Heart beat - class-IX

The cardiac cycle consists of a period of relaxation called diastole, during which the heart fills with blood, followed by a period of contraction called systole. The total duration of the cardiac cycle, including systole and diastole, is the reciprocal of the heart rate. For example, if heart rate is 72 beats/min, the duration of the cardiac cycle is 1/72 beats/min about 0.0139 minutes per beat, or 0.833 second per beat.

This sequential event in the heart which is cyclically repeated is called the cardiac cycle. Each cardiac cycle consists of systole and diastole of both the atria and ventricles. Each cardiac cycle represents one heartbeat. The number of heart beats per minute in resting person is called as normal heart rate. The normal heart rate is about 72 beats per minute. The heart rate is same as pulse rate because the contractions of the heart cause an increase in blood pressure in arteries that leads to noticeable pulse. Hence each heartbeat generates one pulse in the arteries.

The cardiac output of a normal adult healthy person at rest is almost 5 litres. The volume of blood pumped out of the left ventricle in one beat is called the stroke volume. It is 70 ml.

When at rest, the body's metabolic demand decreases, but the heart rate typically stabilizes at a resting rate rather than increasing or decreasing indefinitely.

The pulse is the rhythmic expansion and recoil of the arteries caused by the ejection of blood from the heart during systole.

Blood pressure is the pressure against the walls of the blood vessels produced by the discharge of blood into them by contraction of the left ventricle.

The first heart sound (Lubb) is caused by the closure of the atrioventricular valves at the start of ventricular systole.

first heart sound is produced by the closing of the atrioventricular valves . The first heart sound, or S1, forms the "lub" of "lub-dub" and is composed of components M1 (mitral valve closure) and T1 (tricuspid valve closure). Normally M1 precedes T1 slightly. It is caused by the closure of the atrioventricular valves, i.e. tricuspid and mitral (bicuspid), at the beginning of ventricular contraction, or systole.
So, the correct option is C.( Bicuspid and tricuspid close quickly )

The blood travels around the body and back to the heart in about one minute if the person is at rest. The heart beats 70 times a minute, with each beat the heart pumps 60 to 90 mililiters (2 to 3 ounces) of blood out of the heart. It can move 5 liters of blood in one minute and 7600 liters (2000 gallons) per day.
So, the correct option is "A" (5 Litre).

Calcium is important for heart because the movement of calcium ions help the heart muscles to contract. This occurs because: calmodulin, a protein binds to the sodium channel, helps keep it open. Calcium ions regulate the connection between the protein and the channel by causing the protein to hook up to the channel. This in turn, keeps it open and allows sodium ions to pass through. In the absence of Ca$^2$$^+$ the heart beat will be irregular. 

The first heart sound 'lubb' is made by the closing of the mitral valve and tricuspid valve (atrioventricular valves). The second heart sound is 'dub' and is caused by the closure of the aortic valve and the pulmonary valve. 

Sinoatrial node is a cluster of cells present in the right atria just below the opening of  Vena cava. It autonomously generates electrical impulses that initiate the muscle contraction in the atria.

• The heart produces a characteristic sound at the beginning g of ventricular systole or contraction. 
• These sounds are a result of the closure of the atrioventricular valves, the mitral valve and the tricuspid valve. 
• The sounds produced are “lubb-dub”, lubb being the first of the two. 
  
• So, the correct answer is 'Lubb'.
  

A pacemaker insertion is the implantation of a small electronic device that is usually placed in the chest (just below the collarbone) to help regulate slow electrical problems with the heart. A pacemaker may be recommended to ensure that the heartbeat does not slow to a dangerously low rate.

Heartbeat rate is the number of the beating of the heart per minute.

The parasympathetic nervous system (via the vagus nerve) acts to slow down the heart rate. If this nerve is cut, the inhibitory effect is removed, leading to an increase in heart rate.

Cardiac output is the blood volume pumped in a minute by the core. It is equivalent to the rate of heart multiplied by the quantity of the stroke. So if there are 70 beats per minute and with each heart beat 70 ml of blood is drawn, the power production is 4900 ml / minute. This value is typical of an average resting adult, although during intense practice, cardiac production can achieve up to 30 liters / minute.

The first heart sound which we hear is produced by the simultaneous closure of both the atrioventricular valves namely, the bicuspid (mitral) valve and the tricuspid valve.

