CVS - Cardiovascular system questions and answers PDF

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Cardiovascular system questions and answers...

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Cardiovascular Overview: http://lifeinthefastlane.com/ccc/cardiovascular-physiology-overview/ https://www.youtube.com/playlist?list=PLqTetbgey0adIrd0ektg92EdeR7M38YMu On-line Learning Task 1 1)

What will be the primary role of Justin's cardiovascular system during the run?

To increase the delivery of oxygen and nutrients to, and removal of metabolic waste products from, the organs and tissue of the body that will have increased metabolic demands during exercise (e.g., skeletal muscle, heart). Also to increase the flow of blood to the lungs and skin.

2)

In terms of the function of the HEART, what will it have to be able to do?

Increase cardiac output (the volume of blood the the heart pumps out per minute).

3) What two things determine the amount of blood the heart is able to pump around the body per minute? 1. Heart rate (the number of times the heart beats per minute) 2. Stroke volume (the volume of blood pumped out by the heart per beat)

4) When Justin is resting quietly his heart rate is 55 beats/min and his cardiac output 5.2 litres/min. What is his stroke volume at rest? 95 mL Cardiac Ouptput = Heart Rate x Stroke Volume

5) Justin has a friend, Daniel, who is about the same size as Justin but is not very fit. Daniel smokes, is a little overweight and doesn't really do any regular exercise. Daniel's resting heart rate is 70 beats/min. What other difference in resting heart function would you expect between Daniel and Justin? Why would you expect this difference? Daniel would have a smaller stroke volume. Both need approximately the same resting cardiac output. Justin achieves this with a lower heart rate and higher stroke volume as compared to Daniel.

6)

What region, in a normal heart, is responsible for setting the heart rate?

The sino-atrial node. It is the normal pacemaker of the heart.

7) What is it about the sino-atrial node that makes it responsible for setting the heart rate? The cells of the SA node generate action potentials spontaneously and do this at a higher frequency than any other regions of the heart. This makes them the normal pacemaker of the heart. Because of the conducting system and electrical connection

between cardiac cells all of the heart cells will follow the frequency set by the fastest pacemaker which is the sino-atrial node.

8)

Suggest why Justin's resting heart rate is so much lower than Daniel's.

Justin will have increased parasympathetic input to his heart (SA node). This is an adaptation to endurance training and is linked to the increased stroke volume capacity. As the heart's stroke volume capacity increases the heart rate 'needs' to come down. If it didn't, then cardiac output would increase and this would push the mean arterial pressure up.

9) The race is about to start at any moment and Justin is standing at the starting line. Although he hasn't yet started to run his heart rate has gone up to 75 beats/min. Suggest why this has happened. Anticipation and excitement has led to some sympathetic stimulation and an increase in circulating adrenaline which would increase heart rate. Parasympathetic input to the SA node has probably also been decreased.

10) It is now 20 minutes into the run and Justin has already gone nearly 6 km. He is running at a steady pace which represents about 70% of his maximum work capacity. At this point his heart rate would be expected to be around ____ beats/min, his stroke volume about ___ mL, and cardiac output ___ L/min. Note: You are only expected to make an estimate of what you think the values might be. As a hint remember Justin is 21 years old and very fit. Also remember heart rate and cardiac output will increase in proportion to the intensity of exercise. 150, 135, 20

11) Daniel has also gone on this run. At the start he tried to keep up with Justin but now, 20 minutes into the run he has fallen behind. How would you expect his heart rate, stroke volume, and cardiac output to compare with Justin's at this point? (i.e., For each one, would you expect it to be higher or lower. Higher heart rate, lower stroke volume and lower CO.

12) Now, well into the run, Justin's stroke volume will be considerably larger than it was at rest (compare your responses in questions 4 and 10). During exercise cardiac output is increased by increasing both heart rate and stroke volume. What are the TWO main things that determine the stroke volume? The end-diastolic volume and the level of contractility of the cardiac muscle cells.

