Fluid Dynamics and Cell Membrane Quiz

Chlorine atom: unstable, atomic weight (A.W) can be 35.5 or 36, atomic number (A.N) is 17

Isotope formation: bomb an atom with neutron to create a radioactive isotope, increases atomic weight, same atomic number, becomes radioactive

Electrolytes: electrically charged particles, can be ions, atoms, large radicals, or molecules

Osmotic activity: depends on the number of particles (ions) in a solution, affects the concentration of electrolytes in plasma and interstitial fluid

Plasma: contains predominantly Na+ and Cl- ions, osmotic activity is 300 mOsm/l, anion gap is 16 mmol/l

Cellular ion transport: cells actively extrude Na+, K+ passively enters, prevents Na+ and Cl- diffusion

pH: determined by the relative number of H+ and OH- ions, affects the reaction of fluids

Acids and bases: acids yield H+ ions, bases take up H+ ions, strong acids readily give up H+, weak bases less readily accept H+

Buffers: substances that regulate pH by neutralizing excess H+ ions

Water: adults have approximately 42 liters for men and 55 liters for women, distributed between intracellular and extracellular spaces, plasma, and transcellular fluids, moves freely between compartments to maintain osmolarity equilibrium.

Colloid pressure of plasma proteins (25mmHg) draws fluid into the capillaries.

Hydrostatic pressure pushes fluid out of the capillary to the interstitial compartment.

The cell membrane acts as a barrier between the extra and intracellular space.

Na+ is the main extra-cellular cation while K+ is the main intracellular cation.

Both cations help control the osmolarity across the cell membrane and hence control water shift between the two spaces.

Osmolarity of plasma or ECF is calculated from the formula: Osmolality (mOsmol/kg) = 2(Na+ + K+) + glucose + urea level (mmoI/L)

Normal water balance: Water input includes exogenous (drink 1500, food 1000) and endogenous (metabolic water 300-500 cc/dy).

Water output includes urine (1500/day), insensible water loss (perspiration 600-800 ml, respiration 400 ml, in the faces ~ 100 ml), and sweat (variable).

Insensible water loss is necessary for regulation of body temperature, and the kidneys are the only organs that regulate water loss.

The kidneys filter about 170 liters of water every day, 80% of which is reabsorbed in the proximal tubules, and 20% is reabsorbed in the distal tubules except for the amount passed as urine.

Hydration results in more dilute urine, while dehydration results in a small volume of concentrated urine.

Hydration is controlled by two hormones: ADH and aldosterone.

ADH is secreted by the posterior pituitary under the influence of nervous impulses originating in the supraoptic nucleus of the hypothalamus, and is stimulated by osmoreceptors sensitive to changes in the osmotic pressure of plasma crystalloids.

Aldosterone absorbs water through the reabsorption of sodium.

Water depletion can be caused by lack of intake, diabetes insipidus, unreplaced losses, or increased output.

Water deficit results in a decrease in volume in all body compartments and stimulation of osmoreceptors, leading to an increase in ADH production and increased water resorption from the kidneys.

Clinical picture of water depletion includes intense thirst and weakness, decreased tissue turgor, and oliguria with high specific gravity of urine.

Management of water depletion includes estimating the deficit, treating with water by mouth, and replacing water with I.V. glucose 5% in severe depletion.

Water excess can be caused by excessive administration of water to sodium-depleted patients, over-infusion of 5% glucose I.V, colonic washout with water instead of saline, or T.U.R. syndrome.

Water excess results in an increase in volume of all fluid compartments and hypo-osmolality, leading to a decrease in osmoreceptors and ADH production, and an increase in renal water excretion.

Clinical picture of water excess includes minimal symptoms such as increased urine volume, body weight, and decreased serum Na+ concentration and hematocrite, or more severe symptoms such as brain edema, nausea, vomiting of clear fluid, and convulsions and coma.

Management of water excess includes restricting water intake for mild cases, and forced diuresis with mannitol, dialysis, and I.V. 100-250cc I.V. 5% sodium chloride solution for severe cases.

Electrolyte metabolism involves different inorganic salts that are dissociated into positively charged cations and negatively charged anions.

Under normal conditions, the number of cations (Na+, K+) must equal the number of anions (Cl, HCO3-, Phosphate, sulphate, proteins, and organic acids).

The average daily intake of sodium is 1 mmoL/kg, equivalent to 500 ml of 0.9% normal saline.

Hyponatremia (sodium and water deficiency) can be caused by abnormal GIT loss, ECF loss, excessive sodium loss in urine, or hypovolaemia and adrenocortical insufficiency, among other causes.