Exam 2: Ch. 9
Define heart rate
beat per minute
Through what regulatory mechanisms can a transplanted heart, which does not have any innervation, adjust cardiac output to meet the body's changing needs?
A transplanted heart comes with its own pacemaker but lacks innervation , it adjusts the cardiac output to meet the body 's changing needs by means of both intrinsic control ( the Frank - Starling mechanism ) and extrinsic hormonal influences , such as the effect of epinephrine on the rate and strength of cardiac contraction .
The only point of electrical contact between the atria and the ventricles is the fibrous skeletal rings that surround and support the heart valves. (True or false?)
false -Electrical conduction between atria and ventricles is provided by sinoatrial (SA) node, atrioventricular (AV) node, bundle of His and Purkinje fibers. SA node is the pacemaker and continuously produces electrical impulses, which are sent to transitional cells by the perinodal cells. They are then sent to the right atrium, which makes the atria to contract. Next, the impulse is carried along by the AV node, which is a highly specialized conducting tissue. It slows down the impulse conduction, thereby allowing sufficient time for complete atrial depolarization and contraction. It further sends impulse to the ventricles via the bundle of His and Purkinje fibers, which causes contraction of the ventricles. The fibrous skeleton of the heart surrounds and supports the heart valves along with the separating muscle between atrium and ventricles. The skeleton supports the matter of firm attachment of the cardiac muscle. This is referred to as the cardiac skeletal, which provides an important boundary to the heart.
Entrance of Ca 21 through funny channels is responsible for the unique plateau phase of the action potential in cardiac contractile cells. (True or false?)
false -In the second half of the pacemaker potential, the funny channels are closed and transient Ca channels open before the membrane reaches the threshold. This results in an influx of Ca , which depolarizes the membrane, bringing it to threshold, when the transient Ca channels close. These transient type calcium channels are found in pacemaker, atrial and purkinje cells, whereas the L-type of cells are present in the whole cardiac muscle. However, membrane potential is maintained close to its peak positive level for several hundred milliseconds. It produces a plateau phase of the action potential. It is maintained by activation of slow L-type Ca channels, and a decrease in K permeability in the cardiac contractile cells. The funny current in the cardiac muscle is produced by myocytes as an inward current activated on hyperpolarization to the diastolic range of voltages. It has the properties for generating repetitive activity and for modulating spontaneous heart rate. It is caused due to activation of sodium ion channels.
Use the following answer code to compare the relative magnitudes of the pair of items in question: (a) 5 Item A is greater than item B (b) 5 Item B is greater than item A (c) 5 Item A and item B are approximately equal 1. A. Resistance and pressure in pulmonary circulation B. Resistance and pressure in systemic circulation 2. A. Volume of blood pumped out by left side of heart B. Volume of blood pumped out by right side of heart 3. A. Spontaneous rate of depolarization to threshold in SA node B. Spontaneous rate of depolarization to threshold in ventricular Purkinje fibers 4. A. Velocity of impulse conduction through AV node B. Velocity of impulse conduction through bundle of His and Purkinje fibers 5. A. Rate of ventricular filling in early diastole B. Rate of ventricular filling in late diastole 6. A. Stroke volume when EDV equals 130 mL B. Stroke volume when EDV equals 160 mL 7. A. Normal stroke volume B. Stroke volume on sympathetic stimulation 8. A. Normal stroke volume B. Stroke volume on parasympathetic stimulation 9. A. Volume of blood in ventricles at onset of isovolumetric ventricular contraction B. Volume of blood in ventricles at end of isovolumetric ventricular contraction 10. A. Volume of blood in left ventricle at the time aortic valve opens B. Volume of blood in left ventricle at the time aortic valve closes 11. A. Volume of blood in left ventricle at the time left AV valve opens B. Volume of blood in left ventricle at the time left AV valve closes 12. A. Duration of refractory period in cardiac muscle B. Duration of contraction in cardiac muscle
1. A is greater than b (10,3,5) 2. B is greater than A (1,11,4,6,7) 3. A and B are aprox equal. (12,2,8,9)
What are the three layers of the heart wall? Describe the distinguishing features of the structure and arrangement of cardiac muscle cells. What are the two specialized types of cardiac muscle cells?
