Body Fluid Compartments & Homeostasis Flashcards
Main Function of Kidney
Regulate volume and composition of body fluid within narrow limits
How to compartmentalize body fluid
1) Intracellular Fluid
2) Extracellular Fluid
3) Other- lymph, CSF, humors of eyes, serous fluid, GI secretion
60-40-20
- 60% of BW is total Body water
- 40% BW (or 2/3 TBW)= ICF
- 20% BW ( or 1/3 TBW)= ECF
ECF
- 1/4 of ECF= plasma
- 3/4 of ECF= interstitial fluid
Significance of Plasma
-only fluid that can be acted on directly to control volume and composition of interstitial fluid and ECF
Extracellular Fluid Importance
- intermediary btw cells and external environment
- H20 exchange btw ICF and external must go through ECF
Third Spacing
- too much fluid shift from intravascular into interstitial area
- fluid lost from intravascular space
- due to pulmonary edema, trauma, burns
Normal: all fluid contained in intravascular, intracellular, interstitial space
ECF vs ICF (3)
1) Proteins in ICF can’t permeate enveloping membranes to leave cells
2) active Na-K pump in all cells
3) Na+ is primary ECF cation
k+ is primary ICF cation
- Cl- is next in ECF
Electrolytes ( vs. nonelectrolytes, significance)
Nonelectrolytes:
- covalent bond
- no electrical charge
- glucose, lipids, urea
Electrolytes
- dissociates into ions in water
- Mg+, Na+, Cl-, k+
- have ability to cause fluid shift
Na+ Osm
135-147 mEq/L
Cl- Osm
95-105 mEq/L
K+ Osm
3.5-5.0 mEq/L
HCO3- Osm
22-28 mEq/L
Ca2+ Osm
8.4-10 mg/dL
Pi osm
3.0-4.5 mg/dl
anion gap
8-16 mEq/L
Total Serum protein
6 -7.8 g/dl
albumin
3.5-5.5 g/dl
globulin
2.3-3.5 g/dl
Creatinine
0.6-1.2 mg/dl
Glucose
70-110 mg/dl
Urea Nitrogen (BUN)
7-18 mg/dl
Serum Osm
285-295 mIsm/kg H2O
Blood
- content
- average blood volume
- Disturbances in plasma
- ECF= plasma (60%)
- ICF= RBC (40%)
- average blood volume= 7% ( 5 liters)
- ECF volume loss=> increased total plasma protein (concentration
- ECF volume gain => decreased total plasma protein ( dilution)
Hematocrit
- definition
- amount in women and men
- Disturbances in hematocrit
- fraction of blood in RBC
- Men= 0.4
- F= 0.36
- anemia=0.10
- ECF volume loss=> increased hematocrit (concentration)
- ECF volume gain => decreased hematocrit ( dilution)
- ICF volume loss=> decrease hematocrit (shrinkage of RBCs)
- ICF volume gain=> increased hematocrit (swelling of RBCs)
Gibbs- Donnan Effect
- gradient
- permeable to what
1) Protein particles create a oncotic gradient favoring water into cell
2) Negative charge of protein favor movement of charges into cell
- generate both osmotic and electrochemical gradient across membrane
- Permeable to ion
- impermeable to large proteins
How does our body counter Gibbs-Donnan? What happens when effects not countered?
If not countered-> IC protein would influx water into cell=. swell and death
Counter by:
- Na/K Atpase pump
- maintain high sodium concentration outside cell
- protects cells from swelling and rupturing
- prevent excessive inward movement of water
Two factors that make free fluid movement possible
1) Water molecules diffuse through capillary walls faster than blood
2) Pressure difference inside and outside of vessels (capillary filtration pressure)
Hydrostatic Pressure
- blood pushing against walls of capillary
- forces fluids and solutes through the capillary walls into interstitial fluid
Filtration
capillary blood pressure> plasma colloid osmotic pressure
- fluid leaves capillaries and enter interstitial fluid
Absorption
Capillary blood pressure< plasma colloid osmotic pressure
-water returns to capillaries
Plasma colloid osmotic pressure (in relation to albumin)
- osmotic pulling of albumin in intravascular space brings water into blood vessels
Edema
- definition
- causes (2)
- types of edema
- swelling bc of interstitial fluid volume
Causes
1) changes in capillary hemodynamics (starling forces) => increased filtration
(Normal= 3L)
- affected by plasma, Na+, water
2) Renal Retention of dietary Na+ and water expansion of ECF volume
- inappropriate renal fluid retention
- high BP
- non-pitting edema: swollen cells due to ICF volume
- pitting edema- increase interstitial fluid volume
Starling forces (4)
1) Capillary Hydrostatic pressure (BP)- forces fluid out of capillary to interstitial space
2) Capillary (plasma) oncotic pressure- fluid from interstitial space into capillary
3) Interstitial hydrostatic pressure- fluid back into capillary
4) interstitial oncotic pressure- fluid out of capillary into interstitial space
Types of Tonicity (3)
-Normal NaCl concentration
Normal NaCl concentration= 0.85%
- think of it out of cell!
