Lecture 3 Flashcards
Main function of the kidney:
regulate the volume and composition of the body fluids via filtration, reabsorption and secretion.
Water in Our Body is Compartmentalized
Water exists in 3 locations in our body. What are they?
- ICF - water in the cell. Holds 2/3 of our water.
- ECF- water located outside of the cell, in the plasma and the interstitium.
- Other- lymph, CSF, humors of the eye, serous fluid and GI secretions
___ of our body weight is total body water.
___ of our body weight is water that is located in the ECF.
____ of our body weight is water that is located in the ICF.
60% of our body weight is total body water.
40% of our body weight is water that is located in the ICF.
20% of our body weight is water that is located in the ECF.
60-40-20 rule
Total body water
Our total body water consists of the water in the ECF and ICF.
TBW= ICF + ECF
TBW (total body water)= 0.6 x body weight
ICF= 0.4 * body weight
ECF= 0.2 * body weight
What makes up the fluid in the ECF?
ECF= Interstitial fluid (3/4) + Plasma (1/4)
Interstitial fluid contains 3/4 of the fluid in the ECF.
Plasma contains 1/4 of the fluid in the ECF/.
Plasma and interstitial fluid are separated by what?
Capillary wall
All solutes and water that enter and leave the body do so through the _____.
ECF
What should we remember about the fluid in the ECF and ICF?
The ICF and ECF are in osmotic equilibrium. Water move only when a osmotic pressure gradient exists.
The osmolality in these compartments is equillbriated by shifts in water, not solutes.
_____ is the only fluid that can be acted upon directly to control the volume and composition.
Regulating the volume and composition of the _____ also regulates the volume and composition of the______.
Thus, regulation of _____ affects the entire ____.
Plasma is the only fluid that can be acted upon directly to control the volume and composition. Regulating the volume and composition of the plasma also regulates the volume and composition of the interstitial fluid.
Regulation of plasma affects the entire ECF.
When water enters or exits the body, what compartment is affected?
ECF.
When water is added to the body, it always enters the ECF first. When fluid leaves, it always leaves the body via the ECF.
What is the third space?
Under some pathologic conditions, additional fluid may accumulate in the third space. Fluid build up in the third space occurs when blood vessels contain too much fluid, causing fluid to move from the [intravascular area–> non-functional area of the cell]. Examples include;
- In between tissues and organs of the abdomen- ascites,
- Interstitial areas around the lungs, resulting in pulmonary edema.
This is often seen in burn victims.
What separates our fluid compartments?
Semipermeable membrane, which allows water to move via osmosis but does not allow solutes to move.
ECF
- Primary cation: _______
- Primary anion: ________
ECF
- Primary cation: Na+
- Primary anion: Cl-* and HCO3-
The ionic composition of the [interstitial fluid & plasma] are similar because…
The ionic composition of the interstitial fluid and plasma are similar because they are only separated by a capillary endothelium, a barrier where small ions are permeable.
What is the major difference between the interstitial fluid and plasma?
What can this affect?
The major difference between the IF and plasma is that plasma has more proteins.
This can affect the distribution of cations and anions between the two compartments because plasma proteins have net negative charge that increases the cation concentration to reduce anion concentrations in the plasma. However, this effect is small.
ICF
Primary cation: _______
Primary anion: ________
ICF
- Primary cation: K+
- Primary anion: PO43-
Water can dissolve compounds that are either an electrolytes or non-electrolytes. What is the difference between the two?
- Non-electrolytes- do not dissociate in solution bc covalent bonds. Thus, they do not have a charge. Examples include glucose, lipids and urea.
- Electrolytes- dissociate into ions in water.
Which have a higher osmotic power: electrolytes or non-electrolytes?
Electrolytes have a higher osmotic power than nonelectrolytes because they can dissociate in water.
SOOOO, they have a better ability to cause fluid shifts.
Unequal distribution of Na+ and K+ and their anions are due to what?
Na+/K+ pump, which pumps 3 Na+ out and 2 K+ in.
What is the difference between osmolality and osmolarity?
Osmolality is the number of osmotically active particles/kg of H20.
Osmolarity is the number of osmotically active particles/ liter of total solution.
Does the osmolality differ in the different body fluid compartments?
No.
All compartments have the same osmolarity:
290 mOsm/kg of H2O.
Osmolarity of Na+
135-147 mEq/L
Osmolarity of Cl-
95-105 mEq/L
Osmolarity of K+
3.5-5.0 mEq/L
Osmolarity of HCO3-
22-28 mEq/L
Osmolarity of urea nitrogen (BUN)
7-18 mg/dL
Describe the fluid composition of blood.
Blood is made up of both ECF (plasma, which makes up 60% of blood)
and ICF (RBC, which makes up 40% of blood).
I_ncrease in ECF volume_ = ______ total plasma protein levels
Decrease because of dilution.
Decrease in ECF volume = ____ total plasma protein levels?
