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ZOOL 401 Exam 3
Terms in this set (80)
______ = muscles can respond to a single stimulus with a single AP. Rapid contraction and relaxation occur because 2 processes are occurring at the same time: 1) calcium is being ______ from the SR 2) calcium is being ______ into the SR. The muscle ______ have a chance to develop its full amount of force before the relaxation processes have set in. Generating force requires ______ cycling, which takes time.
3 phases to a muscle twitch
Duration of AP is ______ compared to duration of twitch. Therefore, another AP can stimulate the muscle ______ relaxation is complete. ______ = force produced by second stimulus can be added to force leftover from first stimulus. When multiple AP occur closer together (increased frequency), ______ time is available for relaxation. The force produced by the individual twitches ______. ______ = when the rate of stimulation is high enough, a sustained contraction results. This produces ______ force than that developed by single twitch.
neurons control tension in muscle fiber by altering frequency of action potentials; this works because action potentials don't arrive at the muscle in a synchronized manner (so all fibers are never in relaxation phase of twitch at same time)
Multiple fiber summation
multiple neurons (and motor units) become activated at same time; smaller motor units usually stimulated first because they are more excitable than larger ones
*Muscle length remains constant as force develops (pushing against a wall)
*Force remains same while muscle shortens (doing a bicep curl w/dumbbell)
______ = means to shorten, but we usually use it to mean any type of muscle activity in response to stimulation. Technically, muscle doesn't always shorten: In an ______ contraction, the external muscle length remains constant, and the muscle develops force/tension while pushing or pulling against immovable objects. In an ______ contraction, the muscle force remains constant, while the muscle shortens.
Isometric length-tension curve
______ = peak tension occurs at an optimal resting length. When muscle is stretched, passive ______ builds. This occurs in absence of ______ formation and does not even require muscle ______. Source appears to be found in ______ themselves, but this is not clear.
Deoxygenated blood from body enters heart from vena cava -> right atrium -> tricuspid valve -> right ventricle -> pulmonary semilunar valve -> pulmonary artery -> lungs
Oxygenated blood from lungs enters heart from pulmonary veins -> left atrium -> bicuspid (mitral) valve -> left ventricle -> aortic semilunar valve -> aorta -> body
How blood flows through heart
Left and right
Consists of 2 pumps: ______. Associated with 2 vasculature systems: ______ (right) and ______ (left).
circulation through network of minor vessels that become enlarged and joined (via anastomoses) when a major artery is obstructed
Arterial system (arteries)
Venous system (veins)
Left ventricle of heart -> aorta -> arteries -> arterioles -> capillaries -> venules -> veins -> vena cavae -> right atrium of heart
Superior vena cava
Inferior vena cava
______ = carries blood from the heart. ______ = carries blood to the heart. PATHWAY (red -> purple -> blue). In ______, exchange occurs between blood and interstitial fluid. All veins from upper body drain into the ______. Veins from lower body drain into the ______.
Right ventricle of heart -> pulmonary trunk -> pulmonary arteries -> pulmonary capillaries -> pulmonary venules -> pulmonary veins -> left atrium of heart
PATHWAY (blue -> purple -> red). Note that the pulmonary ______ carry oxygen-rich blood from the lungs back to the heart. The entire ______ is sent to the lungs before being distributed throughout the systemic circulation.
______ = volume of blood that moves past a given point during a given period of time. ______ = blood flow is same through each section. ______ = blood flow through all of these vessels must add up to the total blood through the system.
Blood pressure (BP)
*Average aortic BP = 90 mm Hg (100 mm Hg = 2 psi)
Length/diameter of vessel and consistency/viscosity of blood
*Resistance increases, blood flow decreases
______ = force that causes blood to flow through vessels. Flow occurs in response to ______ between two points (P1-P2). ______ = net effect of all frictional components that oppose blood flow. Determined by ______. F = (P1-P2)/R.
Are found in myocardium of ventricles; responsible for contraction of ventricles
*APs in Ventricular Myocytes
*Kto = transient, outward. Kur = ultra rapid
*Ks = slow delayed
Phase 0 = very fast ______. Opening of voltage-gated fast ______ channels. ______ channels close.
