Guyton Chapter 25
Markers for plasma
125-I-albumin, 31-Cr, RBC, Evan's blud
Total water intake
2300/day
Adult blood voume
7% of body weight, about 5L
Total body water% of an infant
70%
Makers for total body water
D2O (deutreium), 3H20 (radioactive water), antipyrine
Isosmotic Volume Expansion
ECF gains isotonic solution ECF osmolality remains unchanged No movement of fluid across membranes ECF ↑ | ICF - | Osmolarity - | Hct ↓ | Plasma Protein ↓ EX: isotonic fluid infusion
Hyperosmotic Volume Expansion
ECF gains more salt than water (hyperosmotic) ECF osmolarity is increased Fluid moves across memrane from ICF to ECF ECF ↑ | ICF ↓ | Osmolarity ↑ | Hct ↓ | Plasma Protein ↓ EX: high NaCl diet
Hypoosmotic Volume Expansion
ECF gains more water than salt (hypoosmotic) ECF osmolarity is decreased Fluid moves from ECF to ICF ECF ↑ | ICF ↑ | Osmolarity ↓ | Hct - | Plasma Protein ↓ EX: SIADH
Isosmotic Volume Contraction
ECF looses isotonic solution (same water and salt) ECF osmolality does not change, no driving force to move fluid across membranes ECF ↓ | ICF - | Osmolarity - | Hct ↑ | Plasma Protein ↑ EX: diarrhea, bleeding
Hypoosmotic Volume Contraction
ECF looses more salt than water (hypertonic loss), remaining ECF is hypoosmotic ECF osmolarity is decreased Fluids move across membrane from ECF to ICF ECF ↓ | ICF ↑ | Osmolarity ↓ | Hct ↑ | Plasma Protein ↑ EX: adrenal insufficiency (addisons or long term steroids)
Changes that increase capillary filtration rate
Increased capillary filtration coefficient Increased capillary hydrostatic pressure decreased plasma colloid osmotic pressure
Two major fluid compartments
Intracellular (28L) & Extracellular (14L)
Filtration equasion
Kf x (Pc - Pif - πc + πif)
Hematocrit levels
Men - 0.4 Women - 0.36 Severe Anemia - 0.1 Polycythemia - 0.65
Markers for ICF
No markers exist TBW - ECF
Markers for ISF
No markers exist TBW - Plasma
Total body water % of a female
Normal - 50% Lean - 60% Obese - 45%
Total body water % of a male
Normal - 60% (about 42L) Lean -70% Obese - 50%
Calculate osmotic pressure
Osmotic Pressure=CRT C-concentration (osm/L) R-gas constant (62.3 if OP=mmHg) T-Kelvin degrees - 273 + C (310 degrees) OP - 19300mmHg/Osm If C = mOsm/L OP = C x 19.3mmHg
tonicity
Osmotic pressure offered because of the interplay between dissolved solute and a membrane dependant on the concentration of solutes
Divisions of the extracelluar fluid
Plasma - 3L Interstitial Fluid - 11L
Markers for Blood Volume
Plasma Volume/ (1 - Hct)
Edema
The presence of excess fluid in the body tissue
Extracellular Edema causes
abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries failure of the lymphatics to return fluid from the interstitium back to blood
calculate volume
amount/concentration
Water intake regulation
by intrinsic mechanisms (thirst) and by habitat
Increased total interstitial fluid
causes high compliance
Transcellular Fluid
compartment that includes synovial, peritoneal, pericardial, cerebrospinal fuild, and intraocular spaces about 1-2L
Calculate amount
concentration x volume
distribution across capillaries
determined by hydrostatic and colloid osmotic forces
Distribution across cell membranes
determined by osmotic forces (mainly from electrolytes)
Conditions prone to causing intracellular edema
hyponatremia depression of metabolic systems of tissues (hypothyroidism) lack of adequate nutrition to cell (MI) inflamation of tissues (increased permibility)
Causes of extracellular edema
increased capillary pressure (retention of Na & H2O, high BP, vasoconstriction, decreased arteriolar resistance) Decreased plasma proteins ( loss of protein in urine, wound/burn, failure to produce proteins) Increased capillary permeability (immune reaction, toxin, infection, vit deficiency, ischemia, burn) blockage of lymph return (Cancer, infection, surgery, vessel abnormality)
How is water added to the body
ingestion - about 2100 ml/day synthesized as result of oxidation of carbohydrates - about 200ml/day
Output mechanisms
kidneys, lungs, feces, sweat, skin (average 2300)
osmosis
net diffusion of water across a selectively permeable membrane from a region of high water concentration to one that has a lower water concentration
What decreases total body water percent
obesity & age
Rate of diffusion
rate of osmosis
Hypertonic
solution has a higher concentration of solutes (higher osmolarity) cell will shrink
Hypotonic
solution has a lower concentration of solutes (lower osmolarity) cell will expand
Isotonic
solutions have the same osmolarity cell will neither shrink nor swell
Markers for extra cellular fluid
sulfates, mannitol, insulin, 22Na (radioactive sodium)
Osmolality
the osmolal concentration of a solution (amount of stuff in a solution)
Osmole
total number of parties in a solution is measured in osmoles 1 osm = 1 mole of solute
Insensible water loss
we are not consciously aware of - through resp and skin (700ml/day)
safety factors that prevent edema
1) low compliance of the interstitum when interstitial fluid pressure is negative (3mmHg) 2) Increaed lymph flow 10-50x (7mmHg) 3) washdown of interstitial fluid protein concentration (7mmHg)
Calculate Concentration
Amount/Volmune
Hyperosmotic Volume Contraction
ECF looses more water than salt (hypotonic lost), remaining ECF is now hyperosmotic. ECF Osmolarity is increased Fluids move across cell membrane, water flows from ICF to ECF ECF ↓ | ICF ↓ | Osmolarity ↑ | Hct - | Plasma Protein ↑ EX: sweating, fever, DI, Dehydration
