Body Fluids Flashcards
Fundamental principle of physiology?
At all levels of organisation, functional activities are directed at maintaining homeostasis
Characteristics of the ‘‘milieu intérieur’’?
Different from external environment, relatively constant under conditions of health
Most abundant single constituant of the body?
Water
Percentage of body water?
45 to 75%
Water is the medium in which…
solutes are dissolved, metabolic reactions take place
What accounts for the variations in body water between individuals?
Proportion of body fat
Physiological reference individual :
21 y/o 70kg white male
Someone who has more fat will have
a lower percentage in body water
Someone who has less fat will have
a higher percentage in body water
Body water percentage is important for
administering water-soluble medication
Body water is exchanged
between an individual and its environment AND internally between compartments
Water intake (oral fluid)
1.2 L
Water intake (food)
1.1 L
Water intake (from metabolism)
0.4 L
Water output (lungs+skin) can be referred to as
insensible output
Water output (lungs+skin+kidneys+stool) can be reffered to as
obligatory losses
Obligatory water losses
1.5 L
Normal water intake
2.7 L
Facultative water losses vary with…
water intake
(Insensible perspiration vs sweating)
Pure water
Insensible perspiration
(Insensible perspiration vs sweating)
Passive evaporation
Insensible perspiration
(Insensible perspiration vs sweating)
Entire skin surface
Insensible perspiration
(Insensible perspiration vs sweating)
Continuous
Insensible perspiration
(Insensible perspiration vs sweating)
Electrolyte solution
Sweating
(Insensible perspiration vs sweating)
Active secretion
Sweating
(Insensible perspiration vs sweating)
Sweat glands
Sweating
(Insensible perspiration vs sweating)
Heavy work/high temps
Sweating
Water turnover over 24h (adult)
3-4%
Water turnover over 24h (baby)
10%
Constant water volume helps maintain
Normal solute concentrations, normal blood volume and pressure
(Negative water balance vs water intoxication)
Reduced intake
Negative balance
(Negative water balance vs water intoxication)
Excessive loss from gut
Negative balance
(Negative water balance vs water intoxication)
Excessive sweating
Negative balance
(Negative water balance vs water intoxication)
Excessive loss in expired air (dry air at high altitudes)
Negative balance
(Negative water balance vs water intoxication)
Excessive loss in urine
Negative balance
(Negative water balance vs water intoxication)
Excessive intake
Intoxication
(Negative water balance vs water intoxication)
Renal system failure
Intoxication
Can body water compartments exchange water freely between them?
Yes
What are the two majors body compartments?
Intracellular fluid (ICF) and extracellular fluids (ECF)
What fraction of body water does ICF hold?
2/3
What fraction of body water does ECF hold?
1/3
What are the two minor subcompartments?
Interstitial fluid (ISF) and plasma
What percentage of body water does ISF hold?
15%
What percentage of body water does plasma hold?
5%
What are the two minor subcompartments and how much of ECF do they account for?
Lymph (1-2%) and transcellular fluid (<1-2%)
What is plasma?
The medium in which RBCs are suspended
What is an hematocrit (Ht)?
% of blood volume occupied by RBCs
What is the packed cell volume linked to?
Hematocrit
Normal hematocrit value?
45%
What is the true ‘‘milieu intérieur’’?
ISF
What does the lymphatic network filter?
ISF
Where does the lymphatic network converge?
Large veins of the chest
What kind of cells line the cavities in which transcellular fluids are secreted?
Epithelial cells
Do transcellular fluids have specialized functions?
Yes
What is the common method to determine the volume of body water compartments?
The indicator dilution method
What is the formula linked to the indicator dilution method?
V=Q/c
The four characteristics that lead to an indicator choice (indicator dilution method)?
Non-toxic, diffuses evenly, induce no change in distribution of water, easy to mesure
Indicator choice for volume of total body water?
Antipyrine, D2O, T2O
Indicator choice for volume of ECF?
Inulin, sucrose, mannitol
Indicator choice for volume of plasma?
Evan’s Blue
Two membranes an indicator has to pass through to reach the ICF (in order)?
Capillary wall, cell membrane
What do we have to account for when using the indicator dilution method in a clinical situation?
Amount of substance removed by metabolism and excretion
What do body fluids mainly consist of?
Aqueous solutions of inorganic ions with variable amounts of proteins
ICF is rich in which ions?
K+ and Mg2+
ECF is rich in which ions?
Na+ and Cl-
What is the concentration of plasma/ISF in NaCl?
0.9% (dilute sea water?)
What are the 3 artificial physiological solutions by croissant degree of complexity?
Physiological saline, Ringer’s solution, Locke-Ringer solution
Viability of cells depends on…
Relative constancy of the internal environment and exchanges with the internal and (ultimately) the external environment