1. Endothelium: A thin inner layer, unique type of epithelial tissue that lines the entire circulatory systems. 2. myocardium: Middle layer composed of cadiac muscle and constitutes the bulk of the heart wall (myo = muscle) 3. Epicardium: thin external layer that covers the heart (epi = on) Cardiac muscle cells are innerconnected to form branching fibers, adjacent cells joined end to end at speciaized structures called intercalated disc. two speicalized types of cardiac muscle cells --> contractile cells: which are 99% of the cardiac muscle cells, do the mechanical work of pumping. These working cells normally do not initiate their own action potentials. ---> autorhymic cells: small but extremely important remainder of the cardiac cells, do not contract but instead are specialized for initiating and conducting the action potentials responsible for contraction of the working cells.
What are the three basic components of the circulatory system?
1. Heart: pump that imparts pressure to the blood to establish the pressure gradient needed for blood to flow to the tissues. Like all liquids, blood flows down a pressure gradient from an area of higher pressure to an area of lower pressure. This chapter focuses on cardiac physiology (cardia means "heart"). 2. blood vessels: the passageways through which blood is directed and distributed from the heart to all parts of the body and subsequently returned to the heart. The smallest of the blood vessels are designed for rapid exchange of materials between the surrounding tissues and the blood within the vessels 3: blood: the transport medium within which materials being transported long distances in the body, such as O2 , CO2 , nutrients, wastes, electrolytes, and hormones, are dissolved or suspended
Trace a drop of blood through one complete circuit of the circulatory system.
Blood after being delivered to all parts of the body enters the heart through two large veins: superior and inferior vena cava. They carry deoxygenated blood from the body into the right atrium. Blood flows from the right atrium to the right ventricle via the tricuspid valve. The change in pressure and the fulfillment of ventricular blood volume results in the closure of tricuspid valves, preventing the backflow of the blood to the atrium. The flow of oxygenated blood occurs into the pulmonary artery through the pulmonic valve. The pulmonary vein carries oxygen-rich blood from the lungs to the left atrium after the process of oxygenation of blood. Blood in the left atrium flows into the left ventricle through the bicuspid valve followed by the blood filling in ventricles. When ventricular filling is completed, the bicuspid valve then closes to prevent backflow of blood into the left atrium. Blood leaves the heart through the aortic valve into the aorta and reaches all the organs and tissues of our body system. - The heart is a muscular organ that pumps blood through the blood vessels of the circulatory system. The circulation of blood initiates when it enters the heart through two large veins, the inferior and superior vena cava, emptying deoxygenated blood from the body into the right atrium. Blood flows from the right atrium into the right ventricle through the open tricuspid valve. Then, it is transported to the lungs to undergo the process of oxygenation. The pulmonary vein then carries oxygenated blood to the left atrium and blood flows to the left ventricle through the bicuspid valve. It is then delivered and circulated throughout the body by the aorta.
Describe the intrinsic and extrinsic control of stroke volume.
Both intrinsic and extrinsic factors regulate and control the stroke volume. The stroke volume is the amount of volume (ml) that is ejected from the heart during the contraction of each ventricle. It is determined by the difference between the end-systolic volume and end-diastolic volume. The F-S law states the relationship between stroke volume and end-diastolic volume, which serves as the intrinsic factor and controls varying stroke volume. The extent of preload shows direct correlation with stroke volume. The volume of venous return will increase the preload, whereas the decreased venous return causes a reduction in the stroke volume. The greater the volume of the blood pumped out, the longer the cardiac cell will take place to adapt themselves accordingly, to compensate for the refilling of the chamber with the same amount of volume for next ejection. The cardiovascular system is controlled extrinsically by humoral, neuronal chemical, and reflex regulatory mechanisms. These mechanisms control and regulate heart rate, myocardial contractility, and vascular smooth muscle to maintain cardiac output, blood flow distribution, and arterial blood pressure. The neuronal system involves the action of an autonomic nervous system that controls the heart rate and stroke volume. Strong and frequent contraction also affects the stroke volume and influences the end-diastolic volume Thus, the intrinsic and extrinsic factors regulate the efficiency of pumping blood by the heart. -The stroke volume is the difference between the end-diastolic volume (EDV) and end-systolic volume (ESV), which is controlled by both the intrinsic and extrinsic factors. The intrinsic factors control the varying stroke volume and regulate the relationship between the stroke volume and end-diastolic volume, which is stated by F-S law of the heart. The extrinsic factor that controls the stroke volume through regulating the nervous system, increases the cardiac muscle contraction, leading to higher enddiastolic volume.
