BRS Phys Review Flashcards
Total body water is approximately ____ of body weight
60%
When is the percentage of total body water at its highest and and its lowest?
Highest in newborns and adult males
Lowest in adult females and adults with large amounts of adipose tissue
What is the 60-40-20 rule for the distribution of body fluids?
TBW = 60% of body weight
ICF = 40% of body weight
ECF = 20% of body weight
How much of your total body water is made up of ICF?
2/3
What are the major cations and anions of ICF?
Major cations: K+ and Mg+
Major anions: protein and organic phosphates (ATP, ADP, AMP)
How much of your total body water is made up of ECF?
1/3
Describe the composition of ECF as well as its major cations and anions
Composed of interstitial fluid and plasma
Major cation: Na+
Major anion: Cl- and HCO3-
________ makes up 1/4 of the ECF. What are the 2 major proteins?
Plasma (thus it is 1/12 of TBW)
Major plasma proteins: albumin and globulins
If plasma makes up 1/4 of the ECF, what makes up the other 3/4?
Interstitial fluid (makes up 1/4 of TBW)
Describe the composition of interstitial fluid
Same as that of plasma except that it has little protein; thus it is considered an ultrafiltrate of plasma
Volumes of fluid compartments can be measured using a dilution method - in which a known amount of substance is given whose volume of distribution is the body fluid compartment of interest.
What substances are used as indicators for total body water?
Tritiated water
D2O
Antipyrene
Volumes of fluid compartments can be measured using a dilution method - in which a known amount of substance is given whose volume of distribution is the body fluid compartment of interest.
The substance is allowed to _______. The __________ of the substance is measured in plasma.
Equilibrate; concentration
Volumes of fluid compartments can be measured using a dilution method - in which a known amount of substance is given whose volume of distribution is the body fluid compartment of interest.
The substance is allowed to equilibrate. The concentration of the substance is measured in plasma.
How is the volume of distribution calculated based on this info?
Volume = amount/concentration
Volumes of fluid compartments can be measured using a dilution method - in which a known amount of substance is given whose volume of distribution is the body fluid compartment of interest.
What substances are used as indicators for ECF?
Sulfate
Insulin
Mannitol
Volumes of fluid compartments can be measured using a dilution method - in which a known amount of substance is given whose volume of distribution is the body fluid compartment of interest.
What substances are used as indicators for plasma?
Radioiodinated serum albumin (RISA)
Evans blue
Volumes of fluid compartments can be measured using a dilution method - in which a known amount of substance is given whose volume of distribution is the body fluid compartment of interest.
What substances are used as indicators for interstitial fluid compartments?
Interstitial fluid compartments are measured indirectly!
Interstitial fluid volume = ECF volume - plasma volume
Volumes of fluid compartments can be measured using a dilution method - in which a known amount of substance is given whose volume of distribution is the body fluid compartment of interest.
What substances are used as indicators for ICF?
ICF is measured indirectly!
ICF volume = TBW - ECF volume
At steady state, ECF osmolarity and ICF osmolarity are _______. To achieve this, ______ shifts between the ECF and ICF compartments.
Equal; water
What effect would infusion of an isotonic fluid, such as NaCl, have on ECF volume, ICF volume, ECF osmolarity, and Hct and serum [Na+]?
ECF volume increases –> BP increases
ICF volume unchanged
ECF osmolarity unchanged
Hct decreases, [Na+] unchanged
Infusion of an isotonic fluid, such as NaCl, is also called _________
Isosmotic volume expansion
What effect would loss of an isotonic fluid, which occurs with diarrhea, have on ECF volume, ICF volume, ECF osmolarity, Hct and serum [Na+]?
ECF vol decreases –> BP decreases
ICF vol unchanged
ECF osmolarity unchanged
Increased Hct, no change in [Na+]
Loss of isotonic fluid, such as with diarrhea, is also called _______
Isosmotic volume contraction
What effect would excessive NaCl intake have on ECF volume, ICF volume, ECF osmolarity, Hct and serum [Na+]?
ECF increases
ICF decreases
ECF osmolarity increases
Hct decreases
[Na+] increases
Excessive NaCl intake is also called what?
Hyperosmotic volume expansion
What are some key examples of hyperosmotic volume contraction?
Sweating
Fever
Diabetes insipidus
What effect would hyperosmotic volume contraction have on ECF volume, ICF volume, ECF osmolarity, and serum [Na+]?
ECF volume decreases
ICF volume decreases
ECF osmolarity increases
[Na+] increases
What is the key example of Hyposmotic volume expansion?
SIADH [Syndrome of Inappropriate ADH] - resulting in gain of water
What effect would hyposmotic volume expansion have on ECF volume, ICF volume, ECF osmolarity, and serum [Na+]?
ECF increases
ICF increases
ECF osmolarity decreases
[Na+] decreases
Adrenal insufficency is a key example of what type of volume change in body fluids?
Hyposmotic volume contraction (adrenocortical insufficiency = loss of NaCl)
What effect would hyposmotic volume contraction have on ECF volume, ICF volume, ECF osmolarity, Hct and serum [Na+]?
ECF volume decreases
ICF volume increases
ECF osmolarity decreases
Increase in Hct
Decrease in [Na+]
The clearance equation indicates the volume of plasma cleared of a substance per unit time
C = UV/P
Where U is urine concentration, V is urine volume/time, P is plasma concentration
Renal blood flow is _____% of cardiac output and is _______ proportional to pressure difference between the renal artery and renal vein
It is _____ proportional to the resistance of the renal vasculature
25; directly
Indirectly
_________ of renal arterioles, which leads to a decrease in RBF, is produced by activation of the ______ nervous system and angiotensin II.
