Lesson 1 - Anatomy and Physiology

Question 1

Right Side Heart

Answer 1

• the right ventricle (RV) is a pump for the pulmonary system
• the RV delivers un-oxygenated blood from the body, to the lungs
• it projects its volume against minimum resistance (the lungs)
• because the RV meets limited resistance in the lungs, it does not require extreme strength or thick musculature to perform its role
• thin walls: 4-5 mm in thickness
• tricuspid and pulmonic valves

Question 2

Left Side Heart

Answer 2

• the left ventricle (LV) is a pump for the systemic circulation
• the LV delivers oxygenated blood received from the lungs, to the body
• it projects its volume against a large maximum resistance (the body)
• LV requires more strength and thicker muscle than the RV because the LV
  meets high resistance as it ejects blood throughout the body
• thick walls: 8-15 mm thickness (about 2-3 times that of the RV)
• mitral and aortic valves

Question 3

Learn the Anatomy

Answer 3

refer to picture

Question 4

Anatomical location

Answer 4

• the heart lies obliquely behind the costal cartilages, between the 2nd and 6th ribs
• the broad portion is called the base (upper right area)
• the pointed end of the heart is the apex (lower left area)
• PMI (point of maximum impulse) is heard best at the apex

Question 5

Layers of the Cardiac Tissue

Answer 5

Pericardium
– then, moving from the outside in, there are
three more distinctive layers of tissue:
Epicardium
Myocardium
. Endocardium

Question 6

Pericardium

Answer 6

• surrounds and envelops the heart
• includes - fibrous pericardium (tough fibrous outer layer)
  - serous pericardium (thin delicate smooth lining)
• the pericardial sac lies between the fibrous and serous pericardia

Question 7

. Epicardium

Answer 7

• the outer layer of tissue
• squamous epithelial cells overlying
  connective tissue
• this layer adheres to the serous pericardium

Question 8

Myocardium

Answer 8

• the middle section
• consists of cardiac muscle, allowing for
  contraction
• this layer forms most of the heart’s wall
• thickest toward the apex and thins toward the base

Question 9

Endocardium

Answer 9

• this is the innermost layer
• firmly bound to myocardium by connective tissue
• this layer is in contact with the blood inside the heart
• it is much thinner than the epicardium
• made up of endothelial cells and small blood vessels

Question 10

Valves

Answer 10

• there are two AV (Atrio-Ventricular) valves: each one is located between an
  atrium and a ventricle
• and two semilunar valves: leading from a ventricle to a great vessel
• valves allow forward propelling of flow of blood, preventing backward blood flow
• they open and close in response to intra-cardiac pressure changes
• all have 3 cusps (leaflets), except the mitral (bicuspid) valve, which has 2 cusps
• between the atria and the ventricles (AV valves)
• L side: mitral valve
• R side: tricuspid valve
• leading out of the heart, to the great vessels
• aortic valve leads out of the LV
• pulmonic valve leads out of the RV

Question 11

chordae tendoneae

Answer 11

• these allow the valve leaflets to open and close
• they are strong cords of fibrous tendinous tissue
• they are attached to the cusps of the AV valves, and connect to the papillary
  muscles

Question 12

papillary muscles

Answer 12

• these muscles project into the ventricular cavities
• they are muscles that attach to the ventricles
• they become continuous extensions of the chordae tendoneae
  (3d view in notes)
• ventricular contraction opposes the valve cusps, and movement of these
  structures prevents the valves from being pushed backward
• this allows the valve to open in the correct position, and propel blood
  in the right direction
• dysfunction or rupture of a papillary muscle or chordae tendoneae can
  undermine the support of the valve and lead to regurgitation

Question 13

HEMODYNAMICS of the CARDIAC CYCLE (the heart’s mechanical system)

Answer 13

The heart requires a mechanical system. This system includes the anatomy we’ve already studied and ensures blood flow into the heart, through the heart, and out of the heart to support the body.
This is the system that “directs/propels” the blood into the heart, through the heart and out of the heart, in the right direction
(Videos in notes)

Question 14

There are 2 phases to the cardiac cycle

Answer 14

diastole and systole

Question 15

Diastole (relaxation phase)

