The cardiovascular Output

Question 1

Cardiac output is defined as the volume of blood leaving …..

This means the total amount of blood leaving the heart is ….. the cardiac output (which is the same for each side)

Answer 1

Cardiac Output is defined as the volume of blood leaving each ventricle during one minute.

This means the total amount of blood leaving the heart is 2 x the Cardiac Output (which is the same for each side).

Question 2

Cardiac Output 2 (CO) is the product of two cardiac variables, the …… or …… (……, beats per minute) and the volume of blood ejected from the ventrixle ml…. , or stroke volume (SV)

CO(ml/min). or stroke volume (sv)

CO (ml/min) = …(beats/min) x … (ml/beat)

Answer 2

Cardiac Output (CO) is the product of two cardiac variables, the heart rate or stroke rate (HR/SR, beats per minute) and the volume of blood ejected from the ventricle mls per beat, or stroke volume (SV).

CO (ml/min) = SR (beats/min) X SV (ml/beat)

Question 3

Cardiac output 3 CO (mL/min) = ……. x ………..

Heart rate can be taken from at rest or maximun work load

Answer 3

CO (mL/min) = SR (beats/min) X SV (mL/beat)

Question 4

Cardiac Output

The last calculation simply gives a theortetical value

• An increase of SR beyond … beats/min decreases the time allowed for ……… …….. and is associated with a fall of ……, Thus the ouput does not show a linear relationship to heart rate

Answer 4

This last calculation simply gives a theoretical value since:
An increase of SR beyond 140 beats/min decreases the time allowed for ventricular filling and is associated with a fall of CO. Thus, the output does not show a linear relationship to heart rate.

Question 5

Athletes who undergo extreme endurance events such as marathon runners show the following characteristics.
Due to prolonged increased heart muscle activity, …….. occurs and this in turn leads to increased volume of the chambers of the heart.
Stroke volume can increased to well above …… beat as a result.
However, heart rate is maximum at about 180 beats/min, although a general rule is 220-age.
Thus, their CO theoretically can be 180 x 200 = 36 L/min.
As a consequence of the increased st….. ….., even at rest, the CO needs to be about …… L/min.
To compensate many of these athletes have a decreased heart rate at rest (………….) and may have rates as low as 40 beats/min.

Note:  In a normal person such rates would be indicative of conductive block in the heart and the need for a pacemaker

Answer 5

Athletes who undergo extreme endurance events such as marathon runners show the following characteristics.
Due to prolonged increased heart muscle activity, hypertrophy occurs and this in turn leads to increased volume of the chambers of the heart.
Stroke volume can increased to well above 200mL/beat as a result.
However, heart rate is maximum at about 180 beats/min, although a general rule is 220-age.
Thus, their CO theoretically can be 180 x 200 = 36 L/min.
As a consequence of the increased stroke volume, even at rest, the CO needs to be about 5 L/min.
To compensate many of these athletes have a decreased heart rate at rest (parasympathetic intervention) and may have rates as low as 40 beats/min.

Note:  In a normal person such rates would be indicative of conductive block in the heart and the need for a pacemaker

Question 6

A healthy heart pumps out a reasonable amount of blood that has entered its chambers during the previous diastole. At rest this is approx. …… of the total volume because approx …. remains in the …… after each contraction (end-systolic volume).
Thus

Stroke volume(SV) = [End-diastolic volume(EDV)] – [End-systolic volume (ESV)]

To ensure that the left and right ventricles pump equal volumes of blood, three important control factors regulate Stroke Volume:

1. Preload, the …….. on the heart before it contracts,
2. Contractility, the ……… of contraction of individual muscle fibres, and
3. Afterload, the ……… that must be exceeded before …… of blood from the ventricle begins.

