General Principles of CVS Flashcards
1
Q
What is the thoracic cavity?
A
The thoracic cavity is the chamber of the body that houses the lungs and heart.
2
Q
What structures are contained within the mediastinum?
A
The mediastinum contains the heart, great vessels, trachea, oesophagus, thymus, and various nerves and lymphatic structures.
3
Q
What are the boundaries of the mediastinum?
A
The boundaries are:
* Superior: Thoracic inlet
* Inferior: Diaphragm
* Anterior: Sternum
* Posterior: Thoracic vertebrae
* Lateral: Mediastinal pleura
4
Q
How is the mediastinum divided?
A
The mediastinum is divided into superior and inferior parts by an imaginary line from the sternal angle to the intervertebral disc between T4 and T5.
5
Q
What structures are found in the superior mediastinum?
A
The superior mediastinum contains:
* Thymus
* Arch of the aorta
* Brachiocephalic veins
* Upper half of the superior vena cava
* Trachea
* Oesophagus
* Thoracic duct
* Vagus and phrenic nerves
6
Q
What structures are found in the inferior mediastinum?
A
The inferior mediastinum is divided into three parts:
* Anterior: Lymph nodes, fat, remnants of the thymus
* Middle: Heart in pericardium, roots of great vessels, phrenic nerves
* Posterior: Descending aorta, oesophagus, thoracic duct, azygos and hemiazygos veins, sympathetic trunks
7
Q
What is the fibrous pericardium?
A
The fibrous pericardium is a tough, inelastic outer layer that protects the heart and prevents overdistension.
8
Q
What is the serous pericardium composed of?
A
The serous pericardium has two layers:
* Parietal layer: Lines the fibrous pericardium
* Visceral layer: Covers the heart’s surface
9
Q
What is the blood supply to the pericardium?
A
The blood supply comes from:
* Internal thoracic artery
* Aortic arch branches
* Thoracic aorta
* Coronary arteries (visceral layer)
10
Q
What are the main functions of the pericardium?
A
The functions are:
* Protection
* Lubrication
* Limit overexpansion
* Anchorage
* Prevention of infections
* Regulation of heart function
11
Q
What are the four chambers of the heart?
A
The heart has four chambers:
* Right atrium
* Left atrium
* Right ventricle
* Left ventricle
12
Q
What is the function of the right atrium?
A
The right atrium receives deoxygenated blood from the body via the superior and inferior vena cavae.
13
Q
What is the function of the left atrium?
A
The left atrium receives oxygenated blood from the lungs via the pulmonary veins.
14
Q
Which valve is between the right atrium and right ventricle?
A
Tricuspid valve
15
Q
What are the great vessels of the heart?
A
The great vessels include:
* Superior vena cava
* Inferior vena cava
* Pulmonary arteries
* Pulmonary veins
* Aorta
16
Q
What does the right coronary artery supply?
A
The right coronary artery supplies:
* Right atrium
* Right ventricle
* Parts of left ventricle
* Sinoatrial and atrioventricular nodes
17
Q
What are the branches of the left coronary artery?
A
The left coronary artery branches into:
* Left anterior descending artery (LAD)
* Left circumflex artery (LCX)
18
Q
Fill in the blank: The _______ carries deoxygenated blood from the body to the right atrium.
A
Superior and inferior vena cavae
19
Q
True or False: The pulmonary arteries are the only arteries that carry oxygenated blood.
A
False
20
Q
What is the function of the pericardial cavity?
A
The pericardial cavity reduces friction during heartbeats.
21
Q
What is pericarditis?
A
Pericarditis is the inflammation of the pericardium, leading to chest pain.
22
Q
What is pericardiocentesis?
A
Pericardiocentesis is a procedure to remove excess fluid from the pericardial cavity.
23
Q
What artery runs down the front of the heart in the anterior interventricular sulcus?
A
Left Anterior Descending Artery (LAD)
The LAD is critical for the heart’s blood supply.
24
Q
What does the Left Anterior Descending Artery (LAD) supply?
A
- Anterior wall of the left ventricle
- Interventricular septum
- Apex of the heart
- Part of the bundle of His
- Left bundle branch
25
Why is the Left Anterior Descending Artery (LAD) often referred to as the 'widowmaker'?
Blockages can lead to extensive heart muscle damage.
26
What artery curves around the left side of the heart in the coronary sulcus?
Left Circumflex Artery (LCX)
## Footnote
The LCX separates the atria from the ventricles.
27
What areas does the Left Circumflex Artery (LCX) supply?
* Lateral and posterior walls of the left ventricle
* Part of the left atrium
* Sometimes posterior wall of left ventricle
28
What does coronary circulation dominance refer to?
Which coronary artery gives rise to the posterior descending artery (PDA).
29
What is the dominant artery in approximately 80% of people?
Right Coronary Artery (RCA)
## Footnote
This artery gives rise to the PDA.
30
In about 10% of people, which artery gives rise to the PDA?
Left Circumflex Artery (LCX)
31
What is codominant circulation?
Both RCA and LCX contribute to the PDA.
32
What does the Sinoatrial (SA) nodal branch supply?
SA node
33
What does the Right Marginal Artery supply?
Right ventricle
34
What does the Posterior Descending Artery (PDA) supply?
* Posterior interventricular septum
* Posterior wall of left ventricle
* Part of the right ventricle
35
What does the Atrioventricular (AV) nodal branch supply?
AV node
36
What is Coronary Artery Disease (CAD)?
Blockages in arteries, especially the LAD, can lead to myocardial infarction.
37
What condition can reduced blood flow due to narrowed coronary arteries cause?
Angina Pectoris
38
Where does deoxygenated blood enter the heart from the body?
Right atrium via the superior and inferior vena cava.
39
What valve does blood pass through from the right atrium to the right ventricle?
Tricuspid valve
40
What happens in the right ventricle?
It contracts and pushes deoxygenated blood through the pulmonary valve into the pulmonary artery.
41
What is unique about the pulmonary artery?
It carries deoxygenated blood.
42
What happens to blood in the lungs?
Gains oxygen and releases carbon dioxide.
43
What do the pulmonary veins do?
Carry oxygenated blood from the lungs to the left atrium.
44
What valve does blood pass through from the left atrium to the left ventricle?
Mitral (Bicuspid) valve
45
What is the function of the left ventricle?
Pumps oxygenated blood through the aortic valve into the aorta.
46
What is the largest artery in the body?
Aorta
47
What is the right side of the heart responsible for?
Pumping deoxygenated blood to the lungs (pulmonary circulation).
48
What is the left side of the heart responsible for?
Pumping oxygenated blood to the rest of the body (systemic circulation).
49
How does the wall thickness of the right ventricle compare to the left ventricle?
The right ventricle has a thinner wall.
50
What is the shape of the right ventricle?
Crescent or 'C'-shaped
51
What type of valve is the tricuspid valve?
Has three cusps
52
What type of valve is the mitral valve?
Has two cusps
53
What pressure does the right side of the heart operate under?
Low pressure
54
What pressure does the left side of the heart operate under?
High pressure
55
What type of blood does the right side of the heart pump?
Deoxygenated blood
56
What type of blood does the left side of the heart pump?
Oxygenated blood
57
Which side of the heart has a greater oxygen demand?
Left side
58
Which artery supplies the right side of the heart?
Right coronary artery
59
60
Where is the heart located?
Slightly left of the center of the chest, behind the sternum, and between the lungs in the mediastinum.
## Footnote
The heart is in a protective sac called the pericardium.
61
What is the position of the heart's apex?
Pointing toward the left side of the body.
62
What is the position of the heart's base?
Angled upward toward the right shoulder.
63
How many chambers does the heart have?
Four chambers.
64
What is the function of the Right Atrium?
Receives deoxygenated blood from the body through the superior and inferior vena cava.
65
What is the function of the Right Ventricle?
Pumps deoxygenated blood into the lungs through the pulmonary artery for oxygenation.