Answer 15

• the chambers are relaxed, and un-oxygenated blood returning to the heart
  enters the RA (R atrium) via the superior and inferior vena cavas
• and the newly oxygenated blood returning from the lungs enters the LA
  (L atrium) via the pulmonary veins
• the tricuspid and mitral valves are open
• because these valves are open and the heart is relaxed (not contracting), blood
  passively flows from the RA to the RV via the tricuspid valve, and from the LA to
  the LV via the mitral valve
• approximately 80% of ventricular filling occurs during this diastolic phase

Question 16

Systole (contraction phase)

Answer 16

• systole is the heart’s contracting phase and is divided into 2 phases (atrial
  systole and ventricular systole)
• systole occurs when enough blood has entered the individual chambers that
  they need to contract to propel this blood volume

Question 17

Atrial Systole

Answer 17

• during atrial systole, the ventricles are still diastolic (relaxed)
• both atria contract, pushing more blood into the partially-filled relaxed ventricles
• the RA contracts to eject the un-oxygenated blood it received from the system,
  into the RV
• the LA contracts to eject the well oxygenated blood it received from the lungs,
  into the LV
• atrial systole adds about 20% more blood volume into the ventricles
• so, this fills the ventricles to full 100% capacity
• this 20% blood volume is referred to as the “atrial kick”. (remember this term…it
  will resurface throughout the course!)

Question 18

Ventricular Systole

Answer 18

• the pulmonic and aortic valves open
• the tricuspid and mitral valves close, to prevent blood flow back into the atria
• closure of these AV valves causes the first heart sound (LUB) and will be
  discussed further in Lesson 2
• the ventricles now contract
• on the right side of the heart, the RV pumps the un-oxygenated blood through
  the pulmonic valve, through the pulmonary arteries and to the lungs, to be
  oxygenated
• on the left side of the heart, the LV pumps the oxygenated blood returned from
  the lungs through the aortic valve, through the aorta and into the systemic
  circulation, to oxygenate the body’s arterial system
• following ventricular systole, the pulmonic and aortic valves close to prevent
  blood flow back into the ventricles
• closure of these semilunar valves produces the second heart sound (DUB) and
  will be discussed further in Lesson 2

Question 19

CARDIAC CONDUCTION SYSTEM (the heart’s electrical system)

Answer 19

Cardiac performance requires two separate systems, working together. These 2 systems
are the mechanical system and the electrical system
The hemodynamics of the heart (the mechanical system), previously discussed, refers
mostly to the ‘geography’ of the heart, a system through which blood is
propelled and flows through chambers and valves, and an understanding of the
diastolic and systolic phases

The heart’s electrical conduction system generates and conducts electrical impulses

• to be able to interpret cardiac arrhythmias, an understanding of the electrical conduction
  system is required
• once the structures and components of the electrical system are understood, it becomes
  much easier to grasp what is occurring along the conduction system with each arrhythmia
• the following are the basic structures and components of the normal electrical conduction
  system

Question 20

myocardial cells have 3 specialized electrical properties

Answer 20

1. automaticity: the ability to initiate electrical impulses
2. conductivity: the ability to pass, conduct the impulses along to other cells
3. contractility: the ability to cause shortening of cardiac fibers
   - each normal heart beat results from an electrical impulse originating in the SA node

Question 21

of interest

Answer 21

ever wonder why the heart of the patient who is ‘brain-dead’ still beats?…
The heart can keep beating because the brain/nervous system does not send impulses to
the heart ‘telling’ it to contract. The heart relies on its own automaticity to initiate impulses.
(Graphics in notes)

Question 22

SA node

Answer 22

• the SA (Sino-Atrial) node is located on the endocardial surface of the RA
• it is normally the primary pacemaker of the heart
• it is the original impulse generator (cells in the SA node have automaticity)
• the SA node normally initiates impulses at a rate of 60-100 times/minute, and as such,
  the normal heart rate (HR) in adults is 60-100
• the SA node usually stops initiating impulses if another area of the heart originates
  impulses at a rate more rapid than that of the SA node
• in other words, the SA node would allow the faster site to pace the heart

