Cardiovascular lecture

 

Slide Two  (Figure 14-1)

 

-Cardiovascular system is composed of the heart, the body¹s vasculature, and the components of blood (plasma, nutrients, hormones, RBC¹S, etc.)

- Arteries carry oxygenated blood away from the heart and towards the capillaries (site for gas exchange). Veins return deoxygenated blood back to the heart.

- The septum divides the heart into two portions, or ³right² and ³left². The atria receive blood and the ventricles send blood.

- The venae cavae (superior and inferior) returns blood to the right atrium à right ventricle à pulmonary artery à lungs à pulmonary veins à left atrium à left ventricle à aorta à arteries à arterioles à capillaries à venules à veins à venae cavae.

- The pulmonary circulation is from the ³end² of the right ventricle to the ³beginning² of the left atrium.

- The systemic circulation is from the ³end² of the left ventricle to the ³beginning² of the right atrium.

- Can you name the three portal systems? Š.One is in the hypothalamus (hypothalamic-hypophyseal portal system), liver (detoxification of foreign substances), and kidney (filtration).

 

Slide Three  (Figure 14-2)

 

- In the Cardiovascular system, blood flows because there is a pressure gradient formed (Δ P).

- High blood pressure is created in the heart. Pressure is gradually lost because friction acts between the fluid and inner-vessel walls.

- As seen in this picture, the highest mean pressure is found in the aorta. The lowest mean pressure is found in the venae cavae.

- Pressure is commonly measure in mm Hg.

 

Slide Four  (Figure 14-6)

 

- Fluid is not very compressible. Think of a water balloon. If you squeeze it, the pressure will increase.

- The contraction of the ventricles works in the same sort of way. The contracting muscle transfers its pressure to the fluid, which creates this pressure gradient. The pressure created from the ventricles is called the driving pressure.

- Flow rate is proportional to Δ P. P1 is measured at the beginning of the tube. P2 is measured at the end of the tube. P1 -  P2 = Δ P. Notice, the flow rate could be the same for different observed pressures, as long as the Δ P is the same for both cases.

- Flow rate is measure in cm^3/min.

- A narrow vessel will exhibit an increased velocity of flow when compared to a dilated vessel. While this may seem like common sense, mathematically it is proven by Š.     Velocity (cm/min) = Flow Rate (cm^3/min) / Cross-sectional area (cm^2).

 

Slide Five  (Figure 14-7 a & b)

 

- The heart is situated within the thoracic cavity, with the apex pointing down and towards the left of the body. The base lies behind the sternum.

- Notice that the heart lies on the ventral side of the body, between the lungs. The apex rests on the diaphragm.

- Figure ³a² shows the relative position of the atrioventricular and semilunar valves.

 

Slide Six  (Figure 14-7 c & d)

 

- Cardiac Physiologists refer to the heart¹s membrane as the pericardium. Pericardial fluid lubricates the external surface of the heart as it beats. A disease known as pericarditis results in an inflamed pericardium, which reduces pericardial fluid effectiveness. The result is that the heart rubs against the pericardium (Friction Rub).

- The heart mainly consists of myocardium (cardiac muscle).

 

Slide Seven  (Figure  14-7 e & f)

 

- The major blood vessels emerge from the top of the heart (aorta, pulmonary trunk, etc.).

- The aorta and pulmonary artery take blood away from the heart, while the venae cavae and pulmonary veins return blood to the heart.

- The coronary arteries and coronary veins serve as the vasculature for the heart. These are found in three distinct grooves that run across the ventricles.

- Table 14-3 shows where oxygenated blood is found. It also shows how blood is transferred throughout the heart.

 

Slide Eight  (Figure 14-7 g & h)

 

- The heart insures a one-way flow of blood because of valves. The valves, while different in structure, prevent the backward flow of blood.

- The passageway between the atrium and the ventricles are guarded by the atrioventricular valves. These valves are connected to collagenous cords called the chordae tendineae. The ends of the chordae tendinae are connected to ventricular muscle. The muscles are referred to as papillary muscles.

- When the ventricle contracts, the blood pushes the valves closed. It does not going into the atrium because it is tethered by the tendons.