66
What is the function of the Left Atrium?
Receives oxygenated blood from the lungs via the pulmonary veins.
67
What is the function of the Left Ventricle?
Pumps oxygenated blood to the rest of the body through the aorta.
68
What is the location of the Superior Vena Cava?
A large vein that enters the right atrium from above.
69
What is the function of the Inferior Vena Cava?
Collects deoxygenated blood from the lower body and returns it to the heart.
70
Where do the Pulmonary Arteries originate?
From the right ventricle of the heart.
71
What do the Pulmonary Veins do?
Carry oxygenated blood from the lungs back to the heart.
72
What is the location of the Aorta?
Originates from the left ventricle of the heart.
73
What is the function of the Coronary Arteries?
Supply blood to the heart muscle itself (the myocardium).
74
What forms the Right Border of the heart?
Mainly by the right atrium.
75
What forms the Left Border of the heart?
Mostly by the left ventricle, with some contribution from the left atrium.
76
What forms the Superior Border of the heart?
Formed by the right and left atria.
77
What forms the Inferior Border of the heart?
Mainly by the right ventricle, with some contribution from the left ventricle.
78
Where is the Aortic Area for auscultation located?
Right side of the sternum, at the 2nd intercostal space.
79
What is the purpose of auscultating the Pulmonic Area?
To assess the sounds of the pulmonary valve.
80
Where is the Tricuspid Area located?
Left side of the sternum, at the 4th intercostal space.
81
Where is the Mitral Area (Apical Area) located?
Left side of the chest at the 5th intercostal space, in the midclavicular line.
82
What is Erb’s Point used for?
Listening to heart sounds from all four valves.
83
Fill in the blank: The heart is located in a space known as the _______.
mediastinum
84
True or False: The left ventricle is the strongest chamber of the heart.
True
85
What is the relaxation phase of the cardiac cycle called?
Diastole
## Footnote
Diastole includes atrial and ventricular diastole.
86
What occurs during atrial diastole?
Both atria are relaxed and filling with blood from the veins
## Footnote
Blood comes from the superior and inferior vena cava for the right atrium and the pulmonary veins for the left atrium.
87
What happens during ventricular diastole?
The ventricles are relaxed, and blood flows passively from the atria into the ventricles
## Footnote
The atrioventricular (AV) valves are open during this phase.
88
What is the end of diastole marked by?
Atrial systole
## Footnote
Atrial systole is when the atria contract to push remaining blood into the ventricles.
89
What occurs during ventricular systole?
The ventricles begin to contract, increasing pressure and closing the AV valves
## Footnote
This prevents blood from flowing backward into the atria.
90
What happens when ventricular pressure exceeds the pressure in the pulmonary trunk and aorta?
The semilunar valves open, and blood is ejected from the ventricles
## Footnote
The pulmonary valve is on the right and the aortic valve is on the left.
91
What is the function of the right ventricle during the cardiac cycle?
Pumps blood into the pulmonary artery for oxygenation
## Footnote
This is part of the ejection phase during ventricular systole.
92
What is the function of the left ventricle during the cardiac cycle?
Pumps blood into the aorta to distribute it throughout the body
## Footnote
This occurs during ventricular systole.
93
What is isovolumetric relaxation?
The transition phase between systole and diastole where the ventricles relax and blood volume remains constant
## Footnote
The semilunar valves close while the AV valves remain closed.
94
What marks the end of systole?
Isovolumetric relaxation
## Footnote
This phase signifies the beginning of diastole.
95
What are the key events in the cardiac cycle?
* Filling of the ventricles
* Atrial systole
* Ventricular systole
* Ventricular diastole
## Footnote
Each event corresponds to specific phases of the cardiac cycle.
96
How long does the entire cardiac cycle typically last?
About 0.8 seconds
## Footnote
This is based on a normal resting adult heart rate of about 75 beats per minute.
97
What phases is the cardiac cycle divided into?
* Atrial contraction and ventricular filling: Diastole
* Ventricular contraction (ejection of blood): Systole
## Footnote
These phases describe the two main activities of the heart during the cycle.
98
What does blood volume refer to in the cardiac cycle?
The amount of blood in the heart chambers at any given moment during the cardiac cycle
## Footnote
Blood volume changes as the heart fills and contracts
99
What is end-diastolic volume (EDV)?
The maximum amount of blood in a ventricle before contraction (just before systole)
## Footnote
EDV indicates the volume of blood in the ventricles at the end of filling
100
What is end-systolic volume (ESV)?
The remaining blood volume in a ventricle after contraction (systole)
## Footnote
ESV reflects the amount of blood left in the ventricles post-contraction
101
How does blood pressure change during the cardiac cycle?
Blood pressure in the heart chambers increases and decreases, causing the opening and closing of heart valves
## Footnote
This pressure is generated by the contraction and relaxation of the myocardium
102
What happens to ventricular pressure during systole?
Ventricular pressure rises as the ventricles contract, pushing blood out of the heart
## Footnote
This is crucial for blood ejection into circulation
103
What occurs to atrial pressure during the later stages of diastole?
Atrial pressure rises when the atria contract, helping to fill the ventricles
## Footnote
This pressure change is important for efficient ventricular filling
104
What are the two types of heart valves?
Atrioventricular (AV) valves and Semilunar valves
## Footnote
AV valves: tricuspid and mitral; Semilunar valves: pulmonary and aortic
105
What is the function of the atrioventricular (AV) valves?
They separate the atria from the ventricles and open when ventricular pressure is lower than atrial pressure
## Footnote
AV valves prevent backflow into the atria during ventricular contraction
106
When do semilunar valves open?
When ventricular pressure exceeds arterial pressure
## Footnote
This allows blood to be ejected into the pulmonary and systemic circulations
107
What happens when ventricular pressure drops below arterial pressure?
Semilunar valves close to prevent blood from flowing backward into the ventricles
## Footnote
This ensures unidirectional blood flow
108
Describe the direction of blood flow from the atria to the ventricles.
During diastole, AV valves open and blood flows from the atria into the ventricles due to higher atrial pressure
## Footnote
This is essential for ventricular filling
109
What occurs during systole in terms of blood flow from the ventricles?
Ventricles contract, pressure increases, semilunar valves open, and blood is ejected into the pulmonary and systemic circulations
## Footnote
This is critical for delivering oxygenated blood throughout the body
110
How do AV valves respond during ventricular relaxation?
They open as atrial pressure exceeds ventricular pressure, allowing blood to flow from the atria to the ventricles
## Footnote
This is part of the cardiac cycle's filling phase
111
What role do semilunar valves play in backflow prevention?
They close when ventricular pressure drops to prevent blood from flowing back into the ventricles
## Footnote
This maintains the efficiency of the heart's pumping action
112
What is systole?
The phase of the cardiac cycle when the heart muscle contracts, specifically the ventricles.
113
What occurs during ventricular systole?
The semilunar valves open to allow blood flow from the ventricles to the arteries.
114
What is diastole?
The relaxation phase of the cardiac cycle where the heart chambers relax and fill with blood.
115
What happens during ventricular diastole?
The ventricles fill with blood from the atria while the AV valves are open.
116
Define Stroke Volume (SV).
The amount of blood ejected from the ventricles with each heartbeat during systole.
117
What is the formula for Stroke Volume?
Stroke Volume (SV) = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV)
118
What does End-Diastolic Volume (EDV) refer to?
The total volume of blood in the ventricles at the end of diastole, just before systole.
119
What factors affect End-Diastolic Volume (EDV)?
* Venous return
* Ventricular compliance
120
Define End-Systolic Volume (ESV).
The volume of blood remaining in the ventricles after systole.
121
What influences End-Systolic Volume (ESV)?
* Heart contractility
* Afterload
122
What is Ejection Fraction (EF)?
A percentage that represents how much blood the heart pumps out of the ventricles with each beat.
123
How is Ejection Fraction calculated?