Question 23

Internodal Tracts

Answer 23

• these lie between the SA node and AV node, hence the term “inter-nodal”
• the main role of these pathways is to transmit the impulse that has originated in
  the SA node and conduct it through the RA, thereby allowing the RA to contract

Question 24

Inter-atrial Tract

Answer 24

• this tract lies between the two atria, hence the term “intra-atrial”
• the impulse that originated in the SA node must also conduct to the LA, so that
  the LA can contract
• this tract along which impulses travel to the LA is called “Bachman’s Bundle”
• now that the electrical system has conducted the impulse through both atria,
  atrial systole occurs
• in other words, the atria contract to propel the 20% blood volume as previously
  discussed, into the ventricles
• within the atria, there is tissue with automaticity that can initiate impulses (this
  will be discussed in Lesson 4)

Question 25

AV node

Answer 25

• the AV (atrio-ventricular) node is located in the lower RA
• the impulse that originated in the SA node and transmitted through the atria passes
  through the AV node before reaching the ventricles
• the main property of the AV node is its ability to slow/delay the impulse before it
  reaches the ventricles
• this short delay in conduction to the ventricles allows the atria the time they need to
  fully contract, to fill the ventricles to capacity

Question 26

AV junction

Answer 26

• the impulse travels through the AV junction on its route to reaching the ventricles
• cells within the AV junction have automaticity
• so, should the SA node become ischemic or fail to initiate impulses, the AV junction
  can serve as a back-up pacemaker
• the AV junction’s inherent rate of conduction is 40-60 impulses/minute

Question 27

Ventricular System

Answer 27

• let’s go back to that impulse that originated in the SA node…
• after conducting through the atria, the AV node and the AV junction, it continues down
  the conduction system, traveling through the bundle of HIS and the two bundle branches,
  until it reaches the Purkinje fibers
• these fibers spread across both ventricles from the inside to the outside (from the
  endocardium to the myocardium) and are the terminal points of the electrical
  conduction system
• the purkinje fibers rapidly conduct the impulse through the ventricles
• the impulse stimulates the ventricular cells, leading to ventricular contraction
• as the ventricles contract, they eject their contents as discussed earlier (the LV ejects
  oxygenated blood to the body, and the RV ejects un-oxygenated blood to the lungs)
• there are cells within the ventricular conduction system that possess the property of
  automaticity
• so, should the SA node and the AV junction both fail to initiate impulses, rather than the
  heart ‘stopping’ altogether, impulses can be initiated within the ventricles at an inherent
  rate of 20-40 impulses/minute

Question 28

to review…

Answer 28

• normally the SA node initiates impulses at a rate of 60-100 beats per minute
• the impulses travel through both atria along special bands of tissue
• impulses then reach the AV node, where they are slowed/delayed
• the impulses then travel through the AV junction, the ventricles and finally reach the
  purkinje fibers

Question 29

• what happens if the SA node should fail to initiate impulses ?

Answer 29

• to keep the heart from stopping, the heart’s electrical conduction system has 2
  built-in safety mechanisms (cells elsewhere along the conduction system have
  automaticity and can initiate impulses, but with a slower discharge rate):
• 1. if the SA node is not initiating impulses, the AV junction has cells with automaticity that can initiate impulses at a rate of 40-60 times per minute
• 2. if the SA node and AV junction both fail, cells in the ventricles (bundle of HIS) also have automaticity and can generate 20-40 impulses per minute

Question 30

CARDIAC OUTPUT (CO)

Answer 30

• just as one can assess how well the kidneys are functioning by measuring the
  urinary output, so can the heart’s performance be assessed by determining CO
• CO is the volume of blood ejected by the LV, each minute
• the normal CO is approximately 3.6-10 litres
• in other words, the LV propels 3.6 to 10 liters of oxygenated blood to the body, each minute
• CO = HR (heart rate) x SV (stroke volume)
• the normal HR is about 60-100 beats per minute (the SA node’s inherent ability)
• SV is the amount of blood ejected by the LV, with each contraction
• the normal SV is approximately 60-100 ml
• in other words, the LV can accommodate or ‘hold’ about 60-100 ml of blood, so this is
  the amount of blood the LV can pump out with each contraction or beat