Answer 6

A healthy heart pumps out a reasonable amount of blood that has entered its chambers during the previous diastole. At rest this is approx. 60% of the total volume because approx 40% remains in the ventricles after each contraction (end-systolic volume).
Thus

Stroke volume(SV) = [End-diastolic volume(EDV)] – [End-systolic volume (ESV)]

To ensure that the left and right ventricles pump equal volumes of blood, three important control factors regulate Stroke Volume:

1. Preload, the stretch on the heart before it contracts,
2. Contractility, the forcefulness of contraction of individual muscle fibres, and
3. Afterload, the pressure that must be exceeded before ejection of blood from the ventricle begins.

Question 7

Preload

Thus

Stroke volume(SV) = [End-diastolic volume(EDV)] – [End-systolic volume (ESV)]

To ensure that the left and right ventricles pump ……….. of blood, three important control factors regulate Stroke Volume:

1. Preload, the …… on the heart before it contracts,
2. Contractility, the forcefulness of …….of individual muscle fibres, and
3. Afterload, the pressure that must be ….. …… ……. of blood from the ventricle begins.

Answer 7

A healthy heart pumps out a reasonable amount of blood that has entered its chambers during the previous diastole. At rest this is approx. 60% of the total volume because approx 40% remains in the ventricles after each contraction (end-systolic volume).
Thus

Stroke volume(SV) = [End-diastolic volume(EDV)] – [End-systolic volume (ESV)]

To ensure that the left and right ventricles pump equal volumes of blood, three important control factors regulate Stroke Volume:

1. Preload, the stretch on the heart before it contracts,
2. Contractility, the forcefulness of contraction of individual muscle fibres, and
3. Afterload, the pressure that must be exceeded before ejection of blood from the ventricle begins.

Question 8

Preload

A greater preload (stretch) on cardiac muscle fibres just before they contract ………….. …….. …….of contraction. Within limits, the more the heart …… during ……., the greater the force of contraction during …….. This is known as the Frank-Starling law of the heart. In the body, the preload is the …… of blood that fills the ………. at the end of diastole, the EDV. The greater the EDV (preload), within limits, the .. …….. the contraction

Answer 8

A greater preload (stretch) on cardiac muscle fibres just before they contract increases their force of contraction. Within limits, the more the heart is filled during diastole, the greater the force of contraction during systole. This is known as the Frank-Starling law of the heart. In the body, the preload is the volume of blood that fills the ventricles at the end of diastole, the EDV. The greater the EDV (preload), within limits, the more forceful the contraction

Question 9

Factors which affect the EDV

a) Duration of ventricular diastole. When heart rate increases, the duration of diastole is ……. Less filling time means a smaller ….., and the ventricles may contract before they are adequately …….
b) Venous pressure or Venous Return
When venous pressure increases, a …… volume of blood is forced into the ventricles, and the EDV is ……..a) Duration of ventricular diastole. When heart rate increases, the duration of diastole is shorter. Less filling time means a smaller EDV, and the ventricles may contract before they are adequately filled.
b) Venous pressure or Venous Return
When venous pressure ………., a greater volume of blood is forced into the ……, and the EDV is increased.

Answer 9

a) Duration of ventricular diastole. When heart rate increases, the duration of diastole is shorter. Less filling time means a smaller EDV, and the ventricles may contract before they are adequately filled.
b) Venous pressure or Venous Return
When venous pressure increases, a greater volume of blood is forced into the ventricles, and the EDV is increased.

Question 10

Factors affecting venous return 1

venoconstriction - …….. venous return by reducing the …… capacity of the veins to store ……. (60 blood volume in veins at …)
This occurs via a reflex sympathetic constriction of smooth muscle, controlled by the … centre in the medulla.

Muscle pumps - rhythmical skeletal muscular ….. compress the …. in the veins forcing back towards the … Backflow during relaxation of skeletal muscles is prevented by ………. located in the walls of the veins.

Answer 10

i) Venoconstriction - increases venous return by reducing the volume capacity of the veins to store blood ( 60% blood volume in veins at rest). This occurs via a reflex sympathetic constriction of smooth muscle, controlled by the vasomotor centre in the medulla.
ii) Muscle pumps - rhythmical skeletal muscular contractions compress the blood in the veins forcing back towards the heart. Backflow during relaxation of skeletal muscles is prevented by one-way valves located in the walls of the veins.