Phase 1 = early ______. ______ channels inactivated. Opening of ______ channels.
Phase 2 = ______ phase. Ca2+ influx through ______ (long-lasting) channels. Opening of ______ channels.
*APs in Ventricular Myocytes
Phase 3 = rapid ______. ______ channels close. ______ permeability increases because slow delayed rectifier channels (Ks) are still open and rapid delayed rectifier channels (Kr) open.
Phase 4 = ______ membrane potential. Delayed rectifier ______ channels close. ______ is largely maintained by ion exchange pumps.
Absolute refractory period
Supernormal excitability period
______ = lasts as long as the isometric twitch; tetanus is not possible in the heart. ______ = exists because K+ permeability is slightly lower than normal; can get AP with just a mild stimulus, but the AP would be ______ than usual because not all Na+ channels have reset. Cardiac muscle fibers ______ normally stimulated during this period. Dangerous to do so because activity could spread to other tissue that is normally ______ at that time.
Ca2+-dependent Ca2+ release (CICR)
1)Skeletal muscle is innervated by motor neurons; cardiac myocytes ______. 2)AP profile is different. Different ion channels used; ______ duration in cardiac myocytes. 3)Role of calcium is slightly different. ______ calcium contributes to cardiac myocyte contraction via voltage-gated Ca2+ channels on T-tubules; in skeletal muscle, no role for this in contraction. In heart, RyR also participates in ______; this is not used in skeletal muscle contraction.
Calcium-induced calcium release (CICR)
AP is created on ______. AP travels along sarcolemma and into T-tubules, which contain ______ voltage-gated Ca2+ channels. ______ = small amount of extracellular Ca2+ that enters the cell and activates RyR on sarcoplasmic reticulum. ______ = SR releases more Ca2+ into cytoplasm. Ca2+ (mostly from SR) binds to T-T complex, myosin-binding sites are exposed on the actin, cross bridges form, etc.
Skeletal muscle = DHP and RyR1 ______ mechanically connected. Cardiac muscle = DHPR and RyR ______ physically connected. ______ = DHPR lets some calcium in, which stimulates RyR2 to release more calcium.
ATP-dependent calcium pump
Na/Ca exchanger (NCX)
*NCX is an antiport transporter
Calcium is put back into the SR by an ______. Calcium is pumped out of the cell by a ______. One Ca2+ out for every 3 Na+ in. 5000 Ca2+ out per second
What would happen to the strength of contraction if the Na/Ca exchanger did not function? This is the basis for ______ drugs such as digitalis. Note that it targets ______, which is necessary to maintain ______ concentration gradient so that NCX can function.
Cells in ______ generate an AP. Impulse travels ______ through right and left atria and to the AV node. Impulse travels ______ from AV node to left and right ventricles. ______ of the impulse at AV node ensures that atria finish contracting before ventricles start.
Bundle of His
From AV node, impulse enters the ______, which divides into two ______, one for each ventricle. These divide further in each ventricle, eventually becoming ______, specialized cells with high speed of conduction. From here, the impulse passes to muscle fibers in ventricle (______). These cells contract.
*Pacemaker cells at SA node
*Conduction cells such as Purkinje fibers
Electrical conduction system consists of specialized cells that ______ and ______ APs. The AP looks ______ for the various cells in the conduction system.
SA node contains specialized ______ cells that create APs. These cells ______ have a steady resting potential: After each AP, cells repolarize (phase 3) to a value called ______. Then the membrane begins a ______ depolarization (phase 4). When threshold is reached, cells enter a more ______ phase of depolarization (phase 0 or upstroke).
Rapid depolarization (phase 0 or upstroke); due to Ca2+ influx, mainly through ______ (long-lasting) channels. Repolarization (phase 3) occurs when ______ channels close, and ______ channels open (efflux occurs). When voltage reaches -40 mV, ______ open. Channels are activated at -40 to -60 mV; allows a mixed Na+/K+ inward current. This causes ______ Ca2+ channels to open. then the membrane begins a slow, spontaneous depolarization (phase 4). When threshold is reached, ______ Ca2+ channels close and ______ Ca2+ channels open. Cell enters a rapid phase of depolarization.