13) When the end-diastolic volume increases in a normal heart the stroke volume also increases. Briefly describe why this occurs. The strength of contraction of cardiac muscle cells depends on their length. When end-diastolic volume increases, the cardiac muscle cells in the walls of the heart are stretched to longer lengths and they contract with greater force, thereby ejecting a larger stroke volume. This is known as the Frank-Starling Law of the Heart.

14) During exercise the autonomic nervous system plays an important part in increasing the stroke volume of the heart. Which branch of the autonomic nervous system is involved in increasing stroke volume? The sympathetic nervous system.

15) The sympathetic nervous system is able to act to increase the end-diastolic volume of the heart. How is it able to do so? Sympathetic nerves innervate the smooth muscle in the walls of the veins. Sympathetic stimulation causes contraction of the smooth muscle and makes the walls of the veins less distensible, or stiffer. This leads to an increase in the venous pressure, which in turn increases the return of blood to the heart, increasing enddiastolic volume.

16) What other mechanisms could act to increase the return of blood to the heart (venous return) during exercise? The 'skeletal muscle pump'. Contractions of skeletal muscle squeeze on the veins going through them and, because of the presence of one-way valves in the veins, this propels blood toward the heart. During exercise there is increased skeletal muscle activity, making this action important in increasing venous return. The 'respiratory pump'. Alternating increases and decreases in pressure in the abdominal and thoracic cavities during the deep and rapid breathing in exercise assist in propelling blood from the veins in the abdomen to the thorax and heart.

17) The sympathetic nervous system also increases the stroke volume of the heart during exercise by increasing the contractility of the heart. What is meant by the term contractility, and how does the sympathetic nervous system increase the heart's contractility? A change in contractility is a change in the strength of contraction of the heart at the same end-diastolic volume (cardiac muscle cell length). Increased stimulation of sympathetic nerves innervating the ventricles leads to an increase in the amount of calcium entering the cardiac muscle cells (through voltage-activated calcium channels) during the action potential. This in turn leads to an increase in the amount of calcium released from the sarcoplasmic reticulum inside the cardiac muscle cells. The increased calcium entry and release leads to a stronger contraction of the ventricle and a larger stroke volume.

18) During the run, Justin will have increased blood levels of a hormone that is associated with the autonomic nervous system. What is this hormone and where does it come from? What are the main actions of this hormone on the heart? Adrenaline, which is released into the bloodstream by the adrenal medulla. Adrenaline acts to increase the heart rate and the contractility of cardiac muscle (thereby increasing stroke volume). It, therefore, increases cardiac output.

On-line Learning Task 2 1) Justin is now half way through the run and is keeping up a fast, steady pace. His cardiac output is 20 litres/min. How much blood is flowing per minute through his lungs and how much through his systemic circulation? 20 litres/min through his lungs (from the right ventricle) and 20 litres/min through his systemic circulation (from the left ventricle). Remember, cardiac output is the amount of blood pumped out of EACH ventricle per minute.

2) Justin's cardiac output is now about 4 times what it is at rest. How would you expect the blood flow to each of the following organs or tissues to compare to that at rest (i.e., increased, decreased or unchanged)? Heart

increase

Brain

unchanged or very slightly increased

Liver

decreased

Gastrointestinal tract

decreased

Kidneys

decreased

Skeletal muscle

increased

Skin

increased

3) What blood vessels are responsible for controlling the amount of blood flowing through each of these organs/tissues, and how do they do this? The arterioles supplying the organs/tissues. They control the blood flow through changes in their diameter. Their diameter affects the resistance to flow. When the arteriole diameter decreases (constriction) the resistance to flow increases and less blood flows through the arterioles. When the arteriole diameter increases (dilation) the resistance to flow decreases and more blood flows through the arterioles. The diameter of the arterioles is adjusted through contraction or relaxation of smooth muscle which is orientated circularly in the arteriole wall.

4) What is the main mechanism by which the arterioles in skeletal muscle change the blood flow through the muscles during exercise? During exercise the metabolic activity of the skeletal muscles increases substantially. Local chemical changes occur within the muscles as a result of this increased metabolic activity (e.g., decreased O2, increased CO2, increased acidity, adenosine release). These local chemical changes cause the arterioles to dilate and blood flow increases. This is called "active hyperemia".

