Block 5: The Circulatory System

Question 1

List the major functions of the Cardiovascular System.

Answer 1

The major function of the Cardiovascular System is transportation - take in materials, move them throughout the body, and remove the waste.

Materials taken in are O2, nutrients, and water. Materials moved throughout the body are immune cells, hormones, nutrients, and waste. Materials removed are waste, heat, and CO2.

Question 2

Describe the location and the important anatomical features of the heart.

Answer 2

The heart is mostly on the left side of the sternum.

The heart is found in the thoracic cavity within the mediastinum (between the lungs)/pericardial cavity.

The base of the heart (widest part of the heart) is on the superior side and the apex (peak of the heart) is on the inferior side, connected to the diaphragm by fibrous tissue.

Question 3

Describe the layers around the heart.

Answer 3

The pericardium is the protective layer around the heart, and is its own structure. The layers of the pericardium superficial to deep are the fibrous layer (DCT & collagen rich), the parietal pericardium, the pericardial cavity (contains fluid to prevent friction & allows the heart to expand), and the visceral pericardium/epicardium (included in the heart structure).

The wall of the heart also contains layers. From superficial to deep, we have the visceral pericardium/epicardium, myocardium (bulk of the heart with cardiac muscle tissue), and the endocardium (simple squamous & areolar CT to lubricate the chambers).

Question 4

Compare and contrast the two major circulatory systems in the human body.

Answer 4

The two major circulatory systems in the human body are the pulmonary circuit and the systemic circuit.

The pulmonary circuit exchanges gases in the lungs. Arteries carry O2 poor (CO2 rich) blood to the lungs and veins carry O2 rich (CO2 poor) blood back to the heart.

The systemic circuit provides blood to the body. Arteries carry O2 rich (CO2 poor) blood to the body and veins bring O2 poor (CO2 rich) blood back to the heart.

Question 5

Describe the basics of circulation in the heart.

Answer 5

The heart is a double pump, meaning blood has to go through the heart twice before it gets back to its starting point.

Circulation is continuous, unless there is a break within the circuit.

Question 6

Describe the anatomical positioning of the pathway through the pulmonary and systemic circuits.

Answer 6

O2 rich (CO2 poor) blood flows through the left side of the pulmonary and systemic circuits.

O2 poor (CO2 rich) blood flows through the right side of the pulmonary and systemic circuits.

Question 7

Identify the major chambers of the heart, how they receive their blood supply, and any major differences.

Answer 7

The heart contains 4 chambers - 2 atria and 2 ventricles. All four chambers receive blood from both major circuits.

The left and right atria receive blood from the veins.

The left and right ventricles receive blood from the arteries. A major difference between the two ventricles is that the left ventricle is more muscular than the right. This is because the left needs to generate way more force to push blood throughout the entire body versus the right only needs to reach the lungs.

Question 8

Identify the valves of the heart.

Answer 8

The heart has two types of valves: atrioventricular valves (AV) and semilunar valves (SV).

There are two AVs: left and right. The left AV separates the left atrium and left ventricle and has two cusps. The right AV separates the right atrium and the right ventricle and has three cusps.

There are two SVs: the pulmonary and aortic. The pulmonary SV separates the right ventricle and the pulmonary trunk, supplying blood to the pulmonary circuit. The aortic SV separates the left ventricle and aorta, supplying blood to the systemic circuit.

Question 9

Describe the supporting structures of heart valves.

Answer 9

Only AVs have supporting structures. The two supporting structures are Chordae tendineae and Papillary muscles.

Chordae tendineae are made up of DCT and act as a connection point between the ventricle wall and the valve. They are unable to change their own tension, but are able to prevent backflow.

Papillary muscles are made up CT and anchor the Chordae tendineae to regulate their tension. They only open in one direction due to pressure.

Question 10

Describe the functions of heart valves.

Answer 10

Heart valves function to only allow blood to flow in one direction. Blood always follows the pressure gradient.

AVs open for returning blood to enter ventricles. Once the pressure in the ventricles is greater than that of the atria, then ventricular contration occurs and AVs close to prevent backflow.

