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Questions and Answers
What is the primary function of Purkinje fibers in the heart?
What is the primary function of Purkinje fibers in the heart?
- To generate a strong contraction in ventricular muscle cells.
- To regulate blood flow between the ventricles.
- To transmit impulses to a subset of ventricular cardiac muscle cells. (correct)
- To facilitate the exchange of oxygen in myocardial tissues.
Which characteristic differentiates Purkinje fibers from typical cardiac muscle cells?
Which characteristic differentiates Purkinje fibers from typical cardiac muscle cells?
- Purkinje fibers have a well-developed T tubule system.
- Purkinje fibers appear pale-staining due to high glycogen content. (correct)
- Purkinje fibers contain numerous myofibrils.
- Purkinje fibers are smaller than normal cardiac muscle cells.
In which part of the heart are Purkinje fibers primarily located in humans?
In which part of the heart are Purkinje fibers primarily located in humans?
- In the epicardial layer of the ventricles.
- In the atrioventricular node.
- In the subendocardial connective tissue. (correct)
- In the conduction system of the atria.
Which of the following statements is NOT true about the structure of Purkinje fibers?
Which of the following statements is NOT true about the structure of Purkinje fibers?
How do Purkinje fibers extend in some larger animals compared to humans?
How do Purkinje fibers extend in some larger animals compared to humans?
What distinguishes atrial myocardial cells from ventricular myocardial cells?
What distinguishes atrial myocardial cells from ventricular myocardial cells?
What hormone is produced by atrial cardiac muscle cells?
What hormone is produced by atrial cardiac muscle cells?
What triggers the release of atrial natriuretic factor into capillaries?
What triggers the release of atrial natriuretic factor into capillaries?
What is the primary physiological effect of both ANF and BNP?
What is the primary physiological effect of both ANF and BNP?
Which of the following cells stores and releases brain natriuretic peptide?
Which of the following cells stores and releases brain natriuretic peptide?
Where are the receptors for atrial natriuretic factor found?
Where are the receptors for atrial natriuretic factor found?
What is brain natriuretic peptide initially associated with?
What is brain natriuretic peptide initially associated with?
Which of the following statements about the diameter of myocardial cells is true?
Which of the following statements about the diameter of myocardial cells is true?
What is the primary function of the SA node in the heart?
What is the primary function of the SA node in the heart?
Which of the following statements accurately describes SA nodal cells?
Which of the following statements accurately describes SA nodal cells?
Where is the SA node primarily located in the heart?
Where is the SA node primarily located in the heart?
What is a characteristic appearance of SA nodal cells when stained?
What is a characteristic appearance of SA nodal cells when stained?
How do SA nodal cells compare to normal cardiac muscle cells regarding intercalated discs?
How do SA nodal cells compare to normal cardiac muscle cells regarding intercalated discs?
What initiates the contraction of the heart muscle?
What initiates the contraction of the heart muscle?
Which structure receives impulses from the SA node after they spread through the atrial muscle cells?
Which structure receives impulses from the SA node after they spread through the atrial muscle cells?
What is the typical heart rate initiated by the SA node under normal circumstances?
What is the typical heart rate initiated by the SA node under normal circumstances?
What type of tissue surrounds the SA node and contributes to its structure?
What type of tissue surrounds the SA node and contributes to its structure?
What type of fibers conduct the impulse from the SA node to the AV node?
What type of fibers conduct the impulse from the SA node to the AV node?
What is the primary function of the pericardial cavity?
What is the primary function of the pericardial cavity?
Which sequence correctly describes the flow of deoxygenated blood through the heart?
Which sequence correctly describes the flow of deoxygenated blood through the heart?
The chambers of the human heart include which of the following?
The chambers of the human heart include which of the following?
What type of valve allows deoxygenated blood to flow from the right atrium to the right ventricle?
What type of valve allows deoxygenated blood to flow from the right atrium to the right ventricle?
Where does oxygenated blood return after being delivered to the lungs?
Where does oxygenated blood return after being delivered to the lungs?
What is found between the parietal and visceral layers of the serous pericardium?
What is found between the parietal and visceral layers of the serous pericardium?
The pulmonary artery functions to transport blood to which organ?
The pulmonary artery functions to transport blood to which organ?
What is the role of the mitral valve in the heart's blood flow?
What is the role of the mitral valve in the heart's blood flow?
What is the normal volume of pericardial fluid found in the pericardial cavity?
What is the normal volume of pericardial fluid found in the pericardial cavity?
At which superior location do the parietal and visceral layers of the serous pericardium meet?
At which superior location do the parietal and visceral layers of the serous pericardium meet?
What is the primary function of the cardiac skeleton?
What is the primary function of the cardiac skeleton?
Which layer of the heart wall is also known as the visceral reflection of the serous pericardium?