At low concentrations, angiotensin II preferentially constricts ________ arterioles, thereby “protecting” (increasing) the GFR
Vasoconstriction; sympathetic
Efferent
At low concentrations, angiotensin II constricts efferent arterioles, thus protecting/increasing GFR.
What type of drug dilates efferent arterioles and produces a decrease in GFR, thus reducing hyperfiltration and occurance of diabetic nephropathy in diabetes mellitus?
ACE inhibitors (angiotensin-converting enzyme)
How is autoregulation of RBF accomplished?
By changing renal vascular resistance. If arterial pressure changes, a proportional change occurs in renal vascular resistance to maintain a constant RBF
Autoregulation of RBF keeps it constant over the range of arterial pressures from ____ to _____ mm Hg
80-200
What are the 2 mechanisms for RBF autoregulation?
Myogenic mechanism
Tubuloglomerular feedback
What is the myogenic mechanism for autoregulation of RBF?
Renal afferent arterioles contract in response to stretch.
Thus, increased renal arterial pressure stretches the arterioles, which contract and increase resistance to maintain constant blood flow
What is the tubuloglomerular feedback mechanism for autoregulation of RBF?
Increased renal arterial pressure leads to increased delivery of fluid to the macula densa which senses the increased load and causes constriction of the nearby afferent arteriole, increasing resistance to maintain constant blood flow
Renal plasma flow is measured by the degree of clearance (filtration and secretion) of what substance?
Para-aminohippuric acid (PAH)
Clearance of PAH measures effective renal plasma flow (RPF), and underestimates true RPF by ____%. Why is this?
10%
Clearance of PAH does not measure RPF to regions of the kidney that do not filter and secrete PAH
How is RPF calculated?
RPF = C[PAH] = (U[PAH] x V)/P[PAH]
Where U[PAH] is PAH in urine, V is urine flow rate, and P[PAH] is plasma PAH
How is RBF calculated?
RBF = RPF/1-Hct
Note that denominator is fraction of BV occupied by plasma
Measurement of GFR can be measured by the degree of clearance of what substance?
Inulin
How is GFR calculated?
GFR = ([U]inulin x V)/[P]inulin
Both BUN and serum creatinine increase when GFR _________
Decreases
What happens to BUN and serum creatinine in prerenal azotemia (hypovolemia)?
BUN increases more than serum creatinine and there is an increased BUN/creatinine ratio
What happens to GFR with age? Does this affect serum creatinine?
GFR decreases with age, although serum creatinine remains constant because of decreased muscle mass
What is the filtration fraction? How is it calculated?
Fraction of RPF filtered across the glomerular capillaries
Filtration fraction = GFR/RPF
What is the normal filtration fraction?
About 0.20. Thus 20% of the RPF is filtered; the remaining 80% leaves the glomerular capillares by the afferent arterioles and becomes the peritubular capillary circulation
What is the result of an increased filtration fraction?
Increases in the protein concentration of peritubular capillary blood –> increased reabsorption in the PCT
What is the result of a decreased filtration fraction?
Decreases in the protein concentration of peritubular capillary blood and decreased reabsorption in the PCT
What is the driving force for glomerular filtration?
Net ultrafiltration pressure across the glomerular capillaries
T/F: filtration is always favored in glomerular capillaries
True; because the net ultrafiltration pressure always favors the movement of fluid out of the capillary
How can GFR be expressed by the Starling equation?
GFR = Kf[(Pgc-Pbs)-(PIgc-PIbs)
Describe the glomerular barrier
Consists of capillary endothelium, basement membrane, and filtration slits of the podocytes
What lines the glomerular barrier, restricting filtration of plasma proteins?
Anionic glycoproteins (restrict filtration since plasma proteins are also negatively charged)
In glomerular disease, the anionic charges on the barrier may be removed, resulting in proteinuria
Pgc is the glomerular capillary hydrostatic pressure, which is constant along the length of the capillary. What increases Pgc?
Dilation of afferent arterioles or constriction of the efferent arterioles, which then increase net ultrafiltration pressure and GFR
Pi(gc) is glomerular capillary oncotic pressure. It normally _______ along the length of the glomerular capillary
Increases; because filtration of water increases the protein concentration of glomerular capillary blood
Glomerular capillary oncotic pressure is ________ by increases in protein concentration.
Increases in Pi(gc) cause _________ in net ultrafiltration pressure and GFR
Increased; decreases
pi(bs) is bowman’s space oncotic pressure. It is usually ____
Zero; therefore it is ignored because only a small amount of protein is normally filtered
Changes in GFR, RPF, and/or filtration fraction from:
Constriction of afferent arterioles (sympathetic activity)
GFR decreases (caused by decreased PGC)
RPF decreases
Filtration fraction: No change
Changes in GFR, RPF, and/or filtration fraction from:
Angiotensin II
Angiotensin II preferentiall constricts efferent arteriole - so:
GFR increases (caused by increase in PGC)
RPF decreases
Filtration fraction increases
Changes in GFR, RPF, and/or filtration fraction from:
Increased plasma protein concentration
GFR decrease (caused by increased Pi(GC))
RPF: no change
Filtration fraction decreases
Changes in GFR, RPF, and/or filtration fraction from:
Urethral stone
GFR decrease (caused by increased PBS)
RPF: no change
Filtration fraction: decrease
Reabsorption and secretion