SVs open from ventricular contraction to allow blood to flow to the vessels. Once the pressure in the vessels is greater than that of the ventricle, the ventricle relaxes and SVs close to prevent backflow.

Question 11

Describe the pathway of blood flow.

Answer 11

In blood flow, there is no specific starting point because it is a continuous circulation.

O2 poor blood from the systemic circuit enters the heart through the SVC, IVC, and coronary sinus.

O2 poor blood enters the right atrium.

O2 poor blood goes through the right AV (tricuspid valve) and enters the right ventricle.

O2 poor blood goes through the pulmonary SV and enters the pulmonary trunk.

The pulmonary arteries bring O2 poor blood to the pulmonary circuit to be oxygenated.

O2 rich blood leaves the pulmonary circuit and enters the heart through the pulmonary veins.

O2 rich blood enters the left atrium from the pulmonary veins.

O2 rich blood goes through the left AV (mitral valve) and enters the left ventricle.

O2 rich blood goes through the aortic SV and enters the aorta.

O2 rich blood enters the systemic circuit through the aorta.

Question 12

Describe coronary circulation.

Answer 12

Coronary circulation ensures that heart tissue gets the blood it needs through the systemic circuit. There are left and right coronary arteries and veins involved in coronary circulation.

Arteries branch from the ascending aorta to supply blood to the heart and provide an alternative pathway for blood flow when blockages occur.

Veins provide most blood to the heart through the coronary sinus, but also provides the chambers with blood through small veins.

Question 13

Describe each component of coronary circulation.

Answer 13

Left Coronary Artery (LCA) supplies the SA node, left atrium, interventricular septum, and both ventricles. The circumflex branch of the LCA goes from the left atrium to the posterior side of the heart, splitting further into the left marginal branch. The anterior interventricular branch of the LCA continues inferiorly to the anterior side of both ventricles.

Right Coronary Artery (RCA) supplies the SA node, AV node, right atrium, interventricular septum, and both ventricles. The marginal branch of the RCA is on the anterior right ventricle. The posterior interventricular branch of the RCA continues inferiorly to the posterior side of both ventricles.

The veins bring blood from the anterior and posterior sides of the heart from the coronary sinus into the right atrium. The greater cardiac vein brings anterior blood to the coronary sinus and the middle cardiac vein/posterior interventricular vein brings posterior blood to the coronary sinus. The coronary sinus is responsible for bringing 90-95% of blood to the heart.

There are smaller veins that drain into the great and middle veins. Small veins are also responsible for bringing 5-10% of blood to the chambers.

Question 14

In patients with coronary artery disease, what is seen?

Answer 14

Patients with coronary artery disease have restricted circulation due to restricted blood and cell flow.

Question 15

List the structures associated with the cardiac conduction system.

Answer 15

Sinoatrial node (SA node)
Atrial myocardium
Atrioventricular node (AV node)
AV bundle (bundle of His)
Subendocardial conducting network (Purkinje fibers)
Ventricular myocardium

Question 16

Describe the sequence of excitation of the cardiac conduction system.

Answer 16

SA node fires via pacemaker cells.

Excitation spreads through atrial myocardium to reach left atrium.

Quick pause allows atria to fully depolarize before reaching the ventricles through the AV node.

AV node fires and excitation continues to spread down the AV bundle.

Excitation signal reaches Purkinje fibers and spreads through the ventricular myocardium.

Question 17

Describe the sequence of the cardiac muscle action potential.

Answer 17

Pacemaker action potentials open Na+ channels.

Fast depolarization of the membrane due to Na+ influx.

Na+ channels close, causing the peak of the action potential.

Ca2+ channels open, causing a delay between depolarization and repolarization.

Ca2+ channels close (Ca2+ in) and K+ channels open (K+ out) at the same time to prevent drastic changes in membrane potential, causing the plateau of the action potential.

Repolarization occurs.

Question 18

Describe the sequence of the SA node potential.

Answer 18

Slow influx of Na+ (due to chemical gradient from NaK pump) start slow depolarization.