Which layer of the heart wall is also known as the visceral reflection of the serous pericardium?
What is the role of the annulus fibrosus in the heart's anatomy?
What is the role of the annulus fibrosus in the heart's anatomy?
Which structure is an extension of the cardiac skeleton into the interventricular septum?
Which structure is an extension of the cardiac skeleton into the interventricular septum?
Which of the following is NOT a function of the cardiac skeleton?
Which of the following is NOT a function of the cardiac skeleton?
Which statement accurately describes the structural differences between atrial and ventricular cardiac muscle cells?
Which statement accurately describes the structural differences between atrial and ventricular cardiac muscle cells?
What is the primary mechanism of hormone release in atrial and ventricular cardiac muscle cells?
What is the primary mechanism of hormone release in atrial and ventricular cardiac muscle cells?
Which hormone is specifically associated with the ventricular cardiac muscle cells?
Which hormone is specifically associated with the ventricular cardiac muscle cells?
What are the receptor sites for ANF and BNP primarily located?
What are the receptor sites for ANF and BNP primarily located?
What physiological function do ANF and BNP have on the kidneys?
What physiological function do ANF and BNP have on the kidneys?
How are atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) related in terms of storage?
How are atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) related in terms of storage?
Which characteristic distinguishes the hormones ANF and BNP concerning their discovery?
Which characteristic distinguishes the hormones ANF and BNP concerning their discovery?
What is the primary structural difference in the t-tubule system between atrial and ventricular cardiac muscle cells?
What is the primary structural difference in the t-tubule system between atrial and ventricular cardiac muscle cells?
What is the primary role of the cardiac skeleton in the heart?
What is the primary role of the cardiac skeleton in the heart?
Which of the following components is NOT part of the normal myocardial structure?
Which of the following components is NOT part of the normal myocardial structure?
How do the endocardium and myocardium layers differ in their anatomical composition?
How do the endocardium and myocardium layers differ in their anatomical composition?
Which anatomical feature separates the right atrium from the right ventricle?
Which anatomical feature separates the right atrium from the right ventricle?
What is the primary histological feature differentiating atrial and ventricular walls?
What is the primary histological feature differentiating atrial and ventricular walls?
What is a key component of the conduction system located at the junction of the atria and ventricles?
What is a key component of the conduction system located at the junction of the atria and ventricles?
Which layer of the heart wall is primarily responsible for pumping blood?
Which layer of the heart wall is primarily responsible for pumping blood?
What distinguishes the function of the pericardial fluid?
What distinguishes the function of the pericardial fluid?
Which heart chamber receives deoxygenated blood from the body?
Which heart chamber receives deoxygenated blood from the body?
What structure in the heart directly connects the myocardial cells and facilitates synchronous contractions?
What structure in the heart directly connects the myocardial cells and facilitates synchronous contractions?
What role does the pericardial fluid play in the pericardial cavity?
What role does the pericardial fluid play in the pericardial cavity?
What is the correct sequence of blood flow from the body to the lungs through the heart?
What is the correct sequence of blood flow from the body to the lungs through the heart?
Which structure separates the right atrium from the right ventricle?
Which structure separates the right atrium from the right ventricle?
How many chambers does the human heart contain?
How many chambers does the human heart contain?
Where does oxygenated blood enter the heart after being oxygenated in the lungs?
Where does oxygenated blood enter the heart after being oxygenated in the lungs?
What anatomical relationship exists between the parietal and visceral layers of the serous pericardium?
What anatomical relationship exists between the parietal and visceral layers of the serous pericardium?
What happens to blood after it is pumped from the right ventricle?
What happens to blood after it is pumped from the right ventricle?
Which valve allows blood to flow from the left atrium to the left ventricle?
Which valve allows blood to flow from the left atrium to the left ventricle?
How is the pericardial cavity described in terms of its size and purpose?
How is the pericardial cavity described in terms of its size and purpose?
What is the role of the pulmonary semilunar valve?
What is the role of the pulmonary semilunar valve?
What component connects two cardiac muscle cells and binds to actin thin filaments?
What component connects two cardiac muscle cells and binds to actin thin filaments?
Which intermediate filaments are primarily associated with desmosomes in cardiac muscle cells?
Which intermediate filaments are primarily associated with desmosomes in cardiac muscle cells?
What is the primary function of gap junctions in cardiac muscle cells?
What is the primary function of gap junctions in cardiac muscle cells?
How does the thickness of the atrial myocardium compare to the ventricular myocardium?
How does the thickness of the atrial myocardium compare to the ventricular myocardium?
How much thicker is the myocardium of the left ventricle compared to that of the right ventricle?
How much thicker is the myocardium of the left ventricle compared to that of the right ventricle?
What role do intercalated discs play in cardiac muscle cells?
What role do intercalated discs play in cardiac muscle cells?
