main role of kidneys (focused in this section)
maintain stability of…
- extracellular fluid volume
- electrolyte composition
- osmolarity
Intracellular fluid (ICF)
the fluid within cells
- comprises of 2/3 of total body fluid
extracellular fluid (ECF)
- the fluid surrounding cells
– included plasma, interstitial fluid, lymph and transcellular fluid - 1/3 of body fluid
breakdown of ratios of what makes up ECF
– plasma is 1/5th of ECF
– interstitial fluid is abt 4/5ths of ECF
– lymph and transcellular fluid is negligible
transcellular fluid
the portion of total body water contained within epithelial lined spaces
– eg. cerebrospinal fluid
what are the 3 pools of major body compartments for water?
- ICF
- plasma
- ECF
how do the pools of major body compartments for water remain distinct?
presence of “barriers” between them
what do the barriers between body-fluid compartments generally do?
limit movement of water and solutes between the various compartments to differing degrees
what are the two types of barriers?
- barriers between plasma and Interstitial fluid
- barriers between ICF and ECF
at the level of capillaries what happens with water and everything else (other than proteins)?
can freely exchange with interstitial fluid
whats interesting about composition of plasma and interstitial fluid?
almost identical
- except there are proteins in the plasma
barriers between ICF and ECF
- the barrier is the plasma membrane surrounding the cell
- the ICF has proteins that don’t exchange with ECF
conc. of ions in ICF vs ECF
- K+ is higher in ICF
- Na+ is higher in ECF
why are there diff conc. of ions between ICF and ECF
the barrier doesn’t allow passive movement across plasma membrane
- prevents equilibrating by diffusion
what 2 factors are regulated to maintain fluid balance in body?
- EFC volume
- ECF osmolarity
factor regulated to keep fluid balance: EFC volume
- closely regulated to maintain blood pressure
- directly influences BP
- increase ECF volume will increase plasma volume and thus increase BP
- however, mechanisms exists to adjust BP until ECF volume is normal again
whats important in long term regulation of ECF volume
salt balance
factor regulated to keep fluid balance: EFC osmolarity
closely regulated to prevent swelling or shrinking of cells
short term control factors for ECF volume
Baroreceptor reflex
- through ANS on heart and blood vessels it can regulate BP
- when BP is low, cardiac output and total peripheral resistance will increase to raise BP
– opposite for high BP
fluid shifts
- low plasma volume can be temporarily fixed with a shift of fluids out of the interstitial compartment to the plasma
– opposite is true for increased plasma volume
Baroreceptors
- mechanoreceptors located in carotid artery and aortic arch
- detect changes in arteriole BP
cardiac output
the amount of blood pumped by heart per min
total peripheral resistance
resistance to blood flow due to constriction of blood vessels
- higher total peripheral resistance leads to increased BP
Long term control factors for ECF volume
fluid input/output
- a primary function of the kidneys (controlling fluid output) and the thirst mechanism (controlling fluid input)
- urine output control from kidneys is very important for BP regulation
what does salt balance influence
ECF volume
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Module 4: Section 136
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Module 4: Section 228
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Module 4: Section 330
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Module 4: Section 454
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Module 4: Section 516
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Module 4: Section 637
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Module 5: Section 115
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Module 5: Section 223
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Module 5: Section 321
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Module 5: Section 427
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Module 6: Section 146
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Module 6: Section 229
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Module 6: Section 351
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Module 6: Section 450
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Module 6: Section 534
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Module 6: Section 629
