133 Questions
During systole, the ventricles are in a state of relaxation and filling.
False
The cardiac cycle is triggered by the spread of excitation through the arteries.
False
The cardiac cycle consists of only one phase.
False
The first heart sound is caused by the closure of aortic and pulmonary valves at the start of ventricular contraction.
False
Arteries carry blood from organs and tissues back to the heart.
False
Muscular arteries, such as the aorta and pulmonary artery, have numerous layers of elastin fibers in their vessel walls.
False
The tunica externa of blood vessels is the innermost lining of squamous endothelium.
False
Capillaries facilitate exchanges between blood and surrounding cells within organs.
True
The venules return blood to the heart after forming when capillaries re-join.
True
The elastic arteries expand when pressure of the blood decreases during ventricular systole.
False
Arterioles contain the highest percentage of smooth muscle in the vessel wall.
True
Capillaries have very thin walls consisting of a single layer of flat endothelial cells and a thin basement membrane.
True
Capillaries in the kidneys, intestines, and endocrine glands have larger holes in addition to narrow pores, providing greater permeability and rapid exchange.
True
Bulk flow is a mechanism of capillary exchange involving ultrafiltration and reabsorption of protein-free plasma.
True
Systemic veins have thin walls with little smooth muscle or elastin, resulting in high distensibility and little elastic recoil.
True
The main function of precapillary sphincters is to regulate blood flow via venules.
False
Arteries have a thicker layer of smooth muscle but are more elastic than arterioles.
False
Vessel radius supplying individual organs cannot be adjusted independently depending on the body’s momentary needs.
False
Continuous capillaries have larger holes (20-100 nm) in addition to narrow pores.
False
Bulk flow as a mechanism of capillary exchange involves diffusion down the concentration gradient.
False
The refractory period occurs for some time after a previously elicited action potential.
True
The duration of the refractory period differs for fast and slow response cells.
True
The natural pattern of excitation of the heart starts with the SA node, then goes to the ventricles before reaching the AV node.
False
The ECG records the electrical activity of the heart during repolarization only.
False
Cardiac muscle cells are interconnected to form branching fibers through specialized structures known as desmosomes.
True
Cardiac muscle cells become excited and contract individually rather than as a single unit.
False
Gap junctions in cardiac muscle fibers allow cell-to-cell communication.
True
The T wave in an ECG represents atrial depolarization.
False
Automaticity refers to the ability of all cardiac cells to initiate action potentials spontaneously.
False
The refractoriness protects against premature excitation and tetany.
True
The electrical activity of the heart is cyclically initiated and conducted in a disorderly sequence through the heart by autorhythmic cells.
False
Intercalated discs in cardiac muscle contain desmosomes for cell-to-cell communication.
False
During which phase of the cardiac cycle do the ventricles relax and fill?
Diastole
What is the main function of elastic arteries?
Act as pressure reservoirs
Which type of blood vessel serves as rapid-transit conduits for blood from the heart to organs?
Arteries
What is the term for the closure of AV valves at the start of ventricular contraction?
1st heart sound (lub)
What do venules do with blood after forming when capillaries re-join?
Return blood to the heart
What is the main function of muscular arteries?
Carry blood away from the heart to tissues
Which layer of blood vessel walls is comprised of smooth muscle?
Tunica media
What happens to elastic arteries when the pressure of the blood rises during ventricular systole?
They expand and act as a recoil system
What is the innermost lining of squamous endothelium in blood vessels called?
Tunica interna (intima)
What happens during isovolumetric relaxation?
The ventricles relax and fill with blood
What occurs during the ejection period?
The ventricles contract and empty
What is the primary purpose of the refractory period in cardiac cells?
To allow for the recovery of excitability and protect against premature excitation
Which structure is responsible for the natural initiation of excitation of the heart?
SA node
What does the T wave in an ECG represent?
Ventricular repolarization
What is the main function of precapillary sphincters?
Regulate blood flow via venules
Which mechanism is involved in capillary exchange involving ultrafiltration and reabsorption of protein-free plasma?
Bulk flow
What is the primary role of gap junctions in cardiac muscle fibers?
Cell-to-cell communication
Which part of the heart is responsible for the spread of action potentials across muscle cell membranes?
Purkinje fibres
What is the characteristic feature of automatic/pacemaker cells in the heart?
Spontaneous initiation of action potentials
What role does AV conduction delay play in the heart?
Allows ventricles to be relaxed while atria are contracting
What is indicated by the QRS complex in an ECG?
Ventricular depolarization
What is the function of desmosomes in cardiac muscle fibers?
Cell-to-cell anchoring junctions
What is the major function of precapillary sphincters in capillaries?
They control the flow of blood into capillary beds
What is the main determinant of bulk flow in capillaries?
Capillary blood pressure (PC)
What is the function of systemic veins in the circulatory system?