Which of the following best describes the structure of fascia adherens?
Which of the following best describes the structure of fascia adherens?
In addition to ionic communication, what other function do gap junctions serve?
In addition to ionic communication, what other function do gap junctions serve?
Which structure within cardiac muscle cells primarily allows for coupling between them?
Which structure within cardiac muscle cells primarily allows for coupling between them?
Which cardiac structure is primarily responsible for providing mechanical strength to the muscle cells during contraction?
Which cardiac structure is primarily responsible for providing mechanical strength to the muscle cells during contraction?
What is the primary function of the sinoatrial (SA) node within the heart's impulse conduction system?
What is the primary function of the sinoatrial (SA) node within the heart's impulse conduction system?
Which layer of the heart wall is primarily responsible for the contraction and pumping action of the heart?
Which layer of the heart wall is primarily responsible for the contraction and pumping action of the heart?
In the systemic circulation, how is oxygenated blood transported from the heart to the tissues?
In the systemic circulation, how is oxygenated blood transported from the heart to the tissues?
What component of the heart valves ensures they close properly and prevent backflow?
What component of the heart valves ensures they close properly and prevent backflow?
What is the purpose of the Purkinje fibers in the heart?
What is the purpose of the Purkinje fibers in the heart?
What distinguishes pulmonary circulation from systemic circulation?
What distinguishes pulmonary circulation from systemic circulation?
Which type of blood vessel has the thinnest walls and is primarily responsible for nutrient exchange?
Which type of blood vessel has the thinnest walls and is primarily responsible for nutrient exchange?
Which of the following is not a feature of the endocardium?
Which of the following is not a feature of the endocardium?
Which of the following statements about the heart's tunics is correct?
Which of the following statements about the heart's tunics is correct?
What are the two primary components involved in the heart's impulse conduction system?
What are the two primary components involved in the heart's impulse conduction system?
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Study Notes
Atrial Myocardial Cells
- Smaller than ventricular muscle cells (10 µm vs. 15-20 µm)
- Less developed t-tubule system
- More gap junctions
Atrial Natriuretic Factor (ANF)
- Produced, stored, and secreted by atrial cardiac muscle cells
- Stored in electron-dense granules
- Released into surrounding capillaries when the atrial wall is stretched
- Affects cells in the adrenal cortex, kidney, and vascular smooth muscle
- Stimulates the kidney to excrete sodium and water in the urine
- Helps maintain blood volume
Brain Natriuretic Peptide (BNP)
- Stored and released by ventricular cardiac muscle cells
- Discovered in the brain
- Stored in granules and released into surrounding capillaries when the ventricular wall is stretched
- Similar physiological effects as ANF (ANP)
Chambers of the Heart
- Right and left atria
- Right and left ventricles
- Blood flow:
- Deoxygenated blood enters the right atrium via the inferior and superior vena cava
- Passes to the right ventricle through the tricuspid valve
- Pumped through the pulmonary semilunar valve to the pulmonary artery
- Oxygenated blood returns to the left atrium via the pulmonary vein
- Passes through the mitral/bicuspid valve to the left ventricle
Sinoatrial (SA) Node
- Located in the right atrial wall near the superior vena cava opening
- Surrounds a branch of the coronary artery
- Composed of modified cardiac muscle cells (SA nodal cells)
- Spindle-shaped and smaller than normal cardiac muscle cells (5-7 µm diameter)
- Fewer and less organized myofibrils
- Paler staining appearance in H&E or trichrome
- Less developed intercalated discs
- Known as the pacemaker of the heart
Atrioventricular (AV) Node
- Impulse travels from SA node through atrial cardiac muscle cells and internodal fibers to the AV node
- Located in the interatrial septum close to the tricuspid valve
- Composed of smaller and more densely packed cells that exhibit weaker contractions than SA nodal cells
Bundle of His (AV Bundle) and Bundle Branches
- Bundle of His – continuation of AV node into the interventricular septum
- Splits into left and right bundle branches
Purkinje Fibers
- Located in the subendocardial connective tissue
- Transmit impulses to ventricular cardiac muscle cells at the endocardium/myocardium interface
- Larger than normal cardiac muscle cells
- Contain few myofibrils and lack a T tubule system
- Appear pale-staining and vacuolated due to high glycogen content
- Rounded cells and nuclei
Atrial Myocardial Cells
- Smaller than ventricular cells (10 μm vs 15-20 μm in diameter)
- Less elaborate t-tubule system
- More gap junctions
Atrial and Ventricular Muscle Cells Hormonal Production
- Atrial cells: Produce, store, and secrete atrial natriuretic factor (ANF, ANP)