- [Note that the AV valves are different.] The right atrium and right ventricle are separated by the tricuspid valve (three flaps), while the left atrium and the left ventricle are separated by the bicuspid valve (two flaps; also known as the mitral valve). *This can be easily remembered because the right lung has three lobes, while the left lung has two lobes.*

- The other set of valves are found at the opening of the ventricles to the arteries. These prevent pumped blood from returning to the heart. These are called the semilunar valve. Their definitive names are based upon the artery that they serve. They are the aortic valve and the pulmonary valve.

- Their 3-leaf/cup structure fill with blood and snap shut when pressure is exerted on them.

 

Slide Nine  (Figure 14-9)

 

- This slide is nothing new based on the last slide. It just shows cross-sectioned portions of the heart. Note the structures in part d.

- During ventricular contraction, the AV valves are closed to prevent backflow into the atrium. The semilunar valves are open.

- During ventricular relaxation, the semilunar valves are closed to prevent backflow from the arteries. The AV valves are open.

 

Slide Ten  (Figure 14-10)

 

- Part a shows the spiral arrangement of cardiac muscle. During ventricular contraction, the blood is expelled upward from the apex.  

- Heart muscle, while similar to skeletal muscle in some ways, differs in others. One difference is the presence of intercalated disks. The intercalated disks allow force to be transferred from one cell to another because of desmosome presence. Gap junctions are also found within the intercalated disks. This allows for the waves of depolarization to be rapidly spread throughout the heart. This induces a simultaneous contraction between the cells.

- Autorhythmic cells initiate the signal (Katie will expand on this).

 

Slide Eleven  (Figure  14-11)

 

- Signal is initiated in the pacemaker cells (autorhythmic cells).The action potential flows down the t-tubule, where voltage-gated Ca++ channels open. Ca++ enters the cell from and opens the ryanodine receptor-channel.

- Ca++ flows out of the sarcoplasmic reticulum (Calcium-induced Calcium release). Note that this different from muscle cells, where the action potential altered the conformation of the DHP receptor. The DHP receptor then opened the ryanodine receptor, which resulted in Ca++ release.

- Calcium is released into the cytosol, which creates calcium ³sparks² (visual representation from biochemical studies). Many sparks induce a summation of signal.

- Calcium binds to troponin and the contraction is initiated.

- Relaxation occurs when calcium is released from troponin.

- Calcium is transported back into the SR by the Ca++-ATPase. Also, a Na+-Ca++ antiport protein regulates the sodium gradient. Calcium is moved against it¹s electrochemical gradient, while sodium moves down it¹s electrochemical gradient.

 

Slide Twelve  (Figure 14-30)

 

- Epinephrine (from adrenal medulla) and norepinephrine (from sympathetic neurons) bind to Beta adrenergic receptors on the cardiac muscle cells.

- These catecholamines regulate the force of contraction by controlling Ca++ levels.

- Through phosphorylation of the voltage-gated calcium channels, they induce a greater chance for opening, which will increase calcium release.

- Phosphorylation of phospholamban enhances the actions of the Ca++ ATPase, which decreases Ca++ availability in the cytosol. Therefore, a shorter duration of contraction is achieved. This also creates more Ca++ in the SR, which will allow for more forceful contraction.

 

Slide Thirteen  (Figure 14-13) -90 mV à +20 mV

 

- Notice the lengthening of contraction, which is from Ca++ entry. This results in a plateau.

- This helps to avoid tetanus because the action potential is approx. 200 msec. The skeletal muscle action potential is approx. 1-5 msec.

- This is important because the heart must relax to refill with blood.

 

Slide Fourteen  (Figure  14-14)

 

- The skeletal muscle action potential length can result in tetanus (summation of contractions). 

- In cardiac muscle, the refractory period and contraction end simultaneously. This allows the cell to completely relax between contractions. Therefore, tetanus cannot be achieved in cardiac muscle.

 

14-15

Autorhythmic Cells-Generate action potentials spontaneously in the absence of input from the nervous system. They have an unstable membrane potential that starts at -60mv and slowly drifts up to the threshold, and an action potential happens.  Because the membrane potential of this particular cell type never rests, it is called the pacemaker potential.

 

14-16

The speed at which the pacemaker cell depolarizes, sets the rate at which the heart contracts.  However the pacemaker cells can also be controlled by the nervous system.  The sympathetic nervous system can speed up the heart rate, (a), and the parasympathetic nervous system can slow down the heart rate (b).

