intro to physiology - body fluids Flashcards
fluid balance
fluid intake and output are balanced (homeostasis can occur)
fluid intake
water intake via drinking/eating, water enters blood and mixes in with rest of water stores
fluid output
water output via kidneys, lungs, faeces, sweat, skin (not just as sweat)
constituents of body fluids
electrolytes and non-electrolytes
electrolytes
charged ions dissolved in water
-Na+
-K+
-Ca^2+
-Cl-
-proteins (colloids) negatively charged in solution
non-electrolytes
uncharged
-glucose
is blood a constituent of body fluid ?
no, blood cells do not dissolve so are not considered part of body fluid
Na+
plasma: 142 mOsmol/L
interstitial: 139 mOsmol/L
intracellular: 14 mOsmol/L
K+
plasma: 4.2 mOsmol/L
interstitial: 4.0 mOsmol/L
intracellular: 140 mOsmol/L
Ca^2+
plasma: 1.3 mOsmol/L
interstitial: 1.2 mOsmol/L
intracellular: 0 mOsmol/L
Cl-
plasma: 106 mOsmol/L
interstitial: 108 mOsmol/L
intracellular: 4 mOsmol/L
protein
plasma: 1.2 mOsmol/L
interstitial: 0.2 mOsmol/L
intracellular: 4 mOsmol/L
plasma and interstitial fluid values very similar
due to free movement
interstitial fluid and intracellular fluid values very different
due to regulated movement
despite different compositions, the osmolarity of intracellular and interstitial fluid is roughly the same (iso-osmotic)
therefore push/pull of water is balanced
cations (+ve)
-Na+
-K+
-Mg^2+
anions (-ve)
-Cl-
-HPO4^2-
-H2PO4^-
-HCO3^-
-protein
within fluid compartment…
ionic charge balance is EQUAL, despite the no. of ions differing
movement of substances within body fluids
-conc. gradients
-equilibrium
-passive transport
-active transport
passive transport
-simple diffusion
-facilitated diffusion
-osmosis
active transport
-Na+/K+ pump
-bulk transport
diffusion
-chemical gradient: movement from high to low conc
-electrical gradient: movement from +ve to -ve charge or vice versa
electrochemical gradient
balance between electrical and chemical gradients
active transport
-transport of substances against conc. gradient
-requires energy in form of ATP
-specific carrier proteins
Na+/K+ pump
-present on all cells
-maintains unequal conc. of Na+ and K+ across the cell membrane
-Na+ constantly pumped out in exchange for K+ to maintain electrical gradient across membrane
-Na+ higher outside, K+ higher inside
importance of Na+/K+ pump
-cells contain lots of solutes, causing water to move into the cell by osmosis, eventually bursting the cell
-HOWEVER, this is prevented by use of the Na+/K+ pump
-energy is used to pump 3 Na+ out and 2 K+ in, thus balancing the osmotic pressures
-hence, at rest, Na+ conc. is higher outside and K+ is higher inside
primary active transport
DIRECT use of ATP to transport against conc. gradient
(e.g. Na+/K+ pump)
secondary active transport
INDIRECT use of ATP to set up a gradient
(e.g. Na+/glucose co-transporter
Na+/glucose co-transporter
-low intracellular Na+ conc. is maintained by Na+/K+ pump
-when Na+ enters the cell, it takes glucose inside with it, effectively AGAINST its conc. gradient
-important in intestines and kidneys for glucose (re)absorption
osmosis
net rate of diffusion of water across a semi-permeable membrane from a region of high water conc. to low water conc.
when does osmosis occur ?
if the solute is too large to cross the membrane, water moves in order to adjust the conc. of the solute
iso-osmotic
equal conc. of solutes so equal push-pull of water (ICF osmolarity = ECF osmolarity)
osmotic pressure (π)
the amount of pressure required to stop movement of water
Van’t Hoff’s law
π = CRT
where:
C= conc. of solutes (osmoles/L)
R= molar gas constant (8.314 JK-1mol-1)
T= absolute temp. (310K at normal body temp.)
osmolarity
osmolar conc. of a solution is measure in osmoles (osmolarity)
osmolarity for non-electrolytes (e.g. glucose)
osmolarity (osm/L) is EQUAL to the molarity (mol/L)
-Mr of glucose = 180
-therefore, 180g glucose in 1L water gives a 1M (1mol/L) solution
-which is therefore also a 1osm/L solution
osmolarity for electrolytes (e.g. ions)
osmolarity (osm/L) is the molarity MULTIPLIED by the no. of ions in solution
-1M (1mol/L) NaCL = 2 ions
-therefore, 1osm/L x 2 = 2osm/L
tonicity
-describes what happens to cells placed in solution
-a measure of effective osmolarity
-dependent on both osmolarity and whether solutes can enter/exit the cell
iso-tonic
same osmolarity as plasma
major contributors to ECF osmolarity
Na+ and Cl- ions
major contributor to ICF osmolarity
K+ ions
major difference between plasma and interstitial fluid (ISF)
protein levels are LOW in ISF
plasma proteins create…
colloid osmotic pressure (oncotic pressure) so that the plasma (282) has a slightly higher osmolarity than ISF (281), plasma is HYPERtonic to ISF, thus pulling water INTO plasma
(important in preventing loss of blood fluid vol.)
HYPOtonic: conc. less than blood
used for dehydration (pushes water into cells)
HYPERtonic: conc. more than blood
used for hyponatraemia (draws fluid into vascular compartment)
ISOtonic: conc. most like blood
normal saline (0.9% NaCl), used after blood loss (expands blood vol.)