Question 11

Factors affecting venous return 2

Respiratory pumps - During inspiration, the pressure within the …….. ……… and the abdominal pressure …….. This creates a flow of ……. blood from the abdominal region into the thorax and therefore promotes ….. return. Although quiet breathing (rest) ….. in the venous return, the role of the respiratory pump is ……. during exercise due to the greater ………. …… and rate.

iv) Peripheral resistance - the muscular arteries of the body have circularly arranged …….. ……. around them. Contraction of the muscle …….the size of the vessel (vasoconstriction) while …… increases it (vasodilation). Constriction ……. blood flow to the tissues and organs and causes more blood to remain in the ……. between the heart and the tissues. This is said to increase ….. resistance and requires a …….. output and pressure on the part of the heart to maintain flow through the narrowed vessels.

Answer 11

Respiratory pumps - During inspiration, the pressure within the thorax decreases and the abdominal pressure increases. This creates a flow of venous blood from the abdominal region into the thorax and therefore promotes venous return. Although quiet breathing (rest) aids in the venous return, the role of the respiratory pump is enhanced during exercise due to the greater respiratory depth and rate.

iv) Peripheral resistance - the muscular arteries of the body have circularly arranged smooth muscle around them. Contraction of the muscle diminishes the size of the vessel (vasoconstriction) while relaxation increases it (vasodilation). Constriction reduces blood flow to the tissues and organs and causes more blood to remain in the vessels between the heart and the tissues. This is said to increase peripheral resistance and requires a higher output and pressure on the part of the heart to maintain flow through the narrowed vessels.

Question 12

Factors affecting venous return

When heart rate exceeds about 160 beats/min, ….. …… actually declines. At such rapid heart rates, the ventricular ….. ….. is severely shortened, EDV is less, and the ……..thus is lower. People who have slow resting heart rates, on the other hand, usually have large stroke volumes because filling time is prolonged and preload thus is larger.

The Frank-Starling law of the heart e………. the output of the right and left ventricles and keeps the ….. volume of blood flowing to both the ……. and pulmonary circulations. If the left side of the heart pumps a little more blood than the right side, for example, the volume of blood returning to the right ventricle (venous return) increases. With increased EDV, then, the right ventricle contracts …….. forcefully on the next beat, and the two sides are again in ……..

Answer 12

vWhen heart rate exceeds about 160 beats/min, stroke volume actually declines. At such rapid heart rates, the ventricular filling time is severely shortened, EDV is less, and the preload thus is lower. People who have slow resting heart rates, on the other hand, usually have large stroke volumes because filling time is prolonged and preload thus is larger.

The Frank-Starling law of the heart equalises the output of the right and left ventricles and keeps the same volume of blood flowing to both the systemic and pulmonary circulations. If the left side of the heart pumps a little more blood than the right side, for example, the volume of blood returning to the right ventricle (venous return) increases. With increased EDV, then, the right ventricle contracts more forcefully on the next beat, and the two sides are again in balance.

Question 13

Contractility

Myocardial c……… is the at ……….. ……. ……… at any given preload. Substances that increase contractility are called ……. …… agents whereas those that decrease contractility are called negative inotropic agents.

Thus, for a constant preload, the stroke volume is ….. when a positive inotropic substance is present.

Positive inotropic substances often promote ……. inflow during cardiac action potentials, which ……….the force of contraction.

They include stimulation of the sympathetic nervous system, hormones such as ……….. and …….., increased Ca2+ levels in the extra-cellular fluid, and the drug digitalis.

Negative inotropic substances include …… of the sympathetic nervous system, anoxia, acidosis, some anaesthetics (halothane), and increased ….. levels in the extra-cellular fluid.

Answer 13

Myocardial contractility is the strength of contraction at any given preload. Substances that increase contractility are called positive inotropic agents whereas those that decrease contractility are called negative inotropic agents.

Thus, for a constant preload, the stroke volume is larger when a positive inotropic substance is present.

Positive inotropic substances often promote Ca2+ inflow during cardiac action potentials, which strengthens the force of contraction.