 

14-17

Electrical communication begins with an action potential originating from the autorhythmic cells and depolarization works it way rapidly through gap junctions and intercalculated disks.  Depolarization is followed by a wave of contraction that starts in the artia, and moves towards the ventricles.

 

14-18

The SA, or sinoartial node, a set of autorhythmic cells in the right atria, is the start of deplorazation of the heart muscle.  The SA node serves as the main pacemaker for the heart. This depolarization wave spreads quickly though a conducting system of non-contractile fibers called the internodal pathway.  This pathway connects the SA node to the to the atrioventricular node (AV node).  The AV node is a set of autorythmic cells found near the bottom of the right atrium.  From the AV node, the depolarization moves down the atrioventricular bundle (AV bundle), located in the septum between the ventricles. The signal continues into the bundle branches which are divided into the left and right ventricles and then moves into the Purkinje fibers which transmit electrical signals quickly amongst the contractile cells.

 

The reason why the AV node exists and the depolarization doesn¹t just drop straight down through the ventricles is because ventricles must contract bottom to top.  That way blood can be pumped out of them.  Also the AV node delays the action potentials slightly, so that the atria can completely finish contracting by the time that the ventricle starts. This is called the AV node delay.

 

14-19

Einthoven¹s Triangle

An electrocardiogram, or ECG is a recording of the electrical activity of the heart make from electrodes placed on the surface of the skin.  Simply by placing the electrodes on the surface of the skin, we can find out what the heart is doing.  This is because we are basically filled with NaCl and that electrolyte transfers electricity well.  The Einthoven¹s triangle set up is used to measure cardiac events. The leads consist of one positive lead, one negative lead and one ground lead. They are placed on your right arm, left arm and left leg. 

 

Slide based on lab

This shows the different possibilities of leads.  The one that is stared is the one that will produce what is typically seen as an ECG.  The others will give an ECG, just perhaps not the way you are used to. (either upside down or something else). 

 

 

14-20

An ECG shows the sum of the electrical potentials generated by all the cells of the heart at any moment.  Each part of the ECG means something.  The P wave corresponds to the depolarization of the atrium.  The QRS complex corresponds to the progressive way of ventricular depolarization through the heart.  The T wave shows repolarization of the ventricles.  Atrial repolarization is not seen because the atrium repolarizes while the ventricle is depolarizing and is incorporated into the QRS complex. As far as contraction goes, in the latter part of the P segment and in the PR interval the atria contract, and then during the QT interval the ventricles contract.

 

14-21. 

A good description of the cardiac events.  Purple-depolarization. Red-Repolarization.

 

14-22

Just a reminder to not get confused.  An ECG shows the depolarization and repolarization of all the cells.  This graph is a ventricular action potential that is recorded intracellularly on a per cell basis.   Notice that the voltage change is much greater when measuring directly into the cell than from the body surface.

 

14-24

This figure shows a cardiac cycle.  Each cycle has two phases.  One is diastole, where the muscle is relaxed, and systole, where the muscle is contracting.  Because systole and diastole happen at different times for the atria versus the ventricles, they are shown separately. 

1. Beginning with Late diastole, both sets of chambers are relaxed, and passively fill. Ie blood is flowing by gravity from the veins (pulmonary or venae cavae)

2.Then the atria contract and put the remaining blood that was in them into the ventricles. A small amount of blood is pushed back into the veins because there are no one way valves located there.

3. When the depolarization waves hit the apex of the heart, the ventricle begins to contract. Blood is squeezed upwards from the apex towards the base. Blood flow moving upwards shuts the atrial ventricular valves (The mitral and the tricuspid valve).  This produces the first heart sound.  With the semilunar valves closed and the AV valves closed the blood cannot go anywhere. The ventricles continue to contract and this is called, isovolumic ventricular contraction.  At the same time, the atria are relaxing. When atrial pressure is lower than the venous pressure, blood will start flowing back into the atria from the veins.

4. Eventually the ventricles exert enough pressure to open the semilunar valves and push the blood into the arteries.

5. Then the ventricle relaxes.  As the ventricle begins to repolarize and relax, the pressure inside it drops below the pressure in the arteries and blood starts to flow backwards into the heart. The back flow forces the semilunar valves shut and that which is the second heart sound.  Once the semilunar valves close, the ventricles are again sealed.  This is isovolumetric ventricular relaxation.