Cardiac output is the blood volume pumped in a minute by the core. It is equivalent to the rate of heart multiplied by the quantity of the stroke. So if there are 70 beats per minute and with each heart beat 70 ml of blood is drawn, the power production is 4900 ml / minute. This value is typical of an average resting adult, although during intense practice, cardiac output can reach  upto 30 liters / minute.

A special neural centre in the medulla oblangata can moderate the cardiac function through autonomic nervous system (ANS). Neural signals through the sympathetic nerves (part of ANS) can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output. On the other hand, parasympathetic neural signals (another component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output. Adrenal medullary hormones (adrenaline, noradrenaline) can also increase the cardiac output.

Normal activities of the heart are regulated intrinsically, i.e., auto regulated by specialised muscles (nodal tissue), hence, the heart is called myogenic. A special neural centre in the medulla oblangata can moderate the cardiac function through autonomic nervous system (ANS). Neural signals through the sympathetic nerves (part of ANS) can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output. On the other hand, parasympathetic neural signals (another component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output. Adrenal medullary hormones can also increase the cardiac output. Epinephrine / adrenaline increases the heart rate.

Sino-atrial node (SAN) generates the maximum number of action potentials per minute (70-75/min) and therefore, it sets the pace of the activities of the heart. Hence, it is called as the cardiac pacemaker.

During each cardiac cycle two prominent sounds are produced, which can be easily heard through a stethoscope. The first heart sound (lubb) is associated with the closure of the tricuspid and bicuspid valves, whereas the second heart sound (dubb/dupp) is associated with the closure of the semilunar valves. 

The sino-atrial node (SAN) can generate the maximum number of action potentials, i.e., 70-75 /min. It is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called as the natural cardiac pacemaker. 

The cardiac cycle starts with atrial systole. It represents the contraction of the myocardium of the left and right atria by which blood is forced into the ventricles. It progresses to ventricular systole, in which the ventricles contract and blood forced  into the aorta and pulmonary artery. After that atrial diastole occurs which means the relaxation of atria.The cardiac cycle ends with ventricular diastole in which ventricles are relaxing and also filling with blood in preparation of the next cycle.

In the human heart, the sino-atrial node (SAN) can generate 70-75 beats/min and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker. Our heart normally beats 70-75 times in a minute (average 72 beats/min).

The cardiac cycle is regulated by specialized areas in the heart wall, that forms the conduction system of the heart. Two of these areas are tissue mass, called as nodes; the third is a group of fibers, called as the atrio-ventricular bundle. 

During each cardiac cycle two prominent sounds are produced, which can be easily heard through a stethoscope. The first heart sound ('lubb') is associated with the closure of the tricuspid and bicuspid valves, whereas the second heart sound ('dubb'/'dupp') is associated with the closure of the semilunar valves. 

The pressure exerted on the arterial wall during left ventricular contraction pushing blood into the aorta. This is called ventricular pressure or ventricular systole. During ventricular systole closing of atrioventricular valves produces the first heart sound lubb. Thus, the correct option is B.

The cardiac cycle refers to a complete heartbeat from its generation to the beginning of the next beat. The frequency of the cardiac cycle or the heart rate is expressed as heart beats per minute. Normal adult human heart rate ranges from 60-100 bpm. So, the correct answer is option B.

The sino-atrial node (SAN) is a mass of nodal tissue found in the upper part of right auricle. It generates the nerve impulses which is responsible for starting the contraction of the heart. It controls the rhythm of the heart contraction. Hence, it is called as the natural pacemaker of the heart.

Chordae _ tending are numerous, strong inelastic thread like tendons  present in the ventricles of the  mammalian heart.

This sequential event in the heart which is cyclically repeated is called the cardiac cycle. Each cardiac cycle consists of systole and diastole of both the atria and ventricles. Each cardiac cycle represents one heartbeat. The normal heart rate is about 72 beats per minute. The heart rate is same as pulse rate because the pumping action of the heart causes an increase in blood pressure in arteries that leads to noticeable pulse. Hence pulse rate can be defined as the rate at which the blood is pumped.

• The amount of blood pumped by the heart per minute is called the cardiac output.
• The heart of a normal person beats 72 times per minute. This is called the heart rate. During each and every heartbeat, the ventricles pump about 70 ml of blood.
• This is known as stroke volume. This means heart pumps 72 x 70 ml = 5040 ml or approximately 5 liters of blood per minute.
  
  Thus the correct answer is option C.

