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FA Physiology


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Myocardial action potential During phase 0 of the myocardial action potential, -------- ------- ------ channels open.
voltage-gated Na+
Initial repolarization, or phase 1, is when voltage-gated ---- channels begin to open and when voltage-gated Na+ channels ---- (close OR inactivate?).
K+ begin to open. Na+ channels inactivate.
Phase 2 is the plateau, when ------- influx balances ------ efflux.
Ca++ influx balances K+ efflux.
Ca++ influx triggers another Ca++ release from the ------- --------, which leads to myocyte ------.
sarcoplasmic reticulum. contraction
During what phase do the voltage-gated Ca++ channels close?
phase 3
During phase 3, the rapid repolarization phase, there is massive -------- efflux.
During resting potential, the myocyte membrane is highly permeable to what ion?
Where does the pacemaker action potential normally occur?
SA and AV nodes.
The phase 0 stroke of the pacemaker AP differs from that of the ventricular AP in that the pacemaker cells lack fast ------ ------- ------- channels.
voltage-gated Na+
By using Ca++ current for phase 0 upstroke, the conduction velocity is slowed compared to the fast Na+ upstroke of the ventricular AP. What purpose does this slowed conduction serve?
The AV node then prolongs trasmission from the atria to ventricles, allowing for sufficient filling time.
Which phase of the ventricular AP is absent in the pacemaker AP?
phase 2, during which there is Ca++ influx in the ventricular AP.
What ion is responsible for the slow depolarization current in the pacemaker AP? This current accounts for the automaticity of the SA and AV nodes.
Na+ (this is the If, or the funny current)
ACh and catecholemines alter the slope of phase 4, which determines the ------- ------.
heart rate
Phase 4 depolarization occurs during which phase of the cardiac cycle?
During exercise, cardiac output (CO) INITIALLY increases as a result of an increase in -----.
Stroke volume
After prolonged exercise, CO increases as a result of an increase in ------.
heart rate
the product of ----- and ----- equals cardiac output.
stroke volume X heart rate
Fick principle for cardiac output :
CO = (rate of O2 consumption) / (arterial O2 content-venous O2 content)
Formula for mean arterial pressure
What is pulse pressure?
systolic - diastolic
Pulse pressure correlates to what other measure?
stroke volume
What three entities affect stroke volume? (Mnemonic: SV CAP)
contractility, afterload, preload
If afterload is decreased, what happens to stroke volume?
What happens to stroke volume in pregnancy?

Name two other conditions that cause a similar change in SV?

Anxiety and Exercise
What does hypoxia/hypercapnea do to contractility?
What does a decrease in extracellular Na+ do to contractility?
Digitalis increases intracellular ---- ion.
Na+, with a resultant increase in IC Ca++
What does acidosis do to contractility?
Ventricular end diastolic volume is -----.
What is afterload?
diastolic arterial pressure (proportional to peripheral resistance)
What class of drugs decreases preload?
venous dilators (nitroglycerine)
Drugs like hydralazine decrease ------.
afterload (they are vasodilators)
Force of contraction is proportional to -------.
initial length of cardiac muscle fiber (preload)
Sympathetic stimulation will shift the curve on a graph of CO vs. preload up and toward the ---- (right / left).
Ejection fraction is stroke volume divided by -----.
end diastolic volume
EF is an index of ventricular -------.
What is normal EF?
greater than 55%
Viscosity of blood depends mostly on ------
name three conditions in which viscosity increases.
(1) polycythemia
(2) hyperproteinemic state (e.g. multiple myeloma)
(3) hereditary spherocytosis
Resistance is proportional to viscosisty and inversely proportional to ---------.
radius to fourth power.
Decreasing the volume of blood shifts the venous pressure curve to the ------. (on a graph of venous return vs. RA pressure)
On a graph of CO vs. EDV, digitalis (positive inotrope) will shift the curve ------.
Isovolumetric contraction is the period between ---- valve closure and ----- valve opening.
between mitral v. closure / aortic v. opening
During which period is O2 consumption by the heart the highest?
isovolumetric contraction
For each heart sound, give the significance:

mitral and tricuspid valve closure
aortic and pulmonic valve closure
at end of rapid ventricular filling

sound is normal in children but indicates disease in adults
high atrial pressure/ stiff ventricle
For each situation, give the corresponding heart sound.