Ejection Fraction (EF) = (Stroke Volume / End-Diastolic Volume) × 100%
124
What is a normal range for Ejection Fraction?
Typically around 55% to 70%
125
What does a low Ejection Fraction (below 40%) indicate?
It could be an indicator of heart failure or poor cardiac function.
126
Define Cardiac Output (CO).
The volume of blood the heart pumps in one minute.
127
What is the formula for Cardiac Output?
Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR)
128
What is afterload?
The resistance the ventricles must overcome to eject blood during systole.
129
What factors determine afterload?
* Diameter of arteries
* Elasticity of arteries
* Blood pressure in systemic and pulmonary circulations
130
Define preload.
The initial stretching of the cardiac muscle fibers before contraction.
131
What primarily determines preload?
The volume of blood returning to the heart (venous return).
132
What is the relationship between preload and stroke volume?
Greater preload leads to a stronger contraction and greater stroke volume, following Starling’s law.
133
What does the Wiggers Diagram represent?
The Wiggers Diagram is a graphical representation of the events that occur during the cardiac cycle.
134
What parameters are combined in the Wiggers Diagram?
The Wiggers Diagram combines various parameters such as:
* Ventricular pressure
* Aortic pressure
* Ventricular volume
* Electrocardiogram (ECG) data
135
What does the X-axis of the Wiggers Diagram represent?
The X-axis represents time, typically showing one complete cardiac cycle.
136
What does the Y-axis of the Wiggers Diagram typically show?
The Y-axis typically shows pressure (in mmHg) or volume (in milliliters).
137
What key component of the Wiggers Diagram shows the electrical activity of the heart?
The ECG Curve shows the electrical activity of the heart.
138
How does the left ventricular pressure curve compare to the right ventricular pressure curve?
The left ventricular pressure curve typically rises more sharply than the right due to the higher systemic pressure.
139
What does the aortic pressure curve reflect?
The aortic pressure curve reflects the pressure within the aorta as the heart pumps blood into the systemic circulation.
140
What is represented by the ventricular volume curve?
The ventricular volume curve shows the volume of blood in the ventricle during the cardiac cycle.
141
What is the significance of the AV valves in the Wiggers Diagram?
The AV valves (tricuspid/mitral) and semilunar valves (pulmonary/aortic) opening and closing are inferred from the pressure and volume curves.
142
What occurs during Atrial Systole?
During Atrial Systole, the P wave represents the electrical depolarization of the atria, and the volume in the ventricle increases slightly.
143
What does the QRS complex on the ECG represent?
The QRS complex represents the depolarization of the ventricles.
144
What happens during Isovolumetric Contraction?
During Isovolumetric Contraction, the volume of blood in the ventricle remains constant, and ventricular pressure rises sharply.
145
What does the ST segment on the ECG represent?
The ST segment represents the time during which the ventricles are contracting and pushing blood into the arteries.
146
What occurs during Isovolumetric Relaxation?
During Isovolumetric Relaxation, the volume remains constant, and ventricular pressure drops rapidly.
147
What does the T wave on the ECG indicate?
The T wave represents the repolarization of the ventricles.
148
What happens during Ventricular Filling?
During Ventricular Filling, the volume increases as blood flows from the atria into the ventricles.
149
Fill in the blank: Systole is the phase when the _______ contract to pump blood into the arteries.
[ventricles]
150
Fill in the blank: Diastole is the _______ phase when the ventricles fill with blood.
[relaxation]
151
What are the two sounds associated with valve movements in the cardiac cycle?
The two sounds are:
* S1 sound (closure of AV valves)
* S2 sound (closure of semilunar valves)
152
True or False: The diagram shows how pressure rises and falls in the ventricles and aorta.
True
153
What is the relationship between pressure, volume, and valve action in the Wiggers Diagram?
The Wiggers Diagram provides a clear view of the relationship between pressure, volume, and valve action during each phase of the cardiac cycle.
154
What is the myocardium?
The thick, muscular layer of the heart wall responsible for contraction and pumping action of the heart.
155
What are the three main layers of the heart?
* Epicardium (outer layer)
* Myocardium (middle layer)
* Endocardium (inner layer)
156
What is the primary composition of the myocardium?
Cardiac muscle tissue specialized for continuous, rhythmic contractions.
157
What are cardiomyocytes?
Heart muscle cells that are striated, branching, and capable of generating force to pump blood.
158
What is the significance of intercalated discs in cardiomyocytes?
They allow electrical impulses to pass rapidly between cells, enabling coordinated contractions.
159
What is the appearance of cardiac muscle fibers and why?
Striated appearance due to the arrangement of contractile proteins, actin and myosin, forming sarcomeres.
160
How are the muscle fibers of the myocardium arranged?
In a spiral or helix-like arrangement around the heart for efficient contraction.
161
Why are the muscle fibers in the left ventricle thicker than those in the right ventricle?
Due to the higher pressure needed to pump blood throughout systemic circulation.
162
What does it mean for the myocardium to function as a syncytium?
The muscle fibers work together as a coordinated unit for efficient pumping.
163
What role do gap junctions in intercalated discs play?
They enable rapid transmission of electrical signals between adjacent cardiomyocytes.
164
What is the blood supply to the myocardium?
Supplied by the coronary arteries, which branch off the aorta.
165
What is the function of the coronary veins?
They return deoxygenated blood from the myocardium back to the right atrium.
166
What does well-vascularized mean in the context of the myocardium?
It has an extensive network of blood vessels to supply oxygen and nutrients to heart muscle cells.
167
Which ventricle has the thickest myocardium and why?
The left ventricle, because it works harder to pump blood to the entire body.
168
What is the primary function of the myocardium?
Contraction to generate the force needed to pump blood out of the heart.
169
Fill in the blank: The myocardium's ability to contract and relax in a coordinated fashion allows the heart to function as an effective _______.
[pump]
170
What are cardiomyocytes?
Specialized heart muscle cells responsible for the contraction of the heart.
171
What shape do cardiomyocytes typically have?
Cylindrical or branching shape.
172
What is the typical length and diameter of cardiomyocytes?
50-100 micrometers in length and 10-25 micrometers in diameter.
173
What gives cardiomyocytes their striated appearance?
The regular arrangement of actin and myosin within sarcomeres.
174
What are sarcomeres?
The repeating units of myofilaments (actin and myosin) that are the functional units of contraction.
175
How many nuclei do most cardiomyocytes have?
One or two centrally located nuclei.
176
What are intercalated discs?
Specialized connections between adjacent cardiomyocytes.
177
What is the function of desmosomes in intercalated discs?
To hold the cells together, providing mechanical strength.
178
What do gap junctions in intercalated discs do?
Allow the passage of electrical signals between cells.
179
What percentage of a cardiomyocyte's volume can be made up of mitochondria?
About 30-40%.
180
What is the role of the sarcoplasmic reticulum in cardiomyocytes?
Involved in the storage and release of calcium ions (Ca²⁺).
181
What are T-tubules?
Extensions of the cell membrane that penetrate into the cell's interior.
182
What is the primary function of cardiomyocytes?
To contract and relax to facilitate the pumping of blood.
183
What initiates the contraction of cardiomyocytes?
An action potential that triggers the release of calcium ions.
184
What theory explains how actin and myosin filaments interact during contraction?
The sliding filament theory.
185
What allows cardiomyocytes to generate and propagate electrical impulses?
Their ability to coordinate contraction.
186
What is automaticity in cardiomyocytes?
The ability to generate action potentials spontaneously.
187
What does rhythmicity ensure in the heart?
That the heart beats at a consistent rate.
188
Why are cardiomyocytes resistant to fatigue?
Due to high mitochondrial content and reliance on aerobic metabolism.
189
What is cardiac output (CO)?
The volume of blood the heart pumps per minute.
## Footnote
It is a crucial indicator of cardiovascular health and systemic circulation.
190
How is cardiac output calculated?
