Module 4 - Cardiac system Flashcards
how is the heart held in place in the cavity
its protective covering - the pericardial sac - is joined to the sternum via a line of fat called the mediastinal fat
where is the point of attachment of the pericardium and the heart
at the base of the heart - where the great vessels enter and exit
when viewing the heart anteriorly will the pulmonary trunk lie in front or behind the aorta
in front
which chamber of the heart makes up the apex
left ventricle
which artery lies in the right atrioventricular sulcus
right coronary artery
which artery lies in the left atrioventricular sulcus
the circumflex artery ( a branch of the left coronary artery)
in which groove could you find the anterior interventricular coronary artery
anterior interventricular sulcus
where can you find the great, middle and small cardiac veins
great cardiac vein and small cardiac vein are both on the anterior side (small on the right and is shorter, great on the left and is longer superiorly)
middle cardiac vein is on the posterior aspect of the heart and projects down form the coronary sinus
Which chamber of the heart does the coronary sinus drain into
right atrium
why does the heart need a blood supply instead of getting it from inside the chambers ?
the blood moves too fast for sufficient exchange of nutrients and the walls are much too thick
what is a heart attack and what can be the effect of it on the heart
it is when a coronary artery becomes occluded (blocked)
- this means the muscle cells in the heart aren’t getting oxygen and can be damaged or die
what areas do the superior and inferior vena cava drain blood from
superior - head, neck, upper limbs (arms) and thorax
inferior - abdominopelvic cavity and lower limbs (legs)
what are the 4 functions of the heart
- generating blood pressure
- routing blood (systemic and pulmonary)
- ensuring one way flow
- regulating blood supply to match changing metabolic needs
what is the location of the heart in the body
centrally in the mediastinum but angled to the left
what is in the mediastinum
heart,
trachea,
oesophagus,
thymus,
blood vessels,
nerves
what is the structure of the heart coverings and what are their roles
from outermost to innermost:
* fibrous pericardium (anchoring and protection)
* parietal layer of serous pericardium (adheres to fibrous pericardium)
* pericardial cavity (between serous layers)
* visceral layer of serous pericardium (outer layer of the heart/ epicardium)
what are the 3 layers of the wall of the heart
epicardium (visceral pericardium)
myocardium (muscle for contraction)
endocardium (lines chambers + vessels, simple squamous and extends into blood vessels)
what are the 2 first branches off the ascending aorta
left and right coronary arteries
where on the heart do you find large and small coronary arteries
large arteries travel in sulci on the surface of the heart
small arteries penetrate into the myocardium
describe the fibrous skeleton of the heart (structure and 4 functions)
- dense CT ring around 4 valves
- provides anchorage, structural stability, electrical insulation between atria and ventricles.
what does it mean to “have properties of a functional syncytium” and what is the benefit
- behaves as a single cell mass
- allows very fast electrical conduction from one fibre to another
what is the role of the non-contractile fibres in the heart
- they form the specialised pacemaker and conduction system which regulates heart beat
what are the components of the pacemaker/conduction system
- sinoatrial node - initiates electrical signal to cause contraction
- atrioventricular node - sends conduction + results in spontaneous polarisation
- atrioventricular bundle and purkinje fibres - carry rapid electrical impulse which results in contraction
what must happen to the cardiac muscle before it can contract and relax
it must depolarise before it can contract
and it must repolarise before it can relax
When does atrial repolarization occur
during ventricular depolarisation
when can the next cardiac cycle start
AFTER the ventricles have compeletely repolarised
what is the depolarisation sequence in the heart
- Sinoatrial node
- Atrial muscle
- atrioventricular node (slight delay here before moving down)
- right and left bundle branches
- purkinje fibres
- ventricular muscle
what part of the body does not have a stable resting membrane potential and what is the polarisation sequence like
Sinoatrial node
- it slowly depolarises until it reaches threshold where an action potential is triggered
- the membrane then repolarizes and immediately starts to depolarise again
what does ECG stand for and what does it measure
Electrocardiogram - sum of all electrical events during the cardiac cycle as measured on the body surface
what are the 5 letters used to label the ECG and what do they mean
P - first bump = Atrial depolarisation
Q - dip
R - big spike
S second dip
QRS - ventricular depolarisation
T - second bump = ventricular repolarization
name the 3 phases of the cardiac cycle
- atrial depolarisation (electric) followed by atrial systole (mechanic)
- Ventricular depolarisation (e) followed by ventricular systole (m)
- ventricular repolarisation followed by ventricular diastole
what happens during atrial systole
- atrial systole adds the final 20% of blood to the ventricular vol (most blood just flows through - called passive ventricular filling)
what happens during ventricular systole
- AV valve closes as Ventricular pressure increases
- isovolumetric ventricular contraction
- semilunar valves open
- ventricular ejection - blood leaves ventricles
what happens during ventricular diastole
- semilunar valves close
- isovolumetric ventricular relaxation
- AV valves open
- ## rapid ventricular filling (80% - passive filling directly from vena cava through A to V)
what does systole and diastole mean and what polarisation do they correlate with
systole - contraction - depolarisation
diastole - relaxation - repolarisation
what is average heart rate and how long are the cycles.