 

14-26

This figure is a good demonstration of what is happening at each stage in the heart cycle.  It shows the pressures during the cardiac cycle and also maps out the ECG tracing so that you can see how it works.

 

Cardiac Output

Cardiac output is defined as the volume of blood pumped per ventricle per unit of time.  Stroke Volume is the amount of blood pumped by one ventricle during a contraction.

 

14-27

This is describing how the nervous system can control the heart. The basic gist of this is to describe that when the sympathetic nervous system takes over, the heart rate increases, (you know fight or flight idea?) and when you are resting or not in need of a high heart rate, the parasympathetic nervous system takes over.

 

14-31

Cardiac output

 

15-4

Our arteries have something called elastic recoil.  In this figure it is shown that as the ventricle contracts, blood is pushed into the arteries and the arteries must locally expand to take in the blood.  As the valves shut, the elastic recoil of the arteries send blood into the rest of the body, down its pressure gradient.

 

15-5

A graph to review pressure gradients. As you can see the main trend is that the pressure always decreases as it goes down through the veins.  However, there is a varying pressure even in your arteries from systolic pressure to diastolic pressure.  This is how blood pressure is found.  By measuring the systolic and diastolic pressure in your arteries.

 

15-7

So to measure blood pressure you put a blood pressure cuff around your arm, and put a stethoscope on the brachial artery near the bottom of the cuff.  Then you pump the pressure high enough so that no blood can get through. (130-140ish).  Then you slowly let the air out and listen through the stethoscope for the first SWISH of blood.  The swishes are called Korotkoff sounds which are created by pustiles of blood being compressed through by your arteries.  So you remember the number (the systolic pressure) at which you can hear the first sound and then you listen until the sound goes away.  When the artery is silent, that means that it is not compressed.  As soon as you cannot hear the sounds anymore, you record that pressure reading (diastolic pressure).  So for example I could end up with a systolic pressure of 120 and a diastolic pressure of 80, which would be said as 120/80.

 

15-22

This diagram shows how blood pressure is controlled by your body in a negative feed back pathway.  So first your blood pressure is high. This is sensed by the baroreceptors in the carotiod arteries and aorta.  This tells the sensory neurons and is reported to the cardiovascular control center in the medulla oblongata.  It then tells the nervous system to decrease its sympathetic output and increase its parasympathetic output.  Pretty much the most important things are that it then decreases resistance in the arterial system and decreases cardiac output. Both of these things contribute to a lower blood pressure. a

 

MAP

Mean arterial blood pressure

MAP=Diastolic P+ (Systolic P-Diastolic P)(1/3)

 

Questions from 2005 relating to heart material

 

 

What is the correct order of circulation in the body?

a.) Right atrium Right Ventricle Pulmonary Vein Lungs Pulmonary Artery Left Atrium Left Ventricle Aorta Arteries Arterioles Capillaries Venules Veins Venae Cavae

b.) Right atrium Right Ventricle Pulmonary Artery Lungs Pulmonary Vein Left Atrium Left Ventricle Aorta Arterioles Arteries Capillaries Veins Veinules Venae Cavae

c.) Right atrium Right Ventricle Pulmonary Artery Lungs Pulmonary Vein Left Atrium Left Ventricle Aorta Arteries Arterioles Capillaries Venules Veins Venae Cavae

d.) Right Ventricle Right Atrium Pulmonary Artery Lungs Pulmonary Vein Left Ventricle Left Atrium Aorta Arteries Arterioles Capillaries Venules Veins Venae Cavae

 

Name two of the three portal systems in the body.

Kidney, Liver, and Hypothalamic-Hypophyseal Portal System

 

 

Using no more than one sentence, explain why pressure is lost in the systemic circulation.

Friction

 

_Driving Pressure_ is the pressure created in the ventricles.

 

 

If the flow rate is measured as 8 cm^3/min and the cross-sectional area is measured to be 3 cm^2, calculate the velocity.

8/3=2.667 cm per minute

 

The membrane of the heart is called the _pericardium_, while the muscle of the heart is referred to as the _myocardium_.

 

 

The valve found between the left atrium and the left ventricle is the:

a.) Triscuspid valve

b.) Pulmonary valve

c.) Mitral (biscuspid) valve

d.) Aortic valve

 

The atrioventricular valves are connected to collagenous cords that help to "tether" and keep them from going into the atria. Name these cords.