high atrial pressure/ stiff ventricle
aortic and pulmonic valve closure
mitral and tricuspid valve closure
at end of rapid ventricular filling
Dilated CHF is associated with which extra heart sound?
S4 is associated with what condition?
hypertrophic ventricle
For each wave of the jugular venous pulse, give the corresponding physiologic event.

a wave

and elevated (Canon) a wave indicates what
atrial contraction

AV dissociation
c wave
RV contraction; tricuspid valve bulging into atrium and the beginning of each systole
x descent and v wave
relaxation of the right atrium

volume of blood that enters the right atrium during Ventricular systole/increase in atrial pressure due to filling against closed tricuspid valve.
What is the function of the T tubule?
allows depolarization to travel down it, leading to muscle contraction
This band in a skeltal muscle contains MYOSIN filaments (thick filaments)
H band/zone
This band in a skeltal muscle contains only ACTIN filaments (thin filaments)
I band
Which band in a muscle remains the same size?
A band (dark bands)
During muscle contraction, which bands shrink?
H, I, and Z bands
What is the function of the ryanodine receptor?
voltage-sensing CA+2 channel protein in the sacroplasmic reticulum
What is the function of the dihydropyridine receptor?
voltage-sensing CA+2 channel protein in the T-tubule
Where does the calcium come from that stimulates cardiac muscle contraction?
extracellular calcium enters the cell during the plateau of the action potential and stimulates release of calcium from the sarcoplasmic reticulum (calcium-induced calcium release)
Name three ways that cardiac muscle differs from skelatal muscle with regards to its electrophysiolopgy.
1. action potential has a plateau which is due to Ca++ influx.

2. Cardiac nodal cells spontaneously depolarize, resulting in automaticity.

3. Cardiac myocytes are electrically coupled to each other by gap junctions.
How does the action potential in smooth muscle lead to contraction?
The smooth muscle membrane depolarizes, voltage-gated calcium channels open, calcium rushes into the cell, calcium binds to calmodulin, calcium calmodulin complex activates myosin light chain kinase, MLCK phosphorylates myosin light chain which crosslinks with actin and causes contraction.
How is myosin light chain phosphatase involved in relaxation.
It dephosphorylates myosin light chain, making it less able to cross-bridge with actin--allowing relaxation
Muscle contraction is a result of cross-linking between which two proteins?
actin and myosin
____binds to myosin head during a skeletal muscle contraction
Electrocardiogram Identify the significance of each of the following: P wave
atrial depolarization
PR segment
conduction delay through AV node
QRS complex
ventricular depolarization
QT interval
mechanical contraction of ventricles
T wave
ventricular repolarization
ST segment
isoelectric, ventricles depolarized
U wave
caused by hypocalemia
What is masked by the QRS complex?
atrial repolarization
Where is the pacemaker of the heart?
SA node in right atrium
Match the ECG finding with the description of the ECG trace:

1. Progressive lengthening of the PR interval until a beat is "dropped" (a pwave not followed by a QRS complex). Usually asymptomatic.
B. 2nd degree AV block, (Mobitz type I) (wenckebach)
2. A rapid succession of identical, back-to-back atrial depolarziation waves. "sawtooth appearance"
G. Atrial flutter
3. Dropped beats that are not preceded by a change in the length of the PR interval . These abrupt, nonconducted P waves result in a pathologic condition.
C. Mobitz Type II
3. PR interval is prolonged (>200 msec). Asymptomatic
A. AV block 1st degree
4. Chaotic and erratic baseline with no discrete p waves in between irregularly spaced QRS complexes
F. Atrial Fibrillation
5. The atria and ventricles beat independently of each other. Both P waves and QRS complexes are present, although the P waves bear no relation to the QRS complexes. The atrial rate is faster than the ventricular rate.
D. 3rd Degree, complete AV block
6. A completely erratic rhythm with no identifiable waves.
E. Ventricular Fibrillation

a fatal arrythmia witho immediate defibrillation
Name five compensatory mechanisms that are activated when baroreceptors detect low MAP
1. Heart rate increases (beta1)
2. contractility increases (beta1)
3. venous tone--venous return increases (alpha)
5. TPR increases (alpha)
4. kidneys retain sodium and H20 (renin-angiotensin-aldosterone system)
Aortic Arch baroreceptor transmits via what nerve to the medulla?
vagus (X)
Carotid Sinus baroreceptor transmits via what nerve to the medulla?
glossopharyngeal (IX)
Decreasing the stretch on the baroreceptors leads to: (increased/decreased) efferent sympathetic stimulation
Increased. Decreased stretch as a result of decreased MAP decreases the afferent signal from the baroreceptor which leads to an increase in the efferent sympathetic signal from the brain
Hypotension leads to vaso____(constriction/dilation)
What is the effect of a carotid massage?
It increases the pressure in the carotid artery, increases the stretch of the baroreceptors, and leads to a decrease in heart rate.
Which receptor transmits to the medulla, responding only to increase blood pressure
Aortic arch
Name three physiological changes that are sensed by peripheral chemoreceptors (carotid and aortic bodies).
1. decreased pO2 below 60 mmHg;
2. increased pCO2;
3. decreased pH of blood
Central chemoreceptors (in brain) respond to ____ and ____ but do not directly respond to _____.
Respond directly to changes in pH and pCO2, but not pO2
Which organ has the largest share of systemic cardiac output?
Which organ has the highest blood flow per gram of tissue?
Which organ has a large arteriovenous O2 difference
Match the normal pressures with a heart chamber or major vessel: A. Right atrium/vena cava, B. Right Ventricle, C. Pulmonary Artery, D. Left Atrium, E. Left Ventricle, F. aorta <150/10
F. aorta
What does the PWCP approximate?
Pulmonary capillary wedge pressure approximates left atrial pressure.
How is PWCP measured?
Swan-Ganz catheter
What factors regulate blood flow to the following tissues? Heart
local metabolites: O2, adenosine, NO
local metabolites: CO2; H+(pH)
myogenic and tubuloglomerular feedback
hypoxia causes vasoconstriction (only organ in which hypoxia leads to vasoconstriction)
Skeletal muscle
local metabolites: lactate, adenosine, K+
sympathetic stimulation in response to changes in body temperature
Plasma - clotting factors = what?
Blood is ___% of body weight
Blood is ___% plasma.
55% The rest is formed elements (hematocrit)
Plasma is ____% proteins.
Plasma proteins are ___% albumin.
Plasma proteins are ___% globulins
Leukocytes are normally ____% PMNs, ___% lymphocytes, ___% monocytes, ___% eosinophils, ___basophils.
40-70% PMNs, 20-40% lymphos, 2-10% monos, 1-6% eos, <1% basophils
What is MAP in terms of systolic and diastolic pressures
1/3 systolic +2/3 diastolic
What happens to CO if HR is too high
diastolic filling decreases and CO decreases
What is an example of this
ventricular tachycardia