resting is average 75 bpm
cardiac cycle is 0.8 sec
systole is 0.3 sec and diastole is 0.5 sec
what influences heart rate
*Neural factors - because SA and AV nodes are innervated by SNS and ParaNS nerves
- Hormones - adrenaline, noradrenaline, thyroid hormone
- other: body temp, drugs, sleep, psychological factors
what are the 3 cardiac volumes, when are they measured and how many ml are they
EDV (end diastolic vol.) = 120-130 ml
(end of filling ventricles)
ESV (end systolic vol.) = 50-60 ml
(vol. in ventricles after emptying)
SV (stroke vol.) = EDV-ESV = avg. 70ml
what is cardiac output and what is a n average CO
volume ejected per ventricle per minute
CO = HR x SV
usually around 5250ml/min
what is cardiac reserve
the difference between CO at resting and the max CO
how does the parasympathetic NS innervate the heart
- innervates SA and AV nodes via Vagus nerve
- transmitter acetylcholine slows HR, is dominant at rest
how does the sympathetic NS affect the heart
- innervates SA node only
- originates from the thoracic SC
- transmitter is noradrenaline which increases HR
what are the 3 factors that affect stroke volume
- preload
- contractility
- afterload
what is preload
the force/ load on the ventricular muscle just prior to contraction, which is determined by the volume in the ventricles after filling (EDV)
what is starlings law of the heart and what does this affect
the greater the filling of the ventricles the greater the emptying
preload
stroke vol.
which of the factors affecting the heart are intrinsic and extrinsic
preload is intrinsic - within the heart
contractility is extrinsic - external to the heart (dependent on calcium concentration)
what is the main determinant of end diastolic volume (and of preload as well)
Venous return
what is venous return and what should it be equal to
- it is the flow of venous blood back to the heart per unit time
- it should equal cardiac output
what are the 5 factors affecting venous return
- blood volume
- central venous pressure / right atrial pressure
- venous tone + capacity of veins
- skeletal muscle pump
- respiratory pump
define contractility
the inotropic state of the heart (how much the ventricle can contract)
what is the relationship between Ca++ and heart contraction
increased Ca++ = increased contractility
what 3 things increase myocardial contractility (positive inotropic effect)
- sympathetic stimulation (innervate ventricular muscle)
- adrenaline + noradrenaline (act on B1 receptors)
- digoxin (drugs)
what 3 things decrease myocardial contractility (negative inotropic effect)
- decreased sympathetic stimulation
- decreased adrenaline + noradrenaline
- B blockers
what is afterload
the force AGAINST which the ventricles eject blood
why do arteries have pressure
to maintain structure and flow
what is the pulmonary arterial pressure (for right ventricle) - afterload
15-20mmHg
what is the aortic pressure (for left ventricle) - after load
100mmHg
what is the pulmonary arterial pressure and aortic pressure
pulmonary arterial pressure is the pressure that the RIGHT ventricle must overcome to pump blood
aortic pressure is the pressure that the LEFT ventricle must overcome to pump blood
which ventricle has a greater O2 consumption
left - has a greater muscle mass due to higher workload - cardiac muscle contraction generates energy aerobically
where are myocardial infarcts more common
in the left ventricle (due to its higher need for O2 for aerobic metabolism)
what is left ventricular hypertrophy and what does it indicate
- enlargement of the left ventricle
- sign of an overworked heart usually due to high blood pressure ( ventricle is forced to work against an afterload >100 mmHg)
what are the ridges in the pectinate muscle for
to increase surface area of the atria to accommodate changing volume
where is the opening of the coronary sinus and what is it’s role
just below the opening of the vena cava, it returns the blood of the coronary circulation
what is the fossa ovalis
- small oval depression where where the foramen ovale used to be (hole in the heart of babies)
what is the structure and function of the trabeculae carnae
- they are columns of muscle on the inside of the ventricle to create turbulence to promote proper mixing of the blood to stop pooling
what are papillary muscles and chordae tendineae
strings and joining muscles connecting the valves to the ventricles to prevent them from opening backwards and hence preventing the backflow of blood
what is the name for the placement of any 2 electrodes for ECG recordings
a lead