*Plexus = a tangled network of nerves
The heart is innervated by ______ autonomic fibers. These fibers are found in the ______.
______ preganglionic fibers emerge from upper thoracic region of spinal cord and synapse with postganglionic neurons in the sympathetic trunk (chain). Postganglionic fibers exit trunk as ______, which then travel to: the ______ (to increase heart rate) and the walls of the ______ (to increase force of contraction).
______ fibers travel from the medulla to the heart via cranial nerve X (vagus). The right vagus nerve innervates the ______, and the left innervates the ______. This stimulation will decrease heart rate.
Sympathetic stimulation and parasympathetic stimulation of the heart produce opposite effects: ______ stimulation increases heart rate. ______ stimulation decreases heart rate.
Sympathetic neurons release ______, which binds to ______ receptors on the SA nodal cells. This activates the cAMP second messenger system. cAMP increases opening of ______ channels and ______ Ca2+ channels. This increases the inward + current, causing shortening of phase 4 and decreased diastolic potential. ______ is reached sooner. When threshold is reached, ______ Ca2+ channels open, resulting in rapid depolarization (phase 0). The frequency of action potentials increases, which increases heart rate.
*on funny channels only
Funny channels and T-type calcium channels normally open based on ______. Sympathetic ANS stimulation causes these channels to open sooner through: 1) ______ 2) ______.
Parasympathetic neurons release ______, which binds to ______ receptors on the SA nodal cells. Activation closes ______ channels and ______ Ca2+ channels. This decreases inward + current, causing lengthening of phase 4 and increased (more negative) diastolic potential. Activation also opens ______ channels. Efflux further hyperpolarizes cells, which also contributes to lengthening phase 4 and increasing diastolic potential. As a result, it now takes longer than usual to reach threshold potential, and longer to open ______ Ca2+ channels (phase 0). The frequency of action potentials decrease, which decreases heart rate.
G protein-gated K+
The ______ subunit of the G protein decreases adenylate cyclase activity, thereby decreasing cAMP formation and protein kinase activity. This leads to decreased ______ of funny channels and T-type calcium channels, and decreased channel opening. The ______ subunits of the G protein open specialized ______ channels. These channels are different from the voltage-gated K+ channels responsible for phase 3. K+ efflux causes hyperpolarization, which further lengthens the time required to reach threshold.
Heart rate (HR) varies in response to physiological needs. ______ = resting heart rate <60 bpm. ______ = resting heart rate >100bpm. Chronotropic drugs influence HR; often target the SA node: ______ chronotropic drugs increase heart rate. ______: a muscarinic receptor antagonist. ______: a B1-adrenergic receptor agonist. ______ chronotropic drugs decrease heart rate. ______: a B1-adrenergic receptor antagonist (beta-blocker). ______: inactivates (blocks) funny channels; given to patients who cannot take beta-blockers
*SA node = 70 bpm, AV node = 50 bpm, ventricular pacemaker = 30 bpm
Under normal conditions, the ______ sets the heart rate. This is why these nodal cells are called ______ cells. If they don't function properly, then other cells adopt a pacemaker function. These ______ cells create impulses at a slower rate. Their activity is typically suppressed by the ______ because it creates impulses at a higher rate.