Using the formula: Cardiac Output = Heart Rate (HR) × Stroke Volume (SV)
## Footnote
This formula highlights the relationship between heart rate and stroke volume.
191
What is heart rate (HR)?
The number of heartbeats per minute.
## Footnote
An increase in HR generally increases CO, but excessively high HR can reduce filling time.
192
What effect does an excessively high heart rate have on cardiac output?
It can reduce filling time, potentially decreasing stroke volume and cardiac output.
## Footnote
This is due to decreased time for the heart to fill with blood.
193
What is stroke volume (SV)?
The volume of blood ejected by the ventricles with each heartbeat.
## Footnote
It is a key component of cardiac output.
194
What are the components of stroke volume?
* Preload
* Afterload
* Contractility
## Footnote
Each component plays a critical role in determining stroke volume.
195
What is preload?
The degree of ventricular filling or end-diastolic volume (EDV).
## Footnote
According to the Frank-Starling law, increased preload enhances stroke volume.
196
What is afterload?
The resistance the heart must overcome to eject blood.
## Footnote
High afterload can decrease stroke volume.
197
What is contractility?
The inherent strength and vigor of the heart's contraction, independent of preload and afterload.
## Footnote
Enhanced by sympathetic stimulation and calcium availability.
198
What are the factors influencing cardiac output?
* Autonomic Nervous System
* Hormones
* Physical Activity
* Blood Volume
* Pathological Conditions
## Footnote
Each factor can significantly affect cardiac output.
199
How does sympathetic stimulation affect cardiac output?
It increases heart rate and contractility.
## Footnote
This leads to an increase in cardiac output.
200
How does parasympathetic stimulation affect heart rate?
It decreases heart rate.
## Footnote
This can lead to a decrease in cardiac output.
201
What hormones increase heart rate and contractility?
Adrenaline and other catecholamines.
## Footnote
These hormones are released during stress and physical activity.
202
What effect does exercise have on cardiac output?
Increases heart rate and stroke volume, boosting cardiac output.
## Footnote
Exercise demands higher blood flow to meet the body's needs.
203
How does blood volume influence preload?
Increased volume boosts cardiac output, while decreased volume lowers it.
## Footnote
Preload is directly related to the amount of blood returning to the heart.
204
What pathological conditions can alter determinants of cardiac output?
* Heart failure
* Hypertension
## Footnote
These conditions can significantly impact heart function and blood flow.
205
True or False: Cardiac output reflects the efficiency of the heart's pumping action.
True.
## Footnote
It adapts in response to various physiological and pathological stimuli.
206
What is venous return?
The flow of blood back to the heart, particularly to the right atrium from the systemic circulation.
207
Why is venous return critical?
It maintains cardiac output by directly affecting preload, which determines stroke volume and overall cardiac function.
208
What is the primary determinant of venous return?
The pressure gradient between the venules and the right atrium.
209
How does higher venous pressure affect venous return?
It facilitates venous return.
210
What is venous compliance?
The ability of veins to expand or contract in response to changes in blood volume and pressure.
211
How does decreased venous compliance affect venous return?
It can increase venous return by reducing blood volume stored in veins.
212
How does total blood volume influence venous return?
Higher blood volume increases venous return; hypovolemia reduces it.
213
What role does the muscle pump play in venous return?
It compresses veins during skeletal muscle contractions, pushing blood toward the heart.
214
What is the respiratory pump?
A mechanism that helps venous return by creating pressure gradients during breathing.
215
True or False: Gravity always facilitates venous return.
False.
216
How does body position affect venous return?
Lying down reduces gravity's effect and facilitates venous return.
217
What is venous tone?
The degree of constriction of veins, regulated by the sympathetic nervous system and hormones.
218
What effect does venoconstriction have on venous return?
It increases venous return by decreasing the capacity of veins to store blood.
219
How does cardiac function influence venous return?
Poor right heart function increases right atrial pressure, impeding venous return.
220
What is the relationship between arterial pressure and venous return?
High arterial pressure can reduce venous return; lower arterial pressure can facilitate it.
221
How does hydration affect venous return?
Dehydration decreases venous return; fluid retention increases it.
222
What impact does exercise have on venous return?
It improves venous return through muscle pump and increased respiratory pump activity.
223
What hormones promote venoconstriction?
* Norepinephrine
* Angiotensin II
* Vasopressin
224
What hormone can promote venodilation?
Atrial natriuretic peptide (ANP).
225
Fill in the blank: The _______ is a mechanism that helps push blood from the veins in the abdomen toward the heart during inspiration.
respiratory pump
226
What are the two main types of valves in the heart?
Atrioventricular (AV) Valves and Semilunar Valves
227
Where are the Atrioventricular (AV) valves located?
Between the atria and ventricles of the heart
228
What are the two Atrioventricular (AV) valves?
* Mitral Valve (left AV valve)
* Tricuspid Valve (right AV valve)
229
How many cusps does the mitral valve have?
Two cusps (anterior and posterior)
230
What is another name for the mitral valve?
Bicuspid valve
231
How many cusps does the tricuspid valve have?
Three cusps (anterior, posterior, and septal)
232
What are the key structures of the AV valves?
* Leaflets
* Chordae Tendineae
* Papillary Muscles
233
What is the function of the chordae tendineae?
Prevent the valve leaflets from inverting or prolapsing into the atria
234
What is the role of papillary muscles?
Contract to tense the chordae tendineae during ventricular contraction
235
What do the AV valves ensure during diastole?
Blood flows from the atria into the ventricles
236
What histological layer of the AV valves is in contact with blood flow?
Endothelium
237
What is the fibrosa layer made of?
Dense collagen fibers
238
What is the function of the spongiosa layer in the AV valves?
Provides cushioning and flexibility
239
What is the role of the ventricularis layer?
Contains elastin fibers that allow the valve to stretch and return to position
240
What are the two semilunar valves?
* Pulmonary Valve (right semilunar valve)
* Aortic Valve (left semilunar valve)
241
Where is the pulmonary valve located?
Between the right ventricle and the pulmonary trunk
242
Where is the aortic valve located?
Between the left ventricle and the aorta
243
What are the key structures of the semilunar valves?
* Cusps
* Nodules and Lunules
* Sinuses of Valsalva
244
What is the shape of the cusps in the semilunar valves?
Half-moon shaped
245
What do nodules and lunules help with in the semilunar valves?
They help the cusps close properly
246
What do the sinuses of Valsalva prevent?
Prevent the cusps from sticking to the vessel wall during closure
247
When do the semilunar valves open?
During ventricular systole
248
What prevents backflow of blood into the ventricles during diastole?
Semilunar valves
249
What is similar between the histological structure of AV valves and semilunar valves?
Both have an endothelium lined by simple squamous epithelial cells
250
How does the fibrosa layer of the semilunar valves compare to that of the AV valves?
It is generally thicker to withstand higher pressures
251
How developed is the spongiosa layer in the semilunar valves?
Less developed compared to the AV valves
252
What is the function of the ventricularis layer in the semilunar valves?
Contains elastic fibers that help the valves return to the closed position
253
What are the two main heart sounds in a normal, healthy heart?
S1 (First Heart Sound) and S2 (Second Heart Sound)
## Footnote
S1 is described as 'lub' and S2 as 'dub'.
254
What causes the S1 (First Heart Sound)?
Closure of the atrioventricular (AV) valves: Mitral Valve and Tricuspid Valve
## Footnote
S1 occurs at the beginning of ventricular systole.
255
How is S1 characterized?
Low-pitched, long 'lub' sound, louder at the apex of the heart
## Footnote
S1 marks the onset of systole.
256
When does S1 occur in the cardiac cycle?
Just before the ventricles contract, after atrial contraction
## Footnote
S1 is the first sound in the cardiac cycle.
257
What causes the S2 (Second Heart Sound)?
Closure of the semilunar valves: Aortic Valve and Pulmonary Valve
## Footnote
S2 occurs at the beginning of ventricular diastole.
258
How is S2 characterized?
