Module 1:Cardiac Anatomy & Physiology

Question 1

Right atrium receives blood from 3 veins

Answer 1

Inferior Vena cava, superior vena cava & coronary sinus

Question 2

Type of blood in right-sided chambers

Answer 2

Deoxygenated or venous blood

Question 3

How does venous blood travel in right-sided cardiac chamber?

Answer 3

Pumped into the pulmonary trunk from the RV > pulmonary arteries to the lungs > oxygenated > releases CO2

Question 4

Type of blood in left-sided cardiac chambers

Answer 4

Oxygenated (arterial) blood to the body

Question 5

How does blood travel in left-sided cardiac chamber?

Answer 5

LA receives blood from the lungs via the pulmonary veins > LV pumps oxygenated blood to body tissues via the aorta

Question 6

3 layers of tissue in heart wall (outer to inner)

Answer 6

Epicardium, Myocardium and Endocardium

Question 7

Characteristics of Epicardium

Answer 7

Thin, fibrous external surface where the coronary arteries lie

Question 8

Characteristics of Myocardium

Answer 8

Thick, middle layer with involuntary cardiac muscle cells that contract to propel blood

Question 9

Heart valves open and close in response to ?

Answer 9

Pressure changes as the heart contracts and relaxes. This action ensures the unidirectional flow of blood through the heart into the appropriate vessels.

Question 10

2 types of valves

Answer 10

• Atrioventricular Valves (Mitral & Tricuspid valves)

- Semilunar Valves (Pulmonary & Aortic valves

Question 11

Cusps for Tricuspid valve

Answer 11

Anterior, Posterior and Septal cusp

Question 12

Cusps for Mitral valve

Answer 12

Posterior and a large anterior cusp

Question 13

Mitral valve and tricuspid valve are composed of ?

Answer 13

Atrioventricular leaflets, chordae tendineae (chord-ee tend-in-ee) and papillary muscles

Question 14

What are atrioventricular leaflets/cusps?

Answer 14

Triangular flaps of endocardium that emerge from a thin ring of connective tissue (valve annulus)

Question 15

Chordae tendineae?

Answer 15

Free end of each cusp is attached to it.
Delicate cords of fibrous tissue
It is attached to small, cone-shaped, papillary muscles > these muscles are attached at their base to the ventricular wall and maintain tension on the chordae tendineae when the ventricle contracts.

Question 16

Location of the semilunar valves?

Answer 16

Aortic valve is btw left ventricle and the aorta. Pulmonary valve is btw the RV and the pulmonary artery.

Question 17

Cardiac Circulatory system includes the

Answer 17

heart + body’s vascular system

Question 18

Vascular system?

Answer 18

Closed network of arteries and veins (vasculature) transports blood throughout the body. Made up of systemic circuit (body circulation system) + pulmonary circuit (lung circulation system). Blood supplies the body with oxygen, nutrients, and other vital substances and absorbs metabolic products and CO2 for disposal.

Question 19

Circulatory system phases?

Answer 19

1. Systemic Circulation (Portion of the cardiovascular system that carries oxygenated blood away from the heart > to body and returns oxygen-depleted blood back to the heart.
2. Pulmonary Circulation (Movement of blood from the heart > lungs > heart
3. Coronary Circulation (Provides heart with the blood that carries the O2 and nutrients it needs to sustain cardiac tissues)

Question 20

Circulatory System Blood Vessels?

Answer 20

1. Arteries- It carries blood away from the heart, and carry O2 rich blood to the systemic circulation and O2 depleted blood away the heart to the lungs (Pulmonary system)
2. Veins- Carries O2 depleted blood back to the heart from the body and brain. In pulmonary system, the O2-rich blood returns via the 4 pulmonary veins.
3. Capillaries- Smallest of the body’s blood vessels, interact most closely with the body’s tissues. Water, O2 and lipids pass from the capillaries (diffusion). The capillaries also collect waste products (CO2 + Urea) from tissues and pass them into the circulatory system.

Question 21

Purpose of the Circulatory System Blood Vessels?

Answer 21

Arteries carry blood away from the heart.
Veins carry blood to the heart.
Capillaries transport blood from arteries to veins

Question 22

Normal blood flow pathway

Answer 22

Blood from 3 veins (inferior vena cava, superior vena cava & coronary sinus) > RA > RV > Pulmonary trunk > Pulmonary arteries > lungs, becomes oxygenated > pulmonary veins > LA > LV > Aorta > body

Venous blood pressure is relatively low, therefore, the right atrial wall is only 2 mm thick. Like the right atrium, the right ventricle pumps low pressure venous blood, and so has a relatively thin outer wall of 4 to 5 millimeters. The pressure of blood returning from the lungs is low; therefore, the left atrial wall is only 3 mm thick. The left ventricle must pump oxygenated blood through the systemic circuit, which has a higher resistance to blood flow than the pulmonary circuit.

