Body Fluids Flashcards
What is Homeostasis
Keeping constancy of internal environment within cells (human body), even if external environment changes
% of water in various tissues
skin = 70%
muscle = 75%
heart, liver, brain, kindey = 70-80%
bone = 25%
Fat (adipose tissue) = 10%
Lean body mass water content
what is it
Excludes water content of fat
What accounts for the large variation in water content in different individuals
Various fat levels in body create water % differences
Body water along the years
age male female
infant 65% 65%
10-18 59% 57%
18-40 61% 51%
40-60 55% 47%
>65 50% 45%
What makes body water change in male vs females and in both?
males: Have more testosterone which increases muscle mass (more water)
females: oestrogen during puberty = less water
both: Aging = more adipose tissue and muscles diminish, so water is lost
How to find body water
(Mass(kg) x % water)/100 =body water
in kg which can be put in L
How to calculate how much water-soluble medication you can administer
dosing = 10mg/7kg
find body water:
(mass x %H2O)/100
ex: (70kg x 60%)/100 = 42L
conversion body water into mL
ex: 42L = 42 000 mL
Find mass of medication:
mass of person x dosing
ex: 70kg x (10mg/7kg) = 100mg
Final concentration:
mass medication/ body water
100mg/42 000 mL
= 0.0024mg/mL
Important units prefixes
milli (m) = 10^-3
micro = 10^-6
nano (n) = 10^-9
pico (p) = 10^-12
Intakes to maintain water balance (with values)
oral fluid = 1.2L
oral intake as food =1.1L
Oxidative H2O from metabolism = 0.4L
total 2.7L
Outputs to maintain water balance (obligatory + facultative) and values
Obligatory: (always happen)
insensible: total 1.0L
lungs = 0.4L
skin = 0.5L (passive evaporation)
sensible:
Kidneys: urine = 0.5L
Stool: feces = 0.1L
Facultative
Urine = 1.2L
if more H2O is taken in, more urine is produced
Sensible loss: sweat (amount varies)
Total around 2.7L
Characteristics of insensible perspiration
Insensible perspiration
1. pure water
2. passive evaporation
3. entire skin (no need for sweat glands)
4. continuous and obligatory
Characteristics of sweating
- electrolyte solution
- active secretion
- from sweat glands
- activated by heavy work or high temp (non continuous)
Water turnover
over 24 hours
Adults: 3-4% of body weight
Infants: 10%
should only drink baby formula and breast milk because kidneys lose ions
Smaller body volume = water leaves more quickly
Types of negative water balance
- Reduced intake (normal is 1.5L everyday)
- Excessive loss from Gut (people die from dehydration because of diarrhea)
- Excessive sweating
- Excessive loss in expired air (air is dry at high altitudes = need to breath more, so more water lost from lungs)
5.Excessive loss in urine
Types of water intoxications
- Excessive intake (marathon runners that drink too much)
- Renal system failure
Physiological reference individual
21 years old white male
70kg => 60% body water
Body water compartments
total body water = 60%
Intracellular fluid = 2/3 of 60%
Extracellular fluid = 1/3 of 60%
volumes remain constant
dynamic equilibrium
Subdivisions of ECF
Major:
Plasma = 1/4 of ECF
Interstitial fluid = 3/4 of ECF
Minor:
Lymph around 1-2% of ECF
Transcellular fluid
Hematocrit (Ht)
percentage of blood occupied by RBC (erythrocytes)
Ht = (height of RBC column)/ (height of whole blood column)
ex: Ht = 45/100 = 45%
normally 45%
Lymphatic system
network of blind-ended terminal tubules
form larger lymphatic vessels
converge to form large lymphatic duct
drain into large veins in chest
unidirectionnal
Transcellular fluid
Minimal amounts of fluid (<1- 2% of ECF) made by epithelial cell in some body cavities.
Have specialized functions (saliva helps digest food)
Does not affect body fluid balance
Direct method to determine compartment volume
Weigh compartment with substance inside then dry it out and reweigh
or for simple shapes use volume formulas: V=pi(r)^2 x h
Indirect method of determining compartment volume (Indicator dilution method)
Introduce known total quantity (Q) of indicator (died with radioactive material) into vein
allow equilibrium
Remove known volume of blood and centrifuge to get plasma
Measure concentration (c) in unit volume of plasma
Calculate V=Q/c
Indicators used
non-toxic
no change in H2O distribution
easy to measure concentration
Total body water: normal 42L
Antipyrine, D2O, T2O
(can cross all membranes)
Total ECF: normal 14L
inulin, sucrose, mannitol
(Cannot cross cell membrane into intercellular fluid)
Total Plasma: normal 3.5L
evans’ Blue
(cannot cross capillary wall)
ICF = Total BW - ECF
ISF = ECF - plasma
cannot measure lymph nor transcellular fluid
Ionic composition of body fluids
ICF: high in K+ and Mg++
low in Na+ and Cl-
ECF: high in Na+ and Cl- but low in K+ (0.9% NaCl)
Substitute for plasma: Physiological Saline
= 0.9% NaCl
(9g NaCl + H2O to make up 1L)