Higher-pitched, shorter 'dub' sound, loudest at the base of the heart
## Footnote
S2 marks the end of systole.
259
When does S2 occur in the cardiac cycle?
After the ventricles have ejected blood into the aorta and pulmonary arteries
## Footnote
S2 signals the beginning of diastole.
260
What is S2 splitting?
S2 can be heard as two distinct sounds due to aortic valve and pulmonary valve closing at different times
## Footnote
A2 (aortic valve closure) and P2 (pulmonary valve closure) are the components.
261
What typically causes the splitting of S2 to be more pronounced?
Increased venous return during deep inspiration
## Footnote
This delays the closure of the pulmonary valve.
262
Is S1 splitting commonly observed?
No, it is rarely observed under normal conditions
## Footnote
It may occur in conditions like left bundle branch block.
263
What is the S3 (Third Heart Sound)?
Occurs after S2, during the rapid filling phase of the ventricles
## Footnote
S3 is low-pitched, often described as a 'kentucky' sound.
264
In which populations may S3 be considered benign?
Children and young adults
## Footnote
In older adults, S3 is often associated with heart failure.
265
What is the S4 (Fourth Heart Sound)?
Occurs just before S1, during late diastole when the atria contract
## Footnote
S4 is low-pitched, often described as a 'Tennessee' sound.
266
What conditions are associated with pathologic S4?
Increased ventricular stiffness due to hypertension, aortic stenosis, or hypertrophic cardiomyopathy
## Footnote
S4 is usually pathologic.
267
What is a summation gallop?
Occurs when S3 and S4 are heard together, usually in severe heart failure
## Footnote
This indicates significant cardiac compromise.
268
How does the pitch of S1 compare to S2?
S1 is low-pitched, S2 is higher-pitched
## Footnote
S3 and S4 are also low-pitched.
269
Where is S1 typically loudest?
At the apex of the heart
## Footnote
The apex is the lower part of the heart.
270
Where is S2 typically loudest?
At the base of the heart
## Footnote
The base is the upper part of the heart.
271
What distinguishes physiologic heart sounds from pathologic heart sounds?
Physiologic sounds: Normal S1 and S2, S3 and S4 may be benign in younger populations. Pathologic sounds: S3 and S4 usually indicate heart failure or ventricular stiffness.
## Footnote
S1 and S2 abnormalities can indicate various heart conditions.
272
What can cause abnormal S1 and S2 sounds?
Conditions like mitral regurgitation, aortic stenosis, or pulmonary hypertension
## Footnote
These conditions alter the timing and intensity of heart sounds.
273
What is valvular insufficiency?
Valvular insufficiency, also referred to as valvular regurgitation or valve incompetence, occurs when a heart valve does not close properly, allowing blood to flow backward (retrograde flow) into the chamber it was just pumped out of.
274
What factors determine the consequences of insufficient valvular function?
The valve involved, the degree of insufficiency, and how long the condition has been present.
275
What occurs when heart valves are insufficient?
The valve leaflets or cusps fail to form a complete seal, leading to regurgitation.
276
What is a consequence of regurgitant blood flow?
Increased volume and pressure in the affected heart chamber.
277
What is the cause of mitral valve insufficiency?
Often caused by damage to the valve's leaflets or chordae tendineae, due to mitral valve prolapse, rheumatic fever, or ischemic heart disease.
278
What are the consequences of mitral valve insufficiency?
* Volume overload in the left atrium
* Pulmonary congestion and edema
* Left ventricular dilation
* Atrial fibrillation
279
What symptoms may patients with mitral valve insufficiency experience?
* Fatigue
* Shortness of breath
* Palpitations
* Exercise intolerance
280
What causes aortic valve insufficiency?
Can be caused by rheumatic heart disease, infective endocarditis, aortic root dilation, or hypertension.
281
What are the consequences of aortic valve insufficiency?
* Volume overload in the left ventricle
* Left ventricular dilation and hypertrophy
* Decreased cardiac output
* Aortic root dilation
282
What symptoms may patients with aortic valve insufficiency experience?
* Shortness of breath
* Fatigue
* Chest pain (especially with exertion)
* Palpitations
283
What causes tricuspid valve insufficiency?
Often secondary to right ventricular dilation or pulmonary hypertension, or from rheumatic fever or infective endocarditis.
284
What are the consequences of tricuspid valve insufficiency?
* Backflow of blood into the right atrium
* Increased venous pressure
* Right heart failure
285
What symptoms may patients with tricuspid valve insufficiency experience?
* Swelling of the abdomen (ascites)
* Legs (edema)
* Fatigue
286
What causes pulmonary valve insufficiency?
Typically secondary to pulmonary hypertension or may occur after surgery or in congenital conditions like tetralogy of Fallot.
287
What are the consequences of pulmonary valve insufficiency?
* Backflow of blood into the right ventricle
* Right ventricular dilation and hypertrophy
* Right heart failure
288
What symptoms may patients with pulmonary valve insufficiency experience?
* Fatigue
* Shortness of breath
* Symptoms of right heart failure, such as swelling in the legs and abdomen
289
What is a general consequence of insufficient valvular function?
Increased cardiac workload.
290
What is volume overload in the context of valvular insufficiency?
Backward flow of blood causes volume overload in the affected chamber, increasing the workload on the heart.
291
What can pressure overload lead to in valvular insufficiency?
Ventricular hypertrophy.
292
How can chronic valvular insufficiency affect heart rhythm?
It can lead to atrial fibrillation due to atrial enlargement and pressure overload.
293
What is a risk associated with damaged heart valves?
Increased risk of infective endocarditis.
294
What can left-sided valve insufficiencies lead to?
Pulmonary congestion (edema) due to backflow into the lungs.
295
What can right-sided valvular insufficiencies lead to?
Systemic congestion, causing edema, ascites, and liver enlargement.
296
What is a common symptom of reduced cardiac output?
Fatigue.
297
Fill in the blank: Mitral regurgitation can lead to _______.
Atrial fibrillation
298
299
What is the function of the Sinoatrial (SA) Node?
It initiates the electrical impulses and sets the pace for the heart rate.
300
Where is the Sinoatrial (SA) Node located?
In the right atrium near the superior vena cava.
301
What does the SA node generate that travels through the atria?
An action potential.
302
What is the role of the Atrioventricular (AV) Node?
It briefly delays the electrical impulse to allow the atria to fully contract before the ventricles contract.
303
Where is the Atrioventricular (AV) Node located?
At the junction between the atria and ventricles, near the tricuspid valve.
304
What is the Bundle of His also known as?
AV Bundle.
305
What does the Bundle of His do?
Carries the electrical impulse from the AV node down the interventricular septum to the right and left ventricles.
306
What branches from the Bundle of His?
Right and Left Bundle Branches.
307
What is the pathway of the Right and Left Bundle Branches?
They travel along the interventricular septum toward the apex of the heart.
308
What do the Right and Left Bundle Branches carry?
The electrical impulse to the right and left ventricles.
309
What are Purkinje Fibers?
Specialized fibers that spread throughout the ventricles.
310
What is the function of Purkinje Fibers?
Allow for rapid conduction of the electrical impulse to all parts of the ventricles.
311
What is ensured by the rapid conduction of electrical impulses through Purkinje Fibers?
Synchronized contraction of the ventricles.
312
What is the function of the Sinoatrial (SA) Node?
The SA node initiates the electrical impulses that regulate the heart's rhythm and rate.
## Footnote
It is often referred to as the natural pacemaker of the heart.
313
Where is the Sinoatrial (SA) Node located?
In the right atrium, near the superior vena cava.
## Footnote
The SA node generates electrical impulses spontaneously.
314
What is the typical heart rate set by the SA node in a healthy adult?
60-100 beats per minute.
## Footnote
This rate is considered normal for adults.
315
What happens when the electrical impulse generated by the SA node spreads through the atria?
The atrial muscles contract and push blood into the ventricles.
316
What role does the SA node play in heart function?