Chordae Tendineae

 

 

During ventricular contraction, the AV valves are open/closed and the semilunar valves are open/closed.

Closed;Open

 

 

The _intercalated disks_ contain gap junctions and desmosomes that allow waves of depolarization and force to be transferred from cell-to-cell, respectively.

 

 

Name the specific mechanism that allows calcium to be released in cardiac muscle cells.

Calcium-Induced Calcium Release

 

The intracellular calcium levels are regulated by two proteins found within cardiac cells. Name one of the two proteins responsible for this regulation.

Ca++ ATPase or Na+/Ca++ Antiport Protein

 

Briefly explain why cardiac muscle cannot achieve tetanus. Specifically state what ion contributes to this particular type of contraction.

Refractory Period and Contraction End Simultaneously; Calcium is responsible for the action potential "plateau".

 

Name the fluid that lubricates the surface of the heart.

Pericardial Fluid

 

Name one of the two catecholamines responsible for controlling the force and duration of contraction.

Epinephrine or Norepinephrine

 

The area of the heart that rests on the diapragm is the _apex_.

 

A constricted vessel will exhibit an increase/decreased velocity of flow when compared to a dilated vessel.

Increased

 

Name the muscles that are connected to the collagenous cords within the heart. These muscles help to control the function of the AV valves.

Papillary Muscles

 

 

Which leads did you use to fill in electrical axis on the diagram?

 

I, III

 

What is the resting state of the autorythmic cells called?

Pacemaker Potential

 

 

When the sympathetic nervous system acts on the heart, what happens (specifically)?

Speeds up Heart Rate

 

 

What node is the main pacemaker for the heart?

SA Node

 

 

What mechanical function does the AV node allow?

The delay of ventricular contraction AND/OR Allows for correct contraction

 

 

What path does depolarization take from the AV node to the rest of the heart?

AV-Bundle-Branches-purkenje fibers

 

 

Which part of the ventricle contracts first?

Apex

 

 

What is the correct set of leads to get a correct looking ECG?

Left arm (+); Right arm (-); Left Leg (ground)

 

 

What does the Q wave stand for?

Going down bundle branches into Apex

 

 

In an ECG what does the QRS complex relate to? (hint there are two events)

The depolarization of the ventricle and repolarization of the artia

 

 

During which interval in the ECG do the ventricles contract?

Q-T

 

 

How many valves are in the heart?

4

 

 

What mechanism makes valves close?

Fluid flowing back

 

 

What is isovolumetric contraction?

When the ventricle contracts but nothing goes in or out

 

 

What makes the first sound of the heart beating?

The mitral valves snapping shut

 

 

How many leaflets does the mitral valve have?

2

 

 

How many leaflets does the aortic valve have?

3

 

 

When does the ventricle have the least amount of blood in it?

During isovolumic relaxation

 

 

Why doesn't blood from the veins continuously pour into the atria during the heart cycle?

The pressurein the atria is greater than the pressure in the veins and pressure only flows down its gradient.

 

 

What is systole?

Contraction

 

 

A person has an end-diastolic volume of 98 mL, an end-systolic volume of 40 mL and A heart rate of 60 bpm. What is their cardiac out put?

(98-40)x60=3480 ml/m

 

 

Is the strength of an ECG signal greater to, less than or equal to that measured directly in a myocardial cell?

Less than

 

 

What property do arteries have which allows them to send blood forward into the circulatory system?

Elastic recoil

 

 

Blood always flows __down________ its pressure gradient.

 

When measuring blood pressure, what are the noises you hear? What is their specific name?

The pushing of blood through the arteries, turbulent flow, pustules ect

Korotkoff noises

 

 

 

Which artery in your arm do you put the stethoscope on while taking blood pressure?

Brachial

 

 

A person has a diastolic pressure of 130 mm Hg and a systolic pressure of 85 mm Hg. What is their MAP?

85+(130-85)(1/3)=100mm Hg

 

 

Where in the body is blood pressure sensed?

Baroreceptors in the carotid arteries and aorta

 

 

In lab, what happened to your pulse in your thumb when you lowered your hand to the ground?

It got bigger

 

 

Acknowledgements to Katie Richards and Chris Hawkins, Fall 2005 TAs, who initially put this lecture together.