Cardiovascular Physiology I Flashcards
What is cardiac output?
Cardiac output is the amount of blood the heart pumps per minute, calculated as heart rate times stroke volume.
What is the average resting heart rate for an adult?
The average resting heart rate is around 70 beats per minute.
What is the average stroke volume for a 70-kilogram man?
The average stroke volume is about 70 milliliters per beat.
Calculate the resting cardiac output for an adult with a heart rate of 70 beats per minute and a stroke volume of 70 milliliters.
Resting cardiac output = Heart rate × Stroke volume = 70 bpm × 70 mL = 4900 mL or approximately 5 liters per minute.
How much can cardiac output increase during heavy activity?
Cardiac output can increase to about 25 liters per minute during heavy activity.
What percentage of cardiac output typically goes to skeletal muscle at rest?
At rest, about 15% to 20% of cardiac output goes to skeletal muscle.
What happens to blood flow distribution during heavy exercise?
During heavy exercise, 80% to 85% of cardiac output is redistributed to skeletal muscle, while less blood flows to the gut and kidneys.
What is the equation that describes blood flow?
Flow = Pressure gradient / Resistance.
What are the key components to understand regarding cardiac output?
- The signal that causes the heart to beat.
- What happens when that signal is generated.
- How the heart functions as a pump (mechanical actions and electrical activity).
- How cardiac output is regulated.
What role does the cardiovascular system play in meeting increased metabolic demand during exercise?
The cardiovascular system increases cardiac output and redistributes blood flow to skeletal muscles to meet the increased metabolic demand during exercise.
What establishes the electrochemical gradient in cardiac cells?
The electrochemical gradient is established by membrane pumps and channels that maintain high potassium inside the cell, high sodium outside the cell, and low calcium inside the cell.
What is the resting membrane potential of a cardiac myocyte?
The resting membrane potential of a cardiac myocyte is approximately -90 millivolts.
What happens when a cardiac cell depolarizes?
Sodium channels open rapidly, allowing sodium to rush into the cell, causing the membrane potential to become more positive.
What is the role of calcium channels during cardiac depolarization?
Calcium channels open more slowly than sodium channels and remain open longer, allowing calcium to enter the cell, contributing to the positive membrane potential.
How do potassium channels affect the cardiac action potential?
When potassium channels open, potassium leaves the cell, which contributes to the membrane potential becoming more negative after depolarization.
Describe the phases of the cardiac action potential.
The action potential includes an initial spike due to sodium influx, a plateau phase due to calcium influx and potassium efflux, and a return to resting potential as potassium continues to leave the cell.
What is automaticity in cardiac myocytes?
Automaticity is the ability of cardiac myocytes, particularly in the sinoatrial (SA) node, to generate electrical impulses spontaneously, causing the heart to beat independently.
What are the two types of myocytes in the heart?
There are typical myocytes (muscle cells that generate force) and specialized myocytes (conductive cells that serve as pacemakers).
What is the sinoatrial (SA) node’s role in the heart?
The SA node is the dominant pacemaker of the heart, generating electrical signals that trigger heartbeats at a rate of 60 to 100 beats per minute.
Explain the concept of overdrive suppression.
Overdrive suppression occurs when the SA node generates impulses at a faster rate than other pacemaker tissues, preventing those tissues from depolarizing on their own.
What does an electrocardiogram (ECG) measure?
An ECG measures the electrical activity of the heart, displaying the timing of atrial and ventricular depolarization and repolarization.
What does the P wave in an ECG represent?
The P wave represents atrial depolarization.
What does the QRS complex represent in an ECG?
The QRS complex represents ventricular depolarization.
What does the T wave indicate in an ECG?
The T wave indicates ventricular repolarization.
Where is atrial repolarization observed in an ECG?
Atrial repolarization occurs but is typically not visible because it is buried within the QRS complex.
What is the main difference between the cardiac action potential and that of skeletal muscle?
The cardiac action potential has a much longer duration and includes a plateau phase, allowing for sustained contraction, whereas skeletal muscle action potentials are shorter
What is the role of calcium in cardiac myocyte contraction?
Calcium enters the cell during action potentials, triggering further calcium release from the sarcoplasmic reticulum, allowing actin and myosin to interact and generate force.
What are the key components of a cardiac myocyte?
Key components include the sarcolemma (cell membrane), sarcoplasmic reticulum (calcium storage), myofilaments (actin and myosin), and mitochondria.
Describe the process of excitation-contraction (EC) coupling.
EC coupling involves calcium influx during the action potential, calcium release from the sarcoplasmic reticulum, calcium binding to troponin, and the formation of cross-bridges between actin and myosin, leading to contraction.
What happens during the plateau phase of the cardiac action potential?
Calcium channels open, allowing calcium to enter the cell and interact with ryanodine receptors on the sarcoplasmic reticulum, leading to further calcium release.
What is the role of the SERCA pump during relaxation?
The SERCA pump actively transports calcium back into the sarcoplasmic reticulum, reducing intracellular calcium levels and allowing muscle relaxation.
How do sodium-calcium exchangers contribute to calcium regulation?
Sodium-calcium exchangers help remove calcium from the cell, contributing to the decrease in intracellular calcium levels during relaxation.
What is the effect of low calcium levels in cardiac myocytes?
Low calcium levels lead to the release of calcium from troponin, allowing tropomyosin to cover actin binding sites, which prevents actin-myosin interactions and causes relaxation.
