3 Physiology: Water and Water Balance Flashcards
What percent of water is intracellular?
40%
How much of our body weight is water?
60%
What percent of water is extracellular?
20%
What percent of extracellular fluid is plasma?
4%
What percent is classified as “other” and what are they (the “others”)?
16%
1) interstitial fluid (fluid bathing cells)
2) lymph
3) epithelial and glandular secretions
4) aqueous
5) endolymph
6) peritoneal fluid
7) pleural fluid
8) pericardial fluid
9) CSF
10) renal filtrate
The volume, composition, and concentrations of solutes in all compartments are ideally kept within narrow limits.
See figure 1
What influences the degree to which various compartments differ from one another in volume, composition, and concentration of solutes?
Diffusion
Facilitated diffusion
Active transport
Formula for Concentration
(C)=mass/volume
therefore,
volume=mass/C
Formula for Flow
volume/time=flow=mass/(time)(C)
How much is a mole?
Mole=6.02 x 10^23
How many moles in a millimole?
millimole=1 x 10^-3 mole
Formula for Molar
Molar= Moles of Substance/Liter of Solution
Formula for Molal
Molal= Moles of Substance/Liter of H2O
Equivalent=Moles of charge
Formula for this?
Equivalent= (g of substance X)(valence of substance X)/Atomic or Molecular weight of substance X
Charged substances in a solution are called?
Electrolytes
What is a solution?
a homogeneous mixture of one or more substances (solutes) dispersed in a sufficient quantity of dissolving medium (solvent).
The solvent we will ALWAYS be concerned with is H2O.
What are Osmolytes?
Solutes that cause a depression in the freezing point and an elevation in the boiling point (colligative properties) of water.
What are some examples of Osmolytes?
Glucose
Na+
Cl-
Urea
What is a mole of Osmolyte called?
Osmol(e)
What can the concentrations of osmolytes be expressed as?
Osmolarity and Osmolality
Example 1 of osmolyte concentration
1 mole of glucose dissolved in 1 liter of H2O (1 molal glucose) is a 1 osmolal solution.
Molal= moles of substance/liter of H2O
Molal= 1 mole of glucose/ 1 liter of H2O
molal= 1 osmolal solution
Example 2 of osmolyte concentrations (know how to do calculations)
1 mole (=58 grams) of NaCl is added to 1 liter of H2O and the NaCl completely dissociates, there would be 1 mole of Na+ (=23 grams) and 1 mole of Cl- (=35 grams) in the i liter of H2O. The addition of 1 mole of glucose to this solution would yield the following concentrations: the solution is 1 molal Na+ the solution is 1 molal Cl- the solution is 1 molal glucose the solution is 3 osmolal the solution is 1 Eq/L Na+ the solution is 1 Eq/L Cl-
If an osmolyte cannot cross a membrane which allows the passage of H2O, what will occur?
Osmosis
What is osmosis?
is sometimes loosely defined as the diffusion of water through a selectively permeable membran
What happens when you add solute to a large volume of solvent?
it increases the percentage of molecular collisions between water molecules and solute species (IN REALITY, IT DOES NOT ALTER THE CONCENTRATION OF THE SOLVENT IN THE SOLUTION)
And if this occurs on one side of a membrane that does NOT allow passage of those solutes (but does allow passage of water), there will be more water-water collisions in the solution on the other side of the membrane, and therefore a net movement of water from that solution to the one with the greater concentration of impermeant solute.
(SO BASICALLY THIS IS THE DEFINITION OF OSMOSIS: THE MOVEMENT OF SOLVENT MOLECULES THROUGH A PERMEABLE MEMBRANE FROM A LOW SOLUTE CONCENTRATION INTO A REGION OF HIGH SOLUTE CONCENTRATION) (so water is going to move to where there is more solute and less water to try and equal it out)
Osmosis does NOT occur when?
does NOT occur in the absence of impermeant solute (substances that cannot cross membrane)
(solutes which can diffuse across membrane (ex. O2 and CO2) will achieve the same concentration on both sides of the membrane, which will result is solute-water collision of equal frequency on both sides of the membrane, so cause no osmosis) (this is because these solutes will move about the membrane to equal out instead of the liquid)
How might solutions be compared?
by concentrations of osmolytes
What is iso-osmotic solution?
a solution that has the same concentration compared to another solution
What is hypo-osmotic solution?
a solution with a lower concentration compared to another solution
What is hyperosmotic solution?
a solution with a higher concentration compared to another solution
An osmotically active solution is one which causes?
