Guyton Chapter 25

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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


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