Why is the SA node the pacemaker of the heart?
It is a small specialized region in the right atrial wall of the heart. The fastest rate of action potential initiation is localized in the SA node. The electrical impulse starts in the SA node and spreads throughout the cardiac muscle, facilitating the autorhythmic contraction. The pacemaker cells are devoid of resting potential and the ionic movement across the membrane. It is due to the action potential that causes the rapid change in the membrane potential. It has the fastest rate of autorhythmicity at 70 to 80 action potentials per minute. Thus, it is known as the natural pacemaker of the heart. The signal or electrical impulse conduction reaches the atrioventricular (AV) node, transmitting to the ventricular myocytes through the bundle of His and Purkinje fibers. This causes ventricular contraction and generates a pulse, which maintains the rate of heartbeat. - The sinoatrial (SA) node has a faster rate of autorhythmicity than other non-contractile autorhythmic cells, and hence it is known as the pacemaker.
The stroke volume ejected on the next heartbeat after a premature ventricular contraction (PVC) is usually larger than normal. Can you explain why? (Hint: At a given heart rate, the interval between a PVC and the next normal beat is longer than the interval between two normal beats.)
Premature ventricular contractions (PVCs) are the abnormal and non required heartbeat that initiate in the ventricular region of the heart. It disturbs the normal heart rhythm. It produces the symptoms of skipped beats or palpitations The stroke volume is defined as the amount of blood in millilitre (ml) ejected from the heart during ventricular contraction. The ventricular filling occurs during the heart diastolic state, and the ventricular contraction shows the direct correlation with the stroke volume. The filling of ventricles occurs during two subsequent heartbeats. The stroke volume is mostly larger at the contraction after premature ventricular contraction. This is because the time interval between the premature ventricular contraction and the next normal heartbeat is greater compared to an interval between two normal heartbeats. More blood is filled during this time interval, leading to the increase in end-diastolic volume. The stroke volume is increased as compared to the stroke volume, after two normal heart contractions as stated by the F-S law related to heart stroke volume and contraction rate. -The interval between the premature ventricular contraction and the next normal heartbeat is much larger than the interval between two normal heartbeats. This leads to the filling of ventricles for a longer time thus, results in greater end-diastolic volume. According to Frank-Starling law of heart, the stroke volume ejected from the ventricles is also larger.
Discuss autonomic nervous system control of heart rate.
The autonomic nervous system lies in the category of peripheral nervous system, which regulates all the automatic mechanisms and functions of our body. This system involves involuntary efferent neurons correlating with effectors, such as visceral muscles, cardiac muscles, and glandular tissues, managing the responses subconsciously. The autonomic nervous system is categorized into sympathetic and parasympathetic nervous pathways. Both the categories of the autonomic nervous system controls the heart rate and the contractile cells. The contraction in the cells occurs through the generation of actional potential through the natural pacemaker in the heart. The sympathetic input occurs with the postganglionic fibres into the heart from the sympathetic trunk region in our body, which innervates the SA nodes and AV nodes. The release of noradrenaline by the post ganglionic fibres is recognized by the beta receptors, which increases the heart beat and force of contraction. The input of parasympathetic nervous pathway occurs through the vagus nerve, which forms synapse with the postganglionic cells present in SA node and AV node. The receptors recognizing the acetylcholine neurotransmitter released by the sympathetic pathway decreases the pacemaker potential, which in turn result in decrease of heart rate. The sympathetic and parasympathetic nervous pathway is the division of the autonomic nervous system, which controls the physiology of the heart muscles. The nerves from both the nervous system are supplied to the sinoatrial (SA) and atrioventricular (AV) node. It is for controlling the heart rate, contraction of heart muscles, and peripheral resistance of blood vessels. Whereas the sympathetic nerves are strongly innervated in the contractile cells to cause contraction. The parasympathetic nervous system decreases the heart rate along with the force of contraction. The sympathetic nervous system increases the heart rate and force of contraction.
Compare the changes in membrane potential associated with an action potential in a nodal pacemaker cell with those in a myocardial contractile cell. Describe the ionic mechanisms responsible for these changes.
