N 155 M 5.1 Fluid & E-Lyte Balance/Imbalance

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1. Homeostasis: Balance of fluid & e-lytes & acid/bases2. Body Water

a. 60% of a healthy adult’s wt. is waterb. Babies 70 -80% waterc. Women & elderly less water due to less muscle mass, adipose tissue

does not carry as much water as muscles3. Uses of water:

a. Medium for metabolic Rx in cellsb. Transport nutrients, wastes, & other substancesc. Lubricantd. Insulate & shock absorbere. One way to regulate & maintain body temp

4. Distribution of body fluidsa. Intracellular Fluid (ICF) fluid in the cellsb. Extracellualr fluid (ECF) fluid outside the cells

i. Intravascular fluid –fluid in vascular spaceii. Interstitial fluid –(75% of ECF) fluid around cells

iii. Lymph fluidiv. Transcellular fluid – cerebrospinal, pancreatic, pleural,

intraocular, biliary, peritoneal, synovial5. Composition of body fluids

a. Oxygenb. Dissolved nutrientsc. Excretory products of metabolism (CO2)d. Ions – charged particles

6. Ions: e-lytes, particles with charges capable of conducting electricitya. Cation – positive charge = Na+, K+, Ca++, Mg+b. Anions- negative charge = Cl-, SO4-, HCO3-, Hpo4-c. Measured in mEq/L, or mg/dL

i. mEq refers to the chemical combining power of the ion, the capacity for cations & anions to combine to form a molecule

N 155 M 5.1 Fluid & E-Lyte Balance/Imbalance

d. Labs measure e-lytes in IVF or ECFe. Major e-lytes in ECF – Na+, Cl-, HCO3-f. Smaller amt. e-lytes in ICF – K+, Ca++, & Mg+g. Major e-lytes in ICF – K+, Mg+, HPO4-, & SO4-2

7. Osmosisa. Osmosis: movement of water across a cell membrane, from less

concentrated solution to more concentrated solution –trying to equalize the number of particles on each side.

b. Solutes – substances dissolved in liquidi. Crystalloids- salts that dissolve readily into true solutions

(D5%W, 0.9% NS)ii. Colloids- substances such as large proteins that do not readily

dissolve into true solution (Blood products)c. Solvent – the component of a solution that can dissolve a soluted. Water is the solvent in the body

8. Solutes in the body are: e-lytes, oxygen, carbon dioxide, glucose, urea, amino acids, & proteins. Osmosis occurs when the concentration of solutes on one side of a selectively permeable membrane are higher than on the other side.

a. Osmolality: concentration of solutes in body fluids. The total solute concentration in a fluid compartment, measured as parts of solute/kg of water, or rather miliosmols/kg (mOsm/kg). Na+ biggest contributor to osmolality in ECF. (2 times the Na+ (sodium) level is about what your osmolality is)

b. Tonicity refers to osmolalityi. Isotonic: same osmolality as body fluids

ii. Hypertonic: higher osmolality as body fluidsiii. Hypotonic: lower osmolality as body fluids

c. Osmotic pressure: power of a solution to draw water across a semipermeable membrane. More solutes in a solution = higher concentration = higher osmotic pressure ---more of a draw for the water to cross and = dilute the solution, make it less concentrated.

N 155 M 5.1 Fluid & E-Lyte Balance/Imbalance

d. Plasma proteins exert an osmotic pressure called colloid osmotic pressure or oncotic pressure – pulling fluid in from the interstitial space to vascular space.

9. Diffusion: continual intermingling of molecules in liquids, gases, or solids due to random movement of the molecules.

a. Diffusion in the body: through thin membrane via the “split pores” of capillary membranes. Rate of diffusion dependent on the (a.) size of the pores, (b.) concentration of the solution (c.) temperature of solution

b. Larger molecules take more energy to move about and are slower.c. Molecules move from area of high concentration to area of lower

concentration (Down the pressure gradient)d. Higher temperatures increase the rate of movement & diffusion

10. Filtration: fluid & solutes move together across a membrane from one compartment to another, from higher pressure to lower pressure

a. Filtration pressure: pressure in the compartment that results in movement of fluid & substances dissolved in fluid out of the compartment.

b. Hydrostatic pressure is the pressure exerted by a fluid within a closed system on the walls of a container in which it is contained.

i. Hydrostatic pressure of blood is the force exerted by blood against the vascular walls. Fluids move from areas of greater pressure to the area of lesser pressure.

ii. Plasma proteins (albumin) exert an oncotic pressure that opposes hydrostatic pressure & holds fluid in the vascular space. When the hydrostatic pressure is greater than the oncotic pressure then water will seep out of the blood vessels.

11. Active Transport: movement of substances against the concentration (pressure gradient), substances move across a membranes from a less concentrated solution to a more concentrated one by active transport. Metabolic energy is used to do this ---ATP (Adenosine triphosphate).

a. Active transport—a substance combines with a carrier on the outside surface of the cell membrane (Hitchhiker) and they move to the

N 155 M 5.1 Fluid & E-Lyte Balance/Imbalance

inside surface of the cell membrane. Once inside they separate and the substance goes its merry way. A specific carrier is required for each substance, enzymes are required for active transport and energy is expended. Example –sodium potassium pump – moves sodium out of cell and K+ back in.