Increase
Hematocrit is the fraction of RBC in our blood.
Decrease in ECF volume = ____ hematocrit
Incerase in ECF volume= _____ hematocrit
Decrease in ECF volume = INCREASE hematocrit because creates an osmotic grandient from ICF–> ECF.
Increase in ECF volume= DECREASE hematocrit because creates an osmotic gradient from ECF–> ICF.
Hematocrit is the fraction of RBC in our blood.
Decrease in ICF volume = ____ hematocrit
Increase in ICF volume= _____ hematocrit
Decrease in ICF volume = decrease hematocrit because the RBCs shrink
Increase in ICF volume= increase hematocrit because the RBCs swell
How do we measure the volume in a specific compartment?
- Inject a indicator that will disperse evenly throughout the compartment we want to measure and that cannot be metabolized or excreted.
- Get a sample of the fluid that has the dispersed subsrtance and analyze it.
22yo M runs a 10 km race.
Loses 3L of sweat and drinks 3L of water. What changes would we see after the absorption of water?
1. Intracellular volume
2. Intracellular osmolarity
3. Extracellular volume
4. Extracellular osmolarity
1. Intracellular volume- Increase
2. Intracellular osmolarity- decrease
3. Extracellular volume- decrease
4. Extracellular osmolarity- decrease
LOGIC: Sweat has a high concentration of Na+, compared to water. When we sweat–> decrease in Na+ in ECF, creating an osmotic gradient that causes water to flow from ECF–> ICF.
This will decrease ECF volume and increase ICF volume, while decreasing the intracellular osmolarity.
Sweat has a high amount of _____.
Sweat has a high amount of Na+, compared to water.
What is the Gibbs-Donnan Effect?
Gibbs-Donnan effect describe that due to the cell membrane being impermeable to proteins, it creates a clump of anions (-) charged proteins, creating:
1. Osmotic gradient due to a oncotic gradient, favoring movement into the cell.
2. Electrochemical gradient, favoring movement of charges into the cell.
Thus, without counteraction, water would move into the cell and it would swell.
Permeable/ Impermeable
The cell membrane is ______ to ions and _____ to large proteins.
The cell membrane is permeable to ions and impermeable to large proteins.
How do we counteract the Gibb-Donnan effect?
Na/K+ ATPase pump prevents the excessive inward movement of H20.
BECAUSE WATER FOLLOWS Na+, SO WHEN WE MOVE Na+ out, WATER MOVES OUT.
___ moves between the ICF and ECF d/t osmosis.
____ is responsible for the ECF osmotic balance.
_____ is responsible for the ICF osmotic balance.
Water moves between the ICF and ECF d/t osmosis.
Na+ is responsible for the ECF osmotic balance.
K+ is responsible for the ICF osmotic balance.
2 factors make fluid freely movable. What are they?
1. Water difuses faster through the capillary walls than blood.
2. Pressure difference between the inside and outside of the vessel (Hydrostatic capillary pressure).
Forces Involved in Filtration and Reabsorption
- Capillary Hydrostatic Pressure (BP)- favors filtration, movement of fluid and solutes out of capillary into the interstitial fluid.
- Plasma colloid oncotic pressure- large proteins, like albumin, act like sponge and attract water. Favors reabsorption.
- 3. Interstitial oncotic pressure- Favors filtration, but typically 0 mmHg.
- I_nterstitial hydrostatic pressure_- opposes filtration.
When does filtration occur?
Capillary blood pressure > plasma colloid osmotic pressure,
then water and solutes can enter the interstitial fluid.
When does absorption occur?
Capillary blood pressure < plasma colloid osmotic pressure, water will be absorped.
From arteriole–> venule, how does the capillary BP relate to the plasma colloid osmotic pressure?
At the arteriole, the capillary hydrostatic pressure > plasma colloid osmotic pressure.
At the venule end, it will fall below.
What happens to the extra fluid that is filtered out of the capillary?
Goes to the lymphatic vessels.
What is edema and what causes it?
Edema is due to a
- excessive filtration from the vascular space –> interstitium. It does not become apparent until interstitial volume increases by 2.5- 3 L.
- Renal retention of Na+ and water in the ECF.
What is normal plasma volume?
3.0 L
Thus, is edema derived only from the plasma?
What is the result?
No.
As plasma volume decreases d/t fluid movement into the interstitium, the kidney tries to compensate by holding onto Na+ and H20 in the ECF.
This results in high BP and high ECF volumes.
Net filtration=
k(Pc-Pi)-(nc-ni)
What determines the volume/size of the cell?
Cell have a NaCl concentration= ____%
The tonicity of the solution determines the volume or size of the cell.
Cell have a NaCl concentration= 0.85%
Describe what a isotonic, hypertonic and hypotonic solution are.
What would happen to a cell if it were placed in this solution?
-
Isotonic solution is a solution surrounding the cell with a NaCl concentration of 0.85%.
- A cell placed in this solution would see equal movement of water in and out.
