Cardiac Physiology Flashcards
How does heart muscle contract?
Stimulated by nerves and is self-excitable
The entire muscle contracts as a unit
Long (250 ms) absolute refractory period
What is the general structure of cardiac muscle tissue?
Intercalated discs connect the cells together to allow contraction as a unit
How is cardiac muscle arranged?
Spiral arrangement around the heart chambers, contraction reduces the diameter– apex of ventricles gets pulled up
What do the SA and AV nodes provide for the heart?
Rhythmic and automatic beating, initiate action potentials in heart muscles, they have unstable resting potentials called pacemaker potentias
What do pacemaker potentials do?
Depolarize slowly
What does the SA node do?
Contraction of the atria and stimulates the AV node (in right wall of right atrium)
What does the AV node do?
Contraction of the ventricles (in left wall of right atrium)
How many impulses does the SA node generate per minute?
70-80 times
What does the AV node do in the sequence of excitation
delays the impulse 0.1 seconds to allow atria to contract
How long do the atria and ventricles contract for?
Atria (0.1)
Ventricles (0.3)
Where are the nodes of the heart?
Both in the right atrium
Where do bundle branches carry the impulse?
To the apex
Where do the Purkinje fibers carry the impulse to?
To the apex then the ventricular walls
What happens when the SA node fails?
AV node takes over at 50 BPM
What happens if the AV node is damaged?
Ventricle impulse is blocked, atria keep pumping normally but ventricles contract at 30 bpm via the Purkinjie fibers
What does an ectopic focus of the SA node mean?
AV node takes over and makes the RHR 50 BPM, adequate to deliver blood
What does an ectopic focus of the AV node mean?
Purkinje fibers have to take over as the pacemaker, only produce RHR 30 BPM, not enough to deliver blood–requires artificial pacemaker
What are the steps of the EKG?
P wave
QRS complex
T wave
Atrial repolarization
What is the P wave?
Atrial depolarization
What is the QRS complex?
Ventricular depolarization
What is the T wave?
Ventricular repolarization
What is atrial repolarizaiton?
Atrial repolarization (masked by QRS complex)
What stimulates the heart?
The cardioacceleratory center of the medulla via the sympathetic system
What inhibits the heart?
The cardioinhibitory center of the medulla via the parasympathetic system
What is the “lub-dup” sound of the heart?
First sound is AV valves closing, Second sound is the closing of the semilunar valves
What is ventricular diastole?
Ventricular filling, first passive (80%) then atrial contraction fills the ventricles
What is ventricular systole?
AV valves close, semilunar vales open and ventricles eject blood through them
What closes the semilunar valves?
Backflow of blood in aorta and pulmonary trunk
What is fibrillation?
Chambers contracting out of sequence
What type of fibrillation is more serious?
Ventricular fibrillation
How does the SA node signal start the whole contraction of the heart?
SA node stimulates both atria to contract, that signal jumps to the AV node which causes depolarization of the ventricles
Why do diastole and systole overlap?
For quick and efficient heart beats
What is Cardiac Output?
Amount of blood pumped by each ventricle in one minute, product of HR and stroke volume
What is stroke volume?
Amount of blood pumped out by a ventricle with each beat
What is the cardiac reserve?
The difference between resting and maximal CO
What is EDV?
Amount of blood collected in a ventricle during diastole
What is ESV?
Amount of blood remaining in a ventricle after contraction
What is the ejection fraction?
SV/EDV, the fraction ejected
How is SV calculated?
EDV - ESV
What factors affect stroke volume?
Preload
Contractility
Afterload
What is preload?
Amount ventricles are stretched by contained blood
What is afterload?
Back pressure exerted by blood in the large arteries leaving the heart
What is the Frank-Starling Law of the Heart?
Preload of cardiac muscle before they contract is the critical factor controlling stroke volume
How much preload is normal?
130 ml of blood
What factors increase contractility?
Hormones
Calcium and some drugs
Increased stimuli
What factors decrease contractility?
Acidosis
Increased potassium
Calcium channel blockers
What is a murmur?
Abnormal heart sound, from turbulent blood flow, most commonly a heart valve malfunction
What is a stenotic valve?
Stiffened, does no open completely, and allows backflow
What is an incompetent valve?
Scarred or damaged, doesn’t close completely, allows backflow
What causes valve conditions?
Rheumatic fever
How is the sympathetic system activated?
stress, anxiety, excitement, exercise
How is the parasympathetic system activated?
acetylcholine, dominates the autonomic stimulation of the heart and slows down heart rate
How does the vagus nerve affect the heart?
Release ACh
Binds to cholinergic receptors
Decreases membrane permeability
Slows heart rate and force
How do the sympathetic nerves affect the heart?
Release norepinephrine
Bind to adrenergic receptors
Increases membrane permeability
Increases heart rate and force
What do beta blockers do?
lower BP
What does venous return do?
Increased venous return increases pre-systolic stretching of cardiac muscle
What does thyroxine do?
Increases speed and force of heart contractions increases transcription of genes, increases contractile proteins in cardiac muscle
What do the carotid and aortic sinuses do?
Measure BP
What do the carotid and aortic bodies do?
Monitor pH, pCO2, and pO2
