Intro and Electophysiology Flashcards
outer fibrous layer of pericardial sac is called
Parietal Pericardium
inner fibrous layer of pericardial sac is called
Visceral Pericardium
What is the name of the tough fibrous sac that encloses the heart
the pericardial sac
what lubricates the visceral and parietal pericardium
pericardial fluid
Name and describe the 3 layers of the heart wall
- Epicardium: a thin serous membrane on the outer aspect of the heart
- Myocardium: a muscular middle layer of the heart
- Endocardium: a thin serous membrane lining the inner chambers of the heart
What are the two basic cell types of the heart?
Myocardial cells and Conducting cells
What are the “working cells” of the heart?
myocardial cells, they have contractile ability
What is a syncytium?
the branching network of myocardial cells which consist of latticework of protein filaments (actin and myosin)
Name the types of conducting cells
- pacemaker cells
- electrical conducting cells (bundle branches and Purkinje fibers)
Describe cardiomyocytes
branching cells with a central nucleus, surrounded by a sarcolemma
Sarcolemma
membrane surrounding cardiomyocytes
Intercalcated disks
special contact points where the cells connect
Gap junctions (location and function)
gap junctions are located in the intercalcated disks and permit rapid conduction of electrical impulses from one cell to the next
Desmosomes (function)
hold myocardial cells together during contraction
When stimulated, do myocytes contract together or separately?
Myocytes contract together as a single unit during contraction
What is the cardiac skeleton?
What is its function?
Why is it good to have?
1- a “plate of fibrous connective tissue” between the atria and ventricles
2- provides a support structure for the AV and semilunar valves and separates the upper pumping chambers from the lower pumping chambers
3- Electrically insulates the atria from the ventricles. Electrical impulses in the atria must travel through specific conduction pathways to get to the ventricles.
What is systole?
contraction phase
What is diastole?
relaxation phase
Stroke volume (def and normal values)
- amount of blood ejected from ventricles during systole
- usually 60-100 cc of blood ejected into circulation during systole
How does one calculate cardiac output?
Heart rate x Stroke volume= Cardiac output
Preload
stretching force on the ventricular muscle at end diastole
Afterload
pressure against which the heart must pump (e.g. blood pressure in the aorta)
Blood Pressure=
Blood Pressure = Cardiac Output x Peripheral Vascular Resistance
By what means in the heart regulated?
The Brain via autonomic nervous system
Hormones of the endocrine system
Heart tissue
Receptors monitoring adequacy of cardiac output. Located in: blood vessels, kidneys, brain, heart
Baroreceptors (functiona and location)
Baroreceptors detect changes in pressure in the heart and main arteries (aorta and carotid arteries)
Chemoreceptors
detect changes in the chemical composition of the blood
Where does info from baroreceptors and chemoreceptors go?
info from baroreceptors and chemoreceptors is transmitted to the cardioregulatory center in the medulla oblongata
What is the “adrenergic system”
the sympathetic nervous system
What does the sympathetic nervous system do?
- causes release or norepinepherine and epinepherine (from adrenal glands)
- Flight or Flight response
speeds heart; increases myocardial excitability
-“Cardioaccelerator”: increased pacemaker firing, increased impulse conduction through heart, increased force of contraction, coronary vasodilation
How are cardioaccelerator effects caused and what are the effects?
sympathetic system activates beta receptors ->cardioaccelerator effects
- increased rate of pacemaker firing
- increased spread of impulse conduction through heart
- increased force of contraction
- coronary vasodilation
Parasympathetic nervous system:
how is it activated? what does it do?
Vagus nerve stimulates release of acetylcholine
aka. “cholinergic system”
slows heart and slows electrical conduction
“cartdioinhibitor”: decreased rt of SA node pacemaker, decreased rate of condutction through AV node
What does the cardioregulatory center do when blood pressure is too low?
Cardioregulatory center activates sympathetic nervous system which:
- causes release of epinepherine and norepinepherine
- increases heart rate and contractility
- constricts peripheral blood vessels
- > results in increased cardiac output and increased blood presure
Name and describe 4 key properties of myocardial cells
Automaticity: certain cells can produce an electrical impuse without outside nervous stimulation
Excitability: ability to respond to an electrical stimulus
Conductivity: ability to transmit an electrical stiumul from cell to cell
Contractility: ability to contract when electrically stimulated
The Conductive Pathway
specialized cardiac cells that generate and transmit electrical impulses throughout the myocardium
name 2 types of cells in the conductive pathway; what do they do?
