- Stretch receptors that sense decrease in blood volume
- Increased glucose levels in the absence of insulin (insulin allows glucose to enter osmoreceptors to make it ineffective osmole)
- Nausea, severe pain, surgery, trauma, and certain drugs (pain medications, anesthetics, and nicotine)
What is ADH inhibited by?
- Decreases in serum osmolality
- Increases in blood volume
- Pregnancy and ovulation (resets the osmotic threshold and can increase ADH catabolism)
- Alcohol
- Certain drugs
ADH is stimulated by?
Increases in ECF osmolality
Decreases in ECF volume to maintain fluid balance
Increased ADH
influences distal tubule/collecting ducts to concentrate urine (water reabsorbed)
Decreased ADH
sodium is reabsorbed but water is not, so large amounts of dilute urine is produced
The amount of sodium excretion is determined by ____________
intravascular volume
How does the RAAS system regulate water balance?
Renin-Angiotensin-Aldosterone System:
Renin is released by kidney in response changes in:
1. Arterial pressure
2. GFR
2. Decreased wall tension in afferent arteriole
3. Decreased salt to distal tubule
Once in circulation converts angiotensinogen to Angiotensin I
Angiotensin I converted to Angiotensin II
Angiotensin II acts on renal tubules to increase sodium resorption, constricts renal blood vessels (decreases GFR to reduce filtered Na and reabsorb more Na)
Regulates Aldosteroneproduced by the adrenal cortex
Aldosterone acts on collecting tubules to increase sodium reabsorption and increase potassium elimination
Nonelectrolytes
substances that do not dissociate into ions
i.e. glucose and urea
Electrolytes
substances that dissociate in solution to form charged particles
Ions form when electrolytes dissolve. What are the 2 types?
- Cations have a positive charge (Na+)
Due to attraction forces, cations are always accompanied by negatively charged ion - Anions have a negative charge (Cl-)
In the Extracellular space, _______ is the main electrolyte
Na+
Electrolytes in the ECF
-Large amount of sodium, chloride
-Moderate amounts of bicarbonate
-Very little potassium, magnesium, calcium and phosphate
Electrolytes in the ICF
large numbers of negatively charged intracellular proteins
-Large amounts of potassium
-Moderate amount of magnesium
-Small amounts of sodium, chloride, bicarbonate and phosphate
-Minimal or absent calcium
__________ is the most abundant cation in the body. Mostly found in the _______ and scant amounts in the _______
NA+, ECF, ICF
NA+ enters the body through the ___________
GI tract
What eliminates NA+?
Kidneys (90%)
GI tract (10%)
Skin (insensible)
What are the roles of sodium?
-Regulates extracellular and vascular volume
-Na+ and attendant anions (Cl- and HCO3-) account for 95% of osmotic activity in the cell
-As sodium bicarbonate it helps regulate acid-base balance
-Contributes to the function of nervous system as a current carrying cation
_______ are extremely efficiency in regulating sodium
Kidneys
Limited Sodium
reabsorbs almost all sodium leading to dilute urine
Excess sodium
excretes more sodium leading to concentrated urine
What are the systems that regulate sodium?
- SNS- responds to changes in arterial pressure and blood volume by adjusting glomerular filtration rate, regulates tubular reabsorption of sodium and renin release
- RAAS system- released by kidney in response to arterial pressure changes, through the pathway leads to aldosterone release which acts on collecting tubules to increase sodium reabsorption and increasing potassium elimination
- Atrial Natriuretic Protein (ANP) released by atria in response to atrial stretch and overfilling, leading to increased sodium excretion by the kidney
_________Second most abundant cation in the body. Major cation in the _________. ________ concentration is much less.
Potassium, ICF, ECF
90% of potassium is contained in body __________. Stores as related to ______ and _______. 70% is in _________ (declines with muscle mass)
cells, body size, muscle mass, muscle cells
Potassium enters the body through the ___________
GI tract
Potassium is normally eliminated by
Kidneys (90%)
Stool and sweat (10%)
What is the role of potassium?
- Distribution between ECF and ICF regulates resting electrical membrane potentials
**Excitability of nerve and muscle cells
**Contractility of skeletal, cardiac, and smooth muscle - Acid-base balance
- Contributes to reactions necessary to transform carbohydrates into energy, glucose into glycogen, amino acids to proteins
Renal mechanisms conserve or eliminate potassium. How is this done?
-Potassium filtered at glomerulus, reabsorbed at the proximal tubule and loop of Henle then secreted into collecting tubules for elimination
-Aldosterone secretion from adrenal is strongly controlled by potassium levels, if present it transports sodium back into blood and secretes potassium for elimination in the urine
-Transcellular buffers that remove potassium from the serum or release it into the serum as needed
-Potassium/Hydrogen ion exchange in collecting tubules
**High potassium leads to hydrogen being reabsorbed and decreasing pH
**Low potassium leads to hydrogen is excreted and pH increases
Hypertonic solution
: increased concentration
Higher osmolality
Water moves out of cell and cell shrinks
Isotonic solution
equal concentration
Equal osmolality
Water remains constant, cell is unchanged
Hypotonic
decreased concentration
Lower osmolality
Water moves into cell and cell swells
Water balance regulation is controlled by the thirst centers in the __________. How does it regulate thirst?
- Cellular dehydration caused by increase in serum osmolality
- Decrease in blood volume
- Angiotensin II (back up for typical thirst stimulators)
Sodium ECF value
134-145
Sodium ICF value
10-14
Potassium ECF value
3.5-5.0
Potassium ICF value
140-150
Chloride ECF value
98-106 mEq/L
Chloride ICF value
3-4 mEq/L
Bicarb ECF value
24-31 mEq/L
Bicarb ICF value
7-10 mEq/L