It coordinates the atrial contraction and maintains the overall rhythm of the heart.
317
What is the function of the Atrioventricular (AV) Node?
The AV node regulates the electrical impulse's transition from the atria to the ventricles.
318
Where is the Atrioventricular (AV) Node located?
At the junction of the atria and ventricles, just above the tricuspid valve.
319
What does the AV node do with the electrical signal before it passes to the ventricles?
It briefly delays the electrical signal.
320
Why is the delay caused by the AV node important?
It allows the atria to fully contract and empty their blood into the ventricles before the ventricles begin to contract.
321
What happens if the SA node fails?
The AV node can act as a secondary pacemaker, though at a slower rate (around 40-60 beats per minute).
322
What is the role of the AV node in the case of irregular heart rhythms?
It can regulate the conduction of electrical impulses and prevent excessively rapid transmission from the atria to the ventricles.
323
What are Purkinje Fibers?
Specialized fibers that distribute the electrical impulse to the muscle cells of the ventricles.
324
Where are Purkinje Fibers located?
At the end of the bundle branches (right and left).
325
What is the function of Purkinje Fibers?
They rapidly conduct the electrical impulse throughout the ventricular myocardium.
326
How do Purkinje Fibers contribute to ventricular contraction?
They ensure that the ventricles contract simultaneously and efficiently, starting from the apex and moving upward.
327
What is the significance of the rapid conduction by Purkinje Fibers?
It maximizes the efficiency of ventricular systole.
328
Fill in the blank: The AV node can regulate the conduction of electrical impulses if there are _______.
irregularities in the heart's rhythm.
329
True or False: The Purkinje Fibers have slower conduction than the surrounding myocardial tissue.
False.
330
What is an action potential?
A rapid, temporary change in the electrical membrane potential of a cell, particularly neurons and muscle cells.
331
What is the resting membrane potential in neurons?
-70 mV
332
What ions are in high concentration inside a resting neuron?
Potassium ions (K+)
333
What ions are in high concentration outside a resting neuron?
Sodium ions (Na+)
334
What is the permeability of the membrane at rest?
More permeable to K+ than Na+
335
What occurs during the depolarization phase of an action potential?
The membrane potential becomes less negative (more positive).
336
What happens when the membrane potential reaches around -55 mV?
Voltage-gated sodium channels open, allowing Na+ to rush into the cell.
337
What is the peak membrane potential during depolarization?
+30 to +40 mV
338
What occurs during the repolarization phase?
The membrane potential returns to its resting state.
339
What ion channels close during repolarization?
Voltage-gated sodium channels
340
What ion channels open during repolarization?
Voltage-gated potassium channels
341
What is hyperpolarization?
A phase where the membrane potential becomes slightly more negative than the resting potential.
342
What causes hyperpolarization?
Some potassium channels remain open, allowing too much K+ to leave the cell.
343
What is the absolute refractory period?
The period during depolarization and repolarization when no new action potential can be generated.
344
What characterizes the relative refractory period?
Some sodium channels are closed but can be reopened; a stronger-than-usual stimulus is needed.
345
Fill in the blank: The _______ is the membrane potential before an action potential occurs.
Resting Membrane Potential
346
True or False: During the absolute refractory period, a new action potential can be generated with a strong enough stimulus.
False
347
What initiates the heart's electrical activity?
The sinoatrial (SA) node generates a rhythmic action potential due to the 'funny current' (a mix of Na+ and Ca2+ influx)
## Footnote
The SA node is often referred to as the natural pacemaker of the heart.
348
What is the resting membrane potential in heart muscle cells?
-90 mV
## Footnote
This is similar to the resting membrane potential in neurons.
349
What happens mechanically when the heart is at rest?
The heart muscle is relaxed and the chambers fill with blood passively due to venous return
## Footnote
Atria and ventricles fill with blood before contraction.
350
What electrical event occurs during depolarization (systole)?
The action potential spreads from the SA node to the atria, causing atrial depolarization, then to the AV node and ventricles
## Footnote
Depolarization in ventricles is caused by Na+ influx through voltage-gated sodium channels.
351
What mechanical event corresponds to ventricular depolarization?
Ventricular contraction (systole) occurs, increasing pressure and pumping blood
## Footnote
Blood is pushed into the pulmonary artery and aorta.
352
What characterizes the plateau phase during ventricular contraction?
Sustained influx of Ca2+ through L-type calcium channels maintains membrane potential at a positive value
## Footnote
This prolongs the contraction phase.
353
What is the mechanical outcome of the plateau phase?
The ventricles contract fully, expelling blood efficiently
## Footnote
This phase corresponds to the contraction phase of the heart (systole).
354
What occurs during repolarization (diastole)?
Potassium (K+) channels open, allowing K+ to flow out, decreasing the positive charge inside the cell
## Footnote
This returns the membrane potential to around -90 mV.
355
What does ventricular repolarization correspond to in an electrocardiogram (ECG)?
The T wave
## Footnote
The T wave indicates the repolarization of the ventricles.
356
What mechanical event occurs during ventricular repolarization?
Ventricular relaxation (diastole) occurs, allowing the ventricles to refill with blood
## Footnote
This phase is critical for preparing for the next contraction.
357
What happens during hyperpolarization of ventricular muscle cells?
The membrane potential becomes slightly more negative than the resting potential due to continued K+ efflux
## Footnote
This is a short-lived phase.
358
What is the mechanical state of the heart during hyperpolarization?
The heart remains in the diastolic phase, with relaxed ventricles filling with blood
## Footnote
This prepares the heart for the next cycle of depolarization.
359
How does ventricular depolarization relate to blood ejection?
Ventricular depolarization leads to ventricular contraction (systole), increasing pressure and ejecting blood
## Footnote
This is essential for effective blood circulation.
360
What is the effect of ventricular repolarization on blood pressure?
Ventricular repolarization leads to ventricular relaxation (diastole), lowering pressure and allowing refill
## Footnote
This ensures the heart is ready for the next contraction.
361
What is the purpose of the refractory period in the heart?
It ensures that the ventricles cannot contract again until they are fully relaxed
## Footnote
This allows for adequate filling of the heart.
362
What initiates the action potential in the heart?
The sinoatrial (SA) node
## Footnote
The SA node is located in the right atrium and is known as the natural pacemaker of the heart.
363
What is the sequence of propagation for the action potential in the heart?
SA node → atria → atrioventricular (AV) node → bundle of His → Purkinje fibers → ventricles
## Footnote
This sequence ensures coordinated contraction of the heart chambers.
364
What occurs when the action potential reaches the cardiac myocytes?
Opening of voltage-gated sodium (Na+) channels
## Footnote
This leads to depolarization of the myocyte membrane.
365
What causes the rapid depolarization of cardiac myocytes?
Inrush of sodium (Na+) ions through fast sodium channels
## Footnote
This rapid influx changes the membrane potential to a positive value.
366
What is the 'plateau phase' in cardiac myocyte contraction?
A prolonged period of positive membrane potential due to slow calcium (Ca²⁺) influx
## Footnote
This phase is balanced by potassium (K+) exiting the cell.
367
What triggers calcium-induced calcium release (CICR) in cardiac myocytes?
Entry of Ca²⁺ through L-type calcium channels
## Footnote
CICR amplifies the calcium signal by releasing more calcium from the sarcoplasmic reticulum.
368
What role does troponin play in muscle contraction?
Troponin binds calcium, causing a conformational change that exposes actin binding sites
## Footnote
This allows myosin heads to bind to actin filaments.
369
What is the function of the troponin-tropomyosin complex in muscle contraction?
It blocks binding sites on actin filaments under normal resting conditions
## Footnote
This prevents myosin from binding to actin until calcium is present.
370
What is the outcome when myosin heads bind to actin?
Formation of cross-bridges
## Footnote
This is essential for muscle contraction via the sliding filament mechanism.
371
What powers the pivoting of myosin heads during contraction?