The pulse rate is the number of times one can feel a pulse in one minute. The radial artery is present on the thumb side of the wrist. To measure the pulse rate place two fingers between the bone and the tendon over your radial artery. Count the number of beats in 15 seconds, multiply this with four you will get the pulse rate. Therefore The pulse rate can be determined from the arteries.

• This sequential event in the heart that is cyclically repeated is called the cardiac cycle. Each cardiac cycle consists of systole and diastole of both the atria and ventricles. 
• Each cardiac cycle represents one heartbeat. The number of heartbeats per minute in resting person is called a normal heart rate. 
• The normal heart rate is about 72 beats per minute. Hence the unit of measurement of the heartbeat is Beats per minute.

• Lubb is the first sound which has a low pitch and produced by the closure of tricuspid and bicuspid valves (collectively called atrioventricular valves) at the beginning of ventricular systole.
• Dup is the second sound which is sharp and has a high pitch. It is produced by closure of semilunar valves by the end of ventricular systole.

This sequential event in the heart which is cyclically repeated is called the cardiac cycle. Each cardiac cycle consists of systole and diastole of both the atria and ventricles. Each cardiac cycle represents one heartbeat. The normal heart rate is about 72 beats per minute. The heart rate is same as pulse rate because the pumping action of the heart causes an increase in blood pressure in arteries. Hence pulse rate can be measured in the arteries of the neck and arteries of the wrist.

The heart is located in the mediastinum, but the apex of the heart, which is formed by the left ventricle, is directed toward the left side of the chest, making the heartbeat more audible there.

The sympathetic nervous system is responsible for the fight or flight response. This response includes increasing the heart rate to prepare the body for physical activity.

Adrenaline (epinephrine) is the primary hormone released during stress that stimulates the heart to beat faster and with more force. Thyroxine also affects heart rate, but adrenaline is the classic stimulator for immediate heart rate increases.

The heartbeat originates in the sinoatrial (SA) node, which is commonly referred to as the natural pacemaker of the heart. It initiates the electrical impulses that lead to contraction.

The vagus nerve is part of the parasympathetic nervous system and provides inhibitory control over the heart rate. While the SA node generates the beat, the vagus nerve regulates it.

• The impulse for heart beat is originated in SA node. It is known as the pace maker of heart and situated in upper right corner of right atrium. 
• The electrical impulses generated by SA node are conducted to Atrio Ventricular or AV node. 
• From the AV node, the impulses are transmitted to AV bundle, known as bundle of His which convey the impulses of contraction to the apex of myocardium. 
• The impulses cause the Purkinje fibres to sweep upwards and outwards which results in pumping of blood into aorta and pulmonary artery.
• So, the correct sequence of propagation of cardiac impulse is SA node, AV node, Bundle of His, Purkinje fibres.

• Lubb is the first sound which has a low pitch and produced by the closure of tricuspid and bicuspid valves (collectively called atrioventricular valves) at the beginning of ventricular systole.
  
• Dup is the second sound which is sharp and has a high pitch. It is produced by closure of semilunar valves by the end of ventricular systole and beginning of ventricular diastole).

• S1: It is the first sound 'lubb'. It has slow pitch and produced by closure of atrioventricular valves at the beginning of ventricular systole.
• S2: It is the second sound 'dup'. It is sharper and has high pitch. It is produced by closure of semilunar valves by the end of ventricular systole. 
• S3 and S4 are usually faint and may not be audible. S3 is produced during ventricular filling of heart and S4 is produced during atrial systole.

A pulse is the rhythmic expansion and recoil of an artery resulting from the heart's contraction. It directly reflects the frequency of heart contractions, which is the heart rate.

Cardiac output is the product of stroke volume and heart rate. If cardiac output remains relatively constant and stroke volume increases, the heart rate must decrease to maintain the same output.

The SA node acts as the primary pacemaker of the heart, setting the rhythm and rate of the heartbeat. The other structures listed are part of the conduction system but do not set the primary rate.

The heart is entirely made up of cardiac muscles. Muscle cells are also called myocytes. The control of the heart function is by a set of muscles or special node of the modified heart muscle, the sinoatrial node (SAN) located in the atria, so the heart is, therefore, called myogenic.

Heart sounds are noises generated by the closing and opening of the heart valves. In a healthy individual, there are two normal heart sounds called lub and dub. Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of systole. The second heart sound dub is associated with the closure of the semilunar valves at the beginning of diastole.

The first heart sound, 'Lubb', is caused by the closure of the atrioventricular valves. It is longer and lower in pitch compared to the second heart sound, 'Dub', which is caused by the closure of the semilunar valves.