They include stimulation of the sympathetic nervous system, hormones such as noradrenaline and adrenaline, increased Ca2+ levels in the extra-cellular fluid, and the drug digitalis.

Negative inotropic substances include inhibition of the sympathetic nervous system, anoxia, acidosis, some anaesthetics (halothane), and increased K+ levels in the extra-cellular fluid.

Question 14

Afterload

Ejection of blood from the right heart (pulmonary circulation) begins when pressure in the ….. ventricle ……… …. ……. in the pulmonary trunk (about 20mm Hg) and from the left heart (systemic circulation) when the pressure in the l………. …… exceeds the pressure in the aorta (80mm Hg).
At this point, the …..pressure in the ventricles causes blood to press against the …….. …… and push them open.
The pressure that must be overcome before the semilunar valves can open is termed the ……..
When the afterload increases, for example, when …… ………. is elevated, stroke volume decreases, and …. ……. remains in the ventricles at the end of systole.

Answer 14

Ejection of blood from the right heart (pulmonary circulation) begins when pressure in the right ventricle exceeds the pressure in the pulmonary trunk (about 20mm Hg) and from the left heart (systemic circulation) when the pressure in the left ventricle exceeds the pressure in the aorta (80mm Hg).
At this point, the higher pressure in the ventricles causes blood to press against the semilunar valves and push them open.
The pressure that must be overcome before the semilunar valves can open is termed the afterload.
When the afterload increases, for example, when blood pressure is elevated, stroke volume decreases, and more blood remains in the ventricles at the end of systole.

Question 15

Regulation of heart rate 1

The .. …. initiates contraction and, left to itself, would set a constant heart rate of 90-100 beats/minute. However, several factors contribute to the regulation of heart rate. The most important ones are the … and ………….released by the adrenal……. (noradrenaline and adrenaline).

Answer 15

The SA node initiates contraction and, left to itself, would set a constant heart rate of 90-100 beats/minute. However, several factors contribute to the regulation of heart rate. The most important ones are the ANS and hormones released by the adrenal medulla (noradrenaline and adrenaline).

Question 16

Regulation of heart rate 2

Sympathetic Nervous System/Sympathetic Nerves

The activity is controlled by nerves arising from the …….
The postganglionic sympathetic fibres innervate the ………. and …….and the atrial and ventricular muscle.
Their stimulation releases .. ……. on the cardiac muscle fibres.
At the .. …. it speeds up the rate of spontaneous depolarisation causing the cells to fire more rapidly and heart rate increases.
Secondly, in the …… ….. in the atria and ventricles noradrenaline enhances Ca2+ entry through the voltage-gated slow Ca2+ channels and thus ……….contractility.
Thus, with a moderate increase in heart rate, stroke volume does not decline. With maximal …………..stimulation, however, heart rate may reach 250 beats/min. In this case, stroke volume is …….. at rest due to the very short filling time. The highest cardiac output usually occurs at a heart rate between … and 200 beats/min.

Answer 16

Sympathetic Nervous System/Sympathetic Nerves

The activity is controlled by nerves arising from the medulla.
The postganglionic sympathetic fibres innervate the SA node and AV node and the atrial and ventricular muscle.
Their stimulation releases noradrenaline, which binds to b1 receptors on the cardiac muscle fibres.
At the SA node it speeds up the rate of spontaneous depolarisation causing the cells to fire more rapidly and heart rate increases.
Secondly, in the cardiac fibres in the atria and ventricles noradrenaline enhances Ca2+ entry through the voltage-gated slow Ca2+ channels and thus increases contractility.
Thus, with a moderate increase in heart rate, stroke volume does not decline. With maximal sympathetic stimulation, however, heart rate may reach 250 beats/min. In this case, stroke volume is lower than at rest due to the very short filling time. The highest cardiac output usually occurs at a heart rate between 160 and 200 beats/min.

Question 17

Regulation of heart rate 3

These nerves are supplied to the heart via the vagus nerve (X cranial nerve) and they innervate the SA and AV nodes and atrial and ventricular muscles.