Question 31

Factors affecting CO

Answer 31

• adequate CO relies on an adequate SV and an adequate HR
• therefore, if the SV or the HR are affected, the CO will be affected
• SV is influenced by preload, contractility and afterload
• HR is influenced by the autonomous nervous system (sympathetic and parasympathetic)
• the following notes define and explain these influencing factors on SV and HR

Question 32

Preload

Answer 32

• preload is often referred to as LVEDP (left ventricular end diastolic pressure)
• it’s the amount of stretch, tension, pressure within the LV at the end of diastole (the amount
  of wall stretch, caused by the blood volume within the ventricles at the end of diastole)
• it is the load of blood that establishes the initial muscle length of the cardiac fibers just prior
  to contraction
• so, if not enough blood is in the LV at the end of diastole (before the LV contracts), not
  enough blood will be ejected by the LV, thereby leading to a decrease in the CO

Question 33

• consider the example of an accidental limb amputation…(Preload)

Answer 33

• as hemorrhage occurs, less blood returns to the R heart to be oxygenated
• so, the RV sends less blood to the lungs, and the lungs send less blood to the L heart
• the LV has a lesser blood volume, so it doesn’t stretch as much (decreased preload)
• the LV has less oxygenated blood to eject, causing a decreased SV
• this in turn causes a decrease in CO
• as the CO drops, not enough oxygenated blood is perfusing the system (ie. the brain and other vital organs), so the patient becomes symptomatic

Question 34

What can influence preload?…

Answer 34

1) venous return
- the amount of circulating blood volume returning to the heart
2) status of the LV
- ie. does the LV stretch? is it compliant? can it ‘accept’ the blood volume?
3) atrial kick
- if atrial kick is absent, as much as 20% less blood enters the LV, which
leads to less LV stretching
4) status of the mitral valve
- preload decreases with mitral stenosis as blood has difficulty leaving the
LA, causing less LV stretch

Question 35

Contractility

Answer 35

• this is the myocardial muscles’ ability to contract
• it reflects the speed and muscle shortening capacity of the myocardial fibers
• the major factor affecting contractility is the ability of the muscle fibers to shorten
• if the fibers cannot contract effectively, less than optimum amounts of blood are ejected

Question 36

Afterload

Answer 36

• is the amount of stretch, tension, pressure against the LV during peak systole
• afterload reflects the sum of all the loads or the arterial resistance against which
  the LV must ‘work against’ during systole, to eject its blood volume
• it is the amount of ‘push’ that the LV needs as it starts to contract, to move out its
  load of blood

Question 37

What can influence afterload?…

Answer 37

1) status of the aortic valve
- aortic stenosis causes increased afterload as the LV muscle must work
harder to shorten its fibers, to propel blood out the narrowed valve

2) blood viscosity
- ‘thin’ blood ejects with more ease than ‘thicker’ blood

3) systemic vascular resistance (SVR)
- vasoconstriction increases afterload as the LV needs more push, energy
or pressure to propel its blood volume, into the body’s constricted
arteries
- afterload is reduced with vasodilatation as blood is easily propelled into
the dilated vessels

Question 38

• consider the example of high systemic vascular resistance (SVR) in the vasoconstricted patient…(Afterload)

Answer 38

• the LV has difficulty propelling blood into the constricted arteries
• so, less blood is pumped out, meaning the SV drops
• low SV (blood volume/beat) results in low CO (blood volume/minute)
• as the CO drops and less oxygenated blood reaches the brain and other vital organs, symptoms of underperfusion appear

Question 39

Effects of Heart Rates on CO

Answer 39

• HR is influenced by the autonomic nervous system (SNS and PSNS)

Question 40

Sympathetic Nervous System (SNS) dominance

Answer 40

• HR > 100: the ventricles have less time to fill (shortened filling time) because they
  are contracting too rapidly
• therefore, preload is decreased (less LV stretch occurs as less blood enters the LV)
• because less blood entered the LV…less blood will be ejected by the LV
• so, the SV decreases and consequently, the CO decreases
• Example: (the following numbers are chosen at random, to explain the concept)
• HR x SV = CO
• 150 x 20 = 3,000 ml (the normal CO is 3,600 ml to 10,000 ml)
• less than normal CO can cause underperfusion of the system, leading to symptoms