Voltage-gated Ca2+ channels open and cause rapid depolarization.

K+ channels open to allow K+ ions to leave, causing repolarization.

Immediately repeated.

Question 19

Compare and contrast the cardiac muscle action potential and the SA node potential.

Answer 19

Cardiac muscle action potentials and SA node potentials have autorhythmic cells (pacemaker cells) that are not started by the nervous system.

Cardiac muscle action potentials and SA node potentials spread via gap junctions and fiber networks to allow the flow of ions.

Cardiac muscle action potentials use both the SA node and the AV node, while SA node potentials only use the SA node.

SA node potentials have an unstable membrane potential, while cardiac muscle action potentials have a stable membrane potential.

Both cardiac muscle action potentials and SA node potentials use Ca2+, but in a very different way.

Question 20

Identify and discuss each component of a normal ECG.

Answer 20

P wave (atrial depolarization): caused by action potential generated in the SA node

PQ segment (atrial depolarization complete): pause at AV node to allow mechanical atrial systole through AV bundle

QRS complex: atrial repolarization and ventricular depolarization

ST segment (ventricular depolarization complete): same as ventricular cardiomyocyte action potential plateau

T wave (ventricular repolarization): K+ leaves

TP segment (no electrical activity): period of rest and refilling

Question 21

The relationship between pressure and volume within the heart chambers is ______________ (direct/inverse).

Answer 21

Inverse

When there is more pressure in a chamber, blood moves through a valve to its next location, decreasing the volume in the original chamber.

Question 22

Describe the relationship between pressure and volume in the heart chambers during systole and diastole.

Answer 22

Atrial systole: pressure higher in atria, AV valves open, blood moves to ventricles

Atrial diastole: pressure lower in atria, AV valves close, blood in ventricles

Ventricular systole: pressure higher in ventricles, AV valves close & SL valves open, blood moves to arteries

Ventricular diastole: pressure lower in ventricles, SL valves close, blood in arteries

Question 23

Define cardiac output and know how to calculate, given values for heart rate and stroke volume.

Answer 23

Cardiac output is the blood output per minute.

CO = (stroke volume) x (heart rate)

Question 24

List the major determinants of stroke volume.

Answer 24

Stroke volume is the amount of blood pumped by one ventricle per one contraction.

The major determinants of stroke volume are end-systolic-volume, end-diastolic-volume (preload), contractility, and venous return.

The autonomic nervous system also plays a role in both heart rate and cardiac output, causing it to then also play a role in determining stroke volume.

Question 25

Describe Preload and how it relates to stroke volume.

Answer 25

Preload is the degree to which sarcomeres stretch in cardiac muscle cells.

When the sarcomeres stretch, they reach optimal length to generate maximal force. Individual cardiac muscle cells do not stretch much, but because the enter chamber is made up of them there is a large difference between relaxed and stretched cardiac muscle cells in terms of stroke volume.

Venous return is the biggest influence for preload. The amount of blood brought back from the circuits directly determines stretch, which, therefore, determines the amount of blood ejected by the ventricles. If venous return is high, stretch will increase, allowing blood ejected to increase both in amount and rate.

Question 26

Describe Contractility and how it relates to stroke volume.

Answer 26

Contractility is how hard sarcomeres can contract given a certain length. Contractility and preload can occur at the same time but are NOT the same thing.

Contractility is related to calcium levels in cardiac muscle. Higher calcium allows for stronger contractions and thus higher volumes of ejected blood.

To increase contractility via the addition of calcium, we can have sympathetic stimulation, increased levels of hormones from adrenal glands, increased levels of glucagon, and high calcium levels in the ECF.

To decrease contractility via the removal of calcium, we can have low pH levels that cause CO to drop, high potassium levels in the ECF, and calcium channel blockers, which can also be used to drop CO and blood pressure.

Question 27

Describe Afterload and how it relates to stroke volume.

Answer 27

Afterload is the pressure that is needed to be overcome in order to eject blood from the ventricles into the circuits. This is essentially when the pressure in the aorta or pulmonary trunk is higher than that of the ventricles, causing the ventricles to work harder to eject blood.