5) How are the changes that occur in the blood flow through Justin's abdominal organs, such as the kidneys, liver and gastrointestinal tract, brought about?

The arterioles supplying these organs have a rich supply of sympathetic nerves. While Justin is running there is an increase in the sympathetic nerve activity to these arterioles. This causes them to constrict and decreases the blood flow through those organs. (Noradrenaline released from the sympathetic nerves acts on alpha receptors on the smooth muscle in the arteriole wall causing it to contract, thereby constricting the arterioles.)

6) Considering the overall needs of Justin's body during the run, why is it important that the blood flow changes covered in questions 4 and 5 occur? During the run the Justin's skeletal muscles need a great deal of energy to keep working and, therefore, need a large increase in blood flow to supply the oxygen and nutrients the muscles use to obtain this energy. The high blood flow is also needed to remove waste products, such as carbon dioxide and lactic acid, that are produced in large amounts during high levels of muscle activity. The level of activity of the abdominal organs required during exercise is very low, and so these organs do not need high blood flow during exercise. By reducing the blood flow to these organs more of the total blood flow is able to be sent to those tissues that need high blood flow during exercise (skeletal muscles, heart, skin).

7) Why is it important that the blood flow to Justin's heart is increased during the run? During the run Justin's heart needs to deliver a much larger cardiac output. Both the number of contractions per minute (heart rate) and the strength of those contractions (stroke volume) go up. This means the heart has to do a lot of additional work and it needs a large increase in oxygen delivery to do this.

8)

Why is the change in skin blood flow important, and how is it brought about?

During the run Justin's body is producing a lot of heat because of the increased work he is doing. The weather is also very warm and humid. He needs to lose heat so that his body temperature does not rise to dangerous levels. Increasing the blood flow to the skin, together with sweating, is the body's main mechanism for losing heat during exercise. The increased blood flow to the skin is achieved mainly by a decrease in sympathetic nerve activity to the skin arterioles, which causes them to dilate. This response involves the hypothalamus and is part of the body's control system for regulating body temperature.

9) Suggest how it is possible to have increased sympathetic nerve activity to some arterioles but decreased sympathetic nerve activity to others. Where is this coordinated? This is coordinated by 'control centres' in the brain, one of which is the medullary cardiovascular centre (specifically by the vasomotor centre). The medullary cardiovascular centre receives input from receptors such as the arterial baroreceptors and also from other higher brain regions. This allows its output to be programmed in the appropriate way. For example, during exercise the vasomotor centre can send increased sympathetic nerve activity to the arterioles of the abdominal organs but at the same time can decrease the sympathetic nerve activity

to the skin arterioles in response to signals from the temperature control centre in the hypothalamus.

10) How do you think Justin's blood pressure, at this point in the run, would compare with what it was at rest? Comment on how his systolic pressure, diastolic pressure, pulse pressure and mean arterial pressure are likely to have changed. Systolic pressure:

increased (by about 40 - 50%)

Diastolic pressure:

hardly any change

Pulse pressure:

increased (by about 2 to 3 times)

Mean arterial pressure:

11)

increased, but only by about 10 - 20%

Why has the systolic pressure changed in the way it has?

It has increased quite a bit because there has been an increase in stroke volume and the speed at which the stroke volume is ejected. During systole more blood is ejected into the arteries and more quickly. This leads to a greater rise in pressure in the arteries during systole.

12)

Why doesn't the diastolic pressure also increase by a similar amount?

Because the arterioles in the skeletal muscles are very dilated, during diastole blood can flow out of the arteries into the arterioles very quickly. Arterial pressure, therefore, falls quickly during diastole and the diastolic pressure gets down to a value that is not too different from what it is at rest.

13)

What two things determine the mean arterial blood pressure?