The cardiac muscle cells are myogenic in nature as they produce the action potential and are self-excitatory in nature. The heart muscles do contain both contractile and non- contractile muscle cells. The contractile cardiac muscle cells undergo contraction and relaxation for facilitating the function of the heart that is pumping out the blood. Whereas the non-contractile muscle cells generate electrical signals, and are considered as the natural pacemaker of the heart. The non-contractile cardiac cells that are involved in generating and conducting electrical signals to the contractile muscle cell include sinoatrial node (SA node), atrioventricular (AV) node, bundles of His and Purkinje fibers. The initiation of the action potential takes place in the SA node attached to the walls of the right atrium, it generates the 70-80 action potential/min. The SA node is a pacemaker cell that is responsible for initiating the electrical potential of the heart. The SA node depolarizes the cardiac cell of the atrium completely, and allows its contraction before the ventricles. The action potential from the SA node reaches the AV node and causes the conduction of action potential through the bundle of His and Purkinje fibers. Myocardial contractile cells form 99% of the heart's composition, and they do not initiate action potential on their own. They are conducted by the pacemaker cell. They undergo contraction and relaxation and the membrane potential turns from stable at -90mV to 20mV and +30mV. The duration of action potential varies from 200+ msec. The increase in the membrane potential increases the permeability of ions inside the cell through gap junctions. The movement of Na+ ion is facilitated for generating the action potential and depolarization in the cell. Pacemaker cells form 1% of the heart composition whose membrane potential remains unstable and starts at -60mV. The duration of action potential varies from 150+msec. These are the autorhythmic cells of the heart. They are responsible for generating and conducting the action potential on its own and also causes contraction of the working cells. The increase in the membrane potential causes the flow of ions inside the cells, and opens the voltage-gated ion channels. The depolarization in the cell is facilitated through the movement of Ca ions inside the cell.
Why is tetanus of cardiac muscle impossible? Why is this inability advantageous? .
The cardiac muscles are extensively branched and show the presence of intercalated discs, which facilitates the conduction of impulse for the cardiac muscle functionality. The contraction of the skeletal muscles is mostly referred to as twitch, summation, or tetanus. The cardiac muscle serves differences as compared to the skeletal muscle, which prevents them from facing conditions of tetany. The frequency of receiving a stimulus and generating an action potential is increased such that the muscles constantly undergo contraction and never get relaxed. It is referred to as tetanus. The refractory period prevents tetanus occurrence in the skeletal muscle cell. The autorhythmic behavior of pacemaker cells allows the 10 times longer contraction of cardiac muscle as compared to the skeletal muscle cells. The presence of a large amount of mitochondria and myoglobin acts in favor of preventing the heart muscle from failure. The refractory period of the cardiac muscle cell stays longer than that of skeletal muscles. The refractory period of the cardiac muscle is around 250 milliseconds. This refractory period prevents tetanus and protects the heart from getting damaged. The longer refractory period in the cardiac muscle cells, allows the filling of heart chambers until the action potential generates again, causing contraction of the heart. - The increased or maximum frequency of the muscle contraction such that the tension is generated without the occurrence of relaxation, results in tetany. The refractory period is the time in which the cell does not initiate an additional action potential and protects the heart. Cardiac muscle cells do have larger refractory periods than the skeletal muscles, which helps in preventing tetanus. The specialized properties of cardiac muscle cell membrane also prevent the heart from undergoing tetanus. The refractory period is also important for providing enough time to allow the filling of heart chambers until the next contraction occurs.
What are the pathological changes and consequences of coronary artery disease?
The cholesterol in the body reaches through the dietary substance or produced by the liver. The low-density lipoprotein (LDL) or bad cholesterol carries the cholesterol and transports it around the body. The increased level of cholesterol in the body is accumulated in the walls of arteries. This is done through low-density lipoproteins and causes various heart diseases. It also increases the risk of stroke in an individual due to narrowing, calcification, and swelling of arteries. The aggregation of the fatty substance in the arteries results in various heart diseases including angina and myocardial infarction. The blocking of arteries results in reduced flow of blood through them, which affects the heart muscles. The reduced flow of blood through arteries also restricts the supply of oxygen to heart cells. It may result in collapsing of cardiac cells and leads to a heart attack, which is characterized by immense pain in the chest. The dissolving or destruction of the accumulation in the arteries improves the flow of blood, and reduces the risk of heart disease. -The myocardial infarction and angina are few conditions, which are considered as acute coronary syndromes. The treatment pathways involve promoting the disruption of atherosclerotic plaque, and the superimposed formation of the platelet‐rich thrombus. The accumulation of cholesterol in the cells of the coronary artery results in calcification, swelling, and narrowing of the passage.