In healthy adults, there are two normal heart sounds often described as a lub and a dub, that occur in sequence with each heartbeat. These are the first heart sound (S1) and second heart sound (S2), produced by the closing of the atrioventricular valves (AV) and semilunar valves respectively. 

Heart sounds are heard on the surface of the chest in the heart region; they are amplified by and heard more distinctly through a stethoscope. They are caused by the vibrations generated during the normal cardiac cycle and may be produced by muscular action, valvular actions, motion of the heart, or blood passing through the heart. The second heart sound (S2) is shorter and higher pitched than the first, is heard as a dupp and is produced by closure of the aortic and pulmonary valves.

Cardiac output is estimated by heart beat. The amount of blood pumped by the heart per minute is known as cardiac output. Small mammals have high metabolic rates so they faster heart rates than larger-sized mammals. A rabbit at rest normally has a heart rate that ranges from 140 to 180 beats per minute. Stress can cause the heart rate to increase, and the rate in a stressed rabbit can be quite high: well over 300 beats per minute. Therefore the rate of the heartbeat in a rabbit can be ~ 150-300 per minute. 

Systole is the phase of the contraction of the heart while diastole is the phase of the relaxation. During the ventricular systole the following events take place:

The lub is the first heart sound, commonly termed S1, and is caused by turbulence caused by the closure of mitral and tricuspid valves at the start of systole. The second sound, dub or S2, is caused by the closure of aortic and pulmonary valves, marking the end of systole.

One heartbeat in an average man lasts  0.8 second.

The term 'cardiac' is derived from the Greek word 'kardia', meaning heart. It is used in medical terminology to describe anything related to the heart.

This sequential event in the heart which is cyclically repeated is called the cardiac cycle. Each cardiac cycle consists of systole and diastole of both the atria and ventricles. Each cardiac cycle represents one heartbeat. The number of heart beats per minute in resting person is called as normal heart rate. The normal heart rate is about 72 beats per minute. The heart rate is same as pulse rate because the contractions of the heart cause an increase in blood pressure in arteries that leads to noticeable pulse.

The human circulatory system consists of a muscular four-chambered heart, a network of closed branching blood vessels and blood, the fluid which is circulated. Circulation was discovered by William Harvey. He was the first to recognize the full circulation of blood in the human body and to provide experiments and arguments to support this idea.

The human heart is an example of myogenic heart, it possesses cardiac muscle helping the heart to automatically contract spontaneously; which do not need any stimuli as in neurogenic heart. A myogenic heart is capable of generating a cardiac contraction independent of nervous input. In a myogenic heart, contraction is initiated by the cells called myocyte  (Pacemakers)itself instead of an outside occurrence or stimulus such as nerve innervation.

Smaller animals have much higher metabolism; proportionate to body size, smaller animals tend to have a much smaller heart than larger animals. This means that in order to circulate blood at the same rate, the hearts of smaller animals need to pump more times within a specified time because the volume they can pump each time is smaller.

• Heart sounds are noises generated by the closing and opening of the heart valves. In a healthy individual, there are two normal heart sounds called lub and dub. 
  
• Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of systole. 
• The second heart sound dub is associated with the closure of the semilunar valves at the beginning of diastole.
  

The sinoatrial node (SAN) is the impulse-generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava. 

The rate of heartbeat is inversely proportional to the size of the body. Smaller animals have a greater heart rate due to increased metabolic rate than the large animals. 

A valve is a membranous structure present in a hollow organ. It folds or closes to prevent the return flow of the body fluid passing through it. The valves present in between the auricles and ventricles are meant to prevent the backflow of blood from the ventricles to auricles. Valves are also a part of veins.

Heart rate affects both stroke volume and minute volume by altering the length of diastole and thereby the degree of filling and force of contraction. Minute volume and B.P may rise even if the stroke volume falls. This happens with a moderate rise in the heart rate. But if the heart rate is too high, the stroke volume becomes so low that the minute output falls far below the normal.

Atrial systole occurs at the end of ventricular diastole. After the ventricle has pumped its blood, it begins to relax. There is now negative pressure in the ventricle (since it is now empty), and this pressure helps to draw in the blood from the atrium when it enters into systole. So during atrial systole, the bicuspid and tricuspid valves are open, and the pulmonary/aortic semilunar valves are closed. Then during the diastole, the bicuspid and tricuspid valves are closed.