The ACh released from these nerves ……….. the cells and slows ……… through the nodal tissue and hence slows the heart.
Since only a few vagal fibres …… …….. lar muscle, changes in p…………….. activity have little or no effect on contractility of the ……..
They are sometimes designated the CARDIOINH………. N……….

Answer 17

These nerves are supplied to the heart via the vagus nerve (X cranial nerve) and they innervate the SA and AV nodes and atrial and ventricular muscles.
The ACh released from these nerves hyperpolarises the cells and slows transmission through the nodal tissue and hence slows the heart.
Since only a few vagal fibres innervate ventricular muscle, changes in parasympathetic activity have little or no effect on contractility of the ventricles.
They are sometimes designated the CARDIOINHIBITORY NERVES-+*

Question 18

Regulation of heart rate 4

Both types of nerves are …….. active (continuously conducting AP‘s) and the normal ……… …… rate is due to a balance between ……and ………..
At rest the parasympathetic effects predominate. The resting heart rate 70-75 beats/min, usually is lower than the auto-rhythmic rate of the ………. (90-100 beats/min).
With maximal stimulation by the parasympathetic division, the heart rate can slow to 20-30 beats/min or even stop.
Adjustment of heart rate is brought about by changes in both sets of nerves. This leads to a much s…. and more ……… adjustment of Cardiac Output to body needs.

Answer 18

Both types of nerves are tonically active (continuously conducting AP‘s) and the normal resting heart rate is due to a balance between stimulation and inhibition.
At rest the parasympathetic effects predominate. The resting heart rate 70-75 beats/min, usually is lower than the auto-rhythmic rate of the SA node (90-100 beats/min).
With maximal stimulation by the parasympathetic division, the heart rate can slow to 20-30 beats/min or even stop.
Adjustment of heart rate is brought about by changes in both sets of nerves. This leads to a much smoother and more rapid adjustment of Cardiac Output to body needs.

Question 19

Regulation of heart rate 5

The medullary neurones from which the …… nerves to the heart arise constitute the …………. ……. (CIC).
The medullary centre from which nerves arise and pass to the sympathetic nerves in the ……… constitute the …………….q (CAC).
These centres display no spontaneous or automatic activity of their own, but serve as co-ordinating centres for sensory input from many parts of the body and other parts of the brain ……. cortex.

Answer 19

The medullary neurones from which the vagus nerves to the heart arise constitute the CARDIOINHIBITORY CENTRE (CIC).
The medullary centre from which nerves arise and pass to the sympathetic nerves in the cervical cord constitute the CARDIOACCELERATOR CENTRE (CAC).
These centres display no spontaneous or automatic activity of their own, but serve as co-ordinating centres for sensory input from many parts of the body and other parts of the brain such as the limbic system and the cerebral cortex.

Question 20

Receptors involved in cardiac ReflexesBARORECEPTORS 1

These sensory receptors respond to alterations in …… within the walls of organs in which they are located.
The most concentrated and functionally important baroreceptors for cardiac control lie in the two ….. ……., located in the bifurcation of the common carotid arteries in the neck.
There are also important baroreceptors in the …… arc.
They are also found throughout the cardiovascular system, especially the …… and ……….(pulmonary artery, walls of left atrium, pericardium, lungs, and alimentary tract).
The receptors respond to stretch imposed on them by an increase ……. …….. ……… within the vessel and to the rate of change of that pressure, by increasing their firing rate.

Answer 20

These sensory receptors respond to alterations in pressure within the walls of organs in which they are located.
The most concentrated and functionally important baroreceptors for cardiac control lie in the two CAROTID SINUSES, located in the bifurcation of the common carotid arteries in the neck.
There are also important baroreceptors in the aortic arc.
They are also found throughout the cardiovascular system, especially the thorax and abdomen (pulmonary artery, walls of left atrium, pericardium, lungs, and alimentary tract).
The receptors respond to stretch imposed on them by an increase in blood pressure within the vessel and to the rate of change of that pressure, by increasing their firing rate.