Describe the mechanical events (that is, pressure changes, volume changes, valve activity, and heart sounds) of the cardiac cycle. Correlate the mechanical events of the cardiac cycle with the changes in electrical activity.
The electrical signals generated cause various mechanical activites in the heart. *The generation of action potential results in the contraction of the heart. The initiation of the electrical impulse occurs from the sinoatrial node that allows the depolarization of the atria, and is determined through P wave in the electrocardiogram. *The passive flow of blood occurs during the relaxation of cardiac muscle until the achievement of threshold potential as the initiating point for the next cardiac cycle. *The contraction of atria actively fills up the ventricles with the blood. *Further, the electrical impulse from the SA node travels to the AV node and causes its stimulation, which results in depolarization of the ventricles. It is determined by the QRS complex wave in an electrocardiogram. *The depolarization of the ventricles allows its contraction and increased ventricular pressure that leads to the forced opening of the ventricular valve and pumps blood into the arteries. *The depolarization of the ventricle also closes the AV valve that produces "lub" sound. The repolarization of the ventricles is determined by the T wave in the electrocardiogram. During repolarization, the ventricles relax and cause the fall of pressure. Also, the ventricular valves close thereby producing a "dup" sound. The mechanical and electrical activity of the heat, coupled together to conduct and contract cardiac muscles. The electrical signals cause a mechanical response of the heart. The contraction and relaxation of the heart pump the blood through the systemic and pulmonary system. The contraction of the heart is the result of the spread of electrical activity through the nodal pacemaker cell to the contractile cell of the heart. The electrical signals from the sinoatrial (SA) node cause depolarization of the atria that actively pass blood to the ventricles and are represented as P waves in electrocardiograms. The myocardial cells receive the repolarized signals causing its relaxation. This is the mechanical activity or the pumping of the organ in response to the electrical signal transmission.
Distinguish between a stenotic and an insufficient valve.
The heart condition that occurs due to the abnormality in the valve is called valvular heart disease. During valvular heart disease, the valve either becomes stenotic or insufficient. Valvular stenosis results in the stiffness of valve leaflets, which narrows the valve opening and reduces the amount of blood that can flow through it. It reduces the overall functioning of the heart and the rest of the body may not receive adequate blood flow. Valvular insufficiency is the result of leaflets that are not closed completely, allowing the leakage of blood across the backward flow of the valve. This backward flow is referred to as regurgitant flow. The stenotic valve produces a distinct sound (whistle) between the two subsequent heart contractions, which is denoted by lubwhistle-dup, and represents the opening of the valve during systole. The insufficient valve produces a swishy murmur and is denoted by a lub-dup-swish sound, which indicates the closing of the valve during diastole. The sequence of the sound produced by the heart would be lub-whistle-dup-swish-lub-whistle-dup-swish, and so on. - The stenotic and insufficient valves are the causes of valvular heart disease, which is marked by the non-functional behavior of valves in the heart. The stenotic valve is narrower because of the stiff valve leaflet. Whereas the insufficient valve doesn't close properly and tightly. The whistling and swishy sound represents the systolic murmur and diastolic murmur produced by the stenotic valve and insufficient valve, respectively. The whistling murmur takes place between the two subsequent heart sounds that is lub-whistle-dup. It indicates the opening of the valve during systole. The swishy sound is denoted by lub-dub-swish, which indicates closure of the insufficient valve during diastole. The heart sound produced while opening and closing the valve would be lub-whistle-dup-swish-lub-whistle-dup-swish, and so on
Describe the location and function of each of the four heart valves. What keeps each of these valves from everting?
