1 Intro and Electrophysiology Flashcards
What is the pericardial sac?
The tough fibrous sac that encloses the heart
What are the layers of the pericardial sac?
Parietal pericardium (outer)
Visceral pericardium (inner)
Pericardial fluid in between, lubricating the two layers
What are the three layers of the heart wall?
Epicardium - thin serous membrane on outer aspect of the heart
Myocardium - the muscular middle layer
Endocardium - thin serous membrane lining the inner chambers and valves
What are the two basic cell types in the heart?
Myocardial cells - have contractile ability
Conducting cells - pacemaker cells and electrical conducting cells
Describe the myocardial cells
“Working cells” of the heart
Consist of latticework of protein filaments (myosin and actin)
The branching network of myocardial cells in the heart is called…
A syncytium
Cardiomyocytes are ________ cells with a ______ nucleus, surrounded by a membrane called a _________.
Branching
Central
Sarcolemma
Special contact points where myocardial cells connect
Intercalated disks
_________ in the intercalated disks permit rapid conduction of electrical impulses from one cell to the next
Gap junctions
Myocytes all contract together as a single unit with stimulated, thanks to _______ which hold the cells together during contraction
Desmosomes
The right and left atria are separated by…
The interatrial septum
The right and left ventricles are separated by …
The interventricular septum
What are the four valves of the heart?
Mitral
Tricuspid
Pulmonary
Aortic
What controls the mitral and tricuspid valves?
Papillary muscles and chordae tendineae
What does the plate of fibrous connective tissue between the atria and ventricles do?
Provides a support structure for the AV and semilunar valves
Separates the upper pumping chambers from the lower chambers
Electrically insulates the atria from the ventricles - electrical impulses in the atria must travel through specific conduction pathways to get to the ventricles
Systole is the _______ phase and diastole is the _______ phase
Contraction
Relaxation
The amount of blood ejected from the ventricles during systole
Stroke volume
Usually 60-100cc of blood during each systole
What is the formula for cardiac output?
Heart Rate x Stroke Volume
Stretching force on the ventricular muscle at end diastole
Preload
The pressure against which the heart must pump (ie blood pressure in the aorta)
Afterload
Formula for blood pressure
Cardiac Output x Peripheral Vascular Resistance
How is the heart regulated?
By the brain, via the autonomic nervous system
Hormones of the endocrine system
Heart tissue itself
Receptors monitor adequacy of cardiac output (located in blood vessels, kidneys, brain, heart)
______ detect changes in pressure in the heart and main arteries (aorta and carotid)
Baroreceptors
______ detect changes in the chemical composition of the blood
Chemoreceptors
Info from baro- and chemoreceptors is transmitted to the ________ in the ________.
Cardioregulatory center
Medulla oblongata
Sympathetic Nervous System causes release of _____ and _____ from ________
NE and Epi
Adrenal gland
(Why it’s also called the “adrenergic system”)
Effects of the Sympathetic NS on the heart
Fight or flight response
Speeds heart, increases myocardial excitability
Acts as “cardioaccelerator” - increased pacemaker firing, increased impulse conduction through heart, increased force of contraction, coronary vasodilation
In the parasympathetic nervous system, the ________ stimulates the release of ________.
Vagus nerve
Acetylcholine
The “cholinergic system”
Effects of the parasympathetic NS on the heart
Slows heart and slows electrical conduction
“Cardioinhibitor” - decreased rate of SA node pacemaker, decreased rate of conduction through AV node
What happens when BP is too low?
The cardioregulatory center activates the SYMPATHETIC NS —> NE/Epi release —> Inc HR/contractility, vasoconstriction —> Inc CO and BP
What happens when BP is too high?
The cardioregulatory center activates the PARASYMPATHETIC NS —> release of ACh —> Dec HR and lower BP
What are the key properties of myocardial cells?
Automaticity
Excitability
Conductivity
Contractility
The ability of certain cells to produce an electrical impulse without outside nerve stimulation
Automaticity
A key property of myocardial cells
The ability to respond to an electrical stimulus
Excitability
A key property of myocardial cells
Ability to transmit an electrical stimulus from cell to cell
Conductivity
A key property of myocardial cells
Ability to contract when electrically stimulated
Contractility
A key property of myocardial cells
Specialized cardiac cells that generate and transmit electrical impulses throughout the myocardium
The conductive pathway
What are the 2 types of cells in the conductive pathway?
Pacemaker cells - have the ability to spontaneously generate an impulse at a certain rate
Electrical conducting cells - carry the electrical impulses to the appropriate regions of the heart
What are the different pacemaker cells?
Sinoatrial (SA) node
Atrioventricular (AV) node
Bundle of His
Right and Left Bundle Branches
Purkinje fibers
What is the heart’s primary pacemaker?
Sinoatrial (SA) node
Located high in the posterior right atrium
What is the intrinsic rate of the SA node?
60-100 bpm
Pacemaker cells located in the low right atrium
AV node - pathway for impulses to reach the ventricles
The AV node acts as a _______
Gatekeeper for impulses reaching the ventricles by conducting impulses more slowly
Intrinsic rate of the AV node
40-60 bpm
Terminal branches of the right and left bundle branches that spread throughout the myocardium
Purkinje fibers
Intrinsic rate of the purkinje fibers
20-40 bpm
Will take over as pacemaker if the SA and AV nodes fail
The polarized state (or resting state) of myocardial cells consists of ______ ions inside the cell and _______ ions outside the cell
Negatively charged inside
Positively charged outside
The ________ is the difference in the electrical charge between inside and outside the cell
Resting membrane potential
What is depolarization?
When positive ions (Na+) enter the cell, the interior becomes positively charged or “depolarized”
Ca2+ ions also enter, but more slowly
THe change in electrical charge over time is called the action potential of the cell
What is repolarization?
After the cell is depolarized, the positive ions (Na+, Ca2+, K+) leave the cell and the interior of the cell returns to its negatively charged resting state
What it’s he absolute refractory period?
Following depolarization, the cell becomes temporarily resistant to further depolarization
This keeps the wave of depolarization moving forward but also prevents spasms of continued contraction in one area
What is the relative refractory period?
In the late phase of repolarization, a very strong electrical stimulus will cause depolarization
Who invented the EKG?
Willem Einthoven, a Dutch physician and physiologist in 1903 (won Nobel in 1924)
_______ leads have electrodes of opposite polarity (positive and negative)
Bipolar
Limb leads - Leads I, II, III
______ leads have only a positive electrode and a reference point determined by the ECG machine
Unipolar leads
Chest/precordial leads (V1-V6)
Augmented limb leads
Movement toward a positive electrode appears ______ the baseline on the ECG tracing
Above
Movement away from a positive (or towards a negative) electrode appears ______ the baseline
Below
The ECG records the sum of all…
The small directional electrical currents
These are called vectors and their sum is the electrical axis
______ = many small electrical currents in various directions
______ = overall direction of the same of the vectors
Vectors
Axis
The _______ represents atrial depolarization
P wave
The ______ represents ventricular depolarization
QRS wave
The _______ represents ventricular repolarization
T wave
Why is atrial repolarization not represented on the ECG?
B/c it’s hidden in the QRS wave