ATP hydrolysis
## Footnote
This energy is necessary for myosin to move along actin filaments.
372
What occurs during muscle relaxation in cardiac myocytes?
Calcium is pumped back into the sarcoplasmic reticulum and out of the cell
## Footnote
This process allows the muscle to relax after contraction.
373
What happens to the membrane potential during repolarization?
L-type calcium channels close and potassium (K+) channels open
## Footnote
This restores the membrane potential to its resting state.
374
What is systole in the context of cardiac function?
Contraction of the heart muscle
## Footnote
This phase is responsible for pumping blood out of the heart.
375
What is diastole in the context of cardiac function?
Relaxation of the heart muscle
## Footnote
During diastole, the ventricles refill with blood in preparation for the next contraction.
376
Fill in the blank: The process of muscle contraction involves the _______ mechanism.
sliding filament
## Footnote
This mechanism describes how actin and myosin filaments slide past each other during contraction.
377
What is the resting membrane potential of ventricular myocytes?
-85 to -90 mV
378
Which ions are in high concentration inside the ventricular myocytes at rest?
Potassium (K+)
379
What ion channels are open at rest in ventricular myocytes?
Potassium channels
380
What initiates depolarization in ventricular myocytes?
An action potential from an adjacent cell or the His-Purkinje system
381
During depolarization (Phase 0), which ion channels open rapidly?
Voltage-gated sodium channels
382
What is the approximate membrane potential during the peak of depolarization?
+20 to +30 mV
383
What occurs during initial repolarization (Phase 1)?
Sodium channels close and potassium channels open
384
What effect does initial repolarization have on the membrane potential?
It becomes slightly more negative
385
What characterizes the plateau phase (Phase 2) of the ventricular action potential?
Calcium influx balances potassium outflow
386
How long does the plateau phase typically last in ventricular myocytes?
200-300 ms
387
What is the main effect of the plateau phase on heart muscle contraction?
Prevents contracting too quickly, ensuring sustained contraction
388
What happens during repolarization (Phase 3)?
Potassium continues to leave the cell and calcium influx diminishes
389
What is the final resting membrane potential after repolarization?
-85 to -90 mV
390
What restores the ionic gradients after repolarization?
Sodium-potassium pump (Na+/K+ ATPase) and calcium pumps
391
Fill in the blank: Phase 0 corresponds to the _______ complex in an ECG.
QRS
392
Phase 2 of the ventricular action potential is represented by which segment on an ECG?
ST segment
393
Phase 3 of the ventricular action potential is represented by which wave on an ECG?
T wave
394
What does the plateau phase ensure during cardiac function?
Coordinated, sustained contraction of ventricular myocytes
395
True or False: The prolonged depolarization prevents tetany in the heart.
True
396
What is the role of refractory periods in cardiac function?
Prevent premature contractions and allow adequate refill time
397
List the key phases of the ventricular action potential in order.
* Phase 0: Depolarization
* Phase 1: Initial Repolarization
* Phase 2: Plateau Phase
* Phase 3: Repolarization
* Phase 4: Resting Potential
398
What is the pacemaker action potential?
The electrical signal generated by specialized cells in the heart, particularly in the sinoatrial (SA) node and atrioventricular (AV) node.
399
What is the resting membrane potential in pacemaker cells?
It is not stable and gradually depolarizes over time, known as the pacemaker potential.
400
What type of channels are responsible for the slow depolarization during the resting phase?
Funny (If) sodium channels.
401
What ions pass through funny channels in pacemaker cells?
* Sodium (Na+) * Potassium (K+)
402
What is the starting membrane potential for pacemaker cells?
-60 mV
403
What causes the pacemaker potential during phase 4?
The opening of funny channels (If) allowing slow influx of Na+ ions.
404
What additional ion contributes to the gradual depolarization in phase 4?
Calcium (Ca²⁺) via T-type calcium channels.
405
What happens to the membrane potential during phase 0?
It becomes more positive, moving from -40 mV to +10 to +20 mV.
406
What causes the depolarization in pacemaker cells?
Opening of L-type calcium channels allowing rapid influx of Ca²⁺ ions.
407
What occurs during phase 3 of the pacemaker action potential?
Repolarization occurs as potassium (K+) channels open, allowing K+ to exit the cell.
408
What is the effect of K+ efflux during repolarization?
The membrane potential becomes more negative, moving back toward its resting value.
409
What is automaticity in pacemaker cells?
The ability to spontaneously generate action potentials.
410
Which node is the fastest pacemaker in the heart?
The sinoatrial (SA) node.
411
What role does the SA node play in heart function?
It determines the heart rate under normal conditions.
412
What happens if the SA node fails?
Other cells like the AV node can act as secondary pacemakers.
413
What phase initiates the action potential?
Phase 0.
414
Fill in the blank: The pacemaker action potential primarily drives the _______.
P wave (atrial depolarization).
415
What summary characteristic describes the pacemaker action potential?
* Gradual depolarization * Depolarization driven by calcium influx * Repolarization caused by potassium efflux * Automaticity * No stable resting potential
416
True or False: Pacemaker cells have a stable resting membrane potential.
False
417
What is the importance of the pacemaker action potential?
It regulates the heart's rhythm and ensures proper blood circulation.
418
What is cardiac innervation?
The nervous system's control of heart rate, contractility, and rhythm
## Footnote
Cardiac innervation involves both sympathetic and parasympathetic branches of the autonomic nervous system.
419
What is the role of the sympathetic nervous system (SNS) in cardiac function?
Increases heart rate, contractility, and conduction velocity
## Footnote
SNS fibers originate in the thoracic and lumbar spinal cord (T1–T4) and travel to the heart.
420
Where do sympathetic fibers originate?
Thoracic and lumbar spinal cord (T1–T4)
## Footnote
These fibers innervate key structures in the heart.
421
What are the effects of sympathetic stimulation on the sinoatrial (SA) node?
Increases heart rate (positive chronotropy)
## Footnote
The SA node is the primary pacemaker of the heart.
422
What neurotransmitter is involved in sympathetic cardiac stimulation?
Norepinephrine (NE)
## Footnote
NE binds to β-adrenergic receptors, primarily β1 receptors.
423
What is the effect of the parasympathetic nervous system (PNS) on the heart?
Slows heart rate and reduces contractility
## Footnote
The PNS balances the effects of the sympathetic nervous system.
424
Where do parasympathetic fibers originate?
Medulla oblongata (vagus nerve, cranial nerve X)
## Footnote
These fibers primarily innervate the heart.
425
What is the primary function of the atrioventricular (AV) node?
Serves as a gatekeeper, slowing the electrical impulse before it passes into the ventricles
## Footnote
This delay allows time for the ventricles to fill with blood.
426
What is the significance of the delay at the AV node?
Allows time for the ventricles to fill with blood from the atria
## Footnote
The delay is about 100 ms.
427
What initiates the cardiac conduction pathway?
Sinoatrial (SA) node
## Footnote
The SA node generates the electrical impulse that sets the heart rate.
428
What does the P wave on an ECG represent?
Atrial depolarization
## Footnote
Triggered by the SA node.
429
What does the QRS complex on an ECG indicate?
Ventricular depolarization
## Footnote
It reflects the impulse traveling through the Bundle of His, bundle branches, and Purkinje fibers.
430
Fill in the blank: The _______ is the primary pacemaker of the heart.
Sinoatrial (SA) node
431
What is the function of the Bundle of His?
Transmits the electrical signal from the AV node to the right and left bundle branches
## Footnote
Located in the interventricular septum.
432
What do the Purkinje fibers do?
Rapidly conduct the electrical impulse throughout the ventricles
## Footnote
They ensure coordinated contraction of the ventricular myocardium.
433
True or False: The vagal tone dominates during exercise.
False
## Footnote
The vagal tone dominates at rest, while sympathetic input increases during exercise.
434
List the components of the cardiac conduction pathway in order.