The heart is divided into four chambers, which are responsible for the processing of both oxygen-rich and oxygen-poor blood. The chambers of the heart are lined with the four valves, which are as follows: 1. Tricuspid valve: It is located between the right atrium and the right ventricle. Blood flows from the right atrium to the right ventricle through the open tricuspid valve. The end of the atrial systole is followed by the closure of the tricuspid valve, to prevent the backflow of the deoxygenated blood to the right atrium during ventricular contraction. It has three cusps or flaps to which papillary muscles are attached via chordae tendineae. They prevent the valve from everting due to high ventricular pressure. 2. Bicuspid valve: It is also known as mitral valve and is located between the left atrium and left ventricle. When the blood is filled in the left atrium, then this valve opens due to pressure difference generated in the left atrium and ventricle. The flow of blood occurs towards the left ventricle, which is due to the relaxation of ventricular muscles. This action is followed by the closure of the mitral valve, preventing the backflow of the blood to the left atrium when the ventricle contracts. The chordae tendineae and papillary muscles keep the cusps of the bicuspid valves stable during opening and closure. They also maintain the shape and structure of the valve. 3. Pulmonary valve: It is located between the right ventricle and pulmonary artery. As the right ventricle begins to contract, the pulmonary valve is forced open and blood is pumped out of the right ventricle through the pulmonary valve into the pulmonary artery towards the lungs. The pulmonary valves close with the relaxation of ventricles. This semilunar valve shows similarity with the aortic valve, which opens in the ventricular systole. This occurs when the pressure of the right ventricle is more than the pressure in the pulmonary artery. 4. Aortic valve: This valve is located between the left ventricle and the aorta. When the left ventricle contracts, the aortic valve is forced open and the blood is pumped out from the left ventricle to the aorta, possessing the aortic valve as the gateway. Aorta undergoes branching to deliver blood throughout the body. When the left ventricle starts to relax, the aortic valve closes and prevents the blood from flowing back into the left ventricle. The chordae tendineae are commonly known as the heart strings that anchor the wall of ventricles and avoid the valves from everting. The papillary muscles find the attachment with chordae tendineae to form the subvalvular apparatus, which creates the same tension. The papillary muscles attach to the tricuspid and mitral valve of the head -Tricuspid valve is located between the right atrium and right ventricle. It prevents backflow of blood from the right ventricle to the right atrium. Bicuspid valve is located between the left atrium and the left ventricle, and it prevents backflow of blood from the left ventricle to the left atrium. Pulmonary valve is located between the right ventricle and the pulmonary artery. It prevents backflow of blood from the pulmonary artery to the right ventricle. Aortic valve is located between the left ventricle and the aorta, and it prevents backflow of blood from the aorta to the left ventricle. Chordae tendineae and papillary muscles together form a subvalvular apparatus, which creates the tension to prevent the eversion or turning inside-out of the valves present in the heart.
What electrical event does each component of the ECG represent?
The heart is the major organ of the circulatory system; it pumps oxygenated blood throughout the body. The cells (pacemaker) in the heart conduct the electrical signal and allow the heart to perform its function. The electrical activity of the heart is measured through an electrocardiogram. The electrocardiogram records and represents the condition of the heart by displaying the overall activity of depolarization and repolarization through the distinct waveforms. The electrical impulses are recorded in the form of waves that travel through the heart. The different waves are: 1. P waves: The P waves determine the depolarization of the atria. 2. QRS complex: determines the contraction or depolarization of the ventricles. 3. T waves: determines the relaxation or repolarization of the ventricles. 4. The PR segment occurs at the end of the P wave and the beginning of the Q wave. It represents the electrical conduction through the atria and the delay of the electrical impulse in the atrioventricular node. QRS complex represents the travelling of blood from the heart ventricle to the lungs and the body. 5. The ST segment connects the QRS complex and the T wave. It represents the beginning of the electrical recovery of the ventricles. 6. The QT interval represents the time during which the ventricles are stimulated and recover after the stimulation. This interval shortens at a faster heart rate and lengthens at a slower heart rate. The electrocardiogram (ECG) measures the electrical activity of the heart. It records and represents the overall activity that takes place in the heart from the generation of electrical signals, depolarization of cardiac muscle cells, to repolarization of the cells. It records the electrical impulses in the forms of a wave that travels through the heart and causes its contraction and relaxation of cardiac muscle, which allows the pumping of blood. The electrocardiogram (ECG) helps in determining the condition of the heart and detect any heart malfunctioning or disorder. The ECG consist of three waveforms holding distinct significance and representation : 1. P wave: It represents the depolarization of the atria. 2. QRS complex: It represents the depolarization of the ventricles. 3. T wave: Represents the repolarization of the ventricles.