To manage this resistance, the left ventricular wall is relatively thick—12 to 15 millimeters.

Question 23

Cardiac Hemodynamics?

Answer 23

Forces driving the circulation of blood through the body.

The heart adapts its hemodynamic performance to the body’s changing need for oxygen and nutrients, as well as to the cardiovascular changes that occur in aging and disease.

Question 24

Cardiac Cycle

Answer 24

Occurs between the beginning of one heart beat and the beginning of the next. Blood only flows from areas of higher pressure to areas of lower pressure.

Each chamber of the heart has a systole and diastole:

Systole > state of the heart in contraction during which blood is pumped out of a chamber.
Diastole > state of the heart during active relaxation.

Question 25

Cardiac Output

Answer 25

= Volume of blood pumped by heart in 1 min
= HR (no. of heart beats per min) x Stroke volume (Amount of blood ejected from the LV during a heartbeat (L))

Normal cardiac output in adult @ rest = 4-6 L per min

Question 26

Factors that affect Stroke Volume

Answer 26

• Preload (STRETCH)
  Amount of stretch on the ventricle at the end of diastole. Amount of tension in the ventricle just before ventricle contraction. The stretching of the ventricle occurs from the total amount of blood that enters or fills the ventricle. The more blood that enters the ventricle, the greater this stretch, or preload, will be.
  Franklin-Stirling law of heart = Direct relationship between preload and stroke volume – the amount of blood ejected from the heart in a single contraction. The greater the volume of blood that fills the ventricle during diastole, the more the myocardium is stretched, and the greater the preload.
• Afterload (RESISTANCE)
  Pressure in the systemic arteries is relatively high to enable blood circulation throughout the body. The left ventricle works against this arterial pressure when ejecting blood into the systemic circuit.
  Afterload can be thought of as the force that resists this ejection of blood. That means that an increase in afterload corresponds to a decrease in stroke volume.
• Contractility (FORCE)
  Ability of the myocardium to contract and relax. An increase in contractility leads to an increase in stroke volume independently of preload and afterload.
  Contractility is controlled by the forces generated by myofibrils—the strings of protein within the cardiac muscle that contract when stimulated.
  Efficient relaxation of these muscle fibers results in a longer diastolic filling time and less resistance to filling.

The contractile state of the myocardium is expressed clinically as the ejection fraction, which is the ratio of stroke volume to end-diastolic volume.

Each ventricle normally ejects about 65% of its volume per stroke, although this amount varies with changes in metabolic need.

Question 27

Contraction Sequence

Answer 27

1. Ventricular systole
2. Ventricular diastole

In order to create sufficient cardiac output, the atria on top is electrically activated first, which will produce atrial mechanical contractions.

Next, the ventricles experience the electrical activation, resulting in a mechanical contraction that causes systole, a phase of contraction that drives blood flow out of the heart.

Question 28

Depolarisation

Answer 28

Occurs when electrically charged ions travel in and out of cardiac cells. State of contraction.

Question 29

Repolarisation

Answer 29

Cardiac cells in a state of relaxation.

Question 30

Automaticity

Answer 30

Ability of cardiac cells to contract/ depolarise spontaneously without external influence.

Question 31

Action potential

Answer 31

Describes specifically how the energy within each cell is generated and used > heart contraction

Question 32

Action potential of a cardiac cell

Answer 32

• 5 phases ( 0-4)

Phase 0: Rapid upstroke Depolarisation/contraction phase
Phase 1: Early rapid depolarisation
Phase 2: Plateau phase
Phase 3: Repolarisation
Phase 4: Resting phase

Question 33

Effective refractory period

Answer 33

During a cardiac cycle, once an action potential has begun there is a period of time in which a new action potential cannot be initiated.

Occurs in Phases 0, 1, 2, and early Phase 3.

During the ERP, depolarization cannot be initiated no matter how strong the impulse, because it follows the initial depolarization too closely. No matter how much the cell is stimulated during these phases, it will not depolarize.

Think of flushing a toilet. Right after you flush a toilet and the water goes down, if you attempt to flush again too soon, the toilet won’t flush because there is not enough water in the tank. This is analogous to the Effective Refractory Period.

Without the limits ERP places on depolarization, the heart would beat so rapidly it would be unable to fill and eject blood efficiently.

Question 34

Relative refractory period

Answer 34

Period following the effective or Absolute Refractory Period, during which a cardiac cell can be stimulated to depolarize, but only by a stimulus or impulse that is stronger than what is normally required for depolarization.

Again, think of the toilet analogy. If you wait a bit after flushing, there will be enough water in the tank to flush again, even though the toilet may only be half way through the filling process after the last flush. This is analogous to the Relative Refractory Period. The impulse occurring during RRP is responding to high intensity stimuli, and so typically conducts more slowly than normal, and with aberrancy.