* Sinoatrial (SA) node
* Atria
* Atrioventricular (AV) node
* Bundle of His
* Right and Left Bundle Branches
* Purkinje Fibers
435
What does the T wave on an ECG represent?
Ventricular repolarization
## Footnote
It reflects the recovery phase of the ventricles.
436
What is the role of the autonomic nervous system (ANS) in cardiac function?
Regulates heart rate and force of contraction
## Footnote
It consists of sympathetic and parasympathetic inputs.
437
What role does the sympathetic nervous system (SNS) play in cardiac function?
Regulates heart function during increased cardiac output situations like exercise or stress.
438
What neurotransmitter is primarily involved in sympathetic stimulation of the heart?
Noradrenaline (norepinephrine).
439
Define positive chronotropy.
Increase in heart rate.
440
Which node is primarily targeted by sympathetic stimulation to increase heart rate?
SA node.
441
What receptor does noradrenaline bind to in the SA node?
β1-adrenergic receptors.
442
What is the effect of noradrenaline binding to β1-adrenergic receptors on the SA node?
Increases cyclic AMP (cAMP) levels.
443
What is the role of cyclic AMP (cAMP) in the heart?
Activates protein kinase A (PKA) which enhances heart function.
444
What channels are enhanced by increased cAMP in pacemaker cells?
* Funny channels (If)
* T-type calcium channels.
445
What is the outcome of increased depolarization rate in the SA node?
Increased heart rate.
446
Define positive dromotropy.
Increase in conduction velocity.
447
Which structures are responsible for conducting electrical impulses between the atria and ventricles?
AV node and His-Purkinje system.
448
What effect does sympathetic stimulation have on the AV node?
Increases speed of electrical impulse conduction.
449
Define positive inotropy.
Increase in the strength of heart contractions.
450
What happens when noradrenaline binds to β1-adrenergic receptors on myocardial cells?
Increases intracellular calcium levels.
451
What is the role of calcium in myocardial contraction?
Essential for binding to troponin and facilitating contraction.
452
Define positive lusitropy.
Enhanced relaxation of the myocardium.
453
How does sympathetic stimulation facilitate rapid relaxation of the myocardium?
Increases activity of phospholamban, enhancing the serca pump function.
454
What is the significance of faster relaxation in cardiac function?
Allows for better filling of the ventricles before the next contraction.
455
What can result from sympathetic overactivity?
Persistently high heart rate, increased blood pressure, and higher cardiac workload.
456
What pharmacological agents are used to block the effects of noradrenaline?
Beta-blockers (e.g., propranolol, metoprolol).
457
True or False: The sympathetic nervous system increases heart rate during stress.
True.
458
Fill in the blank: Sympathetic stimulation leads to _______ in heart rate.
positive chronotropy.
459
List the four main effects of sympathetic stimulation on cardiac function.
* Increased heart rate
* Increased conduction speed
* Increased force of contraction
* Faster relaxation.
460
What is the overall effect of noradrenaline on cardiac myocytes?
Increases availability of intracellular calcium.
461
What is the function of the serca pump during cardiac relaxation?
Promotes reuptake of calcium back into the sarcoplasmic reticulum.
462
What role does the parasympathetic nervous system (PNS) play in cardiac conduction?
The PNS slows down heart rate and decreases the force of contraction.
463
What neurotransmitter mediates parasympathetic control of the heart?
Acetylcholine (ACh) from the vagus nerve.
464
Where is the parasympathetic influence most noticeable in the heart?
In the SA node and AV node.
465
What is negative chronotropy?
The decrease in heart rate caused by the parasympathetic nervous system.
466
How does acetylcholine (ACh) affect the SA node?
ACh binds to muscarinic receptors, decreasing cAMP and slowing depolarization.
467
What is the effect of decreased cAMP in the SA node?
Reduces the activity of funny sodium channels and T-type calcium channels.
468
What is negative dromotropy?
Slower conduction velocity through the AV node due to parasympathetic stimulation.
469
How does acetylcholine affect conduction through the AV node?
ACh slows conduction by decreasing calcium influx and increasing potassium efflux.
470
What is the clinical significance of a prolonged PR interval on an ECG?
It reflects delayed conduction through the AV node.
471
What is negative inotropy?
The reduction of contractility in the atria due to parasympathetic stimulation.
472
How does acetylcholine affect atrial contractility?
It reduces calcium influx and increases potassium efflux, decreasing contractile force.
473
What is lusitropy?
Enhanced relaxation of the heart muscle following contraction.
474
What effect does acetylcholine have on potassium channels?
It enhances potassium channel function, facilitating rapid repolarization.
475
What is the primary neurotransmitter used by the parasympathetic nervous system in the heart?
Acetylcholine (ACh).
476
What is the effect of acetylcholine binding to M2 receptors?
It activates a G-protein signaling cascade leading to various cardiac effects.
477
True or False: The parasympathetic nervous system has a significant effect on ventricular myocardium.
False.
478
What is vagal tone?
The influence of the vagus nerve that keeps heart rate lower during rest.
479
What is the Valsalva maneuver?
A technique that stimulates the vagus nerve to slow heart rate.
480
What is atropine and its clinical use?
An anticholinergic drug that blocks muscarinic receptors to treat bradycardia.
481
What balance does the parasympathetic nervous system maintain in cardiac function?
It balances the activity of the sympathetic nervous system.
482
What system increases heart rate, conduction speed, and contractility?
Sympathetic Nervous System
## Footnote
Noradrenaline binds to β1-adrenergic receptors in the SA node, AV node, and myocardial cells.
483
What is the effect of acetylcholine on the heart?
Slows heart rate, conduction speed, and reduces atrial contractility
## Footnote
Acetylcholine binds to muscarinic receptors (M2) in the SA node, AV node, and atria.
484
What ions are crucial for action potential propagation in cardiac cells?
Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺)
## Footnote
Changes in ion concentrations affect resting membrane potential and excitability.
485
What condition can hypokalemia cause in cardiac cells?
Arrhythmias
## Footnote
It increases the membrane potential, making cells more excitable.
486
How does hyperkalemia affect cardiac conduction?
Decreases resting membrane potential, leading to slower depolarization
## Footnote
This can result in depressed conduction.
487
What effect does increased temperature have on cardiac conduction?
Accelerates rate of ion channel opening, increasing conduction speed
## Footnote
Higher body temperature can lead to an increased heart rate.
488
What is the effect of thyroid hormones on the heart?
Increase sensitivity of β-adrenergic receptors, enhancing heart rate and conduction velocity
## Footnote
Particularly T3 and T4 hormones.
489
What do beta-blockers do to cardiac function?
Decrease heart rate, slower conduction, and reduced contractility
## Footnote
Examples include propranolol and metoprolol.
490
What pathological condition can disrupt normal cardiac conduction?
Ischemia
## Footnote
Reduced blood flow can damage cardiac tissue and alter electrical properties.
491
What is the Frank-Starling mechanism?
An increase in venous return leads to stretching of cardiac muscle fibers, affecting contraction timing and strength
## Footnote
It can also influence conduction velocity.
492
Fill in the blank: Hypomagnesemia can affect _______ ion channels.
Calcium
## Footnote
This can lead to issues with conduction and arrhythmias.
493
True or False: Aging can slow down cardiac conduction.
True
## Footnote
Changes in the electrical properties of cardiac cells occur with age.
494
What are the effects of adrenaline on the heart?
Increases heart rate, conduction velocity, and myocardial contractility
## Footnote
Acts similarly to noradrenaline during stress.
495
What structural abnormality can lead to arrhythmias?
Cardiac Hypertrophy
## Footnote
Enlargement of heart chambers can affect electrical pathways.
496
What can electrolyte imbalances affect in cardiac cells?
Duration and amplitude of action potential
## Footnote
This influences conduction speed and myocardial contractility.
497
List three factors influencing cardiac conduction pathway.
* Autonomic Nervous System
* Ion Concentrations
* Electrolyte Imbalances