Question 21

Receptors involved in cardiac ReflexesBARORECEPTORS 2

The afferent nerves from these receptors terminate on both the …. and …… The effect of increased blood pressure is as follows:
1. Inhibition of the CAC, decreased sympathetic activity
and
2. Excitation of the CIC, increased parasympathetic (vagal)
activity.
Both effects lead to a ……….. heart rate.

Answer 21

The afferent nerves from these receptors terminate on both the CIC and CAC. The effect of increased blood pressure is as follows:
Inhibition of the CAC, decreased sympathetic activity
and
2. Excitation of the CIC, increased parasympathetic (vagal)
activity.
Both effects lead to a decreased heart rate.

Question 22

Receptors involved in cardiac ReflexesCHEMORECEPTORS 1

These receptors are sensitive to blood oxygen and carbon dioxide levels, and are found in the …….. and ……. Their primary effect is on the ra…. and ……. of breathing, but they do have an effect on heart rate. An increased frequency of discharge is associated with
(a) …….. oxygen levels, or
(b) ………. carbon dioxide levels, in the blood.
This input has the following effect in the medulla:
1. Inhibition of CIC, ……… vagal tone, and
2. Excitation of CAC, ……. sympathetic tone.
Thus there is an increased heart rate as a result.

Answer 22

These receptors are sensitive to blood oxygen and carbon dioxide levels, and are found in the carotid body and aorta. Their primary effect is on the rate and depth of breathing, but they do have an effect on heart rate. An increased frequency of discharge is associated with
(a) decreased oxygen levels, or
(b) increased carbon dioxide levels, in the blood.
This input has the following effect in the medulla:
1. Inhibition of CIC, decreased vagal tone, and
2. Excitation of CAC, increased sympathetic tone.
Thus there is an increased heart rate as a result.

Question 23

Receptors involved in cardiac ReflexesCHEMORECEPTORS 2

These receptors also cause an increased ………….. by stimulation of the vasomotor centre in the ……. The increased peripheral resistance causes an …… force of contraction of the heart. The net result is that a greater volume of blood is pumped ……… around the body, especially to the ……. which will increase oxygen uptake into the blood and increase the amount of …. …….removed from the blood, to return their levels to the bodies needs.

Answer 23

These receptors also cause an increased vasoconstriction by stimulation of the vasomotor centre in the medulla. The increased peripheral resistance causes an increased force of contraction of the heart. The net result is that a greater volume of blood is pumped faster around the body, especially to the lungs which will increase oxygen uptake into the blood and increase the amount of carbon dioxide removed from the blood, to return their levels to the bodies needs.

Question 24

Receptors involved in cardiac ReflexesPROPRIORECEPTORS 1

Proprioceptors in the muscles and tendons, which monitor the position of the …… and muscles, send …….. input to the cardiac centres during exercise and are responsible for the quick rise in heart rate at the onset of physical activity.

Answer 24

Proprioceptors in the muscles and tendons, which monitor the position of the limbs and muscles, send increased input to the cardiac centres during exercise and are responsible for the quick rise in heart rate at the onset of physical activity.

Question 25

Receptors involved in cardiac ReflexesPAIN/NOCIOCEPTORS 1

Any stimulus that is very strong on any peripheral nerve usually results in …….. Such stimulation has the following effects:

1. Inhibition of CIC, ……. vagal tone, and
2. Excitation of CAC, ……… sympathetic tone.

Both effects leading to an increased heart rate.

Answer 25

Any stimulus that is very strong on any peripheral nerve usually results in pain. Such stimulation has the following effects:

1. Inhibition of CIC, decreased vagal tone, and
2. Excitation of CAC, increased sympathetic tone.

Both effects leading to an increased heart rate.

Question 26

Chemical Regulation of Heart rate 1

Certain chemicals influence both the basic physiology of cardiac muscle and heart rate. For example, ……..(lowered oxygen level), …… (low pH), and ……. (high pH) all affect cardiac activity. Two types of chemicals - hormones and ions - have major effects on the heart.