1) Isotonic= NaCl conc equals 85%
- equal movement of water in and out of cell
2) Hypertonic- NaCl conc greater than 85%
- net movement of water OUT of cell => cell shrink
3) Hypotonic ( sweating)= NaCl conc less 85%
- net movement of water INTO cell=> cell swell
Replacement Therapy (2)
1) Crystalloids
- organic/inorganic salts dissolved in sterile water
- exm 0.9% NaCl, lactated Ringer’s , D5W ( dextrose in water)
- does not cross plasma membrane (stays in ECF)
2) Colloids
- large molecules that can’t pass through semipermeable membrane
- stay in INTRAvascular compartment
Van’t Hoff’s Law
- calculate osmotic pressure of a solution
Serum Osmolarity equation
2Na + Glucose/18 + BUN/2.8
Changes in volume depends on…
changes in Na+ balance
Changes in Na+ concentration and osmolarity depends on…
changes in H20 balance
Dehydration
- causes (2)
- types
1) decreased water intake
2) increased fluid loss
Hypernatremic
Hyponatremic
Normal osmolality 300 mOsm/kg
Normal Serum sodium 150 mEq/L
Hypotonic (hyponatremic) dehydration (5) and clinical presentation
SWEATING
1) loss of sodium> loss of water in ECF (serum sodium level below 130-135 mEq/L) 2) sodium conc in ICF greater than ECF 3) Fluid Shift ECF -> ICF 4) Serum Na and Osmolality LESS than normal 5) Swelling, hypovolemia
symptoms: edema, depression, confusion, weakness, anorexia, diarrhea
- HTN, tachycardia, decreased urine output
Hypertonic (Hypernatremic) dehydration
1) loss of water> loss of sodium in ECF (serum sodium above 147-150 mEq/L) 2) sodium conc in ECF greater than ICF 3) Fluid Shift ICF -> ECF 4) Serum Na and Osmolality LESS than normal
symptoms: edema, HTN, weakness, thurst, decreased urine output, confusion, coma
Fluid Shift disturbances (2,3)
1) Volume contraction- decrease ECF volume, blood volume, and BP
2) Volume expansion -
increase ECF volume, blood pressure, edema
1) Isosmotic= no change in body fluid osmolarity
2) hyperosmotic= body fluid osmolarity is increased
3) hyposmotic= body fluid osmolarity is decreased
Darrow- Yannet Diagrams
- effects of clinical conditions on osmolality and volume of ECF and ICF
Darrow- Yannet Diagram: Iso-osmotic volume contraction
- acute fluid loss conditions (hemorrhage, diarrhea, vomiting)
- Decrease ECF volume
- no changes in osmolality and ICF volume
Darrow- Yannet Diagram: Hyper-osmotic volume contraction
-hypotonic fluid loss (dehydration, diabetes insipidus, alcoholism)
- Decrease ECF and ICF volume
- Increase Body Osmolality
Darrow- Yannet Diagram: iso-osmotic volume expansion
-isotonic saline
- Increase ECF volume
- no change in osmolality and ICF volume
Darrow- Yannet Diagram: Hypo-osmotic volume expansion
-Hypotonic fluid (excess water drinking)
- Increase in ECF and ICF volume
- Decrease in body osmolality
EC and IC volume changes significantly due to (5)
1) excess ingestion/ renal retention of water
2) dehydration
3) IV infusion of different types of solution
4) loss of fluid in GI
5) sweating