What is SV in terms of EDV and ESV
Name 4 things that increase myocardial 02 demand
An INCREASE in Afterload, contractility, heart rate, and heart size
What is Wolff-Parkinson-White syndrome
accessory conduction pathway from atria to ventricle (bundle of kent), bypassing AV node. As a result ventricles partially depolarize earlier giving rise to the characteristic
What is the characteristic wave in WPW syndrome
delta wave
What can WPW lead to
reentry current and supraventricular tachycardia
Forces that move fluid out of capillary?
Capillary pressure (Pc) and Interstitial fluid colloid osmostic pressure
Forces that move fluid into capillary?
Interstitial fluid pressure (Pi) and Plasma colloid osmotic pressure
Equation for net filtration pressure?
P net = [(Pc - Pi)] - (colloidc - collidi)]
Conditions that cause edema by increased capillary pressure?
heart failure
Conditions that cause edema by increased capillary permeability?
toxins, infections, burns
Conditions that cause edema by decreased plasma proteins?
nephrotic syndrome, liver failure
Conditions that cause edema by increased fluid colloid osmotic pressure?
lymphatic blockage
What are the physiological responses to high altitude: 1-, 2-, 3-, 4-, 5-, 6-, 7-
1- acute increase in ventilation, 2- chronic increase in ventilation, 3- increase in EPO leading to an increase in hematocrit and hemaglobin (chronic hypoxia), 4- increase in 2,3-DPG, 5- Cellular changes (increase in mitochondria), 6- increase in excretion of bicarbonates to compensate for respiratory alkalosis, 7- chronic hypoxic pulmonary vasoconstriction results in RVH
What is the action of 2,3-DPG?
binds to hemaglobin so that hemoglobin releases more O2
What does acetazolamide doe?
it increases the renal excretion of bicarbonates.
What are 5 important lung products?
Surfactant, prostaglandins, histamine, ACE, Kallikrein
What does surfactant do? What is Surfactant? What makes Surfactant?
It decreases alveolar surface tension which increases complaince, it is made of dipalmitoyl phosphatidylcholine (lecithin), it is produced by type II pneumocytes
What pathologic process has a deficiency of Surfactant?
Neonatal RDS
What are the funcitons of ACE
converst angiotensin I to Angiotensin II, inactivates bradyykinin (ACE inhibitors yield increase bradykinin and cause cough, angioedema)
What is the colapsing pressure
What does Kallikrein do?
It activates bradykinin
What is the Residual volume (RV)?
air left in lung after max expiration
What is the expiratory reserve volume (ERV)?
air that can still be breathed out after nml expiration
What is the tidal volume (TV)?
air that moves into lung with each quiet inspiration (nml = 500ml)
What is the inspiratory reserve volume (IRV)?
Air in excess of tidal volume that moves into lung on max inspiration
What is the vital capacity (VC)?
What is the functional reserve capacity (FRC)?
RV + ERV (volume in lungs after normal espiration)
What is the inspiratory Capacity (IC)?
What is the total lung capacity (TLC)?
Decreased affinity of hemoglobin for O2 = shift ___
A right shift is caused by an increase or decrase in each of the following factors: P50, metabolic needs, PCO2, temperature, H+, pH, altitude, and 2,3-DPG
Increase in all but pH
Fetal Hb curve is shifted ___
Left (increased affinity for O2)
T/F: Pulmonary circulation is normally a low-resistance, low-compliance system
F - Low-resistance, high-compliance
Cor pulmonale and subsequent RV failure are a consequence of pulmonary ______
Hypoxic vasoconstriction that shifts blood away from poorly ventilated regions is caused by ______
Decrease in PaO2
In normal health, O2 is perfusion or diffusion limited?
Perfusion limited - gas equilibrates along the length of the capillary
Which of the following is diffusion limited: CO2, N2O, or CO?
CO - gas does not equilibrate by the time the blood reaches the end of the capillary
When is O2 diffusion limited? What is the equation for Vd?
Exercise, emphysema, fibrosis