This is very important to know, because we don’t want to pace or stimulate the heart during this vulnerable period, potentially causing arrhythmias. Serious, life-threatening rhythm disorders can arise if a depolarization occurs within certain areas of the RRP.

Question 35

Automaticity of cardiac cells

Answer 35

The cardiac cells that polarize the fastest will drive the heart rate. The SA node is the fastest. The faster rate of the SA node activates the depolarization mechanism in other cells. Consequently, the impulse formation abilities of other cells are suppressed and not used.

If the SA node fails to fire, the AV node generally takes the lead, beating at a rate of 40 to 60 beats per minute.

If the AV node also fails to fire, the ventricular cells then have the ability to take over the rhythm, beating at a much slower rate of 20 to 40 beats per minute. This is often referred to as the “escape rhythm.”

Question 36

Automaticity of SA node

Answer 36

This group of cardiac cells sets the pace or rate, the heart will beat by sending out depolarization waves throughout the heart.

When a heart cell depolarizes, all heart cells around it follow and depolarize as well, like a chain of dominos falling after the first domino falls.

Other cardiac cells with slower intrinsic automaticity never have a chance to depolarize on their own because this depolarization wave causes the subsequent cells to contract before the cells’ intrinsic rate kicks in. They were, in effect, “suppressed” or prevented from depolarizing on their own.

cardiac cells are intimately connected to their neighbors, and when a cardiac cell depolarizes in the heart it creates an action potential. That action potential imposes a depolarization of its neighboring cells, causing a domino effect, or wavefront of depolarization.

Question 37

Electrical Impulses that use normal conduction system

Answer 37

• Fast pathway resulting in rapid depolarization

The conduction system is a system of specialized cardiac tissue that controls the heart’s activity.

It controls the speed and rhythm of heart contractions using:

Automaticity, the ability of conduction fibers to spontaneously depolarize,
Conductivity, the ability of cardiac cells to rapidly conduct the electrical impulse.

This electrical control system ensures that the heart keeps pumping, and it adjusts its pumping rate to meet the body’s needs during different activities, for example, sleeping, or intense physical effort.

Question 38

Electrical Impulses that originate outside of the normal conduction system

Answer 38

Cell-to-cell pathway- slow route

Question 39

SA node

Answer 39

Is located in the upper right atrium
Is known as the heart’s natural pacemaker, and
Produces resting rates between 60 to 100 beats per minute

SA node’s rate of automaticity is normally faster than other parts of the heart, and dictates the rate at which the heart beats = “sinus rate.”

The SA Node is a cluster of cells that generates electrical impulses on its own at a rate needed to pump sufficient blood to the body. An electrical impulse proceeds outward from the SA node > a depolarization wave and atrial contraction.

Once a cardiac cell depolarizes, the electrical change in potential causes the cells around it to depolarize, causing a chain-like effect, and all cardiac cells in the atria will then depolarize.

Question 40

Atrioventricular node (AV)

Answer 40

Located between the atrium and the ventricles in the interatrial septum close to the tricuspid valve.

The AV node receives the impulse from the SA node.

Conduction is slow, allowing enough fill time for the ventricles prior to ventricular contraction. If the SA node fails to deliver an impulse to the AV node, the AV junctional tissue will deliver an impulse to the bundle of His at rates between 40 to 60 beats per minute.

Question 41

Bundle of His

Answer 41

Begins conduction to ventricles

AV junctional tissue 40-60 bpm

Question 42

The Purkinje Network

Answer 42

The bundle branches + the Purkinje fibers (interlacing fibres of modified cardiac muscle)

The Purkinje Network distributes the electrical impulse to the cardiac muscle, allowing for depolarization, or contraction, of the ventricle.

It can deliver impulses at rates between 20 to 40 beats per minute; this is known as an “escape” rhythm.

There are two bundle branches—right and left. The left bundle further divides into two fascicles—Anterior and Posterior—probably because of the greater muscle mass of the left ventricle.

Question 43

Conduction system in action

Answer 43

• Impulse Formation at the SA Node
• Depolarization of the Left and Right Atrium
• Delay at the AV Node
  The AV node slows impulse conduction, which allows time for the AV valves to open, and the ventricles to passively fill with blood.

The slowing of the impulse also provides time near the end of ventricular filling for the atria to contract, so blood can actively be pumped from the atria to the ventricles to complete ventricular filling. This portion of ventricular filling is called the “atrial kick” and accounts for 30% of ventricular filling.

Complete ventricular filling is very important in providing the appropriate cardiac output for the patient.

• Conduction at The Bundle Branches
• Conduction Through the Purkinje Fibers
• The Mechanical Contraction of the Ventricle, or Systole
• The Mechanical Relaxation of the Ventricle, or Diastole

Question 44

Pathway of conduction

Answer 44

SA node > AV node (slow conduction) > Bundle of His (front of His-Purkinje network) > Purkinje network > cardiac muscle for depolarisation