Question 41

Parasympathetic Nervous System (PSNS) dominance

Answer 41

• HR < 60: the slow rate provides the LV with plenty of time to fill, but the SV reaches
  a maximum and cannot be increased
• this is because there’s only “so much” space for blood in the LV (there’s only room
  for 60-100 ml of blood in the LV)
• so, the SV may be normal and satisfactory but a slow HR can lead to a drop in CO
• Example: (the following numbers are chosen at random, to explain the concept)
• HR x SV = CO
• 30 x 100 = 3,000 ml (the normal CO is 3,600 ml to10,000 ml)
• again, symptoms can occur due to low CO and system underperfusion

Question 42

CORONARY ARTERIES

Answer 42

• their function is to bring oxygen-rich blood to the myocardium
• O2 is an essential ingredient, producing energy that the heart needs to contract
• first branches off the aorta (the ‘best’ blood that has just been oxygenated by the lungs)
• they then surround and envelop the heart, providing it with blood supply
• there are 2 main coronary arteries (R and L coronary arteries)
• as they travel along and past various cardiac structures, they supply these structures
  with oxygenated blood
• coronary artery blood flow to the heart is delivered from the outside to the inside
  (from the pericardium to the endocardium)

Question 43

Right Coronary Artery (RCA)

Answer 43

• the RCA originates anteriorly, off the aorta
• it lies anteriorly in the area that separates the RA and the RV
• it then travels around posteriorly and descends inferiorly (to behind the heart)

Question 44

• cardiac muscle supplied by the RCA:

Answer 44

• the RA
• large portion of the RV
• most of the inferior wall of the LV
• part of the posterior wall of the LV
• posterior 1/3 of the inter-ventricular septum

Question 45

• electrical structures supplied by the RCA

Answer 45

• SA node (in about 55% of people)
• AV node & AV junction (in about 90% of people)
• Bundle of HIS (in most people)

Question 46

Left Coronary Artery (LCA)

Answer 46

• originates anteriorly, off the aorta
• within a short distance (2-10 mm), it divides into 2 branches
• these 2 branches are the LAD artery and the Circumflex artery
• the LCA supplies a massive LV area
• let’s explore the two branches of the LCA a little further…

Question 47

Left Anterior Descending Artery (LAD)

Answer 47

• the LAD courses anteriorly over the interventricular septum (it lies on the groove
  separating the ventricles)
• it usually circles around the apex (bottom of the heart)
• it terminates in the inferior aspect of the cardiac apex
• cardiac muscle supplied by the LAD Artery:
  - anterior walls of both ventricles
  - anterior 2/3 of the inter-ventricular septum
• electrical structures supplied by the LAD Artery:
  - both bundle branches

Question 48

Circumflex Artery

Answer 48

• almost a mirror image of the RCA
• arises anteriorly from the LCA
• lies anteriorly between the LA and the LV (in the L anterior AV groove)
• travels around posteriorly, and courses around the L side of the heart
• cardiac muscle supplied by the Circumflex Artery:
• the LA
  - lateral wall of the LV
  - part of the posterior wall of the LV
• electrical structures supplied by the Circumflex Artery:
  - SA node (in about 45% of the population)
• AV node & AV junction (in about 10% of the population)
  - proximal bundle branches

Question 49

Lesson Summary:

Answer 49

The right side of the heart receives un-oxygenated ‘used-up’ blood from the body’s veins and pumps it into the pulmonary system to be oxygenated.
The left side of the heart receives oxygenated from the lungs and delivers it to the body, through arteries.
Valves allow for effective propelling of blood within the heart’s chambers and out of the heart.
The electrical conduction system is responsible for initiating/generating impulses.
Normally, impulses originate in the SA node and are then transmitted down specific pathways, until they reach the ventricles.
Diastole is a state of relaxation.
Systole is a state of excitability (contraction).
CO refers to the amount of blood the LV propels to the body, every minute.
SV and HR both have effects on the CO.
There are 2 coronary arteries (the right and the left).
The left coronary artery divides into 2 arteries.
Coronary arteries are responsible for delivering oxygenated blood to the heart’s mechanical and electrical structures.