Osmosis (i.e. causes a net diffusion of water to it)
If an osmolyte CANNOT cross a membrane which allows the passage of H2O, it will exert what?
Osmotic Pressure
The greater the concentration of impermeant osmolyte in the solution, will cause the osmotic pressure to be?
greater (i.e the greater the movement of H2O toward it=more pressure) (more solute in the solution causes greater movement of water toward solutes so causing more pressure)
The net movement of water from one solution to another eventually results in an equal, but opposing what?
hydrostatic pressure
Osmotic pressure can be measured/recorded in?
mm Hg (millimeters of mercury)
Tonicity refers to?
refers to effective osmotic pressure (i.e. whether the movement of water will cause a cell to change in size (volume))
What is an isotonic solution?
a solution which causes a cell to neither shrink nor swell (solution has an equal osmotic pressure compared to its surroundings)
What is a hypotonic solution?
a solution which cause a cell to swell (a solution that has a lower concentration of solutes than it surroundings so water will go into the cell causing it to swell)
a cell may swell to the point where stress on the plasma membrane causes it to rupture (CYTOLYSIS)
What is a hypertonic solution?
a solution which causes a cell to shrink (PLASMOLYSIS) (crenation is a synonym for plasmolysis and occurs in red blood cells)
( a solution that has a higher solute concentration than its surroundings and causes water to leave the cell causing it to shrink)
A solute may cause osmosis at one membrane but not at another. Example?
Na+ causes osmosis at the membrane which separates intracellular fluid from extracellular fluid, but it DOES NOT cause osmosis at the endothelial cell membrane (see figure 1)
What is the most important EXTRACELLULAR OSMOLYTE?
Na+
Using diffusion, facilitated diffusion, or active transport, solutes may move from one fluid compartment to another by:
1) endocytosis (i.e. LDL)
2) exocytosis (e.g. neurotransmitter)
3) pressure filtration at the glomerulus (in kidney) (e.g. glucose)
4) solvent drag (where solutes dissolved in water are transported as the water moves paracellularly (i.e. through tight junctions between cells) (e.g. K+)
See figure one in notes on page 61!!
.
What are the STARLING “FORCES”?
they are recorded as forces/ares, or pressures.
They are:
1) CAPILLARY FLUID HYDROSTATIC PRESSURE (CHP)
2) INTERSTITIAL FLUID HYDROSTATIC PRESSURE (IFHP)
3) PLASMA COLLOID ONCOTIC PRESSURE (PCOP): the osmotic pressure attributable to interstitial proteins
4) INTERSTITIAL FLUID COLLOID ONCOTIC PRESSURE (IFCOP)
Capillary Membrane Permeability
capillary membrane permeability varies in different organs in the body
some capillaries are very permeable (even allowing passage of large solutes such as protein)
an example of an organ with such capillaries is the LIVER
most other capillaries allow only minor passage of proteins but still allow relatively free passage of smaller solutes
the interstitium in the vicinity of these capillaries therefore possesses a lower concentration of protein relative to the interstitium in the vicinity of more permeable capillaries.
Capillary Fluid Hydrostatic Pressure (CHP)
CHP decreases dramatically as one proceeds from the arteriolar to venular ends of a capillary, while the other pressures vary little (PCOP increases and then decreases) or virtually not at all (IFCOP and IFHP).
Algebraic summation of the four Starling Forces shows that there is a net filtration (net movement from plasma to interstitium) at the arteriolar end, and net reabsorption ( net movement from interstitium to plasma) at the venular end, of the capillary.
Renal glomerular capillaries are a notable exception.
.
All four Starling Forces may be what? (One of them is an exception?)
all four may be POSITIVE.
But IFHP has been shown to be negative (i.e. less than atmospheric pressure) in many tissue beds.
That is, there my be a “suction” force in the interstitium; this may be related to lymphatic drainage of tissue beds.
What percent of FILTERED FLUID is REABSORBED (as a result of the combined IFHP AND PCOP) by the time plasma reaches the venule?
90%
What percent of the remaining FILTERED FLUID is normally taken up by the lymphatic system and where is it taken?
10%
it is eventually returned to the circulatory system via veins which drain into the cranial vena cava.
What is EDEMA?
the collection of abnormally high amounts of interstitial fluid.
What are the TWO TYPES of Edema?
Generalized
and
Localized
What are THREE TYPES of LOCALIZED EDEMA?