Are rhythm disturbances in heart rate; caused by heart attack (myocardial infarction), smoking, genetic conditions, and stress; include tachycardia, bradycardia, atrial fibrillation, skipping a beat, etc.; some are silent; can be harmless or an emergency
Atrial fibrillation (Afib or AF)
most common type of arrhythmia; instead of the SA node directing the rhythm, many atrial cells create impulses at same time; impulses spread throughout atria and compete for a chance to travel to AV node; ventricles contract irregularly; heartrate can be 300-600 bpm; consequences include 1) clots -> stroke (because blood doesn't efficiently leave atria 2) heart failure (heart must work harder to pump blood because ventricles don't efficiently fill before contraction occurs)
condition in which heart beats too slowly because the electrical conduction system is partially or completely blocked between the atria and ventricles
impulses are delayed between AV node and ventricles, but they do reach ventricles; rarely causes symptoms or problems; no treatment needed
Second degree (type 1)
impulses are delayed further and further with each subsequent heartbeat until a beat fails to reach to ventricles entirely; most often is physiologic; seen in highly relaxed states and during sleep; doesn't usually require treatment; due to defect in AV node
Second degree (type II)
some electrical impulses are unable to reach ventricles; less common, more serious than type I; serious; usually requires implanted artificial pacemaker; due to defect in His-Purkinje conduction system
Third degree (complete heart block)
none of the impulses from atria reach ventricles; ventricles may generate some impulses on their own called ventricular escape beats; produces very slow heart rate; fatigue, lightheadedness, decreased stamina; usually treated with artificial pacemaker
detects rate of atrial depolarization and stimulates ventricular depolarization accordingly; modern are activated on demand when an arrhythmia is detected; single-lead stimulate the ventricle; double-lead stimulate both atrium and ventricle
*Only shows electrical events; one must infer that contraction has occurred
detects electrical activity of the heart at the body surface; during phases of the cardiac cycle, some portions of the heart are + or - charged due to APs; this difference in electrical potential causes a current to flow in the external medium between these regions of the heart; largest voltage is only 1 mV, but it's sufficient to be detected; converts small surface currents into movements of a pen or spots of light on a cathode ray tube
*Atrial repolarization occurs here but is covered up
______ = atrial depolarization. ______ = ventricular depolarization. ______ = ventricular repolarization.
2:1 heart block
If P is not followed by the QRS complex, or if there is a delay between P and QRS, then conduction is ______ somewhere between atria and ventricles. ______ is a form of second degree AV nodal block and occurs when every other P wave is not conducted through the AV node to get to the ventricles (therefore, every other P wave is not followed by a QRS complex)
*One cardiac cycle = ventricular filling and ejection
______ = events that relate to blood flow from one heartbeat to the next one. What happens on the right side of the heart is ______ to what happens on the left side. The ventricular pump has 2 phases: 1) ______ = ventricles fill with blood 2) ______ = ventricles send blood through aorta and pulmonary trunk.
Venous blood -> into atria -> blood moves passively through open AV valves -> into ventricles
Atria contract -> blood is pushed through open AV valves -> into ventricles
Ventricular filling consists of two events: 1) ventricles fill ______ as venous blood returns to the heart. Atria fill at ______ time. PATHWAY. 2) Towards the end of filling, the atria ______ and add more blood to the ventricle. Normally, this contraction only ______ increases the volume of blood in the ventricles. PATHWAY. The ventricles are ______ during the filling phase. The semilunar valves are ______.
During ventricular ejection, ventricles ______. This increases ventricular pressure: ______ AV valves, prevents blood from flowing into atria. Pushes semilunar valves ______. Blood is pushed into the aorta and pulmonary trunk. After ejection, ventricles ______ and begin to fill with blood again (another filling phase begins).
______ = period of cycle when ventricles are relaxed and filling with blood. ______ = period of cycle when ventricles are contracting and pumping blood out of the heart.
Ventricular filling depends on pressure gradients: when intraventricular pressure ______ atrial pressure, blood moves from atria, forces AV valves open, ventricular filling begins. Ventricular filling is ______ at first. Most filling occurs before atrial contraction, which increases filling 10-30%. As heart rate ______, time available for ventricular filling ______. Now atrial contraction becomes an important contributor to complete ventricular filling.
End-diastolic volume (EDV)
During filling, semilunar valves are closed because: aortic pressure ______ left ventricle pressure and pulmonary artery pressure ______ right ventricle pressure. ______ = congenital or pathological abnormalities of semilunar valves let blood squirt back into ventricles during diastole. ______ = when blood flows back through the aortic valve during diastole. ______ = volume of blood in ventricles at end of ventricular filling i.e. end of diastole
Isovolumetric ventricular contraction
Ventricular contraction marks beginning of ______. When ventricles contract, pressure increases. Now ventricular pressure ______ atrial pressure. Momentary reversal of blood flow through AV valves. Valves fill like boat sails. Blood can't flow into atria. ______ = period during which both AV and semilunar valves are closed. When left ventricular pressure ______ aortic pressure, then aortic valve opens. Now ventricular ejection begins. Blood ejected rapidly at first; slows as pressure builds up.