Carry blood from organs and tissues back to the heart
What is the structure of continuous capillaries?
Endothelial cells are continuous or closely joined
What is the primary characteristic of arterioles in terms of their function?
Regulate arterial blood pressure
What is the primary function of capillaries within organs?
Facilitate exchanges between blood and surrounding tissue cells
Which vessel type has a thicker layer of smooth muscle but less elasticity?
Arteries
What is the primary role of veins in the circulatory system?
Return blood from tissues to the heart
What is the primary factor that facilitates venous return in the circulatory system?
One-way valves & ‘skeletal muscle pump’
What is the main function of arterioles in the circulatory system?
Control the flow of blood into capillary beds
Which vessel type plays a significant role in controlling arterial blood pressure?
Arterioles
Which type of blood vessel contains the highest percentage of smooth muscle in the vessel wall?
Arterioles
What is the primary function of precapillary sphincters?
Regulate blood flow via venules
What is the main determinant of bulk flow in capillaries?
Capillary blood pressure
Which type of capillaries has larger holes in addition to narrow pores, providing greater permeability and rapid exchange?
Fenestrated
What occurs during isovolumetric relaxation?
Ventricles contract while all valves are closed
What is the structure of continuous capillaries?
Endothelial cells are continuous or closely joined with narrow intercellular pores
What role does AV conduction delay play in the heart?
Spread of action potentials across muscle cell membranes
What is the main function of muscular arteries?
Regulate arterial blood pressure
During which phase of the cardiac cycle do the ventricles relax and fill?
Ventricular diastole
What is the primary factor that facilitates venous return in the circulatory system?
One-way valves and 'skeletal muscle pump'
What part of the cardiac cycle indicates closure of AV valves at the start of ventricular contraction?
Isovolumetric contraction
What is indicated by the QRS complex in an ECG?
Purkinje fiber excitation and ventricular depolarization
What is the primary purpose of the refractory period in cardiac cells?
To protect against premature excitation and tetany
Which structure is responsible for the natural initiation of excitation of the heart?
SA node
What is the characteristic feature of automatic/pacemaker cells in the heart?
Spontaneous phase 4 depolarization
What role does AV conduction delay play in the heart?
Allows ventricles to be relaxed while atria are contracting
Which part of the heart is responsible for the spread of action potentials across muscle cell membranes?
Bundle of His
What occurs during the ejection period?
Blood is pumped out of the ventricles into the pulmonary artery and aorta
What do venules do with blood after forming when capillaries re-join?
Transport blood back to the heart
What is the main function of arterioles in the circulatory system?
Regulate blood flow into capillaries
What is the primary function of precapillary sphincters in capillaries?
Regulate blood flow into capillaries
Which phase of the cardiac cycle is characterized by ventricular contraction and emptying?
Systole
What is the term for the two sub-phases or periods during diastole?
Isovolumetric relaxation & filling periods
Which type of arteries serve as rapid-transit conduits for blood from the heart to organs, and act as pressure reservoirs?
Elastic arteries
What type of vessels are formed when capillaries re-join to return blood to the heart?
Venules
What is the middle layer of the arterial walls composed of?
Smooth muscle
What is the main function of capillaries within organs?
Facilitate exchanges between blood and surrounding cells
What is the outer layer of arterial walls comprised of?
Connective tissue (& elastin fibers)
During which phase of the cardiac cycle do the ventricles relax and fill?
Diastole
'Consists of Arteries – carry blood away from heart to tissues' - this statement refers to which component of the circulatory system?
Arterioles
What type of vessels direct the flow of blood from the heart to organs & tissues and back to the heart?
Arteries
Which layer of blood vessel walls is composed of up to 3 'tunics' including tunica externa, tunica media, and tunica interna?
Arteries
What are the two sub-phases or periods of systole?
isovolumetric contraction & ejection periods
What is the function of arterioles in the circulatory system?
Act as pressure reservoirs – provide the driving force for blood during diastole
What is the primary characteristic of arterioles in terms of their function?
Act as pressure reservoirs
What is the main determinant of bulk flow in capillaries?
Pressure gradient
What is the primary function of muscular arteries?
Serve as rapid-transit conduits for blood from heart to organs
What is the structure of continuous capillaries?
Tunica interna (intima), tunica media, tunica externa (adventitia)
What is the middle layer of the arterial walls composed of?
Smooth muscle
What happens to elastic arteries when the pressure of the blood rises during ventricular systole?
Expand and act as a recoil system when the ventricles relax
What type of vessels are formed when capillaries re-join to return blood to the heart?
Venules
What is the main function of systemic veins in the circulatory system?
Return blood to the heart
What is the primary factor that facilitates venous return in the circulatory system?
Muscular compression and one-way valves
What is the function of precapillary sphincters in capillaries?