The cardiac output and the total peripheral resistance. Mean arterial pressure = cardiac output x total peripheral resistance

14) If Justin's cardiac output has gone up about four times what it was at rest why hasn't his mean arterial pressure also gone up a lot? Because of the dilation of the arterioles in his muscles and skin, Justin's total peripheral resistance has fallen. This largely offsets his increased cardiac output, keeping the increase in his mean arterial pressure relatively small.

15) What is an important reflex mechanism that Justin's body would normally use to make quick, short term adjustments to keep his mean arterial pressure relatively constant? The baroreceptor reflex.

16) Why has this reflex not come into play to counteract the rise in his mean arterial pressure and bring it back down to normal during the run?

Central command from brain centres 'resets' the arterial baroreceptors during exercise so that they 'accept' a higher level of mean arterial pressure as being normal and, therefore, don't initiate reflex responses to lower the arterial pressure.

On-line Learning Task 3 1)

What will be the primary role of Justin's respiratory system during the run?

To increase ventilation of the lungs so that sufficient oxygen is delivered to the blood and excess carbon dioxide is removed from the blood.

2) What is meant by the term 'Minute Ventilation' and what two factors determine it? Minute Ventilation is the volume of air moved into and out of the lungs per minute. It is determined by the tidal volume (volume of air breathed in and out in one breath) and the breathing frequency (number of breaths per minute). Minute Ventilation = Tidal Volume x Breathing Frequency

3) How would you expect Justin's minute ventilation during the run to compare with his minute ventilation when he is resting? How would he achieve this change in minute ventilation? During the run, when he is running at near his maximum capacity, his minute ventilation would probably be about 15 to 20 times greater than at rest. This increase in minute ventilation is the result of increases in both his tidal volume and his breathing frequency.

4) Justin is healthy and has no respiratory problems. As he nears the finish of the run he looks over his shoulder and sees another competitor coming to overtake him. He sprints as fast as he can to the finish line and is breathing very fast and hard. Do you think his respiratory system is now working at its maximum capacity and limiting his finishing dash? Justify your answer. No. For normal, healthy individuals ventilation during maximal exercise effort is still below their Maximum Voluntary Ventilation. This shows that they have the capacity to increase ventilation to levels above that achieved during maximal exercise and consequently that ventilation is not a limiting factor for exercise capacity (in a healthy individual).

5)

Where in the brain is the primary control centre that regulates breathing?

In the medulla ('respiratory centre' or 'respiratory rhythm generator' nuclei). The neurons here also receive input from other centres in the brainstem (pons) such as the pneumotaxic centre and apneustic centre involved in setting the breathing pattern.

6) Going back to the start of the race, Justin's ventilation has actually increased even before the starter's gun is fired. What is likely to be the stimulus for this? (Hint: see Figure 13-39 of Vander et al.) Neural input to the respiratory centres from higher brain areas stimulating an increase in ventilation. This is a type of 'central command' and part of our conditioned (or learned) response to exercise.

7) During the run various chemical changes in Justin's blood have the capacity to stimulate his breathing. What are the three main chemical changes that could do this? 1. An increased partial pressure of carbon dioxide (PCO2) 2. A decreased partial pressure of oxygen (PO2) 3. A decreased pH (increased hydrogen ion concentration)

8)

What receptors detect these chemical changes, and where are they located?

Peripheral chemoreceptors in the carotid bodies (at the bifurcation of the common carotid arteries) and aortic bodies (at the arch of the aorta). There are also 'central chemoreceptors' located in the medulla.

9) During the final stages of the run Justin is actually hyperventilating and his arterial PCO2 falls below normal. What could account for this 'hyper-stimulation' of ventilation? Hint: see Vander et al. Figure 13-41) At this point in the run Justin's muscles are producing quite a lot of lactic acid and this is released into the blood. The concentration of hydrogen ions in the blood is increased as a result of this (blood pH decreases) and this stimulates the peripheral chemoreceptors and further increases ventilation.

10) In the alveoli of Justin's lungs oxygen in the alveolar air moves into the pulmonary blood and carbon dioxide leaves the blood and enters the alveolar air. In his muscles, oxyge...