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What is the distribution of fluid in the body?
- 2/3 intracellular
- 1/3 extracellular
- 2/3 interstitial
- 1/3 vascular.
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What is a good index of ECF osmolarity?
- 2*Na concentration
- Full equation: ECF osmolarity = 2*Na+(glucose/18)+(Urea/2.8).
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What is the difference between mOsm/L and mM/L?
- mOsm: concentration of particles
- mM: concentration of molecules.
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What is isotonic concentration?
300 mOsm/L (150mM/L Na).
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What compartment of fluid enlarges/decreases with net changes in body fluid?
Extracellular.
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What can cause a loss of isotonic fluid?
- Diarrhea
- Hemorrhage
- Vomiting.
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What can cause a loss of hypotonic fluid (create hypertonic environment)?
- Dehydration
- Diabetes insipidus
- Alcoholism.
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what are the starling forces, what do they control?
- Capillary hydrostatic
- Interstitial oncotic
- Capillary oncotic
- Interstitial hydrostatic
- Control "bulk flow": net movement in/out of capillaries.
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What is the formula for fluid exchange?
Qf = k[(Ch+Io)-(Ih+Co)].
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How do you calculate blood volume?
Blood volume= plasma volume/(1-Hct).
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What are the two conditions for the development and maintenance of an edematous state?
- Increase in starling forces with bulk flow into interstitium
- Retention of Na and Water by kidneys.
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What are the two types of edema?
- Pitting edema: most common, responds to diuretics
- Non-pitting: lymphedema, lymphatic obstruction (also myxedema: hyperthyroid states).
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What is the most common form of pulmonary edema, first sign, confirmation?
- Cardiogenic
- Dyspnea
- Pulmonary Wedge pressure.
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What are the most common causes of non-cardiogenic (permeability induced) pulmonary edema?
- Gastric Aspirations
- Sepsis
- (ARDS).
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What forms in the absence of a functional epithelium?
- Hyaline membranes, sheets of pink proteinacious material
- (ARDS was also called hyaline membrane disease).
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Definition of membrane conductance?
Number of channels open in a membrane.
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What are the three main groups of channels?
- Ungated (open)
- Voltage gated
- Ligand gated.
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What makes up the net force on an ion across a membrane?
- Concentration force
- Electrical force
- (Electrochemical gradient).
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What is the nernst equation?
Ex= 60/Z*log([Xo]/[xi])
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What are the equilibrium potentials for Na, Cl, K?
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Is a cell's resting membrane potential sensitive to K, why?
- Yes
- There are ungated potassium channels
- Inreased extracellular conc: decreased efflux, depolarization
- Decreased extracellular conc: increased efflux, hyperpolarization.
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Is a cell's resting membrane potential sensitive to Na, why?
- No
- There are no ungated Na channels -- minimal to no Na conductance at resting conditions.
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What causes the absolute (functional) refractory period what does it determine?
- Voltage inactivation of Na Channels
- Length determines frequency of APs.
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What is the relative refractory period?
Greater stimulus than normal required to induce AP.
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What are the three main factors that determine AP velocity?
- Size of AP
- Diameter of axon
- Myelination.
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What region of a neuron has the lowest threshold?
Axon-hillock segment.
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What are the channels found in cardiac cells?
- Voltage Gated Na Channels (Fast)
- Voltage Gated Ca Channels (Slow, L-type)
- Voltage Gated Potassium Channels (2 types).
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What are the two types of voltage gated potassium channels?
- Inwardly Rectifying, iK1
- Delayed Rectifying, iK.
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What are the properties of the Inwardly Rectifying channels?
- Open at rest
- Close with depolarization
- Remain closed during plateau
- Open during repolarization.
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Properties of Delayed Rectifying channels?
- Opens with depolarization, closes once cell is repolarized
- Slow to open (delayed).
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What is the difference between fast and slow (cardiac) fibers?
- Slow fibers lack fast channels
- Fast: Ventricular, Atrial, Purkinje fibers
- Slow: AV, SA nodal fibers.
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What are the four phases of the ventricular AP, physio?
- O: Fast channels open (Na) -> Na influx -> rapid depolarization
- 1: Slight repolarization - closure of Na channels and K current
- 2: Plateau - L-type (Ca) channels open -> Ca influx -> iK1 channels close, preventing K efflux
- 3: Repolarization - L-type Ca channels close, potassium channels open
- 4: gK high - ungated potassium channels and iK1 channels open (delayed close slowly).
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What three factors produce the pacemaker property of specialized cardiac cells?
- if: Funny current
- Decreasing K conductance as iK channels close
- Increasing Ca conductance near the end of prepotential (calcium T-channels).
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What is If (funny current)?
Voltage gated Na channels that open when cell repolarizes, close when depolarizes.
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What phases do SA cells have?
- O: slow channel L-type Ca influx
- 3: rapid potassium efflux
- 4: unstable, gradual depolarization.
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What effect do sympathetics have on the pacemaker?
- Slope of phase 4 increases: increased funny current
- Increased calcium current
- increased potassium current.
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What effect do parasympathetics have on the pacemaker?
- Hyperpolarize by increasing potassium conductance
- Decreased slope of phase 4: decreased funny current.
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What are the intrinsic rates of SA, AV, Purkinje cells?
- SA: 100-120
- AV: 40-60
- Purkinje: 30-40
- Ventricular: slower.
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The PR interval signifies, how long?
- 120-210msec
- Atrial depolarization + conduction delay at AV node.
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QRS duration, indication, prolonged?
- 0.12 seconds
- Ventricular depolarization
- Prolongation: abnormal conduction through ventricles.
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In what direction does ventricular depolarization occur, repolarization?
- Depolarization: Endocardium to epicardium
- Repolarization: Epicardium to endocardium.
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What is first degree (partial block)?
- Conduction slowed through AV node
- PR >200msec.
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What is second degree block?
- Mobitz 1 (Wenckebach): progressively longer PR until dropped QRS
- Mobiz 2: dropped QRS after set of normal beats.
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Third degree block?
- No impulses from atria to ventricles
- atria and ventricles beat independently
- No correlation between P and QRS.
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What is Wolff-Parkinson-White (WPW) syndrome?
- Accessory pathway between atria and ventricles
- EKG: shortened PR, slurred R, widened QRS
- may initiate a reentrant tachycardia.
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Causes of left axis deviation?
- Left heart enlargement
- Conduction defects on left side
- Right heart MI.
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Causes of right axis deviation?
- Right heart enlargement
- Conduction defects on right side
- Left heart MI.
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