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Cardiovascular system
Physiology of the heart
49
Physiology
Graduate
10/09/2010

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Cards

Term
Syncytium
Definition

cardiac cells are interconnected allowing the action potential spreads when one cell becomes excited.

 

Intercalated disc of the cell membranes are fused

with one another = gap junctions

Term
Resting potential in normal cardiac cells
Definition
-85 - 90 mV
Term
resting potential for normal conductive fibers
Definition
-90 - 100 mV
Term
The cause of action potentials of cardiac muscle 
Definition

Opening of 2 channels:

1. Opening of fast sodium channels 

2. slow opening of slow calcium channels or calcium-sodium channels (stay opening for several tenths of a second)

 

 

Term
The cause of the plateau during cardiac action potential
Definition

large quantities of Ca and Na ions into the interior of the cardiac muscle fiber allow for prolonged periods of depolarization

Ca ions that enter during the plateau phase activate the muscle contractile phase

Term
what is the velocity of conduction of the excitatory action potential signal along both atrial and ventricular muscle fibers
Definition
0.3 - 0.5 ms or 1/250 velocity of large nerve fibers  or 1/10 the velocity of skeletal muscle fibers
Term
What is the velocity of conduction for the specialized jeart conductive system - the Purkinje fibers
Definition
4 m/Sec
Term
What is the normal refractory period of the ventricles
Definition
0.25 - 0.30 seconds (the duration of the plateau)
Term
relative refractory period
Definition

0.05sec 

the muscle is more difficult than normal to excite, but can be excited by a strong excitatory signal

Term
excitation - contraction coupling
Definition

action potential->membrane of transverse (T) tubules->longitudinal sarcoplasmic tubules->release of Ca -> into muscle sarcoplasm -> into myofibrils -> catalyze the chemical reactions ->sliding of actin-myosin filaments

Large amts of Ca ions from the T tubules and SR

Strength of contraction cardiac muscle = concentration of Ca ions in ECF

Term
duration of cardiac muscle
Definition

atrium 0.2 seconds

ventricle 0.3 seconds

Term
Systole
Definition
period of contraction
Term
diastole
Definition
period of relaxation when the heart fills with blood
Term
cardiac cycle
Definition
beginning of one heartbeat to the beginning of the next
Term
P wave
Definition

spread of depolarization through the atria and followed by atrial contraction

slight rise in atrial pressure curve immediately after P wave

Term
QRS wave
Definition

0.16 seconds after onset of P wave

result of depolarization of the ventricles

begins slightly before the onset of ventricular systole

Term
ventricular T wave
Definition

repolarization of the ventricles

Occurs before the end of ventricular contraction

Term
Filling of ventricles
Definition

 - lg amts of blood accumulate in R & L atria bc of closed AV valves

 - when systole is over, the ventricular pressures fall 

 - increased pressure in the atria cause AV valves to open

1st 1/3 diastole = rapid filling

2nd 1/3 diastole = small amt of blood of flows

3rd 1/3 diastole = atria contracts

Term
emptying of the ventricles during systole
Definition

1. period of isovolumic (isometric) contraction

2. Period of ejection

3. period of isovolumic (isometric) relaxation

4. End-diastole volume, end-systolic volume, & Stroke volume output

Term
period of isovolumic (isometric) contraction
Definition

 

-after ventricle contraction begins, pressure increases, causing AV valve to close

-Tension increases in the muscle but little or no shortening of the muscle fibers is occuring 

 

Term
period of ejection
Definition

 

-LV pressure rises about 80mmHg & RV pressure rises about 8mmHg

-semilunar valves open

-65-70% empties during the first 1/3 of period = rapid ejection

-30% during last 2/3 = slow ejection

 

Term
period of isovolumic (isometric) relaxation
Definition

-end of systole

- R & L intraventricular pressures decrease rapidly

- AV valves close

Term
End-diastolic volume, End-systolic volume, & stroke volume output
Definition

-normal filling of the ventricles increases the volume of each ventricle to about 110 - 120 ml = end-diastolic volume

 - ventricles empty during systole, the volume decreases to about 70ml = stroke volume output