Typically, this is not an issue for younger individuals. Afterload can also cause hypertension, which is the reduction of the ability for ventricles to eject blood, or ESV.

Question 28

Describe factors that can affect cardiac output.

Answer 28

Abnormal levels of ions are the main factor to affect cardiac output.

Hypocalcemia: decreased calcium levels decreases contractility
Hypercalcemia: increased calcium levels causes spastic contractions of the chambers
Hypernatremia: increased sodium levels inhibit calcium transport, which inhibits contraction
Hyperkalemia: increased potassium levels cause heart blockages and cardiac arrest

Question 29

Define and state the normal values of ESV and EDV.

Answer 29

ESV: end-systolic-volume is the volume in the ventricles after contraction. It usually sits around 60mL and has the smallest volume of blood.

EDV: end-diastolic-volume is the volume in the ventricle after relaxation. It usually sits around 130mL and has the most volume of blood, as ventricular filling is occurring.

Question 30

Define the Frank-Starling mechanism.

Answer 30

The Frank-Starling mechanism is the hearts ability to change the force of contraction, causing a change in SV, in response to venous return.

As venous return increases, SV and velocity of contraction also increase.

Question 31

How can you measure heart rate from an ECG?

Answer 31

First, find two consecutive R waves and count the number of large squares between them. Divide the number of squares by 300 and you will get the individuals heart rate.

Question 32

Define systole, diastole, and contractility.

Answer 32

Systole: ventricular contraction
Diastole: ventricular relaxation
Contractility: the ability for cardiac muscle to contract

Question 33

Compare and contrast the two branches of the autonomic nervous system.

Answer 33

The autonomic nervous system splits into two branches: the sympathetic division and the parasympathetic division.

Sympathetic division:
- dominates in stressful situations
- ganglia originate in the thoracic and lumbar regions of the spinal cord and run down the sides of the vertebral column

Parasympathetic division:
- dominates in calm situations
- ganglia originate in the hypothalamus, brainstem, and sacral region of the spinal cord and run directly on or near target organs
- VAGUS NERVE!!
- dominant for normal control, allowing any blockages to increase heart rate.

The autonomic nervous system is regulated by constantly altering the amount of dominant control given to one branch. Additionally, the branches typically have opposite effects. For example, the sympathetic nervous system may open airways while the parasympathetic may constrict airways.

Question 34

Explain autonomic regulation and its affects on heart rate.

Answer 34

Autonomic regulation is the cardiac center in the medulla that controls ANS affect on heart rate.

The parasympathetic nervous system is influenced by cardioinhibitory centers to slow heart rate, targeting the SA and AV node via the vagus nerve.

The sympathetic nervous system is influenced by cardioacceleratory centers to increase heart rate, targeting the SA and AV nodes, but also muscles and coronary arteries.

Question 35

Discuss how the parasympathetic division of the autonomic nervous system affects heart rate.

Answer 35

When the parasympathetic division is stimulated, heart rate decreases.

K+ permeability increases which drops the membrane potential to cause depolarization.

The depolarization causes pacemaker cell membranes to hyperpolarize and delay the opening of voltage-gated calcium channels.

The delay causes heart rate to decrease due to decreased signals sent through gap junctions.

Question 36

Discuss how the sympathetic division of the autonomic nervous system affects heart rate.

Answer 36

When the sympathetic division is stimulated, heart rate increases.

Na+ permeability increases which increases the rate of depolarization.

Rapid depolarization allows pacemaker cells to reach their threshold more frequently.

This causes heart rate to increase due to more cardiac cycles in less time.

Question 37

What are two SIMPLE ways to increase heart rate using the parasympathetic and sympathetic divisions?

Answer 37

1. Block the parasympathetic division to increase heart rate up to 100bpm.
2. Increase sympathetic division output to increase heart rate anywhere above 100bpm.

Question 38

List other influences of heart rate, besides ANS stimulations.

Answer 38

Age: heart rate declines over time
Gender: females have faster heart rates than males
Exercise: increases heart rate, but decreases long-term
Temperature: higher temps. increase heart rate