- Pacemaker cells-have the ability to spontaneously generate an impulse (“depolarize”) at a certain rate
- Electrical conducting cells: carry the electrical impulses to the appropriate regions of the heart
Sinoatrial (SA) node
the heart’s primary pacemaker
located high in POSTERIOR RIGHT ATRIUM
intrinsic rate is 60-100 bpm
Atriventricular (AV) Node
pathway for impulses to reach the ventricles
located in LOW RIGHT ATRIUM
intrinsic rate is 40-60 bpm
acts as a GATEKEEPER for impulses reaching the ventricles; conducts impulses more slowly
Bundle of His
aka AV Bundle; transmits signal from AV node to heart apex
Right and Left bundle branches
located on either side of interventricular septum
Left Bundle branches into anterior and posterior fascicles
Purkinje fibers
terminal branches of the right and left bundles that spread out through the myocardium
What is the intrinsic rate of Purkinje fibers
20-40 bpm, will take over as pacemaker if SA and AV nodes fail
What takes over as a pacemaker if the SA and AV nodes fail?
Purkinje fibers
Intrinsic rate of SA node
60-100 bpm
Intrinsic rate of AV node
40-60 bpm
Polarized State of myocardial cells
resting state; consists of
NEGATIVELY charged ions INSIDE cell and
POSITIVELY charged ions OUTSIDE cell
Resting Membrane Potetion
the difference in electrical charge between inside and outside the cell
What occurs during DEpolarization?
positive ions (Na+) enter the cell, causing interior to become positively charged or “depolarized”; calcium ions also enter, but more slowly
Action potential of cell
the change in electrical charge over time
aka Voltage of the cell
What occurs during REpolarization?
after cell is depoloarized, the positive ions (Na+, Ca++. K+) leave the cell and the interior of the cell returns to its negatively charged resting state
Absolute refractory period definition and 2 impacts
following depolarization, cell becomes temporarily resistant to further depolarization
- this keeps the wave of depolarization moving forward
- also prevents spasms of continued contraction in one area
Relative refractory period
In late phase of repolarization, a very strong electrical stimulus will cause depolarization
Who invented the first practical ECG? When? Did he receive any accolades?
William Einthoven (Dutch physician and physiologist) invented ECG in 1903 and received a Nobel Prize in Medicine in 1924 for this masterpeice
Bipolar leads (definition and which ones)
bipolar leads have electrodes of opposite polarity (positive and negative)
-The limb leads- leads I, II, and III are BIPOLAR
Unipolar leads (definition and which ones)
have only a positive electrode and a reference point determined by the ECG machine
-the chest/precordial leads (V1-V6), the augmented limb leads
How does movement toward a positive electrode appear on ECG?
movement toward a positive electrode appears above baseline (upright) on the ECG
How does movement away from a positive (toward a negative) electrode appear on ECG?
appears below a baseline
What is a vector?
small directional electrical currents
What is an electrical axis?
the overall direction of the sum of currents (or vectors)
What produces downward deflections on ECG?
impulses travelling away from a positive electrode and/or toward a negative electrode
What produces upward deflections on ECG
Impulses travelling toward a positive electrode
What produces a biphasic waveform on ECG?
impulses travelling perpendicular to the positive elctrode
What is a biphasic waveform?
one that has both a positive and negative deflection
Which leads are on the frontal plane
limb leads I, II, III, aVR, aVF
Which leads are on the horizontal plane
precordial (chest) leads V1 to V6
Which wave represents atrial depolarization?
P wave
What does the QRS wave represent?
ventricular depolarization
Which wave represents ventricular repolarization?
T wave
Which wave represents atrial repolarization?
none, it is hidden in the QRS wave
Which wave represents ventricular depolarization?
QRS wave
What does the P wave represent?
atrial depolarization
What does the T wave represent?
ventricular depolarization
Epicardium:
thin serous membrane on the outer aspect of the heart
Myocardium
muscular middle layer of the heart
Endocardium
thin serous membrane lining the inner chambers of the heart and valves