-the remaining volume in each ventricle, about 40-50 ml = end systolic volume

Term
SV = 
Definition
SV = EDV - ESV
Term
Ejection fraction
Definition

the fraction of the EDV that is ejected

usually about 60%

Term
EF = 
Definition
SV/EDV
Term

AV valve

aka tricuspid valve

aka mitral valve

Definition
prevents backflow from ventricles into the atria during systole
Term
semilunar valves
Definition
prevent backflow from the aorta and the pulmonary arteries into the ventricle during diastole
Term
chordae tendineae
Definition

-papillary muscles contract when the ventricular walls contract

-they pull the vanes of the vavles inward toward the ventricles to prevent their buildging too far back toward the atria during ventricular contraction

Term
semilunar valves
Definition

-aortic and pulmonary artery semilunar valves

-high pressures in the arteries at the end of the systole cause the semilunar valves to snap closed

-velocity of blood ejection through the semilunar valves is far greater than through larger AV valves

-constructed with pliable fibrous tissue

Term
incisura
Definition

-occurs on the aortic pressure curve when the aortic valve closes and backflow of blood is stopped

 

 

Term
first heartbeat sound
Definition

-closing of the AV valves during ventricular contraction

-lower in pitch, longer

Term
second heartbeat sound
Definition

-closing of semilunar valves

-at the end of systole, rapid snap

Term
stroke work output (sw)
Definition
the amount of energy that the heart converts to work during each heart beat pumping blood into arteries
Term
Minute work output (mw)
Definition

the total amount of energy converted to work in 1 minute

MW=SWxHR

Term
Work output in 2 forms
Definition

1. a major proportion is used to move the blood from the low pressure veins to the high pressure arteries (volume-pressure work or external work)

2. a minor proportion of the energy is used to accelerate the blood to its velocity of ejection into arteries through semilunar valves (kinetic energy of blood flow)

Term
Work output of the ventricles
Definition
RV external work output is 1/6 of LV work because sixfold difference is systolic pressures
Term
SW(stroke work)=
Definition
external work or volume pressure work
Term

 

[image]

 

Definition

Phase 1 - period of filling

Phase 2 - period isovolumic contraction

Phase 3 - Period of ejection

Phase 4 - Period of isovolumic relaxation

 

Term
Preload
Definition

the degree of tension on the muscle when it begins to contract

- considered the end-diastolic pressure when the ventricle becomes filled

Term
afterload
Definition

to specify the load against which the muscle exerts its contractile force

- afterload of the ventricle is the pressure in the artery leading from the ventricle

Term
heart muscle energy
Definition

-chemical energy is used to provide the work of contraction

-derived from oxidative metabolism of fatty acids using oxygen

-during contraction, expended chemical energy is converted to heat and a small amt of work output

 

Term
Efficiency of the heart/efficiency of cardiac contraction
Definition

the ratio of work output to total chemical energy expenditure

-maximum efficiency of the normal heart is btw 20 - 25%

Term
venous return
Definition
the amount of blood pumped by the heart each minute is determined almost entirely by the rate of blood flow into the heart from the veins
Term
Frank-Starling Law
Definition

-the intrinsic ability of the heart to adapt to increasing volumes of inflowing blood

-the greater the heart muscle is stretched during filing, the greater the force of the contraction & the greater the quanitity of blood pumped into the aorta

Term
Sympathetic role in the heart
Definition

-the cardiac output can be increased more than 100% by sympathetic stimulation

-can increase the HR from 70 bpm to 180 - 200

-increases the force of the heart contraction to as much as double which increases the volume of blood pumped and ejection pressure

-can increase maximum cardiac output as much as two - three fold 

Term
Parasympathic role in the heart
Definition

-cardiac output can be decreased to as low as zero

-can stop the heart for a few seconds

-can decrease the strength of the heart muscle contractions by 20 - 30%

-the great decrease in HR combined with slight decrease in heart contraction strength can decrease ventricular pumping by 50%+

Term
effect of excess K ions in ECF
Definition

-causes heart to bc dilated and flaccid -> slows the HR

-lg amts can block the conduction through the AV bundle >8mEq/L = cause weakness of the heart & abnormal rhythm = death

Term
effect of excess Ca ions in ECF
Definition

-opposite of K effects

-increased activity ->spastic contractions

-spastic contractions ->lower Ca ions -> cardiac flaccidity

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