Answer 26

Certain chemicals influence both the basic physiology of cardiac muscle and heart rate. For example, hypoxia (lowered oxygen level), acidosis (low pH), and alkalosis (high pH) all affect cardiac activity. Two types of chemicals - hormones and ions - have major effects on the heart.

Question 27

Chemical Regulation of Heart rateHormones

Adrenaline and noradrenaline (from the adrenal medulla) enhance the h……. p…….. efficiency. These effect cardiac muscle fibres in much the same way as sympathetic stimulation by increasing heart rate and contractility. Exercise, stress and excitement cause the ……. to release more of its hormones.
Thyroid hormones also enhance…….. ……… and increase heart rate. One sign of hyperthyroidism is tachycardia (…….. heart rate at rest).

Answer 27

Adrenaline and noradrenaline (from the adrenal medulla) enhance the heart’s pumping efficiency. These effect cardiac muscle fibres in much the same way as sympathetic stimulation by increasing heart rate and contractility. Exercise, stress and excitement cause the adrenal medulla to release more of its hormones.
Thyroid hormones also enhance cardiac contractility and increase heart rate. One sign of hyperthyroidism is tachycardia (elevated heart rate at rest).

Question 28

Chemical Regulation of Heart rateBlood Gases

Oxygen. The level of oxygen in the blood, unless extremely low or prolonged have …………..on heart function. If low and prolonged, hypoxemia interferes with ……
metabolism of the muscle and causes ………… contractions and fall of ……. volume.
Carbon dioxide. Excessive carbon dioxide levels exerts an …………. effect and cause depression of ..and .. node function.
pH. Fall of pH has the same effect as raising carbon dioxide levels.
CO2 + H2O <> H2CO3 <> H+ + HCO3-

A rise of pH is associated with …….. and thus stroke volume increases.

Answer 28

Oxygen. The level of oxygen in the blood, unless extremely low or prolonged have little direct effect on heart function. If low and prolonged, hypoxemia interferes with aerobic metabolism of the muscle and causes weakened contractions and fall of stroke volume.
Carbon dioxide. Excessive carbon dioxide levels exerts an anaesthetic-like effect and cause depression of SA and AV node function.
pH. Fall of pH has the same effect as raising carbon dioxide levels.
CO2 + H2O  H2CO3  H+ + HCO3-

A rise of pH is associated with hyperexcitability and thus stroke volume increases.

Question 29

Chemical Regulation of Heart rateIons - Sodium

The chief function of extracellular ……. is to maintain ……….relationships and excitability. Normally sodium levels are kept within very narrow limits.
On the isolated heart … effects of sodium are seen until its concentration is raised …… times normal. Then it will affect calcium inflow and …… the force of contraction.
If the sodium is decreased to 10-20% of normal, then the rate of ………of the nodal tissue is also slowed, and the heart rate ……

Answer 29

The chief function of extracellular sodium is to maintain osmotic relationships and excitability. Normally sodium levels are kept within very narrow limits.
On the isolated heart no effects of sodium are seen until its concentration is raised 2-3 times normal. Then it will affect calcium inflow and reduce the force of contraction.
If the sodium is decreased to 10-20% of normal, then the rate of depolarisation of the nodal tissue is also slowed, and the heart rate decreases.

Question 30

Chemical Regulation of Heart rateIons - Potassium

Increasing …………….potassium concentrations 2-3 times normal values ………. conduction velocity through the …… …….(slows heart rate) and causes a heart block, arrhythmias and localised fibrillation (rates up to 200-300 beats per minute).
Ectopic foci develop more ……, where other areas of the heart, other than nodal tissue, assume pacemaker activity. Such areas compete with the …. node to stimulate the cardiac muscle. The heart muscle may be divided into several separately contracting areas, each controlled by its own pacemaker. The development of circular repetitive areas of depolarisation constitute ‘circus movements‘. Different areas of the muscle contract at different times and co-ordination is lost. In most cases throwing the heart into a simultaneous state of ……….. by the application of external shock (defibrillation) usually re-establishes the co-ordination necessary for ……… circulation of blood.
Decreases in intracellular potassium concentration causes a ……………. and a corresponding decreased in heart rate (lengthening of the Q-T interval).