Ventricles relax immediately after ______ (T wave). Ventricular pressure decreases. Eventually ventricular pressure ______ aortic pressure. ______ = blood flow reverses, aortic semilunar valves catch and close, now blood can't flow from aorta back to heart (both AV and semilunar valves are closed). ______ = momentary reversal in blood flow results in a brief drop in aortic pressure that appears in an aortic pressure tracing. Closing of semilunar valves marks end of ______ and beginning of ______.
Can hear 2 distinct sounds: ______ = closure of AV valves (beginning of systole). ______ = closure of semilunar valves (end of systole). Due to turbulence of blood flow rushing against closed valves. Additional sounds associated with abnormal heart conditions. ______ = high velocity jet of blood flowing through narrowed opening of an obstructed valve. Produces higher pitch sound = ______. Some valve abnormalities let blood leak ______; heard during normal periods of silence.
Cardiac output (CO or Q)
Depends on stroke volume and heart rate (CO = SV
Stroke volume (SV)
*SV = EDV-ESV
______ = amount of blood pumped from left ventricle to aorta in 1 minute; 5 L/min. ______ = volume of blood ejected from one ventricle in single beat; difference between end-diastolic volume (EDV) and end-systolic volume (ESV); ______ = # beats/minute (average 72 bpm). Total blood volume in all vessels and in heart = 5L. It takes a red blood cell ~1 minute to travel through entire circulation
In a healthy system, SV is fairly ______. If blood volume drops or if heart weakens, then SV ______ and CO is maintained by ______ HR. Drugs or conditions that increase HR are called ______ chronotropic factors. Those that decrease HR are ______ chronotropic factors. Heart rate is also controlled by the input from the nervous system: ______ increases HR, ______ decreases it.
In general, increasing HR will ______ CO, unless the HR is very high. Note that the upper limit for conduction of impulses through AV node limits HR to 250 bpm. With tachycardia of > 150-170 bpm, CO actually begins to ______. There isn't enough time to complete ventricular filling during ______. As a results, EDV decreases, which causes SV to decrease
Recall that CO = HR*SV. SV is an important contributor to CO. Recall that SV = EDV-ESV. Changes in EDV and/or ESV will impact SV (and therefore CO). In general, SV is regulated by: 1) ______ mechanisms (Frank-Starling law) 2) ______ mechanisms (sympathetic ANS).
*Starling's law of the heart
the heart pumps whatever volume of blood it receives (within limits); heart adjusts its output (SV) in response to changes in input (venous return i.e. EDV); SV increases in response to increased EDV, all other factors remaining constant
F-S Law describes a mechanism used by the heart to regulate ______. This mechanism is already ______ the design of the heart. Therefore, it is called an ______ mechanism (occurs within the heart itself). The F-S Law is based on the observation that when EDV ______, the length of the cardiac muscle fibers in the ventricles ______, too. In ______, recall that there was an optimal length for muscle contraction. If the fibers were stretched too much or not enough, then maximum force could not be generated.
In the ______, the length-tension relationship is not bell-shaped. Instead, the tension (force) developed continues to ______ when the muscle fibers are stretched. In other words, ______ fiber length correlates with ______ force of contraction (tension).
Note the units on the x- and y-axes are different in the length-tension relationship graphs in skeletal muscle and heart. Sarcomere stretching in ventricular myocytes will be based on the maximum volume of blood in the ventricles (______). If this increases, then ______ stretching of the fibers. So "length" is replaced with this on x-axis in graph for heart. In the heart, the force generated by the ventricular myocytes directly impacts the ______ of blood. If the force of contraction is greater, then ______ will increase. So "tension" is replaced with this on the y-axis in the graph for the heart.
*Increased afterload = increased cardiac workload
______ = volume of blood in ventricles at end of diastole (end diastolic pressure). Increased in: hypervolemia, regurgitation of cardiac valves, and heart failure. ______ = resistance left ventricle must overcome to circulate blood. Increased in: hypertension and vasoconstriction.
