Osmosis and Osmotic Pressure

What is diffusion?

movement of solute down its concentration gradient through the membrane

What is osmosis?

movement of a solvent down its concentration gradient through membrane

What is the 60/40/20 rule?

60% of body weight is total body water

40% of body weight (2/3 total body water) is intracellular fluid

20% of body weight (1/3 of total body water) is extracellular fluid

What is osmolarity?

number of solute particles in the solution (mOsm/L)

What is osmolality?

number of solute particles per kg of water (mOsm/kg)

What is osmotic pressure?

pressure gradient created by difference in solvent concentrations on either side of membrane, and the pressure needed to stop water movement across a semipermeable membrane

What is tonicity?

describes the concentration of non-permeable solutes in an external solution relative to the inside of the cells

What are the three different types of tonicity?

isotonic, hypertonic, hypotonic solutions

What is an isotonic solution?

solution has same solute concentration outside the cell as inside the cell

What is the result of an isotonic solution?

no net movement of water

What is a hypertonic solution?

solution has higher solute concentration than inside the cell

What is the result of hypertonic solutions?

water leaves the cell, cell shrinks

What is a hypotonic solution?

solution has lower solute concentration outside the cell than inside the cell

What is the result of a hypotonic solution?

Water enters the cell, cell swells

What determines osmotic pressure?

concentration of solute, number of dissolved particles, temperature, membrane permeability

What pressures regulate capillary fluid exchange?

• capillary hydrostatic pressure

• capillary oncotic pressure

• interstitial hydrostatic fluid pressure

• interstitial oncotic pressure

What is capillary hydrostatic pressure?

Pressure that forces fluid and dissolved molecules through the capillary pores and into ISF

What is capillary oncotic pressure?

Plasma proteins draw fluid from ISF into the blood

What is interstitial hydrostatic fluid pressure?

pressure to force fluid into the capillary from the interstitial fluid

What is interstitial oncotic pressure?

pulls fluid from capillary into the interstitial fluid

What is the serum osmolality equation?

2[Na] + [Blood urea nitrogen]/2.8 + [glucose]/18

Hypovolemic hyponatremia clues and GI losses?

GI Losses: vomiting, diarrhea, diuretics, burns

Clues: tachycardia dry mucosa, orthostasis

What is euvolemic hyponatremia?

normal total body sodium, increased total body water

What could cause euvolemic hyponatremia?

too much antidiuretic hormone, adrenal insufficiency, psychogenic polydipsia, hypothyroid

What are the cues for euvolemic hyponatremia?

urine Osm greater than 100 mOsm/kg, no edema

What is hypervolemic hyponatremia?

increased total Na+, but even more water

Congestive heart failure, liver cirrhosis, and nephrotic syndrome are all consistent with what type of hyponatremia?

hypervolemic

What are cues for hypervolemic hyponatremia?

edema, ascites

Hyperglycemia and an osmolar gap (toxins) indicates what?

elevated serum Osm