Answer 30

Increasing extracellular potassium concentrations 2-3 times normal values decreases conduction velocity through the nodal tissue (slows heart rate) and causes a heart block, arrhythmias and localised fibrillation (rates up to 200-300 beats per minute).
Ectopic foci develop more easily, where other areas of the heart, other than nodal tissue, assume pacemaker activity. Such areas compete with the SA node to stimulate the cardiac muscle. The heart muscle may be divided into several separately contracting areas, each controlled by its own pacemaker. The development of circular repetitive areas of depolarisation constitute ‘circus movements‘. Different areas of the muscle contract at different times and co-ordination is lost. In most cases throwing the heart into a simultaneous state of depolarisation by the application of external shock (defibrillation) usually re-establishes the co-ordination necessary for efficient circulation of blood.
Decreases in intracellular potassium concentration causes a hyperpolarisation and a corresponding decreased in heart rate (lengthening of the Q-T interval).

Question 31

Chemical Regulation of Heart rateIons - Calcium

Calcium. Increases of calcium in the …. will cause excitation of the heart (heart rate will increase and the force of contraction will strengthen).
Prolonged …. creates a state resembling tetany, with failure of the muscle to ……; called ‘calcium rigor‘.
Decreases in calcium causes cardiac …… (similar to the effects of high ECF potassium).

Answer 31

Calcium. Increases of calcium in the ECF will cause excitation of the heart (heart rate will increase and the force of contraction will strengthen).
Prolonged elevation creates a state resembling tetany, with failure of the muscle to relax; called ‘calcium rigor‘.
Decreases in calcium causes cardiac flaccidity (similar to the effects of high ECF potassium).

Question 32

Regulation of Heart rateOther Factors - Temperature

Temperature.
This is not of great physiological importance in the human. However, ……. is associated with metabolism of increased quantities of fuels, with increased production of heat. The heat is absorbed by the bloodstream and raises its temperature slightly. The reactions of the SA node are accelerated slightly by the ……. temperature, and the heart rate rises by perhaps 3-4 beats/min. The rapid transfusion of blood that is still cold (from storage ‘blood bank‘) has been associated with an ……… incidence of heart block, indicating that transmission of …….. is affected by a fall of …………… of the blood.

Answer 32

Temperature.
This is not of great physiological importance in the human. However, exercise is associated with metabolism of increased quantities of fuels, with increased production of heat. The heat is absorbed by the bloodstream and raises its temperature slightly. The reactions of the SA note are accelerated slightly by the increased temperature, and the heart rate rises by perhaps 3-4 beats/min. The rapid transfusion of blood that is still cold (from storage ‘blood bank‘) has been associated with an increased incidence of heart block, indicating that transmission of impulses is affected by a fall of temperature of the blood.

Question 33

Regulation of Heart rateOther Factors - Digitalis

This is a ‘cardiac glycoside‘ that exerts an i…… effect as described previously. It is used to increase the e…… of cardiac contraction.
It also increases the rate of spontaneous ……….., decreases conduction velocity of cardiac muscle, and shortens the refractory period of muscle.
The line between therapeutic and …… doses is very fine and subject to individual variation.

Answer 33

This is a ‘cardiac glycoside‘ that exerts an inotropic effect as described previously. It is used to increase the efficiency of cardiac contraction.
It also increases the rate of spontaneous depolarisation, decreases conduction velocity of cardiac muscle, and shortens the refractory period of muscle.
The line between therapeutic and toxic doses is very fine and subject to individual variation.

Question 34

Regulation of Heart rateOther Factors – Various

Atropine and caffeine.
These substances i………. heart rate.

Amyl………, nitrogly…., acetylch…… and small doses of alcohol.
These all have the effect of decreasing heart rate.

Answer 34

Atropine and caffeine.
These substances increase heart rate.

Amylnitrate, nitroglycerine, acetylcholine and small doses of alcohol.
These all have the effect of decreasing heart rate.