The Cardiovascular System (2) Flashcards
(85 cards)
State the formula for cardiac output.
CO = SV X HR
SV = stroke volume
CO is always per minute.
State the formula for blood flow.
Flow = pressure gradient/resistance (of vessels)
Pressure gradient is the difference in pressure between the beginning and end of the blood vessel.
What is total peripheral resistance?
Total peripheral resistance (TPR) is the sum of all the peripheral vasculature in systemic circulation.
What is the pericardium? State its layers.
The heart is enclosed within the pericardium. The pericardium consists of a visceral layer, a parietal layer and the lubricating pericardial fluid between them, to reduce friction when beating.
State the layers of the myocardium (heart muscle).
Endocardium and myocardium
Label the diagram.
1=right coronary artery
2=anterior descending branch of left coronary artery
3=left coronary artery
4=left pulmonary veins
5=great cardiac vein
6=circumflex branch of left coronary artery
7=posterior descending branch of right coronary artery
8=right pulmonary veins
Intrinsic automaticity of the heart
The heart contracts rhythmically as a result of action potentials that it generates by itself. Contractile cells are 99% of the cardiac muscle cells. Autorhythmic cells: initiate and conduct the action potentials responsible for contraction of working cells. THERE IS NO REQUIREMENT FOR EXTERNAL NEURAL INPUT. There are specialized pacemaker areas of the heart, namely: the sinoatrial and atrioventricular nodes, bundle of His and Purkinje fibers.
However, the sympathetic and parasympathetic systems still effect on the heart for its rate and contractile strength.
State the innervation of the heart.
The vagus nerve innervates the SA and AV nodes. The sympathetic cardiac nerves of T1,2,3,4 innervate the SA and AV nodes and the ventricular myocardium.
Compare isotonic and isometric muscle contractions. What changes occur in the heart?
Isotonic contractions is where the muscle changes length while generating force. This leads to volume load and chamber dilation. Isometric contractions occur without any change in muscle length, maintaining a constant tension. This leads to pressure load and chamber hypertrophy.
Rest reverses these changes.
What type of hypertrophy is seen in: hypertension, infarction, diabetes, exercise?
Hypertension: concentric hypertrophy
Infarction: ECCENTRIC/concentric hypertrophy
Diabetes: eccentric/concentric hypertrophy
Exercise: eccentric hypertrophy
Describe the pacemaker activity of cardiac autorhythmic cells.
Beginning at -60mV, funny (f) channels open allowing Na+ influx while K+ permeability decreases. As the membrane depolarizes, transient-type (T) Ca²⁺ channels open, leading to a further influx of Ca²⁺. This gradual depolarization continues until the threshold potential (-40mV) is reached. At threshold, long-lasting Ca²⁺ channels open, causing a rapid influx of Ca²⁺ and thus the steep depolarization phase. At about 10mV, Ca²⁺ channels close. K+ channels open, leading to efflux of K+, restoring the membrane potential back toward -60 mV. This process repeats to support the regular beating of the heart.
How is the SA node connected to the left atrium?
Interatrial pathway
State the intrinsic rate of action potential production for each neural structure in the heart.
SA node: 75
AV node: 50
Bundle of His: 30
Purkinje fibers: 30
in AP/s
Describe the electrical conduction in the heart.
SA node depolarizes. Electrical activity goes rapidly to AV node via internodal pathways. Depolarization spreads more slowly across atria. Conduction slows through AV node. Depolarization moves rapidly through the ventricular conducting system (bundle of His and Purkinje fibers) to the apex of the heart. Depolarization waves spread up from the apex.
Describe the behaviour of action potentials in cardiac contractile cells and the respective contractile response.
RED: The membrane potential rises rapidly from -90 mV to 30 mV due to Na+ influx. Initial repolarization occurs in the form of a slight dip due to transient K+ efflux. L-type Ca channels open to balance the K+ and maintain the depolarized state. In repolarization, Ca channels close and the K+ efflux repolarizes the membrane potential to -90mV. This is then the resting membrane potential, ready for the next AP.
BLUE: The contraction develops slightly after depolarization. The peak contraction occurs during the plateau phase of the action potential. Relaxation occurs as repolarization progresses.
BLACK: This is the period within which another action potential cannot be initiated, preventing tetanus in cardiac muscle.
Describe the events of each segment.
P=atrial depolarization, blood is ejected from the atria through the valves, into the ventricles.
PR=AV nodal delay, preventing simultaneous atrioventricular contraction
QRS=ventricular depolarization to push blood into arteries. Atria repolarize simultaneously
ST=ventricles are contracting and emptying
T=ventricular repolarization
TP=ventricles are relaxing and filling
RR=heart rate
In what arrangement are ECG leads placed?
A total of 12 leads are placed, 4 on the limbs and others are placed on the 4th and 5th intercostal spaces.
Classify tachycardia.
> 100BPM
Classify bradycardia.
<60BPM, depending on patient
Identify extrasystole on an ECG.
Premature ventricular contraction
Identify ventricular fibrillation on an ECG.
Erratic changes in contractions. The heart is shaking. Electric shock by defibrillator is needed.
Identify complete heart block on an ECG.
Atria and ventricles beat independently. P waves bear no consistent relationship to QRS complexes.
Identify myocardial infarction on an ECG.
ST segment elevation is seen. Reciprocal ST depression and hyperacute T waves are seen in turn.
Describe the cardiac cycle.
The cardiac cycle is all the events associated with the flow of blood through the heart during a single complete heartbeat. It repeats approximately once every second. In late diastole, both the atria and the ventricles are relaxed. Blood passively flows from the atria to the ventricles due to the pressure gradient. The AV valves are open, while the semilunar valves remain closed. In atrial systole, the atria contract, pushing additional blood into the ventricles. The ventricles are thus optimally filled. In isovolumic ventricular contraction, the ventricles begin to contract, increasing intraventricular pressure. The AV valves close, preventing backflow. Semilunar valves also remain closed as the arterial pressure requirement has not yet been met. In ventricular ejection, ventricular contraction furthers, further increasing intraventricular pressure, forcing the semilunar valves open. Blood is ejected into the pulmonary artery and aorta. AV valves remain closed, preventing regurgitation. In isovolumic ventricular relaxation, ventricles relax, decreasing pressure. Blood flows back to the heart, filling the cusps of the semilunar valves, causing them to close and preventing backflow. Once ventricular pressure drops below atrial pressure, the AV valves open again, and the cycle repeats.