*F-S Law - if EDV increases, then SV increases; all of blood that reaches heart can be pumped out.
*Ventricle walls have some elasticity to them
What happens if preload increased? This means that ______ blood is returned to the heart. So the ventricular walls will be stretched ______. This will: 1) ______ force of contraction, which will be seen as ______ SV 2) Cause the stretched walls of the ventricle to snap back to a non-stretched position, due to ______. This action will contribute to force generation.
What happens if afterload increases? This means that aortic pressure ______. In order for the left ventricle to generate enough pressure to open the semilunar valve, ______ force is going to be needed. It generates force based on how stretched the walls are, which is determined by ______. Instead of opening valve at 80 mmHg pressure, perhaps now it will require 100 mmHg. It will take ______ for left ventricle to generate force needed to overcome afterload. So aortic semilunar valve will open and ejection will occur ______ than usual. Not all of the blood will have been ejected before ventricular repolarization (relaxation) occurs. SV ______, leaving more blood behind in ventricle, so ESV ______.
*In other words, in the case of increased afterload, F-S Law provides for more forceful contraction during next cardiac cycle. This helps maintain constant cardiac output despite changes in aortic pressure.
Frank-Starling takes care of things on the ______ cardiac cycle. The blood that was left behind (extra ESV), when added to normal diastolic filling from pulmonary veins, results in increased ______. Now the ventricle walls (and sarcomeres) will be extra stretched so ______ force will be generated, the aortic semilunar valve will open sooner. ______ will increase, but ______ will be normal. F-S Law affects each ventricle independently; adjusts the vigor of contraction on ______ basis.
In summary, this law explains how SV changes in response to EDV, which allows CO to remain relatively ______. What if blood pressure is chronically elevated, producing a chronically high afterload? More permanent changes will occur: Heart will increase in ______ (hypertrophy) and individual muscle fibers will contain more ______. ______ = can occur in both ventricles; a response to abnormal afterload placed on heart because of disease (hypertension).
Force of contraction
Ionotropic drugs such as digitalis (digoxin): Increase ______ and shift Frank-Starling curve ______.
*Extrinsic control of SV
Factors outside of heart can increase vigor of ventricular contraction ______ changing EDV. Changes in contractility result from changes in rate and extent of ______ movement into cytoplasm; impacted by sympathetic nervous system
Consequence #1: ______ rate and force of contraction. Sympathetic ANS stimulation ______ rate and extent of calcium movement from sarcoplasmic reticulum (SR) and from outside cell by ______ DHPR and RyR2. This ______ the rate and force of contraction of ventricles, which ______ SV.
DHPR and RyR2
Activation of ______ adrenergic receptors activates cAMP and protein kinases, which phosphorylate ______. This facilitates channel opening and entry of calcium into the cytoplasm, which ______ rate and force of contraction.
______ stimulation increases contractility independently of EDV. Increased contractility and rate will ______ the rate at which force develops, so the aortic semilunar valve will be opened ______, causing SV to ______.
Consequence #2: ______ rate of relaxation. Sympathetic ANS stimulation ______ rate at which the SERCA pump moves calcium from cytoplasm to the SR. This ______ rate of relaxation. This is very important during ______. Recall that sympathetic ANS stimulation increases HR. At very high HR, cardiac output is limited by inadequate filling during ______. By ______ rate of relaxation, sympathetic ANS stimulation shortens ______, which increases the duration of ______. Now there is more time for ventricular filling to occur (EDV increases).
Activation of ______ adrenergic receptors activates cAMP and protein kinases, which phosphorylate ______, so that it can no longer inhibit SERCA activity. Now calcium is more quickly removed from the cytoplasm, ______ relaxation.
Summary of how SV can be altered: Increase SV, increase ______. Increase ______, increase SV (F-S law). Increase ______, increase SV. Increase ______, increase contracility (and HR). Increase ______, decrease SV.
Changes in ______ will change SV (F-S law; intrinsic). Changes in ______ result from changes in cytoplasmic calcium and occur independently of EDV (sympathetic ANS; extrinsic). Although these are independent mechanisms, they work ______ to produce even greater changes in SV.
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