1) Pleural Effusion
2) Ascites (Peritoneal Effusion)
3) Pericardial Effusion
What causes EDEMA and what are the causes of each?
a) INCREASED CHP (Capillary Fluid Hydrostatic Pressure)
1) decreased radius of veins (e.g. compression caused by neoplasia)
2) increased fluid in the venous system (e.g. right-sided heart failure)
b) DECREASED PCOP
1) starvation (decreased synthesis of plasma protein)
2) kidney disease (filtration of protein with subsequent loss in urine)
3) liver disease (decreased synthesis of plasma protein)
c) INCREASED IFCOP
1) inflammation (increased permeability of endothelium, allowing leakage of plasma protein)
2) tissue damage (loss of intracellular protein to interstitium)
3) inadequate or obstructed lymph flow (e.g. neoplasia)
What is NORMAL HYDRATION?
normal fluid volume and plasma osmolarity of 290-300 mOsm (300 mOsm is a commonly utilized round number value found in textbooks, even though it is hyperosmotic/hypertonic)
What is NORMOVOLEMIA?
normal blood volume
What is a GOOD ROUGH estimate of plasma osmolarity?
2 [Na+] (mEq/L or mM/L)
What is an EVEN BETTER estimate of plasma osmolarity?
2 [ Na+] (mEq/L or mM/L) + [Glucose/18] (mg/dL) + [Urea/3] (mg/dL)
What is DEHYDRATION?
less than normal fluid volume
What is HYPOVOLEMIA?
less than normal blood volume.
What does the term “INSENSIBLE” refer to?
water losses in exhaled air, through the skin or in the feces.
“insensible” technically means “not sensed”
really means they are difficult to measure.
What does the term “SENSIBLE” refer to?
water lost in urine, a volume that is easily measured.
Plasma in the animal is HYPERTONIC during DEHYDRATION because?
because water loss exceeds loss of osmolytes, relative to their normal concentrations in plasma.
What is the most common form of dehydration?
HYPERTONIC DEHYDRATION
What are the common causes of hypertonic dehydration?
1) Respiration (water, but not osmolyte, is lost upon exhalation)
2) Sweat (humans)
3) Inappropriate production of hypotonic urine
What is the RESULT of hypertonic dehydration?
increased osmolarity of extracellular fluid (ECF) ➡ increased osmolarity of intracellular fluid (ICF), until new hyperosmotic equilibrium is achieved.
Plasma in the animal is ISOTONIC during DEHYDRATION because?
because isotonic fluid is lost
What are common causes of ISOTONIC DEHYDRATION?
1) Hemorrhage
2) Sweat (horses)
What is the result of ISOTONIC DEHYDRATION?
decreased volume of ECF (extracellular fluid)
HYPOVOLEMIA
Plasma in the animal is HYPOTONIC during DEHYDRATION because?
because loss of osmolyte exceeds loss of water, relative to their normal concentrations in plasma.
What are common causes of HYPOTONIC DEHYDRATION?
1) HYPOTONIC dehydration is not as common as HYPERTONIC dehydration.
if there is excessive loss of extracellular osmolyte (e.g. Na+ and an accompanying anion, such as Cl-) as might occur in diarrhea or kidney disease, it is often accompanied by excessive loss of water.
2) Sweat (horses)
What is the result of HYPOTONIC DEHYSRATION?
decreased osmolarity of extracellular luid (ECF) ➡decreased osmolarity of intracellular fluid (ICF), until new hyposmotic equilibrium is achieved.
Hypotinic dehydration ma be caused by loss of isotonic fluid, followed by hypotonic replacement.
What is OVERHYDRATION?
greater than normal fluid volume
What is HYPERVOLEMIA?
greater than normal blood volume
As venous pressure increases, the likelihood of edema increases.
Plasma in the animal is HYPOTONIC during OVERHYDRATION because?
because gain of water exceeds gain of osmolyte, relative to concentration in plasma.
Causes of HYPOTONIC OVERHYDRATION are?
not common
1) psychogenic
2) excess reabsorption of water by kidney tubules (e.g excessive secretion of ADH or an ADH-like substance)
3) drowning
What is the result of HYPOTONIC OVERHYDRATION?
decreased osmolarity of ECF ➡ decreased osmolarity of ICF, until new hyposmotic equilibrium is achieved
Plasma in the animal is ISOTONIC during OVERHYDRATION because?
because isotonic fluid is gained
What are the causes of ISOTONIC OVERHYDRATION?
1) Iatrogenic
2) Excess reabsorption of Na+ by kidney tubules. Excess secretion of the hormone aldosterone is a well-documented cause.
What is the result of ISOTONIC OVERHYDRATION?
and increase in ECF volume, but no change in osmolarity .