-
Hypertonic solution = NaCl concentration >0.85%.
- A cell placed in this solution would shrink.
-
Hypotonic solution= [NaCl] < 0.85%.
- If a cell is placed in this solution, it will swell.
Describe sweat
Sweat has a high amount of Na, compared to water.
The loss of sweat would create a hypotonic environment.
How can we tx fluid and electrolyte imbalances?
1. Colloid IV bags- large molecules that do not cross the semipermeable membrane. They increase intravascular volume but pulling fluid from the ECF d/t high oncotic pressure.
2. Crystalloid IV bags- have organic or inorganic salts dissolved in water, such as glucose and NaCl-. Normal saline (0.9%) and lactated Ringers (LR) are commonly used. Other are 0.45% NaCl and D5W, 5% dextrose in water.
What are properties of crystalloids?
- Remain in the ECF. Thus, they do not cross the plasma mebrane.
- Distributed evenly in the ECF, diffusing across the capillary wall to equillibriute intravascular (plasma) and interstitial volumes.
What are the main solutes in the ECF?
1. Na+
2. Glucose
3. Urea
Because water is in osmotic equilibrium across the capillary endothelium and the plasma membrane of cells, measurement of the plasma osmolality also provides a measure of the osmolality of the ECF and ICF.
How do we calculate the plasma osmolality?
Osmolarity= 2[Na] + glucose/18 + BUN/2.8
OR
Plasma osmolality= 2 (plasma[Na])
Body fluid volumes in the ECF are regulated by changes in ______.
Serum osmolality and its main determinant, [Na+], are regulated by changes in _______.
Body fluid volumes in the ECF are regulated by changes in Na+.
Serum osmolality and its main determinant, [Na+], are regulated by changes in H2O.
A change in Na= a change in volume.
A change in H20–> changes in what?
1. [Na+]
2. osmolarity
Dehyrdation can occur due to what two situations.
1. Decrease in H20 intake
2. Increase in fluid loss, often d/t V/D, diuresis and sweating
Dehydration can be divided into 2 types based on the serum [Na+].
What are they?
1. Hypernatremic (hypertonic) dehydration
2. Hyponatremic (hypotonic) dehyrdration
Hypernatremic (hypertonic) dehydration
- We lose more water than Na+, thus the serum Na+ is more than 147-150.
- [NaICF] < [NaECF]
- Water moves from[ICF–> ECF] d/t osmotic equillibrium, causing shrinkaeg of brain cells but excess ECF.
***Serum osmolality will exceed 300 mOsm/kg
Hyponatremic (hypotonic) dehydration
- We lose more Na+, than water from the ECF (Na+ levels drop below 130-135 mEq/L)
- [NaICF] > [NaECF], decreasing the ECF osmotic pressure.
- Water moves from ECF–> ICF to establish an osmotic equillbrium
- Serum Na+ and osmolality will be less than normal.
This is seen in sweating.
What happens to the cells in hyponatremia?
Increased ICF causes cell swelling, edema, confusion, weakness.
What are the results of hypernatremia?
1. Increased ECF–> edema and increased BP.
2. High Na+–> muscle weakness and hyperactive reflexes
3. Decreased ICF–> Thirst, decreased urine output, coma.
What are the 2 basic principles of fluid shift?
- Water moves rapidly across the cell membrane so that it can always try to stay in equillibrium.
- Cell membranes are almost completely impermeable to many solutes; thus, the number of osmoles in the ECF and ICF stays thesame unless solutes are added or lost from the ECM.
Fluid shift disturbances are categorized by whether they involve a increase or decrease in ECF volume.
What is volume contraction and volume expansion?
- Volume contraction–> decrease in ECF volume, causing a decreased blood volume and decreased BP.
2. Volume expansion–> increase in ECF volume, causing an increased BP and edema.
Fluid shift disturbances are categorized by whether they cause a change in the osmolarity of the body fluid.
1. Isosmotic
2. Hyperosmotic
3. Hyposmotic
1. Isosmotic- no change in body fluid osmolarity
2. Hyperosmotic- increase body fluid osmolarity
3. Hyposmotic- decrease in body fluid osmolarity
DARROW -YANNET DIAGRAMS
LOOKS AT THE FLUID SHIFT
(osmolality and volume of the ECF and ICF)
Draw and describe
What happens to the diagram during iso-osmotic volume contraction.
Draw.
- hemorrage
- Diarrhea
- Vommitting
- decrese ECF
- no change in osmoality or ICF volume
What happens to the diagram during hyper-osmotic volume contraction.
Draw.
- Dehydration
- DB insipidus
- alcoholism
- decrease ECF volume
- Increase osmomilarity
- decrease in ICF volume
What happens to the diagram during isomotic volume expansion.
Draw.
- Isotonic NaCl (saline) solution
What happens to the diagram during hypo-osmotic volume expansion.
Draw.
- Excess water intake
- SIADH (syndrome of inappropriate ADH)