Vd = (Vt) x (PaCO2 -PeCO2)/PaCO2
Pa = arterial & Pe = expired air
What is the ideal V/Q ratio?
V/Q = 1 (permits adequate oxygenation)
At the base of the lung, there is greater ventilation, perfusion, or both?
Both are greater
What is V/Q at the apex of the lung?
V/Q = 3 (wasted ventilation)
What is V/Q at the base of the lung?
V/Q = 0.6 (wasted perfusion)
V/Q = 0 implies _____
Airway obstruction (shunt)
V/Q = infinity implies ______
Blood flow obstruction (physiological dead space)
Organisms such as TB that thrive in high O2 flourish in the apex or base of the lung?
During exercise (increased cardiac output), the vessels in the apex of the lung ___-------_______
Vasodilate such that V/Q approaches 1 (versus normal apex V/Q of 3)
CO2 is transported from tissue to lungs in these 3 forms: ______
(1) Bicarbonate (2) Bound to hemoglobin (3) Dissolved CO2
What percentage of CO2 is transported in the form of bicarbonate?
What is the intracellular enzyme that converts CO2 into H2CO3?
Carbonic anhydrase
H2CO3 is broken down into H+ and HCO3. What happens to the H+?
H+ combines with Hb to form HHb (deoxyhemoglobin)
H2CO3 is broken down into H+ and HCO3. What happens to the HCO3?
HCO3 is pumped out of the red blood cell in exchange for Cl-
What is the Haldane effect?
Oxygenation of hemoglobin promotes the dissociation of CO2 from hemoglobin
What does kallikrein do
Activates bradykinin
What affect to ACE inhibitors have on bradykinin
Increase bradykinin, which lead to cough and angioedema
Equation for clearance?
Cx = UxV/Px; Cx = clearance of X; Ux = urine concentration of X; Px = plasma concentration of X; V = urine flow rate
Significance of Cx < GFR?
net tubular reabsorption of X
Significance of Cx > GFR?
net tubular secretion of X
Significance of Cx = GFR?
no net secretion or absorption of X
The two determinants of filtration across the glomerular filtration barrier are - and -.
size and charge
Components of filtration barrier?
Fenestrated capillary endothelium, fused basement membrane with heparin sulfate, epithelial layer
What comprises epithelial layer?
podocyte foot processes
The charge on the fused basement membrane is -.
The charge barrier is lost in - , characterized by what four findings?
nephrotic syndrome, albuminuria, hypoproteinemia, generalized edema, hyperlipidemia
What substance is freely filtered and is neither reabsorbed nor secreted?
Clinically, - clearance is a good measure of GFR.
Equation for GFR
GFR = U(in) X V/P(in) = C(in)
Where in nephron is PAH secreted?
proximal tubule
By what mechanism is it secreted?
2Ëš active transport. Mediated by a carrier system for organic acids
What drug competively inhibits PAH's secretion?
What substance entering the nephron is filtered AND secreted?
Equation for effective renal plasma flow?
ERPF = U(pah) X V/P(pah) = C(pah)
Equation for renal blood flow?
RBF = RPF/1-Hct
Equation for filtration fraction?
Class of substances responsible for dilating afferent arteriole?
Class of drug that inhibits production of above substances?
Substance responsible for constricting efferent arteriole?
angiotensin II
Class of drugs that inhibits production of angiotensin II?
ACE inhibitors
What factors do you need to know to calculate free water clearance?
urine flow rate, urine osmolarity, plasma osmolarity
Equation for free water clearance?
C(H2O) = v - C (osm)
Where is glucose absorbed in the nephron?
proximal tubule
At what plasma glucose level does glucosuria begin?
200 mg/dL
At what plasma glucose level is the glucose threshold mechanism (Tm) saturated?
350 mg/dL
How many carrier systems involved in amino acid reabsorption?
Where does 2Ëš active transport occur?
proximal tubule
Substances reabsorbed in the early proximal tubule?
all glucose and amino acids; most bicarbonate, sodium, and water
- is secreted in the early proximal tubule, which acts as a buffer for -.
ammonia, H+
