40 Questions
What is the function of the internodal pathway in the heart?
To route the direction of electrical signals so the heart contracts from apex to base
Which structure sets the pace of the heartbeat at 70 bpm?
SA node
Under what conditions can the AV node and Purkinje fibers act as pacemakers?
AV node delay with slower conductional signals through nodal cells
What is the role of the Purkinje fibers in the heart?
To transmit electric signals down the atrioventricular bundle to left and right bundle branches
What are the primary sites of exchange between blood and interstitial fluid?
Capillaries
Which cells are associated with capillaries and contribute to capillary impermeability?
Pericytes
What is the driving pressure for blood flow reflected by?
Mean Arterial Pressure (MAP)
How is Mean Arterial Pressure (MAP) calculated?
$MAP = SP + rac{1}{3}(DP - SP)$
What aids venous return?
One-way valves and skeletal muscle pump
What determines mean arterial pressure?
Cardiac output and peripheral resistance
What is responsible for removing excess fluid volume?
Kidney
Which blood vessels act as a volume reservoir?
Veins
What measures the strength of the pressure wave produced by ventricular contraction?
Pulse pressure
What are the smallest blood vessels?
Capillaries
What is the primary cell type in capillary walls?
Endothelial cells
What contributes to capillary impermeability?
Pericytes
What is the volume of blood pumped per contraction known as?
Stroke volume (SV)
What causes the second heart sound (dup) in the cardiac cycle?
Vibrations from the closure of semilunar valves
What does the Electrocardiogram (ECG) represent?
Summed electrical activity of the heart
When does atrial systole occur in the cardiac cycle?
When the atria contract, driving the last 20% of blood volume into the ventricles
What determines the cardiac output (CO)?
Heart rate and stroke volume
What is the first heart sound (lub) produced by in the cardiac cycle?
Closure of AV valves during isovolumic ventricular contraction
What is the average cardiac output (CO) value per minute?
5 L/min
What does the Wiggers diagram illustrate?
Mechanical events of the cardiac cycle
What represents the completion of ventricular filling in the cardiac cycle?
Atrial and ventricular diastole
When does ventricular ejection occur in the cardiac cycle?
When the semilunar valves open
What is the cardiac cycle primarily concerned with?
Opening and closing of the AV and semilunar valves
What does the pressure-volume curve represent in the cardiac cycle?
Changes in ventricular pressure and volume
Which division modulates heart rate through parasympathetic and sympathetic control?
Autonomic division
What influences end-diastolic volume (EDV) and stroke volume?
Venous return
What determines afterload and ejection fraction?
EDV and arterial resistance during ventricular contraction
Which factor influences stroke volume by affecting muscle length and norepinephrine?
Contractility
What is the state of partial contraction in most blood vessels?
Muscle tone
Which structures contain smooth muscle, elastic and fibrous connective tissue, and endothelium?
Walls of blood vessels
What are metarterioles and precapillary sphincters responsible for?
Directing blood flow
What type of vessels act as pressure reservoirs?
Arteries
Which division involves intricate interactions between the nervous and endocrine systems?
Autonomic control of heart rate
What is the primary control of heart rate under normal conditions?
Parasympathetic activity
What is the spontaneous depolarization rate of the SA node when both sympathetic and parasympathetic inputs are blocked called?
Tonic control
What influences contractility by increasing it with positive inotropes and decreasing it with negative inotropes?
Nervous and endocrine systems
Study Notes
Autonomic Control of Heart Rate and Factors Influencing Stroke Volume
- The autonomic division modulates heart rate through parasympathetic and sympathetic control, with parasympathetic activity normally dominating.
- Tonic control involves the spontaneous depolarization rate of the SA node when both sympathetic and parasympathetic inputs are blocked.
- Multiple factors influence stroke volume, including contractility, length-tension relationships, and the Frank-Starling law of the heart.
- Venous return, affected by skeletal muscle contractions and pressure changes in abdominal and thoracic veins, influences end-diastolic volume (EDV) and stroke volume.
- Contractility, influenced by norepinephrine and muscle length, is not the same as the length-tension relationship, but both affect stroke volume.
- Contractility is controlled by the nervous and endocrine systems, with positive inotropes increasing contractility and negative inotropes decreasing it.
- Afterload, determined by EDV and arterial resistance during ventricular contraction, and ejection fraction, determine stroke volume.
- The walls of blood vessels contain smooth muscle, elastic and fibrous connective tissue, and the inner layer is endothelium, which regulates blood pressure and vessel growth.
- Arteries act as pressure reservoirs and have thick layers of vascular smooth muscle, while arterioles are sites of variable resistance and are less elastic and more muscular.
- Metarterioles are branches of arterioles with a partial smooth muscle layer and precapillary sphincters that open and close to direct blood flow.
- Vascular smooth muscle in blood vessels can cause vasoconstriction and vasodilation, and muscle tone is a state of partial contraction in most blood vessels.
- The autonomic control of heart rate and the factors influencing stroke volume are complex and involve intricate interactions between the nervous and endocrine systems, as well as the properties of cardiac and vascular structures.
Test your knowledge of the autonomic control of heart rate and factors influencing stroke volume with this quiz. Explore topics such as parasympathetic and sympathetic control, factors influencing stroke volume, venous return, contractility, afterload, and vascular smooth muscle function. Gain insights into the intricate interactions between the nervous and endocrine systems, as well as the properties of cardiac and vascular structures.
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