Describe the normal spread of cardiac excitation. What is the significance of the AV nodal delay? Why is the ventricular conduction system important?
The regulation of the contraction and relaxation of the heart, which is much more needed for filling up the ventricles and pumping the blood out of the heart. The regulation is mediated through the sinus node present in the heart. The conduction of electrical potential or cardiac excitation is initiated through the node present at the walls of the right atrium, that is the sinoatrial (SA) node. The signals from the SA node move to the AV node near to the septum in the right atrium. The AV node causes the conduction of the action potential to the ventricles. AV nodes are divided into two branches that consist of a bundle of muscle fibers (bundle of His) that provide electrical signals to the right ventricle and left ventricle separately. The bundle of His is followed by Purkinje fibers that transmit these signals to the left and right ventricles, respectively. It also allows ventricular contraction followed by the atrial contraction. In order to achieve complete depolarization in the atria for its contraction before the contraction of ventricles, the speed of conduction of action potential is slowed down through AV nodes. This slow conduction of action potential across the AV node is referred to as AV node delay. The AV node delay ensures the contraction of atria followed by the ventricular contraction. The conduction of action potential through ventricles occurs in a specialized manner that causes the contraction and relaxation of the ventricles. The contraction of the ventricles plays an important role in the ejection of the blood out of the heart. The ventricular conduction system allows the rapid propagation of the action potential through the atrium to the ventricles. The AV node allows the movement of the electrical signals from the atrium to the ventricles. The action potential from the AV nodes reaches the septum, and then to left and right ventricles through the bundle of His and Purkinje fibers, respectively -The natural pacemaker in the heart or sinus node generates electrical signals for the relaxation and contraction of the heart. The transmission of electrical impulse involves the use of the atrioventricular (AV) node and bundles of His and Purkinje fibers to the whole cardiac muscle. The potential from the SA node depolarizes the atrium leading to atrial contraction whereas the AV node transmitted signals results in the contraction of both the ventricles. The atrial contraction occurs before the ventricular contraction. The delay or slow conduction of action potential through the AV node is referred to as AV node delay. The delay in conduction allows complete depolarization of the atria and results in contraction before the ventricular contraction occurs. The ventricular conduction system is specialized for the contraction of the ventricles that is responsible for the ejection of the blood out of the heart. The rapid propagation of the action potential takes place from the AV node. It moves towards the ventricle through the bundle of His and Purkinje fibers
Circle the correct choice in each instance to complete the statement: The first heart sound is associated with closing of the (AV/semilunar) valves and signals the onset of (systole/diastole), whereas the second heart sound is associated with closing of the (AV/semilunar) valves and signals the onset of (systole/diastole).
When the ventricular pressure exceeds atrial pressure at the beginning of the systole, the atrioventricular valve which consists of tricuspid and bicuspid valves, closes and produces first heart sound. It is a single sound as both the tricuspid and bicuspid valves close simultaneously. The valves are generally used for preventing the backflow of blood and facilitates the unidirectional flow. The papillary muscles are attached to the cusps or leaflets of the tricuspid and mitral valves via chordae tendineae, which helps the opening and closing of valves. The second heart sound is the result of closure of semilunar valves consisting of aortic and pulmonary valves. This is due to the higher pressure in the aorta during the onset of diastole. The pressure in the right ventricle falls below the pressure in the pulmonary artery resulting in the closure of the pulmonary valve. These sounds occur in a sequence. Systole occurs when the heart contracts to pump blood out and diastole occurs when the heart relaxes after contraction. - Closing of atrioventricular (AV) valve produces first heart sound and signals the starting of systole, whereas closing of semilunar valves results in second heart sound and signals starting of diastole.
