Water Transport Osmosis Flashcards
1
Q
Water Mass In the Human Body
A
- total body water in liters is 60% of body weight, where 1 liter of water weighs 1 Kg.
- standard patient weighing 70 Kg has TBW of 42 liters
- the ICF is 2/3 of TBW, or 28 L of 70 Kg (40%)
- ECF is 1/3, or 14 L for 70 Kg (20%)
2
Q
ICF Volume
A
- maintained within narrow limits by solute transport mechanisms driving water into or out of the cell by osmosis
- ICF volume is important because an optimal concentration of intracellular solutes, organic and inorganic, anionic and cationic, is essential for optimal function of all cells, given the enormous diversity of organ-specific cell functions
3
Q
ECF volume
A
- distributed in 2 compartments or volumes which exist inside or outside the vasculature
- the intravascular fluid volume is approximately 7% of body weigh of 5L for a 70 kg patient
- intravascular fluid is divided into hematocrit where 55% of blood is plasma (3L) and 45% of blood volume is cellular (2L)
- plasma is 25% of ECF
- the extravascular fluid volume or the interstitial fluid volume is the remaining 75% ECF volume approximately 11L
- regulated within normal limits by balancing the excretion of water by the kidney to match the consumption of water by the mouth
- maintaining intravascular volume within normal limits is essential to maintain blood pressure which drives blood flow to and from the organs
4
Q
Edema
A
-pathophysiological shift of fluid from the intravascular to extravascular compartment and indicates an increase in TBW measured as an increase in body weight
5
Q
Facilitated diffusion
A
- aquaporins mediate membrane transport of water through facilitated diffusion
- they do not mediate transport of solutes across the membrane
6
Q
Simple diffusion of water
A
- in addition to facilitated transport
- the transport of water across cell membranes may also occur by an unmediated pathway by a process of simple diffusion where water molecules pass through membrane lipids without membrane protein interaction
7
Q
Aquaporin
A
- occurs through a water filled pore in the protein spanning the cell membrane and is much faster than water transport by simple diffusion
- identified in human red blood cells
- also expressed and functions in kidney epithelia cells where it mediates transcellular transfer of fluid across the renal epithelia
- is involved in the transepithelial formation of aqueous humor in the eye and CSF in the brain
- also functions in the regulation of fluid exchange in the lung, in the formation of bile fluid formation in skeletal, cardiac and smooth muscle
8
Q
Osmosis
A
- describes the process of net movement of water caused by a concentration difference of water between two compartments
- both by simple diffusion of water and by facilitated diffusion of water mediated by aquaporin
- will go in either direction, driven by differences in particle numbers
- net transport of water across the cell membrane always occurs in a direction down the water concentration gradient from the intra- or extracellular compartment where osmolarity is low to the extra- or intracellular compartment where osmolarity is high
9
Q
Chemical potential
A
- is a measure of the free energy
- spontaneous processes always lower the total free energy of a system, and always to equalize the free energy in the various compartments of a system, accessible to spontaneous processes
- a gradient of water chemical potential exists across the membrane, higher water chemical potential on the left side of the membrane and lower chemical potential on the right side
- the gradient of water chemical potential is the driving force for net water movement and water flows spontaneously into the solution containing for higher concentration of solute, which raises the level of water in the right compartment
10
Q
Difference in osmotic pressure
A
- difference in osmotic pressure across the membrane drives net transfer of water across the membrane from the compartment with lower osmotic pressure (lower osmolarity/higher water concentration) to the compartment with higher osmotic pressure (higher osmolarity/lower water concentration)
- the balance or imbalance of these two opposing forces across the capillary wall determines the presence of absence of edema
11
Q
Isotonic solution
A
- any solution or body fluid with an osmotic pressure or osmolarity equal to plasma is iso-osmolar or isotonic relative to plasma
- when placed where intra-and extracellular osmolarity is equal at 300 mOsm/L no concentration gradient for water exist across the cell membrane and there is no net movement of water occurs into or out of the cell, cell volume remains constant
12
Q
Hypertonic solution
A
- solutions or body fluids with a great osmolarity than plasma are hyper-osmolar or hypertonic
- when dehydrated, in negative water balance
- extracellular osmolarity is greater than intracellular osmolarity an outwardly directed water concentration gradient is created driving net efflux of water from cell and cells shrink due to a decrease in intracellular volume
13
Q
Hypotonic solution
A
- less osmolarity than plasma
- when overhydrated, in positive water balance
- where extracellular osmolarity is less than intracellular osmolarity an inwardly directed water concentration gradient is created driving net influx of water into the cell and the cells swells due to an increase in intracellular volume
14
Q
Response of cells
A
- changes in extracellular tonicity is to shrink or decrease cell volume in hypertonic solutions or swell and increase cell volume in hypotonic solutions
- the addition (swelling) and subtraction (shrinking) of water from cells in response to changes in extracellular tonicity (osmolarity) is to decrease and increase the intracellular tonicity (osmolarity) toward the extracellular tonicity (osmolarity)
15
Q
Normal conditions of ICF and ECF
A
- osmolarity is isosmotic (300 mOsm/L)
- ICF is 2/3 and ECF is 1/2 of total blood water