Section of the nephron that is impermeable to sodium?
thin descending loop of Henle
Substances actively reabsorbed in the thick ascending loop of Henle?
Na+, K+, Cl-
- and - are indirectly reabsorbed in the thick ascending loop of Henle.
Ca+2 and Mg+2
Substances actively reabsorbed in the early distal convoluted tubule?
Na+ and Cl-
Reabsorption of - is under the control of - (hormone) in the early distal convoluted tubule,
Ca+2, PTH
Substances regulated by aldosterone in collecting tubules?
Na+, K+
Reabsorption of water is regulated by - in the collecting tubules?
Osmolarity of the medulla can reach a concentration of -.
1200 mOsm
Relative concentration equation for comparing concentrations of substances in renal tubule to plasma?
[tubular fluid]/[plasma]; TF/P
Substance with highest TF/P?
Why does this substance have the highest TF/P?
Its both filtered and secreted
Substances with lowest TF/P?
glucose and amino acids
Why do these substances have the lowest TF/P's?
They are reabsorbed almost completely in the early proximal tubule
What substance has a TF/P = 1?
Where does renin come from in the kidney?
Cells in the juxta-glomerular apparatus
Mechanism stimulating renin release?
Decrease in blood pressure in kidneys
What does renin do?
Cleaves angiotensinogen to angiotensin I
Angiotensin I is then cleaved by -, primarily in the -, to make -?
angiotensin converting enzyme, lung capillaries, angiotensin II
4 actions of angiotensin II?
1) Potent vasoconstriction, 2) Release of aldosterone from adrenal cortex, 3) release of ADH from the posterior pituitary, 4) Stimulates hypothalmus to increase thirst.
Overall actions of angiotensin II?
Increase intravascular volume and blood pressure
- (hormone) released from the - may act as a "check" on the renin-angiotensin system in such cases as heart failure.
ANP, atria
Endothelial cells of peritubular capillaries secrete - in response to hypoxia.
What is the enzyme responsible for converting 25-OH vitamin D to I,25-(OH)2?
What hormone activates this enzyme?
What is the function of secreted prostaglandins in the kidney?
Vasodilation of the afferent arterioles to increase GFR
Class of drugs that can cause renal failure in high vasoconstrictive states due to inhibition of prostaglandin production?
NSAIDS. Prostaglandins are keeping the afferent arterioles vasodilated to maintain GFR. Inhibition of prostaglandin production leads to acute renal failure.
Name two stimuli for ADH secretion?
Increased plasma osmolarity; decreased blood volume
Two actions of ADH other than increasing water permeability in the collecting duct
Increase urea absorption in the collecting duct; Increase Na/K/2Cl activity in thick ascending limb
Hormones stimulated to be released by a decrease in blood volume?
ADH, aldosterone, angiotensin II (via renin)
Hormones that increase Na+ reabsorption?
Aldosterone (distal tubule); angiotensin II (proximal tubule
Three effects of PTH on the kidney?
1) Increase Ca+2 reabsorption, 2) Decrease phosphate reabsorption, 3) Increase vitamin D production
Hormone that decreases sodium reabsorption?
What is the primary disturbance in Metabolic acidosis?
a decrease in bicarbonate
What is the compensation?
Increased CO2 by decreased respiration
What are common causes?
diabetic ketoacidosis (production of ketone acids), diarrhea (loss of GI bicarb), salisylate overdose, acetazoleamide (diuretic) OD, lactic acidosis, renal failure (can't excrete organic acids), ethylene glycol ingestion
What is the primary disturbance in respiratory acidosis?
A build-up in CO2
What are some common causes?
hyperventilation, high altitude, pneumonia and pulmonary embolus (hypoxemia causes hyperventilation_
What is the primary disturbance in metabolic alkalosis?
increased bicarbonate
What is the Henderson Haselbach equation?
pH = pKa + Log (HCO3-)/(.03*pCO2)

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