Regulate blood flow into the capillaries
What is the role of precapillary sphincters in the circulatory system?
Regulate blood flow via capillaries
What are the three main types of capillaries based on the size of water-filled pores?
Continuous, Fenestrated, Discontinuous (sinusoidal)
What are the two mechanisms of capillary exchange between blood and surrounding tissues?
Passive diffusion, Bulk flow
What is the primary function of venules in the circulatory system?
Return blood from tissues to the heart
What are the determinants of bulk flow in capillaries?
Capillary blood pressure (PC), Plasma-colloid osmotic pressure (πP), Interstitial fluid hydrostatic pressure (PIF), Interstitial fluid colloid osmotic pressure (πIF)
What is the primary role of systemic veins in the circulatory system?
Serve as blood reservoir or capacitance vessels
How is the control of the tone (constriction or dilatation) of arterioles mediated?
Via nervous & chemical mechanisms
What is the main role of arterioles in the circulatory system?
Major resistance vessels
What are the two sub-phases or periods during diastole?
Rapid filling phase, Slow filling phase
How do continuous capillaries differ from fenestrated capillaries?
Continuous capillaries have narrow intercellular pores, while fenestrated capillaries have larger holes in addition to narrow pores.
What is the characteristic feature of veins in terms of their structure?
Thin walls with little smooth muscle or elastin
How do arterioles contribute to controlling arterial blood pressure?
Vessel radius supplying individual organs can be adjusted independently
What is refractoriness in cardiac cells?
Inability of more than enough stimulus to elicit an action potential
What is the primary basis of automaticity in cardiac cells?
If current & spontaneous phase 4 depolarisation
What is the sequence of electrical conduction through the heart during the natural pattern of excitation?
SA node -> Atria -> AV node -> Bundle of His -> Purkinje fibres -> Ventricles
What are the three distinct waveforms in a normal ECG and their corresponding representations?
P wave represents atrial depolarization, QRS complex represents ventricular depolarization, T wave represents ventricular repolarisation
What is the primary function of gap junctions in cardiac muscle fibers?
Cell to cell communication junctions
What differentiates the refractory period in fast response cells from slow response cells?
Fast response cells have faster recovery of excitability, while slow response cells have slower recovery of excitability
What is the primary function of the Electrocardiogram (ECG or EKG)?
It records the electrical activity of the heart during depolarization and repolarization
What is the primary role of the AV conduction delay in the heart?
It allows ventricles to be relaxed while atria are contracting
What is the structural basis for the functional syncytium of cardiac muscle?
Cardiac muscle cells interconnected to form branching fibres with intercalated discs
What are the two types of membrane junctions present within an intercalated disc in cardiac muscle?
Desmosomes and gap junctions
What is the primary characteristic of normal cardiac automatic or pacemaker cells?
Ability to initiate/fire action potentials spontaneously
What is the primary characteristic feature of cardiac cells during the refractory period?
Inability of more than enough stimulus to elicit an action potential
Study Notes
Cardiac Cycle
- During diastole, ventricles relax and fill.
- The cardiac cycle consists of more than one phase.
- The first heart sound is caused by the closure of AV valves at the start of ventricular contraction.
Blood Vessels
- Arteries carry blood away from the heart to organs and tissues.
- Muscular arteries, such as the aorta and pulmonary artery, have numerous layers of elastin fibers in their vessel walls.
- Elastic arteries expand when pressure of the blood decreases during ventricular systole.
- Arterioles contain the highest percentage of smooth muscle in the vessel wall.
- Capillaries facilitate exchanges between blood and surrounding cells within organs.
- Venules return blood to the heart after forming when capillaries re-join.
- Systemic veins have thin walls with little smooth muscle or elastin, resulting in high distensibility and little elastic recoil.
Capillary Exchange
- Bulk flow is a mechanism of capillary exchange involving ultrafiltration and reabsorption of protein-free plasma.
- Continuous capillaries have larger holes (20-100 nm) in addition to narrow pores, providing greater permeability and rapid exchange.
Cardiac Muscle Cells
- Cardiac muscle cells are interconnected to form branching fibers through specialized structures known as desmosomes.
- Gap junctions in cardiac muscle fibers allow cell-to-cell communication.
- Automaticity refers to the ability of all cardiac cells to initiate action potentials spontaneously.
- The refractory period protects against premature excitation and tetany.
Electrical Activity of the Heart
- The ECG records the electrical activity of the heart during repolarization only.
- The T wave in an ECG represents ventricular repolarization.
- The SA node is responsible for the natural initiation of excitation of the heart.
- Intercalated discs in cardiac muscle contain desmosomes for cell-to-cell communication.
Test your knowledge of the general properties of cardiac cells and refractoriness with this quiz from the MPharm PHA112 course. Explore concepts such as absolute/effective and relative refractory periods and their role in protecting against premature excitation.
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