The link that coordinates coronary blood flow with myocardial oxygen needs is _____.
adenosine
Which of the following is the proper sequence of cardiac excitation? a. SA node → AV node → atrial myocardium → bundle of His → Purkinje fibers → ventricular myocardium b. SA node → atrial myocardium → AV node → bundle of His → ventricular myocardium → Purkinje fibers c. SA node → atrial myocardium → ventricular myocardium → AV node → bundle of His → Purkinje fibers d. SA node → atrial myocardium → AV node → bundle of His → Purkinje fibers → ventricular myocardium
d -The SA node, which is the pacemaker, sends electrical impulse to the atrial myocardium, causing contraction of the atria. The node is itself the location of originating and conducting the electrical signal impulse in the myocardium. The impulses are then transferred to the AV node, which delays the impulse between atrial and ventricular contraction. Further, it is sent to the ventricular myocardium through the bundle of His and Purkinje fibers, which causes ventricular contraction. The contraction allows the pumping of blood from the heart throughout the body.
What percentage of ventricular filling is normally accomplished before atrial contraction begins? a. 0% b. 20% c. 50% d. 80%
d. 80%
Sympathetic stimulation of the heart a. increases the heart rate b. increases the contractility of the heart muscle c. shifts the Frank-Starling curve to the left d. both (a) and (b) e. all of the above 11.
e -The heart rate is increased as a result of epinephrine secretion, which is released by the sympathetic stimulation during fight or flight situations. Sympathetic stimulation and the release of epinephrine enhances the heart's contractility. This stimulation also affects the stroke volume.
Match the following: 1. receives O2 -poor blood from the venae cavae 2. prevent backflow of blood from the ventricles to the atria 3. pumps O2 -rich blood into the aorta 4. prevent backflow of blood from the arteries into the ventricles 5. pumps O2 -poor blood into the pulmonary artery 6. receives O2 -rich blood from the pulmonary veins (a) AV valves (b) semilunar valves (c) left atrium (d) left ventricle (e) right atrium (f) right ventricle
e,a,d,b,f,c
The heart lies in the left half of the thoracic cavity. (True or false?)
false -The heart is a hollow, muscular organ about the size of a clenched fist. The heart lies near the midline (in the middle) of the thoracic cavity between the sternum and vertebrae. It rests on a muscular diaphragm. About 67% of the mass of the heart is located to the left of the midline.
The left ventricle is a stronger pump than the right ventricle because more blood is needed to supply the body tissues than to supply the lungs. (True or false?)
false -The left and right side of the heart pump an equal amount of blood. The capacity of blood retained in each side is also similar. The volume of deoxygenated blood being pumped to the lungs by the right ventricle is processed. It undergoes the process of oxygenation to become oxygen-rich blood. The same blood is returned to the heart for getting delivered to the tissues by the left ventricle. The pressure applied by the left ventricular muscle is more as compared to the right ventricular muscle. This is due to its increased contractility for pumping oxygenated blood throughout the body. The ventricles have thicker walls due to muscular vasculature and generate high blood pressure. The irregular muscular columns called trabeculae carneae, which cover all of the inner ventricular surfaces except that of the conus arteriosus, in the right ventricle, covers the whole of inner ventricles wall. These muscles show higher pumping pressure of blood.
Adjacent cardiac muscle cells are joined end to end at specialized structures known as ___, which contain two types of membrane junctions: ___ and ___.
intercalated disc, desmosomes, gap junctions
Define end diastolic volume (EDV)
is the volume of blood in the ventricle when filling is complete at the end of diastole.
Define cardiac output
the amount of blood pumped by both the ventricle per minute.
Define cardiac reserve
the difference in the general rate of pumping blood, and the maximum capacity of the heart to pump the blood.
Define ejection fraction
the ratio of stroke volume and end-diastolic volume.
Define stroke volume
the volume of blood pumped out by each ventricle each beat
Define end-systolic volume (ESV)
the volume of blood remaining in the ventricle when ejection is complete at the end of systole.
The atria and the ventricles each act as a functional syncytium. (True or false?)
true -The heart consists of two separate functional syncytium, the atrial syncytium and the ventricular syncytium. These are separated from each other by the fibrous tissue, which surrounds the valvular rings. The conduction of action potential from the atrial syncytium into the ventricular syncytium is done by the atrioventricular (AV) bundle. It is a specialized conductive system. The cells of syncytium are interconnected by specialized membranes of the gap junctions and are multinucleated. These structures are synchronized electrically in an action potential, facilitating the conduction of signals. The atrial syncytium results in contraction of atria, whereas the ventricular syncytium results in the contraction of ventricular muscles.