- ANF is stored in electron-dense granules
- Released into surrounding capillaries when atrial wall is stretched
- Ventricular cells: Store and release brain natriuretic peptide (BNP)
- BNP was first discovered in the brain
- Stored in granules and released into surrounding capillaries when ventricular wall is stretched
ANF and BNP Physiological Effects
- Both molecules have receptors in adrenal cortex, kidney, and vascular smooth muscle cells
- ANF and BNP stimulate the kidney to excrete sodium and water in urine
- They play a role in maintaining blood volume
Intercalated Disc Microanatomy
- Fascia adherens: Connects two cardiac muscle cells via a junction that binds to actin thin filaments in each cell
- Desmosomes: Connect cells via desmin and vimentin intermediate filaments
- Gap junctions: Allow for ionic communication and coupling between cardiac muscle cells
Myocardial Thickness
- Atrial myocardium is thinner than ventricular myocardium
- Left ventricle myocardium is three times thicker than right ventricle myocardium
Pericardium and Heart
- Pericardium: Fibrous sac surrounding the heart
- Fibrous pericardium: Outer layer of dense irregular connective tissue
- Serous pericardium: Inner layer
- Parietal layer: Lines the fibrous pericardium
- Visceral layer: Adheres to the heart surface (also known as the epicardium)
- Pericardial cavity: Space between visceral and parietal layers of the serous pericardium
- Contains pericardial fluid for lubrication
Chambers of the Heart
- Four chambers: right and left atria, right and left ventricles
- Blood flow path:
- Deoxygenated blood from body enters through superior and inferior vena cava into the right atrium.
- Passes through the tricuspid valve to the right ventricle.
- Pumped through the pulmonary semilunar valve to the pulmonary artery for oxygenation in the lungs.
- Oxygenated blood returns to the left atrium through the pulmonary veins.
- Passes through the bicuspid (mitral) valve into the left ventricle.
Cardiac Skeleton
- Location: Located between atria and ventricles
- Components:
- Annulus fibrosus: Dense irregular connective tissue rings surrounding the heart valves
- Trigona fibrosi: Triangular islands of connective tissue that strengthen the annuli fibrosi
- Septum membranaceum: Extension of the cardiac skeleton into the interventricular septum
- Functions:
- Separates atrial and ventricular musculature
- Sites of origin and insertion for cardiac muscle
- Stabilizes valves
- Limits valve diameter
- Prevents spread of electrical impulses except through the conduction system
Heart Wall Layers
- Epicardium: Outer layer
- Visceral layer of serous pericardium
- Analogous to the tunica adventitia of blood vessels
- Contains mesothelium, connective tissue, and adipose tissue
- Myocardium: Middle layer
- Composed of cardiac muscle tissue
- Endocardium: Inner layer
- Lines the heart chambers
- Composed of endothelium, connective tissue, and smooth muscle
Relationship to Blood Vessels
- Epicardium is analogous to tunica adventitia
- Myocardium is analogous to tunica media
- Endocardium is analogous to tunica intima
Atrial and Ventricular Walls
- Atrial walls: Thinner than ventricular walls
- Contain less muscle tissue due to lower pressure pumping requirements
- Ventricular walls: Thicker than atrial walls
- Left ventricle wall is three times thicker than the right ventricle due to the higher pressure required to pump blood to the systemic circulation
- Distinguishable at the LM level by thickness and muscle fiber arrangement
Cardiac Impulse Conduction System
- Sinoatrial (SA) node: Pacemaker of the heart
- Initiates the electrical impulse for heart contraction
- Atrioventricular (AV) node: Delays the impulse to allow for atrial contraction
- Bundle of His: Conducts the impulse to the ventricles
- Purkinje fibers: Specialized cells that rapidly conduct the impulse to ventricular muscle cells
SA and AV Nodal Cells vs Myocardial Cells
- SA and AV nodal cells: Smaller, fewer myofibrils, less organized, more gap junctions
- Allow for a slower, more controlled conduction of the electrical impulse
- Myocardial cells: Larger, more myofibrils, highly organized, fewer gap junctions
- Allow for rapid and efficient transmission of the electrical impulse throughout the heart
Purkinje Fibers
- Located in the subendocardial layer of the ventricular walls
- Larger than normal myocardial cells, with fewer myofibrils and numerous gap junctions
- Allow for rapid conduction of impulses to the ventricular myocardium
Heart Valves
- Structure: Composed of dense connective tissue covered by endothelium
- The core arises from the annulus fibrosus
- Leaflets are attached to the papillary muscles via chordae tendineae
- Function: Ensure one-way blood flow through the heart
- Histological organization: Dense irregular connective tissue with collagen and elastic fibers
- Papillary muscles: Projections of ventricular muscle that anchor chordae tendineae
- Visible in LM sections of the heart
- Chordae tendineae: Fibrous cords that prevent valves from prolapsing back into atria during ventricular contraction
- Visible in LM sections of the heart
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